VTEC, Variable Valve Timing and Lift Electronic Control is a valve train system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. This system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani. It can be said that VTEC, the original Honda variable valve control system, originated from REV (Revolution-modulated valve control) introduced on the CBR400 in 1983 known as HYPER VT EC. VTEC was the first system of its kind, though other variable valve timing and lift control systems have been produced by other manufacturers (MIVEC from Mitsubishi, VVTL-i from Toyota, VarioCam Plus from Porsche, VVL from Nissan, etc).

i-VTEC

(intelligent-VTEC) introduced continuously variable camshaft phasing on the intake cam of DOHC VTEC engines. The technology first appeared on Honda’s K-series four cylinder engine family in 2001 (2002 in the U.S.). In the United States, Honda first debuted the technology on the 2003 Honda Civic Si EP3 with the economy version.

Valve lift and duration are still limited to distinct low- and high-RPM profiles, but the intake camshaft is now capable of advancing between 25 and 50 degrees (depending upon engine configuration) during operation. Phase changes are implemented by a computer controlled, oil driven adjustable cam gear. Phasing is determined by a combination of engine load and rpm, ranging from fully retarded at idle to somewhat advanced at full throttle and low rpm. The effect is further optimization of torque output, especially at low and midrange RPM.

K-series

The K-Series motors have two different types of i-VTEC systems implemented. The first is for the performance motors like in the RSX Type S or the TSX and the other is for economy motors found in the CR-V or Accord. The performance i-VTEC system is basically the same as the DOHC VTEC system of the B16A’s; both intake and exhaust have 3 cam lobes per cylinder. However the valvetrain has the added benefit of roller rockers and continuously variable intake cam timing. Performance i-VTEC is a combination of conventional DOHC VTEC with VTC.

The economy i-VTEC is more like the SOHC VTEC-E in that the intake cam has only two lobes, one very small and one larger, as well as no VTEC on the exhaust cam. The two types of motor are easily distinguishable by the factory rated power output: the performance motors make around 200 hp (150 kW) or more in stock form and the economy motors do not make much more than 160 hp (120 kW) from the factory.

R-series

The new SOHC i-VTEC implementation is an entirely new implementation that was introduced on the 2006 Honda Civic’s R-series four cylinder SOHC engines. This implementation uses the so-called “fuel economy cam” and “high output cam” on one of the two intake valves of each cylinder (another intake valve is fixed). The “fuel economy cams” are designed to retard the closure of one intake valve and are activated between 1000-3500RPM and under low load condition. When “fuel economy cams” are activated, the intake valve closes well after the piston has started moving upwards in the compression stroke. During this time, the drive-by-wire throttle valve is open wider than normal. Due to the delayed closing of intake valve, a part of the intake mixture that has entered the combustion chamber is forced out again into the intake manifold. That way, the engine “emulates” a lower displacement than its actual one (its operation is also similar to an Atkinson cycle engine, with uneven compression and combustion strokes), which reduces pumping losses thus reducing fuel consumption and increases its efficiency. VTEC-off on the R18A means it can be considered to be running “high output cams”. When the right conditions are achieved for fuel economy, VTEC engages the 2nd set, the ‘low’ or ‘economy’ cams. Thus VTEC-on on the R18A means it is running low cams.

According to Honda, this measure alone can reduce pumping losses by 16%. Under heavier loads, the engine switches back into its “high output cams”, and it operates like a regular 4 stroke Otto cycle engine. This implementation of i-VTEC was initially introduced in the R18A1 engine found under the bonnet of the 8th generation Civic, with a displacement of 1.8 L and an output of 140 PS (100 kW; 140 hp). Recently, another variant was released, the 2.0 L R20A2 with an output of 150 PS (110 kW; 150 hp), which powers the EUDM version of the all-new CRV. SOHC i-VTEC

With the continued introduction of vastly different i-VTEC systems, one may assume that the term is now a catch-all for creative valve control technologies from Honda.

i-VTEC VCM

In 2003, Honda introduced an i-VTEC V6 (an update of the J-series) that includes Honda’s cylinder deactivation technology which closes the valves on one bank of (3) cylinders during light load and low speed (below 80 km/h (50 mph)) operation. The technology was originally introduced to the US on the Honda Odyssey minivan, and can now be found on the Honda Accord Hybrid, the 2006 Honda Pilot, and the 2008 Honda Accord.

i-VTEC VCM was also used in 1.3L 4-cylinder engines used in Honda Civic Hybrid.

i-VTEC i

It is a version of i-VTEC with direct injection.

It was first used in 2003 Honda Stream.

This is how an ivtec engine works

And this is the Honda Hybrid System

Reference: www.wikipedia.org

www.world.honda.com

Twin-turbo

Twin-Turbo, also called bi-turbo by some, refers to a TURBOCHARGED engine on which two turbochargers compress the intake charge. There are two different twin turbo configurations, parallel twin-turbo and sequential twin-turbo.

Contents 1 parallel twin turbo 2 sequential twin turbo 3 compound turbocharging

// Parallel Twin-Turbo

Parallel Twin-Turbo refers to a turbocharger configuration in which two identical turbochargers equally split the turbocharging duties. Each turbocharger is driven by one half of the engine’s spent exhaust energy. In most applications, the compressed air from both turbos is combined in a common intake manifold, and sent to the individual cylinders. Both turbos function simultaneously, unlike sequential twin-turbos. Commonly each turbocharger is mounted to its own individual exhaust/turbo manifold, however on inline-type engines both turbochargers could be mounted to a single turbo manifold. Parallel twin turbos are usually applied to V-shaped engines where one turbo is assigned to each cylinder bank, providing packaging symmetry, and simplifying plumbing; however, it is not uncommon for a parallel set-up to be used on an inline engine. Nissan’s RB26DETT is an inline-6 that uses a twin-turbo set-up, the twin-turbo inline-6 in the BMW 335i(E90) coupe also utilizes a parallel twin-turbo set-up. Toyota’s 1992 Supra with the 1JZ-GTE (Japan only) 6 cylinder inline engine also used this same configuration, as does Nissan’s 1990-1996 Z32 300ZX in its V6 VG30DETT, and Audi’s 1997-2004S4(B5), 1997-2004 A6, and 2003-2004 RS6.

While a parallel twin-turbo set-up theoretically has less TURBO LAG than a single turbocharger set up, because of marginally-reduced combined inertial resistance, and often simplified exhaust plumbing, the fact that both turbos spool at more or less the same time means that there is still a noticeable bit of lag, especially in high-flow turbo/high boost applications. One way to counter this is to use a light pressure set up where the turbos are designed to output less boost but spool earlier, however, this set up sacrifices top end power. Another system would be the use of Variable geometry turbocharger, this system changes the angle of the guide vanes depending on the exhaust pressure giving the system excellent power throughout the rev range. Once used mainly in turbocharged diesel engines,Porsche was the first to use it in a mass-production gasoline-powered vehicle in 2006 with the 911turbo(977).

Parallel operation of the turbochargers can still be used to great effect as demonstrated by the Bugatti Veyron; which runs four relatively small turbochargers in parallel.

Sequential Twin-Turbo

Sequential Twin-Turbo refers to a set up in which the motor can utilize only one turbocharger for lower engine speeds, and both turbochargers at higher engine speeds. During low to mid engine speeds, when available spent exhaust energy is minimal, only one turbocharger (the primary turbocharger) is active. During this period, all of the engine’s exhaust energy is directed to the primary turbocharger only, lowering the boost threshold, and increasing power output at low engine speeds. Towards the end of this cycle, the secondary turbocharger is partially activated (both compressor and turbine flow) in order to pre-spool the secondary turbocharger prior to its full utilization. Once a preset engine speed or boost pressure is attained, valves controlling compressor and turbine flow through the secondary turbocharger are opened completely. At this point the engine is functioning in a full twin-turbocharger form, providing maximum power output. Sequential twin-turbocharger systems provide a way to decrease turbo lag without compromising ultimate boost output and engine power. Examples of cars with a sequential twin-turbo setup include the 1993-2002 Toyota supra turbo, the 1992-2002 Mazda RX-7(FD3S), and the 1986-1988 Porsche 959. With recent advancements in turbocharger design, sequential twin turbo systems have fallen out of favor because they are seen as unnecessarily costly and complex.

Compound turbocharging

Compound turbocharging is a technique used to achieve extremely high pressure ratios by having one turbocharger pressurize the air coming into the inlet of another. It is common in racing with diesel engines (For example tractor pulling) due to their combustion properties that take well to high boost pressures and are not limited by fuel stability like spark ignition engines. Boost pressures of around seven bar gauge pressure (101 psi) are common and as high as 10 bar (145psi) in some cases. A normal turbocharger has a maximum pressure ratio of around three but there are turbochargers in existence specially designed for high boost which have maximum pressure ratios of typically 4-5. In this configuration one turbocharger is used to pressurize the air coming into the inlet of the other, resulting in a multiplication of the pressure ratios. Same goes for exhaust plumbing. For example if both turbochargers are running at pressure ratios of 3.0 and the atmospheric pressure is one bar the resulting pressures will be three bar absolute pressure at the inlet of the second turbocharger and nine bar absolute pressure (eight bar gauge) at the inlet manifold of the engine. The pressure ratio in this example becomes nine.

L-Jetronic Injection System

Expansion Chamber (Tuned Exhaust Pipe)

This article will show you how an expansion chamber (also known as a tuned pipe)

actually works through the use of a step-by-step explanation and a few graphics.

What it does

An expansion chamber which has been properly matched to an engine will effectively

supercharge the mixture of gas and air inside the cylinder. This is done by pulling

extra mixture into the cylinder and by pressing wasted mixture back in through the

exhaust port.

How it works

As the descending piston opens the cylinder exhaust port, the action of the exhaust

pressure wave rushing through the tuned pipe at the speed of sound initiates a

sequence of events that enhance the engines torque and horsepower output.

