Heat EngineHeat EngineIn In engineeringengineering and and thermodynamicsthermodynamics, a , a

heat engineheat engine performs the conversion of performs the conversion of heatheat energyenergy to to mechanical workmechanical work by by exploiting the exploiting the temperaturetemperature gradient gradient

between a hot "between a hot "sourcesource" and a cold "" and a cold "sinksink". ". Heat is Heat is transferredtransferred from the source, from the source,

through the "through the "working bodyworking body" of the engine, " of the engine, to the sink, and in this process some of the to the sink, and in this process some of the heat is converted into heat is converted into workwork by exploiting by exploiting

the properties of a working substance the properties of a working substance (usually a (usually a gasgas or liquid). or liquid).

• A heat engine typically uses energy A heat engine typically uses energy provided in the form of provided in the form of heatheat to do to do workwork and then exhausts the heat which and then exhausts the heat which cannot be used to do cannot be used to do workwork. . Thermodynamics is the study of the Thermodynamics is the study of the relationshipsrelationships between heat and between heat and workwork. . The The first lawfirst law and and second law of thermodynamicssecond law of thermodynamics constrain the operation of a heat constrain the operation of a heat engine. The first engine. The first lawlaw is the application is the application of conservation of energy to the of conservation of energy to the system, and the second sets limits on system, and the second sets limits on the possible efficiency of the machine the possible efficiency of the machine and determines the direction of energy and determines the direction of energy flow. flow.

Parts Parts • The parts of an engine vary depending on the engine's type. For a The parts of an engine vary depending on the engine's type. For a

four-strokefour-stroke engine, key parts of the engine include the engine, key parts of the engine include the crankshaftcrankshaft (purple), one or more (purple), one or more camshaftscamshafts (red and blue) and (red and blue) and valvesvalves. For a . For a two-stroketwo-stroke engine, there may simply be an engine, there may simply be an exhaustexhaust outlet and outlet and fuelfuel inlet instead of a valve system. In both types of engines, there are 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 one or more cylinders (grey and green) and for each cylinder there is a is a spark plugspark plug (darker-grey), a (darker-grey), a pistonpiston (yellow) and a (yellow) and a crankcrank (purple). A single sweep of the cylinder by the piston in an upward (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke and the downward or downward motion is known as a stroke and the downward stroke that occurs directly after the air-fuel mix in the cylinder is stroke that occurs directly after the air-fuel mix in the cylinder is ignited is known as a power stroke.ignited is known as a power stroke.

• A A WankelWankel engine engine has a triangular rotor that orbits in an has a triangular rotor that orbits in an epitrochoidalepitrochoidal (figure 8 shape) chamber around an eccentric shaft. (figure 8 shape) chamber around an eccentric shaft. The four phases of operation (intake, compression, power, The four phases of operation (intake, compression, power, exhaust) take place in separate locations, instead of one single exhaust) take place in separate locations, instead of one single location as in a reciprocating engine.location as in a reciprocating engine.

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

Engine CycleEngine Cycle• Two-strokeTwo-stroke• Engines based on the Engines based on the two-stroke cycletwo-stroke cycle use two strokes (one use two strokes (one

up, one down) for every power stroke. Since there are no up, one down) for every power stroke. Since there are no dedicated intake or dedicated intake or exhaustexhaust strokes, alternative methods strokes, alternative methods must be used to must be used to scavengescavenge the cylinders. The most common the cylinders. The most common method in spark-ignition two-strokes is to use the method in spark-ignition two-strokes is to use the downward motion of the piston to pressurize fresh downward motion of the piston to pressurize fresh chargecharge in the in the crankcasecrankcase, which is then blown through the cylinder , which is then blown through the cylinder through ports in the cylinder walls. Spark-ignition two-through ports in the cylinder walls. Spark-ignition two-strokes are small and light (for their power output), and strokes are small and light (for their power output), and mechanically very simple. Common applications include mechanically very simple. Common applications include snowmobilessnowmobiles, , lawnmowerslawnmowers, , weed-whackersweed-whackers, , chain sawschain saws, , jet skisjet skis, , mopedsmopeds, , outboard motorsoutboard motors and some and some motorcyclesmotorcycles. . Unfortunately, they are also generally louder, less efficient, Unfortunately, they are also generally louder, less efficient, and far more polluting than their four-stroke counterparts, and far more polluting than their four-stroke counterparts, and they do not scale well to larger sizes. Interestingly, the and they do not scale well to larger sizes. Interestingly, the largest compression-ignition engines are two-strokes, and largest compression-ignition engines are two-strokes, and are used in some locomotives and large ships. These are used in some locomotives and large ships. These engines use engines use forced inductionforced induction to scavenge the cylinders. to scavenge the cylinders.

