Internal Combustion Engine Volumetric efficiency

Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways, but most notably the size of the valve openings compared to the volume of the cylinder and streamlining the ports. Engines with higher volumetric efficiency will generally be able to run at higher RPM, and thus power, settings as they will lose less power to moving air in and out of the engine.

There are several standard ways to improve volumetric efficiency. A common approach for manufacturers is to use a larger number of valves, see multi-valve, which cover a greater area of the cylinder head. Carefully streamlining the ports increases flow capability. This is referred to as Porting and is done with the aid of an air flow bench for testing. Today, automobile engines typically have four valves per cylinder for this reason. Many high performance cars in the 1970s used carefully arranged air intakes and "tuned" exhaust systems to "push" air into and out of the cylinders through the intrinsic resonance of the system. Two-stroke engines take this concept even further with expansion chambers that returns the escaping air-fuel mixture back to the cylinder. A more modern technique, variable valve timing, attempts to address changes in volumetric efficiency with changes in RPM of the engine -- at higher RPM the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine.

More "radical" solutions include the sleeve valve design, in which the valves are replaced outright with a rotating sleeve around the piston, or alternately a rotating sleeve under the cylinder head. In this system the ports can be as large as necessary, up to that of the entire cylinder wall. However there is a practical upper limit due to the strength of the sleeve, at larger sizes the pressure inside the cylinder can "pop" the sleeve if the port is too large.

Forced induction

Forced induction is a term used to describe internal combustion engines that are not naturally aspirated. Instead, a gas compressor is added to the air intake, thereby increasing the quantity of oxygen available for combustion. This compressed air is normally referred to as Boost or charge air.


Introduction

Forced induction can be used to increase the power of an engine or its efficiency, or both, without much extra weight. The ambient air that the engine is normally ingesting enters the compressor inlet of turbocharger or supercharger that is inline along the air intake tract. This effectively increases the pressure and density of the air, which allows for a much greater percentage of oxygen per volume of air intake to be added to the air/fuel mixture. The effects are an increase to the effective capacity of the engine without an increase in physical size. The forced induction approach has the advantage that the intake pressure may be regulated according to the engine speed, thus providing power from extra capacity at high speed, but without wasting fuel at lower speeds. A Nitrous Oxide system is also a form of forced induction. A simple oxidizer is injected either directly (direct port) or by a single fogger...with fuel(wet nitrous system) or without fuel(dry nitrous system).

Two of the commonly used forced induction technologies are turbochargers and superchargers. They differ mainly in the power source for the compressor. Turbochargers are driven by the exhaust gases of the engine, whereas superchargers are driven by a geartrain or belt connected to the crankshaft of the engine.


Comparison

Strengths and weaknesses vary according to the method of forcing induction largely based upon the inherent design functions of both. A turbocharger acts as an obstacle to exhaust gases due to its placement in the exhaust system tract. A supercharger uses torque generated from the rotational mass internal to the engine through the crank pulley. A turbo relies on the volume and velocity of exhaust gases to spool, or spin the turbine wheel. The turbine wheel is connected to the compressor wheel via a common shaft. The compressor wheel compresses the intake charge increasing the charge density by a large factor. The amount of time that it takes a turbocharger to reach the onset of boost is referred to as lag. A supercharger is 'on' all of the time, meaning that it is capable of producing a linear increase of boost up until redline. It is easier to target a desired boost with a turbocharger as there are many forms of boost controllers that allow a user to adjust to desired boost fairly easily. In order to achieve desired boost with a supercharger, a larger or smaller pulley must be installed.


Intercooling

A fundamental principle to forced induction is that compressing air raises its temperature. As a result, the charge density is reduced and the cylinders receive less fresh air than the system’s boost pressure prescribes. The risk of pre-ignition or "knock" in internal combustion engines greatly increases. These drawbacks are countered by charge-air cooling, which passes the air leaving the turbocharger or supercharger through a heat exchanger typically called an intercooler. This is done by cooling the charge air with an ambient flow of either air (air-air intercoolers) or liquid (liquid to air intercoolers), the charge air density is increased and the temperature is reduced.