The positive pressure pulse leaves the exhaust port

As the mixture is combusted inside the cylinder, the piston is forced downward and

opens the exhaust port. The force of the exhaust pressure leaving the cylinder creates

a positive pressure pulse as it moves out into the expansion chamber.

The time between exhaust port opening and transfer port opening is called “exhaust

lead”. Exhaust lead allows the high-pressure exhaust gases in the cylinder to blowdown

(reducing pressure) before the transfer port opens. If this doesn’t happen,

exhaust particles may back-flow into the crankcase and contaminate and heat the

incoming fuel/air charge, thereby robbing the engine of power. Positive pressure pulse

leaves the exhaust port forcing exhausted gas and air into he chamber

Negative pressure waves

The inertia of the out flowing exhaust particles out into the divergent code creates

negative pressure waves and a strong partial vacuum (about minus 7psi) near the still

opening exhaust port shortly after the transfer port has opened. In addition to the

sucking out tail-end exhaust gases, these suctions cause fresh air/fuel mixture to be

sucked through the transfer port into the combustion chamber.

Negative pressure is created as the waves expand into the divergent cones

Positive pressure waves

The remaining energy in the negative pressure wave continues through the pipe and is

reflected off the convergent cone at the rear of the unit and returns to the engines

exhaust port. During this point, the negative pressure will actually end up pulling

extra fresh gas and air into the header of the expansion chamber.2

Positive pressure waves echo back from the convergent cone, towards the engine

Supercharging through the exhaust port

Finally just as the transfer ports inside the cylinder are closing, the returning positive

pressure wave compresses the extra fuel and air mixture back into the cylinder

through the exhaust port. The cylinder now contains the extra mixture for the next

combustion—effectively supercharging the engine and increasing efficiency and

performance.

Positive pressure forces over scavenged mixture back into the cylinder

The Resonator

• When a wave hits the hole, part of it continues into the chamber and part of it

is reflected. The wave travels through the chamber, hits the back wall of the

muffler and bounces back out of the hole.

• The length of this chamber is calculated so that this wave leaves the resonator

chamber just after the next wave reflects off the outside of the chamber.

• Ideally, the high-pressure part of the wave that came from the chamber will

line up with the low-pressure part of the wave that was reflected off the

outside of the chamber wall, and the two waves will cancel each other out.

• In reality, the sound coming from the engine is a mixture of many different

frequencies of sound, and since many of those frequencies depend on the

engine speed, the sound is almost never at exactly the right frequency for this

to happen.

• The resonator is designed to work best in the frequency range where the

engine makes the most noise; but even if the frequency is not exactly what the

resonator was tuned for, it will still produce some destructive interference.

• Some cars, especially luxury cars where quiet operation is a key feature, have

another component in the exhaust that looks like a muffler, but is called a

resonator.

• This device works just like the resonator chamber in the muffler — the

dimensions are calculated so that the waves reflected by the resonator help

cancel out certain frequencies of sound in the exhaust.

• There are other features inside this muffler that help it reduce the sound level

in different ways.

• The body of the muffler is constructed in three layers: Two thin layers of

metal with a thicker, slightly insulated layer between them. This allows the

body of the muffler to absorb some of the pressure pulses.

• Also, the inlet and outlet pipes going into the main chamber are perforated

with holes. This allows thousands of tiny pressure pulses to bounce around in

the main chamber, canceling each other out to some extent in addition to being

absorbed by the muffler’s housing.

• Resonators are like little mufflers, and are usually the “straight through”

type. They are added at the end of the exhaust system to take care of any

noise that has made it through the muffler. The muffler quiets the noise of

the exhaust by “muffling” the sound waves created by the opening and

closing of the exhaust valves. When an exhaust valve opens, it discharges

the burned gases at high pressures into the exhaust pipe, which is at low

pressure. This type of action creates sound waves that travel through the

flowing gas, moving much faster than the gas itself (up to 1400 m.p.h.),

that the muffler must silence. It generally does this by converting the

sound wave energy into heat by passing the exhaust gas and its

accompanying wave pattern, through perforated chambers of varied

sizes. Passing into the perforations and reflectors within the chamber

forces the sound waves to dissipate their energy.

ENGINE DYNAMOMETER

Chassis dynamometer

A chassis dynamometer measures power delivered to the surface of the “drive roller”

by the drive wheels. The vehicle is often parked on the roller or rollers, which the car

then turns and the output is measured. Modern roller type chassis dyne systems use

the Salvisberg roller, which improved traction and repeatability over smooth or

knurled drive rollers. On a motorcycle, typical power loss at higher power levels,

mostly through tire flex is about 10% and gearbox chain and other power transferring

parts are another 2% to 5%. Other types of chassis dynamometers are available that

eliminate the potential wheel slippage on old style drive rollers and attach directly to

the vehicle’s hubs for direct torque measurement from the axle. Hub mounted dynos

include units made by Dynapack and Rototest. These dynes should read about 10% to

15% higher than a “rear wheel” chassis dyne. Chassis dynos can be fixed or portable.

Modern chassis dynamometers can do much more than display RPM, Horsepower,

and Torque. With modern electronics and quick reacting, low inertia dyne systems,

it’s now possible to tune to best power and the smoothest runs, in real-time. It’s also

common to, on a retail level, with a wideband 02 Sensor, graphed along with RPM, to

“tune to an air fuel ratio”. Some, like Dynojet and others can also add vehicle

diagnostic information to the dyno graph as well. This is done by gathering data

directly from the vehicle’s PCM via OBD communication. Because of frictional and

mechanical losses in the various drive train components, the measured rear wheel

brake horsepower is generally 15-20 percent less than the brake horsepower measured

at the crankshaft or flywheel on an engine dynamometer.

Other sources, after researching several different “engine” dyno software packages,

found that the engine dyno user can integrally add “frictional loss” channel factors of

+10% to +15% to the flywheel power, raising the claim that 20% to 25% or even

more power is actually lost between the crankshaft at high power outputs.

SIMPLE CARBURETOR OPERATION

The venturi principle in operation

The pumping action of the pistons creates a vacuum which is amplified

by the venturi in the carburetor. This pressure drop will pull fuel from the

float bowl through the fuel nozzle. Unfortunately, there is not enough

suction present at idle or low speed to make this system work, which is

why the carburetor is equipped with an idle and low speed circuit.

Accelerator pump system

When the throttle is opened, the air flowing through the venturi starts

flowing faster almost immediately, but there is a lag in the flow of fuel

out of the main nozzle. The result is that the engine runs lean and

stumbles. It needs an extra shot of fuel just when the throttle is opened.

This shot is provided by the accelerator pump, which is nothing more

than a little pump operated by the throttle linkage that shoots a squirt of

fuel through a separate nozzle into the throat of the carburetor.

Idle and low-speed system

The vacuum in the intake manifold at idle is high because cause the

throttle is almost completely closed. This vacuum is used to draw fuel

into the engine through the idle system and keep it running. Vacuum acts

on the idle jet (usually a calibrated tube that sticks down into the main

well, below the fuel level) and sucks the fuel into the engine. The idle

mixture screw is there to limit the amount of fuel that can go into the

engine.

The main metering system

The main metering system may be the simplest system of all, since it is

simply the venturi principle in operation. At cruising speeds, the engine

sucks enough air to constantly draw fuel through the main fuel nozzle.

The main fuel nozzle or jet is calibrated to provide a metering system.

The metering system is necessary to prevent an excess amount of fuel

flowing into the intake manifold, creating an overly rich mixture.

Power circuit

The main metering system works very well at normal engine loads, but

when the throttle is in the wide-open position, the engine needs more fuel

to prevent detonation and give it full power. The power system provides

additional fuel by opening up another passage that leads to the main

nozzle. This passageway is controlled by a power valve.

Float circuit

When the fuel pump pushes fuel into the carburetor, it flows through a

seat and past a needle which is a kind of shutoff valve. The fuel flows

into the float bowl and raises a hinged float so that the float arm pushes

the needle into the seat and shuts off the fuel. When the fuel level drops,

the float drops and more fuel enters the bowl. In this way, a constant fuel

supply is maintained.

ExhausTEC FEATURES

• ExhausTEC is incorporated in Silencer to induct optimum

volume of air-fuel mixture inside combustion chamber at mid

range engine

revolutions i.e. @ 3000-4000 rpm for improving low end torque and

drive-ability.

ExhausTEC – Advantages and Benefits

Advantages

• Improved volumetric efficiency.

• Improved & optimized low end torque.

• Improved Scavenging.

Benefits

• Less frequent gear shifting in city driving conditions.

• Less frequent clutch operation.

• Subsequent increase in fuel efficiency (Mileage).

• Better engine performance – Power & Pick-up.

• Improved drive-ability especially at low and mid range engine

R.P.M.

ExhausTEC – The unique ExhausTEC

technology allows you to rev up when your

heart feels like and the engine will pick up

instantaneously irrespective of the gear you

are in. It improves engine torque even at low

rpms and is optimized to get maximum

performance from the engine. Gives a feeling

of abundant latent power at any stage of

riding, which ensures effortless pulling for

any load conditions.

• So wats the cost of installing the ExhausTEC on pulsar dtsi v1??

IT WILL COST AROUND 3600/- , FROM AUTHORISED

DEALER.THE PORFORMENCE WILL INCREASE A BIT, ENGIN

NOTE WILL CHANGE AND MARGINALINCREASE IN EFFICINCY.

• its exhaust TEC = Torque Expansion Chamber 80 % of

the exhaust is allowed to leave from the Bike n rest 20%

is accumulated n sent back into the chamber which hits

the pistons to give u that extra torque n push/ jerk when u

throttle. only makes a little difference in the initial pick

up of the pulsar, which every1 brags about

Why would spent exhaust gases be sent into the exhaust

chamber? What purpose does it serve?