• Four-strokeFour-stroke• Engines based on the Engines based on the four-stroke cyclefour-stroke cycle or or

Otto cycle have one power stroke for Otto cycle have one power stroke for every four strokes (up-down-up-down) and every four strokes (up-down-up-down) and are used in cars, larger are used in cars, larger boatsboats and many and many light light aircraftaircraft. They are generally quieter, . They are generally quieter, more efficient and larger than their two-more efficient and larger than their two-stroke counterparts. There are a number stroke counterparts. There are a number of variations of these cycles, most notably of variations of these cycles, most notably the the AtkinsonAtkinson and and MillerMiller cycles. Most cycles. Most trucktruck and automotive Diesel engines use a four-and automotive Diesel engines use a four-stroke cycle, but with a compression stroke cycle, but with a compression heating ignition system. This variation is heating ignition system. This variation is called the called the diesel cyclediesel cycle..

• Bourke EngineBourke Engine• In this engine, two diametrically opposed cylinders In this engine, two diametrically opposed cylinders

are linked to the crank by the crank pin that goes are linked to the crank by the crank pin that goes through the common scottish yoke. The cylinders through the common scottish yoke. The cylinders and pistons are so constructed that there are, as in and pistons are so constructed that there are, as in the usual two stroke cycle, two power strokes per the usual two stroke cycle, two power strokes per revolution. However, unlike the common two stroke revolution. However, unlike the common two stroke engine, the burnt gases and the incoming fresh engine, the burnt gases and the incoming fresh airair do not mix in the cylinders, contributing to a do not mix in the cylinders, contributing to a cleaner, more efficient operation. The scotch yoke cleaner, more efficient operation. The scotch yoke mechanism also has low side thrust and thus greatly mechanism also has low side thrust and thus greatly reduces friction between pistons and cylinder walls. reduces friction between pistons and cylinder walls. The The Bourke cycleBourke cycle's combustion phase more closely 's combustion phase more closely approximates approximates constant volume combustionconstant volume combustion than than either four stroke or two stroke cycles do. It also either four stroke or two stroke cycles do. It also uses less moving parts, hence needs to overcome uses less moving parts, hence needs to overcome less less frictionfriction than the other two reciprocating types than the other two reciprocating types have to. In addition, its greater have to. In addition, its greater expansion ratioexpansion ratio also also means more of the heat from its combustion phase means more of the heat from its combustion phase is utilized than is used by either four stroke or two is utilized than is used by either four stroke or two stroke cyclesstroke cycles

• Controlled Combustion EngineControlled Combustion Engine• These are also cylinder based engines may be either single These are also cylinder based engines may be either single

or two stroke but use, instead of a crankshaft and piston or two stroke but use, instead of a crankshaft and piston rods, two gear connected, counter rotating concentric cams rods, two gear connected, counter rotating concentric cams to convert reciprocating motion into rotary movement. to convert reciprocating motion into rotary movement. These cams practically cancel out sideward forces that These cams practically cancel out sideward forces that would otherwise be exerted on the cylinders by the pistons, would otherwise be exerted on the cylinders by the pistons, greatly improving mechanical efficiency. The profiles of the greatly improving mechanical efficiency. The profiles of the cam lobes(which are always odd and at least three in cam lobes(which are always odd and at least three in number) determine the piston number) determine the piston traveltravel versus the torque versus the torque delivered. In this engine, there are two cylinders that are delivered. In this engine, there are two cylinders that are 180 degrees apart for each pair of counter rotating cams. 180 degrees apart for each pair of counter rotating cams. For single stroke versions, there are the same number of For single stroke versions, there are the same number of cycles per cylinder pair as there are lobes on each cam, cycles per cylinder pair as there are lobes on each cam, twice as much for two stroke units.twice as much for two stroke units.