Alcohol/Water Injection

Additionally, alcohol injection is an effective means of cooling the charge air. Methanol is the preferred alcohol due to its elemental properties, and is normally mixed with water to prevent evaporation. Methanol is typically injected pre throttle body. Methanol, unlike nitrous oxide or forced induction itself, doesn't add more oxygen to the charge, but by its low evaporation point changes from a liquid to a gas as its introduced into the air charge. The evaporation process uses the heat from the intake charge to complete the phase change. The alcohol is also a fuel in the charge which will cause a rich condition if used in excess. Due to the lower intake temperatures and denser air charge more power is exerted from the engine. Methanol is typically used in conjunction with poor quality fuel(pump gas) in order to run higher than normal boost pressures.

Like was stated above, adding forced induction increases the amount of air an engine can use for combustion, in effect allowing more fuel to be used with the available oxygen. Further, it increases an engine's dynamic compression ratio. As compression ratio increases, so does the threat of knock and therefore the need for higher octane fuel.

Homogeneous Charge Compression Ignition (HCCI)

Introduction

Homogeneous Charge Compression Ignition, or HCCI, is a form of internal combustion in which well mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be translated by an engine into work and heat.

HCCI has characteristics from each of the two most popular forms of combustion used in IC engines: homogeneous charge spark ignition (gasoline engines) and stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the concentration and temperature of the mixture are raised by compression until the entire mixture reacts simultaneously. Stratified charge compression ignition also relies on the heat and concentration resulting from compression, but combustion occurs at the boundary of unmixed fuel which is injected to initiate combustion.

The defining characteristic of HCCI is that the ignition occurs at several places at a time which makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently challenging to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine like emissions along with diesel engine like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without aftertreatment catalytic converter. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet automotive emission regulations.



History

HCCI engines have a long history, even though HCCI has not been as widely implemented as spark ignition or diesel injection. It is essentially an Otto combustion cycle. In fact, HCCI was popular before electronic spark ignition was used. One example is the hot-bulb engine which used a torch-heated head to add heat to the inducted gases. The extra heat combined with compression induced the conditions for combustion to occur.


Operation


Methods

A mixture of fuel and air will ignite when the concentration and temperature of reactants is sufficiently high. The concentration and/or temperature can be increased several different ways:

* High compression ratio
* Pre-heat induction gases
* Forced induction
* Retain or reinduct exhaust

Once ignited, combustion occurs very quickly. When auto-ignition occurs too early or with too much chemical energy combustion is too fast. In such cases, high in-cylinder pressures can destroy an engine. For this reason, HCCI is typically operated at lean overall fuel mixtures.



Advantages

* HCCI is closer to the ideal Otto cycle than spark ignited combustion.

* Lean operation leads to higher efficiency than in spark ignited gasoline engines

* Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. In fact, due to the fact that peak temperatures are significantly lower than in typical spark ignited engines, NOx levels are almost negligible.

* Since HCCI runs throttleless, it eliminates throttling losses



Disadvantages

* High peak pressures
* High heat release rates
* Difficulty of control
* Limited power range
* High carbon monoxide and hydrocarbon pre-catalyst emissions




Control

Controlling HCCI is a major hurdle to more widespread commercialization. HCCI is more difficult to control than other popular modern combustion methods.

In a typical gasoline engine, a spark is used to ignite the pre-mixed fuel and air. In diesel engines, combustion begins when the fuel is injected into compressed air. In both cases, the timing of combustion is explicitly controlled. In an HCCI engine, however, the homogeneous mixture of fuel and air is compressed, and combustion begins whenever the appropriate conditions are reached. This means that there is no well-defined combustion initiator that can be directly controlled. An engine can be designed so that the ignition conditions occur at a desirable timing. However, this would only happen at one operating point. The engine could not change the amount of work it produces. This could work in a hybrid vehicle, but most engines change their energy production to meet user demand.

To achieve dynamic operation in an HCCI engine, the control system must change the conditions that induce combustion. Thus, the engine must control either the compression ratio, inducted gas temperature, inducted gas pressure, or quantity of retained or reinducted exhaust.

Several approaches have been suggested for control



Variable compression ratio

There are several methods of modulating both the geometric and effective compression ratio. The geometric compression ratio can be changed with a movable plunger at the top of the cylinder head. The effective compression ratio can be reduced from the geometric ratio by closing the intake valve either very late or very early with some form of variable valve actuation. Both of the approaches mentioned above require large amounts of energy to achieve fast responses and are expensive.