The final stroke is the exhaust stroke where the exhaust valve

opens as the piston moves from BDC to TDC. How will the gases

enter the chamber?? The exhaust valve would close as soon the

piston comes down as the intake valve opens.

i am not really 100% sure abt the principle behind the

ExhausTEC. but it has something to do with the generation of a

secondary pressure wave which helps the silencer to scavenge the

spent gases fully from the cylinder, so that during the intake

stroke there is more volume for the fresh charge. more fresh

charge, more BANG and more power.

Induction of optimum volume of

air-fuel mixture i.e. Improved

volumetric efficiency.

ExhausTEC

ExhausTEC stands for Exhaust Torque Expansion Chamber, a Bajaj Auto trademark.

The technology involves use of a small chamber connected to the exhaust pipe of the

engine to modify the back-pressure and the swirl characteristics, with an aim to improve

the low-end performance of the bikes. This was attempted in response to the issue of a

reported lack of low-end response in Bajaj’s single-cylinder four-stroke engines. The

ExhausTEC technology is claimed to be highly effective in improving the overall

engine response, especially the low-end torque characteristics. This enhanced

performance is claimed to come at no loss of top-end performance or engine

smoothness.

Expansion chamber

An Expansion chamber is an exhaust system used on a two-stroke cycle engine to

enhance its power output by improving its volumetric efficiency. It makes use of the

energy left in the burnt exhaust exiting the cylinder to aid the filling of the cylinder for

the next cycle. It is the two-stroke equivalent of the tuned pipes (or headers) used on

four-stroke cycle engines.

How it works

The high pressure gas exiting the cylinder initially flows in the form of a “wavefront” as

all disturbances in fluids do. The exhaust gas pushes its way into the pipe which is

already occupied by gas from previous cycles, pushing that gas ahead and causing a

wave front. Once the gas flow itself stops, the wave continues on by passing the energy

to the next gas down stream and so on to the end of the pipe. If this wave encounters

any change in cross section or temperature it will reflect a portion of its strength in the

opposite direction to its travel. For example a high pressure wave encountering an

increase in area will reflect back a low pressure wave in the opposite direction. A high

pressure wave encountering a decrease in area will reflect back a high pressure wave in

the opposite direction. The basic principle is described in wave dynamics. An expansion

chamber makes use of this phenomenon by varying its diameter (cross section) and

length to cause these reflections to arrive back at the cylinder at the desired times in the

cycle.

Parts of an expansion chamber

There are three main parts to the expansion cycle.

Blowdown

When the descending piston first exposes the exhaust port on the cylinder wall, the

exhaust flows out powerfully due to its own pressure without assistance from the

expansion chamber and so the diameter/area over the length of the first portion of the

pipe is constant or near constant with a divergence of 0 to 2 degrees which preserves

wave energy. This section of the system is called the “head pipe” (the exhaust port

length is considered part of the head pipe for measurement purposes). By keeping the

head pipe diameter near constant, the energy in the wave is preserved because there is

no expansion until needed later in the cycle. In any case the flow leaving the cylinder

during most of the blowdown process is sonic or supersonic and therefore no wave

could travel back into the cylinder against that flow.

Transfer

Once the exhaust pressure has fallen to near atmospheric level the piston uncovers the

transfer ports. At this point energy from the expansion chamber can be used to aid the

flow of fresh mixture into the cylinder. To do this the expansion chamber is increased in

diameter so that the out going high pressure wave reflects a negative pressure wave

back toward the cylinder. This negative pressure arrives in the cylinder during the

transfer cycle and greatly increases the flow of fresh mixture into the cylinder and can

even suck fresh mixture out into the headpipe. This part of the pipe is called the

divergent (or diffuser) section and it diverges at 6 to 12 degrees. It may be made up of

more than one diverging cone depending on requirements.

Port blocking

When the transfer is complete the piston is on the way back up on its compression

stroke but the exhaust port is still open, an unavoidable problem with the two stroke

design. To help prevent the piston pushing fresh mixture out the open exhaust port a

strong high pressure wave from the expansion chamber is timed to arrive during the

compression stroke. The port blocking wave is created by reducing the diameter of the

chamber. This is called the convergent section (a.k.a baffle cone or section). The

outgoing high pressure wave hits the narrowing convergent section and reflects back a

high pressure wave to the cylinder which arrives in time to block the port during the

compression stroke and can push back into the cylinder any fresh mixture drawn out

into the head pipe. The convergent section is made to converge at 8 to 90 degrees

depending on requirements.

Combined with the high pressure wave there is a general rise in pressure in the chamber

caused by deliberately restricting the outlet with a small tube called the stinger. The

stinger restricts flow out of the chamber to cause higher pressure during the

compression cycle and empties the chamber during the compression/power stroke to

ready it for the next cycle. The stingers length and inside diameter are selected to match

the engines requirements. (The inside diameter has the greatest effect and so is the most

sensitive of the two.)

Complicating Factors

The operation of expansion chambers in practice is not as straightforward as described

above. Waves traveling back up the pipe encounter the divergent section in reverse and

reflect a portion of their energy back out. Temperature variations in different parts of

the pipe cause reflections and changes in the local speed of sound. Sometimes these

secondary wave reflections can inhibit the desired goal of more power.

It is useful to keep in mind that although the waves traverse the entire expansion

chamber over each cycle, the actual gasses leaving the cylinder during a particular cycle

do not. The gas flows and stops intermittently and the wave continues on to the end of

the pipe. The hot gasses leaving the port form a “slug” which fills the header pipe and

remains there for the duration of that cycle. This causes a high temperature zone in the

head pipe which is always filled with the most recent and hottest gas. Because this area

is hotter, the speed of sound and thus the speed of the waves that travel theough it are

increased. During the next cycle that slug of gas will be pushed down the pipe by the

next slug to occupy the next zone and so on. The volume this “slug” occupies constantly

varies according to throttle position and engine speed. It is only the wave energy itself

that traverses the whole pipe during a single cycle. The actual gas leaving the pipe

during a particular cycle was created two or three cycles earlier.

Expansion chambers almost always have turns and curves built into them to

accommodate their fit within the engine bay. Gasses and waves do not behave in the

same way when encountering turns. Waves travel by reflecting and spherical radiation.

Turns causes a loss in the sharpness of the wave forms and therefore must be kept to a

minimum to avoid unpredictable losses.

Calculations used to design expansion chambers take into account only the primary

wave actions. This is usually fairly close but errors can occur due to these complicating

factors.

How Expansion chambers are made

There are three main methods of fabricating expansion chambers.

Hand formed

Flat sheet metal is rolled into cones and round sections, which are then welded together

section by section. Although time consuming, it is usually the method chosen for

development of a new design due to its flexibility, accuracy and low tooling costs.

Hydro forming

Two flat representations of the required finished pipe are cut out of sheet metal. The

edges of the two identical flat cutouts are welded together forming a sandwich. On one

end of the pipe a fitting is welded and high-pressure water is pumped into the cavity

between the sheets. The pressure inflates the flat sheet into its final rounded shape. This

method can be quicker than hand forming and only slightly more costly in tooling,

however it requires a number of trials before a finished design as accurate as hand

formed or stamped can be produced. All curves must be made in a single plane so

cutting apart and re-welding is often required but the final product can be as good as a

stamped pipe if enough care is taken to be precise.

Stamping

Flat sheet metal is pressed between a male and female mold in the shape of the required

pipe. Each half of the pipe is stamped this way and the two halves are welded together.

Stamping requires expensive tooling and machinery and is used only for mass

production.

(Note-Functionally, expansion chambers need not be round in cross section but in

practice a round shape is the best acoustically and is the only shape which (at a

reasonable weight) can withstand the intense vibration and pounding without cracking.)

Summary

All these events need to be synchronized with the engine port timings and speed. An

expansion chamber “tuned” for 8,000 rpm will not deliver the proper wave timings at

4,000 or 11,000 rpm. In fact it is likely to incur a power loss outside its “tuned” range.

The length of the pipe determines at what time the waves arrive back at the cylinder.

Longer pipes require more time for the waves to traverse and so will be tuned to a lower

rpm than a shorter pipe. The shorter the pipe the higher the rpm it is tuned to.

The rate of convergence/divergence of the cones determines the duration of the wave

returned. A gentle taper give a long duration but weaker return wave while a steeper

taper gives a short but strong return wave. The longer the wave, the broader the RPM

range at which it is useful. This extra power band width is at the sacrifice of peak

torque.

The diameter of the center or dwell section determines the ratio of scavenging suction

to port blocking pressure as well as the over all energy recovery. The resulting volume

determines the maximum pressure rise with large volumes giving less pressure rise. The

fatter the pipe the harder it sucks but the weaker the blocking pressure. Thinner pipes

will scavenge less but block the port very strongly. The optimum diameter is related to

compression ratio, the quality of the transfer port layout and its scavenging efficiency.

A variety of devices are used to try to extend the tuned range of the expansion chamber.

Pipes that slide like a trombone adjust the timing to match the rpm changes of the

running engine. Devices that control the exhaust port timing to vary blowdown duration

as well as extending the tuned range of the expansion chamber. Valves that open at

certain speeds to absorb or dump waves arriving at undesirable times.

Another approach to altering the tuned RPM of an expansion chamber is to alter the

speed of the pressure waves inside the exhaust pipe. The speed at which pressure waves

travel is greatly affected by temperature: higher temperature means faster wave speed.

As a result, expansion chambers can be retuned for higher-than-design RPM resonance,

by increasing the average temperature of the exhaust gases inside the pipe. Techniques

to achieve this increase in gas temperature can include: insulating the pipe (thermal

wrap), restricting flow from the pipe (smaller stinger diameter), or by retarding the

ignition timing at the correct RPM (a later burn allows more heat to escape into the

pipe).

Conversely, a pipe can be retuned to work at a lower-than-design RPM range by

reducing the temperature of the exhaust gases. Injecting water or a water-alcohol mix

into the headpipe of an expansion chamber can reduce temperatures significantly,

enough to lower the tuned RPM of an exhaust system by as much as 1500- 2000 RPM.