• WankelWankel• The The WankelWankel engine engine operates with the same separation of operates with the same separation of

phases as the four-stroke engine (but with no piston phases as the four-stroke engine (but with no piston strokes, would more properly be called a four-phase strokes, would more properly be called a four-phase engine), since the phases occur in separate locations in the engine), since the phases occur in separate locations in the engine; however like a two-stroke piston engine, it provides engine; however like a two-stroke piston engine, it provides one power 'stroke' per revolution per rotor, giving it similar one power 'stroke' per revolution per rotor, giving it similar space and weight efficiency.space and weight efficiency.

• GasGas turbine turbine• With With gasgas turbine cycles (notably turbine cycles (notably Jet enginesJet engines), ),

rather than use the same piston to compress and rather than use the same piston to compress and then expand the gases, instead separate then expand the gases, instead separate compressors and compressors and gasgas turbines are employed; turbines are employed; giving continuous power. Essentially, the intake giving continuous power. Essentially, the intake gasgas (air normally) is compressed, and then (air normally) is compressed, and then combusted with a combusted with a fuelfuel, which greatly raises the , which greatly raises the temperature and volume. The larger volume of hot temperature and volume. The larger volume of hot gasgas from the combustion chamber is then fed from the combustion chamber is then fed through the through the gasgas turbine which is then easily able to turbine which is then easily able to power the compressor.power the compressor.

• Disused methodsDisused methods• In some old non-compressing internal combustion In some old non-compressing internal combustion

engines: In the first part of the piston downstroke a engines: In the first part of the piston downstroke a fuel/air mixture was sucked or blown in. In the rest fuel/air mixture was sucked or blown in. In the rest of the piston downstroke the inlet valve closed and of the piston downstroke the inlet valve closed and the fuel/air mixture fired. In the piston upstroke the fuel/air mixture fired. In the piston upstroke the the exhaustexhaust valve was open. This was an attempt valve was open. This was an attempt at imitating the way a piston at imitating the way a piston steam enginesteam engine works. works.

• FuelFuel and oxidizer types and oxidizer types• Fuels used include petroleum spirit (Fuels used include petroleum spirit (North AmericanNorth American

term: term: gasolinegasoline, , BritishBritish term: petrol), term: petrol), liquifiedliquified petroleum gas petroleum gas, , vapourizedvapourized petroleum gas petroleum gas, , compressed natural gascompressed natural gas, , hydrogenhydrogen, , diesel fueldiesel fuel, , jet fueljet fuel, , landfill gaslandfill gas, , biodieselbiodiesel, , biobutanolbiobutanol, , peanut oilpeanut oil and other and other vegoilsvegoils, , bioethanolbioethanol, , biomethanolbiomethanol (methyl or (methyl or wood alcoholwood alcohol) and other ) and other biofuelsbiofuels. Even fluidised metal powders and . Even fluidised metal powders and explosives have seen some use. Engines that use explosives have seen some use. Engines that use gases for gases for fuelfuel are called are called gasgas engines and those that engines and those that use liquid hydrocarbons are called use liquid hydrocarbons are called oiloil engines. engines. However, gasoline engines are unfortunately also However, gasoline engines are unfortunately also often colloquially referred to as 'gas engines'.often colloquially referred to as 'gas engines'.

• The main limitations on fuels are that the The main limitations on fuels are that the fuelfuel must must be easily transportable through the be easily transportable through the fuel systemfuel system to to the the combustion chambercombustion chamber, and that the , and that the fuelfuel release release sufficient sufficient energyenergy in the form of in the form of heatheat upon upon combustioncombustion to make use of the engine practical. to make use of the engine practical.