Variable induction temperature

This technique is also known as fast thermal management. It is accomplished by rapidly varying the cycle to cycle intake charge temperature. It is also expensive to implement and has limited bandwidth associated with actuator energy.



Variable exhaust gas percentage

Exhaust gas can be very hot if retained or reinducted from the previous combustion cycle or cool if recirculated through the intake as in conventional EGR systems. The exhaust has dual effects on HCCI combustion. It dilutes the fresh charge, delaying ignition and reducing the chemical energy and engine work. Hot combustion products conversely will increase the temperature of the gases in the cylinder and advance ignition.



Variable valve actuation

Variable valve actuation allows control over the compression ratio and the exhaust gas percentage. However, fully variable valve actuation is complicated and the componentry is expensive.



High peak pressures and heat release rates

In a typical gasoline or diesel engine, combustion occurs via a flame. Hence at any point in time, only a fraction of the total fuel is burning. This results in low peak pressures and low energy release rates as fuel is burnt over a longer period of time. In HCCI, however, the entire fuel/air mixture ignites and burns nearly simultaneously resulting in high peak pressures and energy release rates. To withstand the higher pressures, the engine has to be structurally stronger, and that means heavier.

Several strategies have been proposed to lower the rate of combustion. Two different blends of fuel can be used. That way, the two fuels will ignite at different points of time resulting in lesser combustion speed. The problem with this idea is the requirement to set up an infrastructure to supply the blended fuel. Dillution, for example with exhaust, reduces the pressure and combustion rate at the cost of work production.



Power

In a gasoline engine, power can be increased by increasing the fuel/air charge. In a diesel engine, power can be increased by increasing the amount of fuel injected. The engines can withstand a boost in power because the heat release rate in these engines is slow. In HCCI however, the entire mixture burns nearly simultaneously. Increasing the fuel/air ratio will result in even higher peak pressures and heat release rates. Also, increasing the fuel/air ratio (also called the equivalence ratio) increases the danger of knock. In addition, many of the viable control strategies for HCCI require thermal preheating of the charge which reduces the density and hence the mass of the air/fuel charge in the combustion chamber, reducing power. These factors makes increasing the power in HCCI inherently challenging.

One way to increase power is to use different blends of fuel. This will lower the heat release rate and peak pressures and will make it possible to increase the equivalence ratio. Another way is to thermally stratify the charge so that different points in the compressed charge will have different temperatures and will burn at different times lowering the heat release rate making it possible to increase power. A third way is to run the engine in HCCI mode only at part load conditions and run it as a diesel or spark ignition engine at full or near full load conditions. Since much more research is required to successfully implement thermal stratification in the compressed charge, the last approach is being studied more intensively.


Carbon Monoxide and Hydrocarbon emissions

Since HCCI operates on lean mixtures, the peak temperatures are lower in comparison to spark ignition and diesel engines. The low peak temperatures prevent the formation of NOx. However they also lead to incomplete burning of fuel especially near the walls of the combustion chamber. This leads to high carbon monoxide and hydrocarbon emissions. An oxidizing catalyst would be effective at removing the regulated species since the exhaust is still oxygen rich.


Difference from Knock

Engine knock or pinging occurs when some of the unburnt gases ahead of the flame in a spark ignited engine spontaneously ignite. The unburnt gas ahead of the flame is compressed as the flame propagates and the pressure in the combustion chamber rises. The high pressure and corresponding high temperature of unburnt reactants can cause them to spontaneously ignite. This causes a shock wave to traverse from the end gas region and an expansion wave to traverse into the end gas region. The two waves reflect off the boundaries of the combustion chamber and interact to produce high amplitude standing waves.

A similar ignition process occurs in HCCI. However, rather than part of the reactant mixture being ignited by compression heating ahead of a flame front, ignition in HCCI engines occurs due to piston compression. In HCCI, the entire reactant mixture ignites (nearly) simultaneaously. Since there are very little or no pressure differences between the different regions of the gas, there is no shock wave propagation and hence no knocking. However at high loads (i.e. high fuel/air ratios), knocking is a possibility even in HCCI.

Combustion chamber

Internal Combustion Engine

A combustion chamber is part of an engine in which fuel is burned. The leftover hot gases produced by this combustion tend to occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber. This pressure can be used to do work, for example, to move a piston on a crankshaft. The energy can be converted to various types of motion or to produce thrust when directed out of a nozzle as in a rocket or jet engine.