The heat absorbed as the liquid changes into a gas is responsible for the drop in

temperature. As a result, the two stroke exhaust can be tuned to stay “on the pipe” over

a remarkably wide RPM range, if the designer takes advantage of all the tools available.

Retrieved from “http://en.wikipedia.org/wiki/Expansion_chamber”

Expansion Chamber

The expansion chamber can be considered as a simple low

pass filter. The transmission loss performance is

determined by the cross-sectional area ratio between the

inlet and outlet ducts and the volume. With the single

expansion chamber the transmission loss falls to zero when

a half wavelength or multiple thereof equates to the length

of the chamber.

Extending the inlet and outlet pipes into the volume will give a more abrupt impedance

change and hence a larger transmission loss.

The transmission loss is given by:

where

f = frequency [Hz]

fn = resonant frequency [Hz]

c = speed of sound [ms-1]

S = cross-sectional area of inlet and outlet ducts [m2]

Sc = cross-sectional area of expansion chamber [m2]

Lc = length of expansion chamber [m]

Due Tempi & Le Espansioni Theory

How Two Strokes and Expansion Chambers Work

(I think this fabulous animation was created by Joseph Schuster. It doesn’t show a Rumi

engine, but this is a similar design.)

A two stroke (“due tempi” in Italian) is an engine in which each piston moves 2 stokes

for each firing of the spark plug. Two stoke engines do not have valves or the

associated cams. The intake of air and fuel and exhaust are controlled by ports in the

cylinder walls that are covered and uncovered by the movement of the piston.

Compared to 4 stroke engines, 2 stroke engines are light (no valve train) and they fire

twice as often creating more power than a similar 4 stroke. Additionally, oil is mixed

with the fuel (called premix) and is used to lubricate the crankcase. The animation

above illustrates the engines function.

When the piston moves toward the spark plug (up), the following things happen:

Below the piston, air and fuel (along with the premixed oil) are sucked into the

crankcase through the intake port uncovered by the piston. The oil in the fuel lubricates

the big and small ends of the crank, cylinder walls and other bearings in the crankcase.

Above the piston the waste gasses are forced out the exhaust port, and after that port is

closed off by the rising piston the charge is compressed for ignition.

After ignition the piston moves away from the spark plug (down) and the following

things happen: The power generated by the ignition of the charge turns the crank.

Above the piston the spent charge starts to escape out the exhaust port as it is uncovered

by the piston. Below the piston the fuel and air mixture in the crankcase is being

compressed. The intake port opens next as the piston uncovers it and the air and fuel is

forced through the intake port into the combustion chamber. This charge being forced

into the combustion chamber also pushes the spent charge out the exhaust port.

Now if that all makes sense, it may be clear that there is inefficiency with the intake and

exhausts ports: both happen to be open at the same time during some of the process!

Why doesn’t the intake charge just slide across the piston and out the exhaust port?

Well, to some degree it does. Note that Rumi’s have a deflector on the piston crown; a

ridge that is designed to divert the charge some and help prevent the intake from just

sliding through the combustion chamber. But this is where the expansion chamber

exhaust comes into effect. The expansion chamber is designed so that at certain RPMs

the exhaust gasses resonate just right and help suck out the spent gasses and then reflect

back and compress the charge back into the combustion chamber! This is what two

stroke riders mean when they say the engine “comes onto the pipe” at the right RPM the

engine becomes much more powerful as the expansion chamber starts to help the

engine run much more efficiently. Obviously, this effect can greatly improve a two

stroke engine’s performance!

Note that the engine in the illustration above has a reed valve between the carburetors

and the crankcase. This valve prevents the intake charge from escaping out the

carburetors. Rumi’s do not have this valve and this explains why Rumi’s never rust

behind the engine: they are always covered by a thin film of oil that escapes the

carburetors’!

Our objective with the 5-stroke engine is to develop a gasoline engine with fuel consumption and emission levels comparable to that of current diesel engines, without the serious problem of particulate and NOx emissions that plague diesels.

The engine concept, which was invented by Gerhard Schmitz, has been developed by Ilmor into a working engine using a rapid prototype cast cylinder head, a machined from solid cylinder block and separate electrically powered oil and water pumps. Two overhead camshafts operate the conventional coil spring valvegear with the HP camshaft running at 0.5 x crank speed and the LP camshaft running at 1 x crank speed. The engine is also turbocharged to increase the engine rating.

Principle of operation

The 5-stroke concept engine utilizes two fired cylinders (High Pressure – HP) operating on a conventional 4-stroke cycle which alternately exhaust into a central expansion cylinder (Low Pressure – LP), whereupon the burnt gases perform further work. The LP cylinder decouples the expansion and compression processes and enables the optimum expansion ratio to be selected independently of the compression ratio.

Running of the concept engine has produced impressive fuel consumption readings over a very wide operating range. This is because at the onset of knock a greater percentage of work can be extracted in the LP cylinder, giving a degree of self compensation.

Further development

Having run the proof of concept engine, Ilmor is now looking to produce a second phase development engine for in-vehicle testing. The performance targets for this engine are as follows:

• Brake Specific Fuel Consumption of 215 g/kWh
  (10% improvement on current 4 stroke technology)

• 20% lighter than existing production engines

• Power density of 150 bhp/L

Advantages of the 5-stroke concept

• A secondary cylinder provides an additional expansion process enabling extra work to be extracted, hence increasing thermodynamic efficiency.

• The engine runs an overall expansion ratio approaching that of a diesel engine – in the region of 14.5:1

• Minimised pumping work due to the downsizing effect from highly rated firing cylinders.

• The compression ratio can be reduced to delay knock onset without a reduction in performance.

• Because the firing cylinders can be very highly rated, the engine is relatively compact.

• The fuel consumption does not rise as rapidly with increasing BMEP, as retarding rejects more energy into the expansion cylinder.

• The engine uses 100% conventional technology and so requires no new manufacturing techniques.

5-stroke performance figures

• Engine capacity 700cc (turbocharged)

• Peak power 130 bhp @ 7000 rpm

• Peak torque 166 Nm @ 5000 rpm

• Fuel consumption of only 226 g/kWh

Ilmor is using its race engine expertise to bring developments to the field of energy efficient engines. Motor racing is not generally associated with fuel economy, but the lessons learned during periods of intense engine development can be applied with great effect to create highly fuel efficient engines.

Fuel efficiency can be improved by downsizing engines – creating the same amount of power from a smaller swept volume (smaller capacity) which typically burns a smaller amount of fuel. High performance engine design is all about extracting as much power as possible from a defined capacity by the use of intelligent design, low friction coatings or even completely new concepts. All of this knowledge can therefore be applied to maximise the power output of a small capacity, fuel efficient engine.

Our flexible approach ensures that we are able to build on a concept and develop innovative, tailored and most importantly working solutions for our clients, allowing physical testing and ongoing development of the concept.

• Designs to customer specification

• Cost effective solutions

• Rapid manufacture / Rapid prototype / Short lead time

• Sub system or complete engine

5-stroke concept engine

One such example of this application of our engineering knowledge is the patented 5-stroke engine which Ilmor is currently developing. Our objective with the 5-stroke engine is to develop a gasoline engine with fuel consumption and emission levels comparable to that of current diesel engines, without the serious problem of particulate and NOx emissions that plague diesels.

The simplest way to demonstrate the 5-stroke principle was considered to be a 3 cylinder layout with two fired 4-stroke cylinders (High Pressure – HP) alternately exhausting into a central expansion cylinder (Low Pressure – LP) which provides a further expansion process on the exhaust gases (the 5th stroke).

The engine uses a rapid prototype cast cylinder head, a machined from solid cylinder block and separate electrically powered oil and water pumps. Two overhead camshafts operate the conventional coil spring valvegear with the HP camshaft running at 0.5 x crank speed and the LP camshaft running at 1 x crank speed. The engine is also turbocharged to increase the engine rating.

Reference: www.ilmor.co.uk

“The design goal is pretty simple, we wanted to take the 5.3L V8 and make it more efficient. We wanted the customer to have the same characteristics of throttle response, power, general performance and towing capability that we had with the original LM7–and provide the customer with a more fuel-efficient package.” – GM Engines division manager.

All corporate politics aside, the engineers at GM Powertrain have designed yet another mechanical marvel, and it’s all due to some remarkably modest changes to the very robust Gen III architecture on which the Gen IV is based. The new DOD-specific hardware includes two-stage switching lifters, a lifter oil manifold assembly (located in the valley of the engine), a redesigned lube circuit and oil pump, electronic throttle-by-wire operation, a pressure-activated muffler valve, and an improved E40 engine controller running DOD-specific software.

The “high value” 60-degree OHV V-6, ie the DoD Junior Engines, will become the staple engine in vehicles which typically had the old 3100-, 3400- and more recent 3500-series engines.



Reference: http://www.superchevy.com/technical/engines_drivetrain/accessories_electronics/0405sc_gmdod/index.html

(sample post – to be deleted later)

Internal combustion engine

From Wikipedia, the free encyclopedia

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (December 2008)

The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanical energy.^[1][2][3][4]

The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described.^[1][2][3][4]

The internal combustion engine (or ICE) is quite different from external combustion engines, such as steam or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixed with or contaminated by combustion products. Working fluids can be air, hot water, pressurised water or even liquid sodium, heated in some kind of boiler by fossil fuel, wood-burning, nuclear, solar etc.

A large number of different designs for ICEs have been developed and built, with a variety of different strengths and weaknesses. Powered by an energy-dense fuel (which is very frequently petrol, a liquid derived from fossil fuels) the ICE delivers an excellent power-to-weight ratio with few safety or other disadvantages. While there have been and still are many stationary applications, the real strength of internal combustion engines is in mobile applications and they dominate as a power supply for cars, aircraft, and boats, from the smallest to the biggest. Only for hand-held power tools do they share part of the market with battery powered devices.

Contents [hide] 1 Applications 2 Classification 2.1 Principles of operation 3 History 4 Engine configurations 4.1 Four stroke configuration 4.1.1 Operation 4.1.2 Combustion 4.2 Two stroke configuration 4.3 Wankel 4.4 Gas turbines 4.5 Jet engine 5 Engine cycle 5.1 Two-stroke 5.2 Four-stroke 5.3 Diesel cycle 5.4 Six-stroke 5.5 Brayton cycle 5.6 Obsolete 6 Fuels and oxidizers 6.1 Fuels 6.2 Oxidizers 7 Engine capacity 8 Common components 8.1 Combustion chambers 8.2 Ignition system 8.2.1 Spark 8.2.2 Compression 8.2.3 Ignition timing 8.3 Fuel systems 8.3.1 Carburetor 8.3.2 Fuel injection 8.3.3 Fuel pump 8.3.4 Other 8.4 Oxidiser-Air inlet system 8.4.1 Natural aspirated engines 8.4.2 Superchargers and turbochargers 8.4.3 Liquids 9 Parts 9.1 Valves 9.1.1 Piston engine valves 9.1.2 Control valves 9.2 Exhaust systems 9.3 Cooling systems 9.4 Piston 9.5 Propelling nozzle 9.6 Crankshaft 9.7 Flywheels 9.8 Starter systems 9.9 Lubrication Systems 9.10 Control systems 9.11 Diagnostic systems 10 Measures of engine performance 10.1 Energy efficiency 10.2 Measures of fuel/propellant efficiency 11 Air and noise pollution 12 See also 13 References 14 Bibliography 15 External links

//

[edit] Applications

Internal combustion engines are most commonly used for mobile propulsion in vehicles and portable machinery. In mobile equipment, internal combustion is advantageous since it can provide high power-to-weight ratios together with excellent fuel energy density. Generally using fossil fuel (mainly petroleum), these engines have appeared in transport in almost all vehicles (automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives).

Internal combustion engines appear in the form of gas turbines as well where a very high power is required, such as in jet aircraft, helicopters, and large ships. They are also frequently used for electric generators and by industry.

[edit] Classification

At one time the word, “Engine” (from Latin, via Old French, ingenium, “ability”) meant any piece of machinery—a sense that persists in expressions such as siege engine. A “motor” (from Latin motor, “mover”) is any machine that produces mechanical power. Traditionally, electric motors are not referred to as “Engines”; however, combustion engines are often referred to as “motors.” (An electric engine refers to a locomotive operated by electricity.)

Engines can be classified in many different ways: By the engine cycle used, the layout of the engine, source of energy, the use of the engine, or by the cooling system employed.

[edit] Principles of operation

Reciprocating:

• Two-stroke cycle
• Four-stroke cycle
• Six-stroke engine
• Diesel engine

• Atkinson cycle

Rotary:

• Wankel engine

Continuous combustion:
Brayton cycle:

• Gas turbine
• Jet engine (including turbojet, turbofan, ramjet, Rocket etc.)

[edit] History

[edit] Engine configurations

Internal combustion engines can be classified by their configuration.

[edit] Four stroke configuration

[edit] Operation

Basic Information As their name implies, operation of a four stroke internal combustion engines have 4 basic steps that repeat with every two revolutions of the engine:

1. Intake
   • Combustible mixtures are emplaced in the combustion chamber
2. Compression
   • The mixtures are placed under pressure
3. Power
   • The mixture is burnt, almost invariably a deflagration, although a few systems involve detonation. The hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
4. Exhaust
   • The cooled combustion products are exhausted into the atmosphere

Many engines overlap these steps in time; jet engines do all steps simultaneously at different parts of the engines.

[edit] Combustion

All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with oxygen from the air (though it is possible to inject nitrous oxide in order to do more of the same thing and gain a power boost). The combustion process typically results in the production of a great quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at very high temperature; the temperature reached is determined by the chemical make up of the fuel and oxidisers (see stoichiometry).

The most common modern fuels are made up of hydrocarbons and are derived mostly from fossil fuels (petroleum). Fossil fuels include diesel fuel, gasoline and petroleum gas, and the rarer use of propane. Except for the fuel delivery components, most internal combustion engines that are designed for gasoline use can run on natural gas or liquefied petroleum gases without major modifications. Large diesels can run with air mixed with gases and a pilot diesel fuel ignition injection. Liquid and gaseous biofuels, such as ethanol and biodiesel (a form of diesel fuel that is produced from crops that yield triglycerides such as soybean oil), can also be used. Some engines with appropriate modifications can also run on hydrogen gas.

Internal combustion engines require ignition of the mixture, either by spark ignition (SI) or compression ignition (CI). Before the invention of reliable electrical methods, hot tube and flame methods were used.

Gasoline Ignition Process

Gasoline engine ignition systems generally rely on a combination of a lead-acid battery and an induction coil to provide a high-voltage electrical spark to ignite the air-fuel mix in the engine’s cylinders. This battery is recharged during operation using an electricity-generating device such as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar (1.28 MPa), then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.

Diesel Ignition Process

Diesel engines and HCCI (Homogeneous charge compression ignition) engines, rely solely on heat and pressure created by the engine in its compression process for ignition. The compression level that occurs is usually twice or more than a gasoline engine. Diesel engines will take in air only, and shortly before peak compression, a small quantity of diesel fuel is sprayed into the cylinder via a fuel injector that allows the fuel to instantly ignite. HCCI type engines will take in both air and fuel but continue to rely on an unaided auto-combustion process, due to higher pressures and heat. This is also why diesel and HCCI engines are more susceptible to cold-starting issues, although they will run just as well in cold weather once started. Light duty diesel engines with indirect injection in automobiles and light trucks employ glowplugs that pre-heat the combustion chamber just before starting to reduce no-start conditions in cold weather. Most diesels also have a battery and charging system; nevertheless, this system is secondary and is added by manufacturers as a luxury for the ease of starting, turning fuel on and off (which can also be done via a switch or mechanical apparatus), and for running auxiliary electrical components and accessories. Most new engines rely on electrical and electronic control system that also control the combustion process to increase efficiency and reduce emissions.

[edit] Two stroke configuration

Engines based on the two-stroke cycle use two strokes (one up, one down) for every power stroke. Since there are no dedicated intake or exhaust strokes, alternative methods must be used to scavenge the cylinders. The most common method in spark-ignition two-strokes is to use the downward motion of the piston to pressurize fresh charge in the crankcase, which is then blown through the cylinder through ports in the cylinder walls.

Spark-ignition two-strokes are small and light for their power output and mechanically very simple; however, they are also generally less efficient and more polluting than their four-stroke counterparts. In terms of power per cubic centimetre, a single-cylinder small motor application like a two-stroke engine produces much more power than an equivalent four-stroke engine due to the enormous advantage of having one power stroke for every 360 degrees of crankshaft rotation (compared to 720 degrees in a 4 stroke motor).

Small displacement, crankcase-scavenged two-stroke engines have been less fuel-efficient than other types of engines when the fuel is mixed with the air prior to scavenging allowing some of it to escape out of the exhaust port. Modern designs (Sarich and Paggio) use air-assisted fuel injection which avoids this loss, and are more efficient than comparably sized four-stroke engines. Fuel injection is essential for a modern two-stroke engine in order to meet ever more stringent emission standards.

Research continues into improving many aspects of two-stroke motors including direct fuel injection, amongst other things. The initial results have produced motors that are much cleaner burning than their traditional counterparts. Two-stroke engines are widely used in snowmobiles, lawnmowers, string trimmers, chain saws, jet skis, mopeds, outboard motors, and many motorcycles. Two-stroke engines have the advantage of an increased specific power ratio (i.e. power to volume ratio), typically around 1.5 times that of a typical four-stroke engine.

The largest internal combustion engines in the world are two-stroke diesels, used in some locomotives and large ships. They use forced induction (similar to super-charging) to scavenge the cylinders; an example of this type of motor is the Wartsila-Sulzer turbocharged two-stroke diesel as used in large container ships. It is the most efficient and powerful internal combustion engine in the world with over 50% thermal efficiency.^{[5][6][7][8][9]} For comparison, the most efficient small four-stroke motors are around 43% thermal efficiency (SAE 900648); size is an advantage for efficiency due to the increase in the ratio of volume to surface area.

Common cylinder configurations include the straight or inline configuration, the more compact V configuration, and the wider but smoother flat or boxer configuration. Aircraft engines can also adopt a radial configuration which allows more effective cooling. More unusual configurations such as the H, U, X, and W have also been used.

Multiple crankshaft configurations do not necessarily need a cylinder head at all because they can instead have a piston at each end of the cylinder called an opposed piston design. Because here gas in- and outlets are positioned at opposed ends of the cylinder, one can achieve uniflow scavenging, which is, like in the four stroke engine, efficient over a wide range of revolution numbers. Also the thermal efficiency is improved because of lack of cylinder heads. This design was used in the Junkers Jumo 205 diesel aircraft engine, using at either end of a single bank of cylinders with two crankshafts, and most remarkably in the Napier Deltic diesel engines. These used three crankshafts to serve three banks of double-ended cylinders arranged in an equilateral triangle with the crankshafts at the corners. It was also used in single-bank locomotive engines, and continues to be used for marine engines, both for propulsion and for auxiliary generators.

[edit] Wankel

The Wankel engine (rotary engine) does not have piston strokes. It operates with the same separation of phases as the four-stroke engine with the phases taking place in separate locations in the engine. In thermodynamic terms it follows the Otto engine cycle, so may be thought of as a “four-phase” engine. While it is true that three power strokes typically occur per rotor revolution due to the 3/1 revolution ratio of the rotor to the eccentric shaft, only one power stroke per shaft revolution actually occurs; this engine provides three power ’strokes’ per revolution per rotor giving it a greater power-to-weight ratio than piston engines. This type of engine is most notably used in the current Mazda RX-8, the earlier RX-7, and other models.

[edit] Gas turbines

A gas turbine is a rotary machine similar in principle to a steam turbine and it consists of three main components: a compressor, a combustion chamber, and a turbine. The air after being compressed in the compressor is heated by burning fuel in it. About two-thirds of the heated air combined with the products of combustion is expanded in a turbine resulting in work output which is used to drive the compressor. The rest (about one-third) is available as useful work output.