In a reciprocating engine, the moving pistons are flush with the top of the cylinder block at top dead centre, and the combustion chamber is therefore the recess in the cylinder head which contains the valves. Some engines use a dished piston and in this case the combustion chamber can be considered as partly within the cylinder. Various shapes of combustion chamber have been used, such as L-head (or flathead) for side-valve engines, "bathtub","hemispherical" and "wedge" for overhead valve engines and "pent-roof" for engines having 3, 4 or 5 valves per cylinder. The shape of the chamber has a marked effect on power output, efficiency and harmful emissions; the designer's objectives are to burn all of the mixture as completely as possible while avoiding excessive temperatures (which create NOx). This is best achieved with a compact rather than elongated chamber. The intake valve/port is usually placed to give the mixture a pronounced "swirl" (the term is preferred to "turbulence" which implies uncontrolled movement) above the rising piston, improving mixing and combustion. Finally, the spark plug must be situated in a position from which the flame front can reach all parts of the chamber at the desired point, usually around 15 degrees after top dead centre. It is strongly desirable to avoid narrow crevices where stagnant "end gas" can become trapped, as this tends to detonate violently after the main charge, adding little useful work and potentially damaging the engine.


Steam Engine

The term combustion chamber is also used to refer to an additional space between the firebox and boiler in a steam locomotive. This space is used to allow further combustion of the fuel, providing greater heat to the boiler.

Two-stroke Engine Basic Operation

The two-stroke engine is simple in construction, but complex dynamics are employed in its operation. A typical simple two-stroke contains a piston whose face is shaped, an exhaust port on one side of the cylinder, and a transfer port on the other side. The downward movement of the piston first uncovers the exhaust port, allowing most of the exhaust to be expelled, and then uncovers the transfer port through which an air-fuel mixture (the fuel normally has some oil mixed in) is let into the cylinder. The piston then moves upwards, compressing the mixture which is ignited by a spark plug, driving the piston back down.


In more detail:

Intake and compression

The rising piston creates a partial vacuum in the sealed crankcase. A connection (inlet port) between the crankcase and the carburetor is uncovered by the piston as it rises, and the air-fuel mixture is sucked into the crankcase. At the same time, the air-fuel mixture already in the cylinder is being compressed as the piston gradually moves up.


Steps of two-stroke cycle:

Expansion stroke:

The piston is at Top Dead Center (TDC)
Crank is at 0 or 360°.

In real engines the process is completed from 0 to 150° but in this model it is completed at 120°.


Intake/Compression stroke:

The piston moves from Bottom Dead Center (BDC) to TDC.

The intake port is opened and working substance flows in.

Intake gases move inside due to partial vacuum; also, blowers are used to push intake gases in.

The vacuum opens the reed valve (thin flexible sheets made of steel, glass fiber or even carbon fiber) allowing the mixture to enter the crankcase.

The air-fuel mixture already in the cylinder is compressed.
As the piston nears the top of the stroke, the ignition system ignites the charge in the combustion chamber.

In diesel engines, at 11-13° before TDC fuel is injected. Before that point, only air is compressed. Fuel is injected only in the last stage of compression.



Exhaust and scavenging process:

The piston moves from TDC to BDC.

At 120°, the exhaust port is opened and exhaust gases move out of the cylinder due to gas pressure.

After 10-40°, fresh scavenging gases are then let into the cylinder through the transfer port(s).

The air/fuel/oil mixture that was let into the cylinder pushes the exhaust out the exhaust port.

The piston, then, compresses the air/fuel/oil mixture and lets left over exhaust out.



Power and exhaust

When the piston reaches the top of its stroke, the mixture is ignited, and the piston is forced down by the rapidly expanding combustion gases.

As the piston descends, a hole in the side of the cylinder connected to the exhaust pipe (exhaust port) is opened, allowing the burned gases to escape.

Furthermore, the descending piston closes the inlet port and pressurizes the crankcase. This also pushes some mixture from the crankcase back to the inlet tract, causing the reed valve to close and preventing the mixture from entering the air filter.

The air fuel mixture is forced into passageways that connect the crankcase to the cylinder. Holes connecting these passages to the upper cylinder (transfer ports) are uncovered by the descending piston and air-fuel mixture is forced into the upper cylinder. The transfer ports are just a bit lower than the top of the exhaust port, so there is a period of time when fresh air-fuel mixture is coming in while exhaust is leaving. The incoming fresh charge assists in forcing the exhaust gas out.