[edit] Jet engine

Jet engines take a large volume of hot gas from a combustion process (typically a gas turbine, but rocket forms of jet propulsion often use solid or liquid propellants, and ramjet forms also lack the gas turbine) and feed it through a nozzle which accelerates the jet to high speed. As the jet accelerates through the nozzle, this creates thrust and in turn does useful work.

[edit] Engine cycle

[edit] Two-stroke

This system manages to pack one power stroke into every two strokes of the piston (up-down). This is achieved by exhausting and re-charging the cylinder simultaneously.

The steps involved here are:

1. Intake and exhaust occur at bottom dead center. Some form of pressure is needed, either crankcase compression or super-charging.
2. Compression stroke: Fuel-air mix compressed and ignited. In case of Diesel: Air compressed, fuel injected and self ignited
3. Power stroke: piston is pushed downwards by the hot exhaust gases.

[edit] Four-stroke

Engines based on the four-stroke (“Otto cycle”) have one power stroke for every four strokes (up-down-up-down) and employ spark plug ignition. Combustion occurs rapidly, and during combustion the volume varies little (“constant volume”).^[10] They are used in cars, larger boats, some motorcycles, and many light aircraft. They are generally quieter, more efficient, and larger than their two-stroke counterparts.

The steps involved here are:

1. Intake stroke: Air and vaporized fuel are drawn in.
2. Compression stroke: Fuel vapor and air are compressed and ignited.
3. Combustion stroke: Fuel combusts and piston is pushed downwards.
4. Exhaust stroke: Exhaust is driven out. During the 1st, 2nd, and 4th stroke the piston is relying on power and the momentum generated by the other pistons. In that case, a four cylinder engine would be less powerful than a six or eight cylinder engine.

There are a number of variations of these cycles, most notably the Atkinson and Miller cycles. The diesel cycle is somewhat different.

[edit] Diesel cycle

Most truck and automotive diesel engines use a cycle reminiscent of a four-stroke cycle, but with a compression heating ignition system, rather than needing a separate ignition system. This variation is called the diesel cycle. In the diesel cycle, diesel fuel is injected directly into the cylinder so that combustion occurs at constant pressure, as the piston moves.

[edit] Six-stroke

First invented in 1883, the six-stroke engine has seen renewed interest over the last 20 or so years.

Four kinds of six-stroke use a regular piston in a regular cylinder (Griffin six-stroke, Bajulaz six-stroke, Velozeta six-stroke and Crower six-stroke), firing every three crankshaft revolutions. The systems capture the wasted heat of the four-stroke Otto cycle with an injection of air or water.

The Beare Head and “piston charger” engines operate as opposed-piston engines, two pistons in a single cylinder, firing every two revolutions rather more like a regular four-stroke.

[edit] Brayton cycle

A gas turbine is a rotary machine somewhat similar in principle to a steam turbine and it consists of three main components: a compressor, a combustion chamber, and a turbine. The air after being compressed in the compressor is heated by burning fuel in it, this heats and expands the air, and this extra energy is tapped by the turbine which in turn powers the compressor closing the cycle and powering the shaft.

Gas turbine cycle engines employ a continuous combustion system where compression, combustion, and expansion occur simultaneously at different places in the engine—giving continuous power. Notably the combustion takes place at constant pressure, rather than with the Otto cycle, constant volume.

[edit] Obsolete

The very first internal combustion engines did not compress the mixture.^{[citation needed]} The first part of the piston downstroke drew in a fuel-air mixture, then the inlet valve closed and, in the remainder of the down-stroke, the fuel-air mixture fired. The exhaust valve opened for the piston upstroke. This attempt at imitating the principle of a steam engine were very inefficient.

[edit] Fuels and oxidizers

Engines are often classified by the fuel (or propellant) used.

[edit] Fuels

Nowadays, fuels used include:

• Petroleum:
  • Petroleum spirit (North American term: gasoline, British term: petrol)
  • Petroleum diesel.
  • Autogas (liquified petroleum gas).
  • Compressed natural gas.
  • Jet fuel (aviation fuel)
  • Residual fuel
• Coal:
  • Most methanol is made from coal.
  • Gasoline can be made from carbon (coal) using the Fischer-Tropsch process
  • Diesel fuel can be made from carbon using the Fischer-Tropsch process
• Biofuels and vegoils:
  • Peanut oil and other vegoils.
  • Biofuels:
    • Biobutanol (replaces gasoline).
    • Biodiesel (replaces petrodiesel).
    • Bioethanol and Biomethanol (wood alcohol) and other biofuels (see Flexible-fuel vehicle).
    • Biogas
• Hydrogen (mainly spacecraft rocket engines)

Even fluidized metal powders and explosives have seen some use. Engines that use gases for fuel are called gas engines and those that use liquid hydrocarbons are called oil engines, however gasoline engines are also often colloquially referred to as, “gas engines” (“petrol engines” in the UK).

The main limitations on fuels are that it must be easily transportable through the fuel system to the combustion chamber, and that the fuel releases sufficient energy in the form of heat upon combustion to make practical use of the engine.

Diesel engines are generally heavier, noisier, and more powerful at lower speeds than gasoline engines. They are also more fuel-efficient in most circumstances and are used in heavy road vehicles, some automobiles (increasingly so for their increased fuel efficiency over gasoline engines), ships, railway locomotives, and light aircraft. Gasoline engines are used in most other road vehicles including most cars, motorcycles, and mopeds. Note that in Europe, sophisticated diesel-engined cars have taken over about 40% of the market since the 1990s. There are also engines that run on hydrogen, methanol, ethanol, liquefied petroleum gas (LPG), and biodiesel. Paraffin and tractor vaporizing oil (TVO) engines are no longer seen.

Hydrogen

At present, hydrogen is mostly used as fuel for rocket engines. In the future, hydrogen might replace more conventional fuels in traditional internal combustion engines. If hydrogen fuel cell technology becomes widespread, then the use of internal combustion engines may be phased out.

Although there are multiple ways of producing free hydrogen, those methods require converting combustible molecules into hydrogen or consuming electric energy. Unless that electricity is produced from a renewable source—and is not required for other purposes— hydrogen does not solve any energy crisis. In many situations the disadvantage of hydrogen, relative to carbon fuels, is its storage. Liquid hydrogen has extremely low density (14 times lower than water) and requires extensive insulation—whilst gaseous hydrogen requires heavy tankage. Even when liquefied, hydrogen has a higher specific energy but the volumetric energetic storage is still roughly five times lower than petrol. However the energy density of hydrogen is considerably higher than that of electric batteries,^{[citation needed]} making it a serious contender as an energy carrier to replace fossil fuels. The ‘Hydrogen on Demand’ process (see direct borohydride fuel cell) creates hydrogen as it is needed, but has other issues such as the high price of the sodium borohydride which is the raw material.

[edit] Oxidizers

Since air is plentiful at the surface of the earth, the oxidizer is typically atmospheric oxygen which has the advantage of not being stored within the vehicle, increasing the power-to-weight and power to volume ratios. There are other materials that are used for special purposes, often to increase power output or to allow operation under water or in space.

• Compressed air has been commonly used in torpedoes.
• Compressed oxygen, as well as some compressed air, was used in the Japanese Type 93 torpedo. Some submarines are designed to carry pure oxygen. Rockets very often use liquid oxygen.

• Nitromethane is added to some racing and model fuels to increase power and control combustion.
• Nitrous oxide has been used—with extra gasoline—in tactical aircraft and in specially equipped cars to allow short bursts of added power from engines that otherwise run on gasoline and air. It is also used in the Burt Rutan rocket spacecraft.
• Hydrogen peroxide power was under development for German World War II submarines and may have been used in some non-nuclear submarines and was used on some rocket engines (notably Black Arrow and Me-163 rocket plane)
• Other chemicals such as chlorine or fluorine have been used experimentally, but have not been found to be practical.

[edit] Engine capacity

For piston engines, an engine’s capacity is the engine displacement, in other words the volume swept by all the pistons of an engine in a single movement. It is generally measured in litres (L) or cubic inches (c.i.d. or cu in or in³) for larger engines, and cubic centimetres (abbreviated cc) for smaller engines. Engines with greater capacities are usually more powerful and provide greater torque at lower rpm, but also consume more fuel. Apart from designing an engine with more cylinders, there are two ways to increase an engines’ capacity. The first is to lengthen the stroke: the second is to increase the pistons’ diameter (See also: Stroke ratio). In either case, it may be necessary to make further adjustments to the fuel intake of the engine to ensure optimum performance.

[edit] Common components

[edit] Combustion chambers

Internal combustion engines can contain any number of combustion chambers (cylinders), with numbers between one and twelve being common, though as many as 36 (Lycoming R-7755) have been used. Having more cylinders in an engine yields two potential benefits: first, the engine can have a larger displacement with smaller individual reciprocating masses, that is, the mass of each piston can be less thus making a smoother-running engine since the engine tends to vibrate as a result of the pistons moving up and down. Doubling the number of the same size cylinders will double the torque and power. The downside to having more pistons is that the engine will tend to weigh more and generate more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease fuel efficiency and robs the engine of some of its power. For high-performance gasoline engines using current materials and technology—such as the engines found in modern automobiles, there seems to be a break-point around 10 or 12 cylinders after which the addition of cylinders becomes an overall detriment to performance and efficiency. Although, exceptions such as the W16 engine from Volkswagen exist.

• Most car engines have four to eight cylinders with some high performance cars having ten, twelve—or even sixteen, and some very small cars and trucks having two or three. In previous years, some quite large cars such as the DKW and Saab 92, had two-cylinder or two-stroke engines.
• Radial aircraft engines (now obsolete) had from three to 28 cylinders; an example is the Pratt & Whitney R-4360. A row contains an odd number of cylinders so an even number indicates a two- or four-row engine. The largest of these was the Lycoming R-7755 with 36 cylinders (four rows of nine cylinders), but it did not enter production.
• Motorcycles commonly have from one to four cylinders, with a few high performance models having six; although, some ‘novelties’ exist with 8, 10, or 12.
• Snowmobiles Usually have one to four cylinders and can be both 2 stroke or 4 stroke, normally in the in-line configuration however there are again some novelties that exist with V-4 Engines
• Small portable appliances such as chainsaws, generators, and domestic lawn mowers most commonly have one cylinder, but two-cylinder chainsaws exist.
• Large reversible two cycle marine diesels have a minimum of three to over ten cylinders. Freight diesel locomotives usually have around 12 to 20 cylinders due to space limitations as larger cylinders take more space (volume ) per kwh, due to the limit on average piston speed of less than 30 ft/sec on engines lasting more than 40000 hours under full power.

[edit] Ignition system

The ignition system of an internal combustion engines depends on the type of engine and the fuel used. Petrol engines are typically ignited by a precisely timed spark, and diesel engines by compression heating. Historically, outside flame and hot-tube systems were used, see hot bulb engine.

[edit] Spark

The mixture is ignited by an electrical spark from a spark plug—the timing of which is very precisely controlled. Almost all gasoline engines are of this type. Diesel engines timing is precisely controlled by the pressure pump and injector.

[edit] Compression

Ignition occurs as the temperature of the fuel/air mixture is taken over its autoignition temperature, due to heat generated by the compression of the air during the compression stroke. The vast majority of compression ignition engines are diesels in which the fuel is mixed with the air after the air has reached ignition temperature. In this case, the timing comes from the fuel injection system. Very small model engines for which simplicity and light weight is more important than fuel costs use easily ignited fuels (a mixture of kerosene, ether, and lubricant) and adjustable compression to control ignition timing for starting and running.

[edit] Ignition timing

For reciprocating engines, the point in the cycle at which the fuel-oxidizer mixture is ignited has a direct effect on the efficiency and output of the ICE. The thermodynamics of the idealized Carnot heat engine tells us that an ICE is most efficient if most of the burning takes place at a high temperature, resulting from compression—near top dead center. The speed of the flame front is directly affected by the compression ratio, fuel mixture temperature, and Octane rating or cetane number of the fuel. Leaner mixtures and lower mixture pressures burn more slowly requiring more advanced ignition timing. It is important to have combustion spread by a thermal flame front (deflagration), not by a shock wave. Combustion propagation by a shock wave is called detonation and, in engines, is also known as pinging or Engine knocking.

So at least in gasoline-burning engines, ignition timing is largely a compromise between an earlier “advanced” spark—which gives greater efficiency with high octane fuel—and a later “retarded” spark that avoids detonation with the fuel used. For this reason, high-performance diesel automobile proponents such as, Gale Banks, believe that

There’s only so far you can go with an air-throttled engine on 91-octane gasoline. In other words, it is the fuel, gasoline, that has become the limiting factor. … While turbocharging has been applied to both gasoline and diesel engines, only limited boost can be added to a gasoline engine before the fuel octane level again becomes a problem. With a diesel, boost pressure is essentially unlimited. It is literally possible to run as much boost as the engine will physically stand before breaking apart. Consequently, engine designers have come to realize that diesels are capable of substantially more power and torque than any comparably sized gasoline engine.^[11]

[edit] Fuel systems

Fuels burn faster and more efficiently when they present a large surface area to the oxygen in air. Liquid fuels must be atomized to create a fuel-air mixture, traditionally this was done with a carburetor in petrol engines and with fuel injection in diesel engines. Most modern petrol engines now use fuel injection too – though the technology is quite different. While diesel must be injected at an exact point in that engine cycle, no such precision is needed in a petrol engine. However, the lack of lubricity in petrol means that the injectors themselves must be more sophisticated.

[edit] Carburetor

Simpler reciprocating engines continue to use a carburetor to supply fuel into the cylinder. Although carburetor technology in automobiles reached a very high degree of sophistication and precision, from the mid-1980s it lost out on cost and flexibility to fuel injection. Simple forms of carburetor remain in widespread use in small engines such as lawn mowers and more sophisticated forms are still used in small motorcycles.

[edit] Fuel injection

Larger gasoline engines used in automobiles have mostly moved to fuel injection systems (see Gasoline Direct Injection). Diesel engines have always used fuel injection system because the timing of the injection initiates and controls the combustion.

Autogas (LPG) engines use either fuel injection systems or open- or closed-loop carburetors.

[edit] Fuel pump

Most internal combustion engines now require a fuel pump. Diesel engines use an all-mechanical precision pump system that delivers a timed injection direct into the combustion chamber, hence requiring a high delivery pressure to overcome the pressure of the combustion chamber. Petrol fuel injection delivers into the inlet tract at atmospheric pressure (or below) and timing is not involved, these pumps are normally driven electrically. Gas turbine and rocket engines use electrical systems.

[edit] Other

Other internal combustion engines like jet engines and rocket engines employ various methods of fuel delivery including impinging jets, gas/liquid shear, preburners and others.

[edit] Oxidiser-Air inlet system

Some engines such as solid rockets have oxidisers already within the combustion chamber but in most cases for combustion to occur, a continuous supply of oxidiser must be supplied to the combustion chamber.

[edit] Natural aspirated engines

When air is used with piston engines it can simply suck it in as the piston increases the volume of the chamber. However, this gives a maximum of 1 atmosphere of pressure difference across the inlet valves, and at high engine speeds the resulting airflow can limit potential power output.

[edit] Superchargers and turbochargers

A supercharger is a “forced induction” system which uses a compressor powered by the shaft of the engine which forces air through the valves of the engine to achieve higher flow. When these systems are employed the maximum absolute pressure at the inlet valve is typically around 2 times atmospheric pressure or more.

Turbochargers are another type of forced induction system which has its compressor powered by a gas turbine running off the exhaust gases from the engine.

Turbochargers and superchargers are particularly useful at high altitudes and they are frequently used in aircraft engines.

Duct jet engines use the same basic system, but eschew the piston engine, and replace it with a burner instead.

[edit] Liquids

In liquid rocket engines, the oxidiser comes in the form of a liquid and needs to be delivered at high pressure (typically 10-230 bar or 1–23 MPa) to the combustion chamber. This is normally achieved by the use of a centrifugal pump powered by a gas turbine – a configuration known as a turbopump, but it can also be pressure fed.

[edit] Parts

For a four-stroke engine, key parts of the engine include the crankshaft (purple), connecting rod (orange), one or more camshafts (red and blue), and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines there are one or more cylinders (grey and green), and for each cylinder there is a spark plug (darker-grey, gasoline engines only), a piston (yellow), and a crankpin (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke. The downward stroke that occurs directly after the air-fuel mix passes from the carburetor or fuel injector to the cylinder (where it is ignited) is also known as a power stroke.

A Wankel engine has a triangular rotor that orbits in an epitrochoidal (figure 8 shape) chamber around an eccentric shaft. The four phases of operation (intake, compression, power, and exhaust) take place in what is effectively a moving, variable-volume chamber.

[edit] Valves

All four-stroke internal combustion engines employ valves to control the admittance of fuel and air into the combustion chamber. Two-stroke engines use ports in the cylinder bore, covered and uncovered by the piston, though there have been variations such as exhaust valves.

[edit] Piston engine valves

In piston engines, the valves are grouped into ‘inlet valves’ which admit the entrance of fuel and air and ‘outlet valves’ which allow the exhaust gases to escape. Each valve opens once per cycle and the ones that are subject to extreme accelerations are held closed by springs that are typically opened by rods running on a camshaft rotating with the engines’ crankshaft.

[edit] Control valves

Continuous combustion engines—as well as piston engines—usually have valves that open and close to admit the fuel and/or air at the startup and shutdown. Some valves feather to adjust the flow to control power or engine speed as well.

[edit] Exhaust systems

Internal combustion engines have to manage the exhaust of the cooled combustion gas from the engine. The exhaust system frequently contains devices to control pollution, both chemical and noise pollution. In addition, for cyclic combustion engines the exhaust system is frequently tuned to improve emptying of the combustion chamber.

For jet propulsion internal combustion engines, the ‘exhaust system’ takes the form of a high velocity nozzle, which generates thrust for the engine and forms a colimated jet of gas that gives the engine its name.

[edit] Cooling systems

Combustion generates a great deal of heat, and some of this transfers to the walls of the engine. Failure will occur if the body of the engine is allowed to reach too high a temperature; either the engine will physically fail, or any lubricants used will degrade to the point that they no longer protect the engine.

Cooling systems usually employ air (air cooled) or liquid (usually water) cooling while some very hot engines using radiative cooling (especially some Rocket engines). Some high altitude rocket engines use ablative cooling where the walls gradually erode in a controlled fashion. Rockets in particular can use regenerative cooling which uses the fuel to cool the solid parts of the engine.

[edit] Piston

A piston is a component of reciprocating engines. It is located in a cylinder and is made gas-tight by piston rings. Its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In two-stroke engines the piston also acts as a valve by covering and uncovering ports in the cylinder wall.

[edit] Propelling nozzle

For jet engine forms of internal combustion engines a propelling nozzle is present. This takes the high temperature, high pressure exhaust and expands and cools it. The exhaust leaves the nozzle going at much higher speed and provides thrust, as well as constricting the flow from the engine and raising the pressure in the rest of the engine, giving greater thrust for the exhaust mass that exits.

[edit] Crankshaft

Most reciprocating internal combustion engines end up turning a shaft. This means that the linear motion of a piston must be converted into rotation. This is typically achieved by a crankshaft.