As the piston reaches the bottom and then starts to rise again, the transfer ports are closed by the piston and the air/fuel mixture is compressed. The next cycle starts.



Design issues

A major problem with the two-stroke engine has been the short-circuiting of fresh charge from intake to exhaust which increases fuel consumption and emissions of unburned hydrocarbons. The cylinder ports and piston top are shaped to minimize this mixing of the intake and exhaust flows. Furthermore, a tuned pipe with an expansion chamber provides back pressure at just the right time to push fresh air-fuel mixture sneaking out the exhaust back in again.

The major components of two-stroke engines are tuned so that optimum airflow results. Intake and exhaust pipes are tuned so that resonances in airflow give better flow.

Two-stroke engines typically mix lubricants, two-stroke oil, with their fuel (either manually at refueling or by injecting oil into the fuel stream); this mixture lubricates the cylinder, crankshaft and connecting rod bearings. The lubricant is subsequently burned, resulting in undesirable emissions. An independent lubrication system from below, as is used in four-stroke designs, cannot be used in the above-described engine design, since the crankcase is being used to hold the air-fuel mixture.

This problem has been addressed in newer engines which employ gasoline direct injection, similar to diesel two-strokes.

History Of Internal Combustion Engines

The first internal combustion engines did not have compression, but ran on what air/fuel mixture could be sucked or blown in during the first part of the intake stroke. The most significant distinction between modern internal combustion engines and the early designs is the use of compression and in particular of in-cylinder compression.

* 1509: Leonardo da Vinci described a compression-less engine. (His description may not imply that the idea was original with him or that it was actually built.)

* 1673: Christiaan Huygens described a compression-less engine.

* 1780's: Alessandro Volta built a toy electric pistol in which an electric spark exploded a mixture of air and hydrogen, firing a cork from the end of the gun.

* 17th century: English inventor Sir Samuel Morland used gunpowder to drive water pumps.

* 1794: Robert Street built a compression-less engine whose principle of operation would dominate for nearly a century.

* 1806: Swiss engineer François Isaac de Rivaz built an internal combustion engine powered by a mixture of hydrogen and oxygen.

* 1823: Samuel Brown patented the first internal combustion engine to be applied industrially. It was compression-less and based on what Hardenberg calls the "Leonardo cycle," which, as this name implies, was already out of date at that time. Just as today, early major funding, in an area where standards had not yet been established, went to the best showmen sooner than to the best workers.

* 1824: French physicist Sadi Carnot established the thermodynamic theory of idealized heat engines. This scientifically established the need for compression to increase the difference between the upper and lower working temperatures, but it is not clear that engine designers were aware of this before compression was already commonly used. It may have misled designers who tried to emulate the Carnot cycle in ways that were not useful.

* 1826 April 1: The American Samuel Morey received a patent for a compression-less "Gas Or Vapor Engine".

* 1838: a patent was granted to William Barnet (English). This was the first recorded suggestion of in-cylinder compression. He apparently did not realize its advantages, but his cycle would have been a great advance if developed enough.

* 1854: The Italians Eugenio Barsanti and Felice Matteucci patented the first working efficient internal combustion engine in London (pt. Num. 1072) but did not get into production with it. It was similar in concept to the successful Otto Langen indirect engine, but not so well worked out in detail.

* 1860: Jean Joseph Etienne Lenoir (1822 - 1900) produced a gas-fired internal combustion engine closely similar in appearance to a horizontal double-acting steam beam engine, with cylinders, pistons, connecting rods, and flywheel in which the gas essentially took the place of the steam. This was the first internal combustion engine to be produced in numbers. His first engine with compression shocked itself apart.

* 1862: Nikolaus Otto designed an indirect-acting free-piston compression-less engine whose greater efficiency won the support of Langen and then most of the market, which at that time, was mostly for small stationary engines fueled by lighting gas.

* 1870: In Vienna Siegfried Marcus put the first mobile gasoline engine on a handcart.

* 1876: Nikolaus Otto working with Gottlieb Daimler and Wilhelm Maybach developed a practical four-stroke cycle (Otto cycle) engine. The German courts, however, did not hold his patent to cover all in-cylinder compression engines or even the four stroke cycle, and after this decision in-cylinder compression became universal.