[edit] Flywheels

The flywheel is a disk or wheel attached to the crank, forming an inertial mass that stores rotational energy. In engines with only a single cylinder the flywheel is essential to carry energy over from the power stroke into a subsequent compression stroke. Flywheels are present in most reciprocating engines to smooth out the power delivery over each rotation of the crank and in most automotive engines also mount a gear ring for a starter. The rotational inertia of the flywheel also allows a much slower minimum unloaded speed and also improves the smoothness at idle. The flywheel may also perform a part of the balancing of the system and so by itself be out of balance, although most engines will use a neutral balance for the flywheel, enabling it to be balanced in a separate operation. The flywheel is also used as a mounting for the clutch or a torque converter in most automotive applications.

[edit] Starter systems

All internal combustion engines require some form of system to get them into operation. Most piston engines use a starter motor powered by the same battery as runs the rest of the electric systems. Large jet engines and gas turbines are started with a compressed air motor that is geared to one of the engine’s driveshafts. Compressed air can be supplied from another engine, a unit on the ground or by the aircraft’s APU. Small internal combustion engines are often started by pull cords. Motorcycles of all sizes were traditionally kick-started, though all but the smallest are now electric-start. Large stationary and marine engines may be started by the timed injection of compressed air into the cylinders – or occasionally with cartridges. Jump starting refers to assistance from another battery (typically when the fitted battery is discharged), while bump starting refers to an alternative method of starting by the application of some external force, e.g. rolling down a hill.

[edit] Lubrication Systems

Internal combustions engines require lubrication in operation that moving parts slide smoothly over each other. Insufficient lubrication subjects the parts of the engine to metal-to-metal contact, friction, heat build-up, rapid wear often culminating in parts becoming friction welded together eg pistons in their cylinders. Big end bearings seizing up will sometimes lead to a connecting rod breaking and poking out through the crankcase.

Several different types of lubrication systems are used. Simple two-stroke engines are lubricated by oil mixed into the fuel or injected into the induction stream as a spray. Early slow-speed stationary and marine engines were lubricated by gravity from small chambers similar to those used on steam engines at the time—with an engine tender refilling these as needed. As engines were adapted for automotive and aircraft use, the need for a high power-to-weight ratio led to increased speeds, higher temperatures, and greater pressure on bearings which in turn required pressure-lubrication for crank bearings and connecting-rod journals. This was provided either by a direct lubrication from a pump, or indirectly by a jet of oil directed at pickup cups on the connecting rod ends which had the advantage of providing higher pressures as the engine speed increased.

[edit] Control systems

Most engines require one or more systems to start and shutdown the engine and to control parameters such as the power, speed, torque, pollution, combustion temperature, efficiency and to stabilise the engine from modes of operation that may induce self-damage such as pre-ignition. Such systems may be referred to as engine control units.

Many control systems today are digital, and are frequently termed FADEC (Full Authority Digital Electronic Control) systems.

[edit] Diagnostic systems

Engine On Board Diagnostics (also known as OBD) is a computerized system that allows for electronic diagnosis of a vehicles’ powerplant. The first generation, known as OBD1, was introduced 10 years after the U.S. Congress passed the Clean Air Act in 1970 as a way to monitor a vehicles’ fuel injection system. OBD2, the second generation of computerized on-board diagnostics, was codified and recommended by the California Air Resource Board in 1994 and became mandatory equipment aboard all vehicles sold in the United States as of 1996.

[edit] Measures of engine performance

Engine types vary greatly in a number of different ways:

• energy efficiency
• fuel/propellant consumption (brake specific fuel consumption for shaft engines, thrust specific fuel consumption for jet engines)
• power to weight ratio
• thrust to weight ratio
• Torque curves (for shaft engines) thrust lapse (jet engines)
• Compression ratio for piston engines, Overall pressure ratio for jet engines and gas turbines

[edit] Energy efficiency

Once ignited and burnt, the combustion products—hot gases—have more available thermal energy than the original compressed fuel-air mixture (which had higher chemical energy). The available energy is manifested as high temperature and pressure that can be translated into work by the engine. In a reciprocating engine, the high-pressure gases inside the cylinders drive the engine’s pistons.

Once the available energy has been removed, the remaining hot gases are vented (often by opening a valve or exposing the exhaust outlet) and this allows the piston to return to its previous position (top dead center, or TDC). The piston can then proceed to the next phase of its cycle, which varies between engines. Any heat that isn’t translated into work is normally considered a waste product and is removed from the engine either by an air or liquid cooling system.

Engine efficiency can be discussed in a number of ways but it usually involves a comparison of the total chemical energy in the fuels, and the useful energy extracted from the fuels in the form of kinetic energy. The most fundamental and abstract discussion of engine efficiency is the thermodynamic limit for extracting energy from the fuel defined by a thermodynamic cycle. The most comprehensive is the empirical fuel efficiency of the total engine system for accomplishing a desired task; for example, the miles per gallon accumulated.

Internal combustion engines are primarily heat engines and as such the phenomenon that limits their efficiency is described by thermodynamic cycles. None of these cycles exceed the limit defined by the Carnot cycle which states that the overall efficiency is dictated by the difference between the lower and upper operating temperatures of the engine. A terrestrial engine is usually and fundamentally limited by the upper thermal stability derived from the material used to make up the engine. All metals and alloys eventually melt or decompose and there is significant researching into ceramic materials that can be made with higher thermal stabilities and desirable structural properties. Higher thermal stability allows for greater temperature difference between the lower and upper operating temperatures—thus greater thermodynamic efficiency.

The thermodynamic limits assume that the engine is operating in ideal conditions: a frictionless world, ideal gases, perfect insulators, and operation at infinite time. The real world is substantially more complex and all the complexities reduce the efficiency. In addition, real engines run best at specific loads and rates as described by their power curve. For example, a car cruising on a highway is usually operating significantly below its ideal load, because the engine is designed for the higher loads desired for rapid acceleration. The applications of engines are used as contributed drag on the total system reducing overall efficiency, such as wind resistance designs for vehicles. These and many other losses result in an engines’ real-world fuel economy that is usually measured in the units of miles per gallon (or fuel consumption in liters per 100 kilometers) for automobiles. The miles in miles per gallon represents a meaningful amount of work and the volume of hydrocarbon implies a standard energy content.

Most steel engines have a thermodynamic limit of 37%. Even when aided with turbochargers and stock efficiency aids, most engines retain an average efficiency of about 18%-20%.^[12][13] Rocket engine efficiencies are better still, up to 70%, because they combust at very high temperatures and pressures and are able to have very high expansion ratios.^[14]

There are many inventions concerned with increasing the efficiency of IC engines. In general, practical engines are always compromised by trade-offs between different properties such as efficiency, weight, power, heat, response, exhaust emissions, or noise. Sometimes economy also plays a role in not only the cost of manufacturing the engine itself, but also manufacturing and distributing the fuel. Increasing the engines’ efficiency brings better fuel economy but only if the fuel cost per energy content is the same.

[edit] Measures of fuel/propellant efficiency

For stationary and shaft engines including propeller engines, fuel consumption is measured by calculating the brake specific fuel consumption which measures the number of pounds of fuel that is needed to generate an hours’ worth of horsepower-energy. In metric units, the number of grams of fuel needed to generate a kilowatt-hour of energy is calculated.

For internal combustion engines in the form of jet engines, the power output varies drastically with airspeed and a less variable measure is used: thrust specific fuel consumption (TSFC), which is the number of pounds of propellant that is needed to generate impulses that measure a pound an hour. In metric units, the number of grams of propellant needed to generate an impulse that measures one kilonewton per second.

For rockets— TSFC can be used, but typically other equivalent measures are traditionally used, such as specific impulse and effective exhaust velocity.

[edit] Air and noise pollution

Internal combustion engines such as reciprocating internal combustion engines produce air pollution emissions, due to incomplete combustion of carbonaceous fuel. The main derivatives of the process are carbon dioxide CO₂, water and some soot—also called particulate matter (PM). The effects of inhaling particulate matter have been studied in humans and animals and include asthma, lung cancer, cardiovascular issues, and premature death. There are however some additional products of the combustion process that include nitrogen oxides and sulfur and some uncombusted hydrocarbons, depending on the operating conditions and the fuel-air ratio.

Not all of the fuel will be completely consumed by the combustion process; a small amount of fuel will be present after combustion, some of which can react to form oxygenates, such as formaldehyde or acetaldehyde, or hydrocarbons not initially present in the fuel mixture. The primary causes of this is the need to operate near the stoichiometric ratio for gasoline engines in order to achieve combustion and the resulting “quench” of the flame by the relatively cool cylinder walls, otherwise the fuel would burn more completely in excess air. When running at lower speeds, quenching is commonly observed in diesel (compression ignition) engines that run on natural gas. It reduces the efficiency and increases knocking, sometimes causing the engine to stall. Increasing the amount of air in the engine reduces the amount of the first two pollutants, but tends to encourage the oxygen and nitrogen in the air to combine to produce nitrogen oxides (NO_x) that has been demonstrated to be hazardous to both plant and animal health. Further chemicals released are benzene and 1,3-butadiene that are also particularly harmful; and not all of the fuel burns up completely, so carbon monoxide (CO) is also produced.

Carbon fuels contain sulfur and impurities that eventually lead to producing sulfur oxides (SO) and sulfur dioxide (SO₂) in the exhaust which promotes acid rain. One final element in exhaust pollution is ozone (O₃). This is not emitted directly but made in the air by the action of sunlight on other pollutants to form “ground level ozone”, which, unlike the “ozone layer” in the high atmosphere, is regarded as a bad thing if the levels are too high. Ozone is broken down by nitrogen oxides, so one tends to be lower where the other is higher.

For the pollutants described above (nitrogen oxides, carbon monoxide, sulphur dioxide, and ozone) there are accepted levels that are set by legislation to which no harmful effects are observed—even in sensitive population groups. For the other three: benzene, 1,3-butadiene, and particulates, there is no way of proving they are safe at any level so the experts set standards where the risk to health is, “exceedingly small”.

Finally, significant contributions to noise pollution are made by internal combustion engines. Automobile and truck traffic operating on highways and street systems produce noise, as do aircraft flights due to jet noise, particularly supersonic-capable aircraft. Rocket engines create the most intense noise.