* 1879: Karl Benz, working independently, was granted a patent for his internal combustion engine, a reliable two-stroke gas engine, based on Nikolaus Otto's design of the four-stroke engine. Later Benz designed and built his own four-stroke engine that was used in his automobiles, which became the first automobiles in production.

* 1882: James Atkinson invented the Atkinson cycle engine. Atkinson’s engine had one power phase per revolution together with different intake and expansion volumes making it more efficient than the Otto cycle.

* 1891 - Herbert Akroyd-Stuart builds his oil engine leasing rights to Hornsby of England to build engines. They build the first cold start, compression ignition engines. In 1892 they install the first ones in a water pumping station.

* 1892: Rudolf Diesel develops his Carnot heat engine type motor burning powdered coal dust.

* 1893 February 23: Rudolf Diesel received a patent for the diesel engine.

* 1896: Karl Benz invented the boxer engine, also known as the horizontally opposed engine, in which the corresponding pistons reach top dead centre at the same time, thus balancing each other in momentum.

* 1900: Rudolf Diesel demonstrated the diesel engine in the 1900 Exposition Universelle (World's Fair) using peanut oil.

* 1900: Wilhelm Maybach designed an engine built at Daimler Motoren Gesellschaft—following the specifications of Emil Jellinek—who required the engine to be named Daimler-Mercedes after his daughter. In 1902 automobiles with that engine were put into production by DMG.


Applications

Internal combustion engines are most commonly used for mobile propulsion systems. In mobile scenarios internal combustion is advantageous, since it can provide high power to weight ratios together with excellent fuel energy-density. These engines have appeared in almost all automobiles, motorbikes, many boats, and in a wide variety of aircraft and locomotives. Where very high power is required, such as jet aircraft, helicopters and large ships, they appear mostly in the form of gas turbines. They are also used for electric generators and by industry.

Internal combustion engine

The internal combustion engine is anfucken retared engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause shitty movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.

This contrasts with external combustion engines, such as steam engines, which use the combustion process to heat a separate working fluid, typically water or steam, which then in turn does work, for example by pressing on a steam actuated piston.

The term Internal Combustion Engine (ICE) is almost always used to refer specifically to reciprocating engines, Wankel engines and similar designs in which combustion is intermittent. However, continuous combustion engines, such as Jet engines, most rockets and many gas turbines are also internal combustion engines.


Operation

All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with air, although other oxidisers such as nitrous oxide may be employed. Also see stoichiometry.

The most common fuel in use today are made up of hydrocarbons and are derived from petroleum. These include the fuels known as diesel, gasoline and liquified petroleum gas. Most internal combustion engines designed for gasoline can run on natural gas or liquified petroleum gases without modifications except for the fuel delivery components. Liquid and gaseous biofuels, such as Ethanol can also be used. Some can run on Hydrogen.

All internal combustion engines must have a means of ignition to promote combustion. Most engines use either an electrical or a compression heating ignition system. Electrical ignition systems generally rely on 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 can be recharged during operation using an electricity-generating device, such as an alternator, driven by the engine. Compression heating ignition systems, such as diesel engines and HCCI engines, rely on the heat created in the air by compression in the engine's cylinders to ignite the fuel.

Once successfully ignited and burnt, the combustion products, hot gases, have more available energy than the original compressed fuel/air mixture (which had higher chemical energy). The available energy is manifested as high temperature and pressure which can be translated into work by the engine. In a reciprocating engine, the high pressure product 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 - TDC). The piston can then proceed to the next phase of its cycle, which varies between engines. Any heat not translated into work is normally considered a waste product, and is removed from the engine either by an air or liquid cooling system.


Parts

The parts of an engine vary depending on the engine's type. For a four-stroke engine, key parts of the engine include the crankshaft (purple), 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), a piston (yellow) and a crank (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke and the downward stroke that occurs directly after the air-fuel mix in the cylinder is ignited is 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, exhaust) take place in separate locations, instead of one single location as in a reciprocating engine.

A Bourke Engine uses a pair of pistons integrated to a Scotch Yoke that transmits reciprocating force through a specially designed bearing assembly to turn a crank mechanism. Intake, compression, power, and exhaust all occur in each stroke of this yoke.