CylindersCylinders• Internal combustion engines can contain any number of cylinders Internal combustion engines can contain any number of cylinders

with numbers between one and twelve being common, though as with numbers between one and twelve being common, though as many as 36 (many as 36 (Lycoming R-7755Lycoming R-7755) have been used. Having more ) have been used. Having more cylinders in an engine yields two potential benefits: First, the cylinders in an engine yields two potential benefits: First, the engine can have a larger displacement with smaller individual engine can have a larger displacement with smaller individual reciprocating masses (that is, the mass of each piston can be less) reciprocating masses (that is, the mass of each piston can be less) thus making a smoother running engine (since the engine tends to thus making a smoother running engine (since the engine tends to vibrate as a result of the pistons moving up and down). Second, vibrate as a result of the pistons moving up and down). Second, with a greater displacement and more pistons, more with a greater displacement and more pistons, more fuelfuel can be can be combusted and there can be more combustion events (that is, combusted and there can be more combustion events (that is, more power strokes) in a given period of time, meaning that such more power strokes) in a given period of time, meaning that such an engine can generate more torque than a similar engine with an engine can generate more torque than a similar engine with fewer cylinders. The down side to having more pistons is that, fewer cylinders. The down side to having more pistons is that, over all, the engine will tend to weigh more and tend to generate over all, the engine will tend to weigh more and tend to generate more internal friction as the greater number of pistons rub against more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease the inside of their cylinders. This tends to decrease fuelfuel efficiency efficiency and rob the engine of some of its power. For high performance and rob the engine of some of its power. For high performance gasoline engines using current materials and technology (such as gasoline engines using current materials and technology (such as the engines found in modern automobiles), there seems to be a the engines found in modern automobiles), there seems to be a break point around 10 or 12 cylinders, after which addition of break point around 10 or 12 cylinders, after which addition of cylinders becomes an overall detriment to performance and cylinders becomes an overall detriment to performance and efficiency, although exceptions such as the efficiency, although exceptions such as the W16W16 engine from engine from VolkswagenVolkswagen exist. exist.

• Most Most carcar engines have four to eight cylinders, with some engines have four to eight cylinders, with some high performance cars having ten, twelve, or even sixteen, high performance cars having ten, twelve, or even sixteen, and some very small cars and and some very small cars and truckstrucks having two or three. In having two or three. In previous years some quite large cars, such as the previous years some quite large cars, such as the DKWDKW and and Saab 92Saab 92, had two cylinder, two stroke engines. , had two cylinder, two stroke engines.

• RadialRadial aircraftaircraft engines, now obsolete, had from three to 28 engines, now obsolete, had from three to 28 cylinders, such as the cylinders, such as the Pratt & Whitney R-4360Pratt & Whitney R-4360. A row . A row contains an odd number of cylinders, so an even number contains an odd number of cylinders, so an even number indicates a two- or four-row engine. The largest of these indicates a two- or four-row engine. The largest of these was the was the Lycoming R-7755Lycoming R-7755 with 36 cylinders (four rows of with 36 cylinders (four rows of nine cylinders) but never entered production. nine cylinders) but never entered production.

• Motor cyclesMotor cycles commonly have from one to four cylinders, commonly have from one to four cylinders, with a few high performance models having six (though with a few high performance models having six (though some 'novelties' exist with 8, 10 and 12). some 'novelties' exist with 8, 10 and 12).

• SnowmobilesSnowmobiles usually have two cylinders. Some larger (not usually have two cylinders. Some larger (not necessarily high-performance, but also touring machines) necessarily high-performance, but also touring machines) have four. have four.

• Small portable appliances such as Small portable appliances such as chainsawschainsaws, generators , generators and domestic and domestic lawn mowerslawn mowers most commonly have one most commonly have one cylinder, although two-cylinder chainsaws exist. cylinder, although two-cylinder chainsaws exist.

Ignition SystemIgnition System• Internal combustion engines can be classified by their Internal combustion engines can be classified by their

ignition systemignition system. The point in the cycle at which the . The point in the cycle at which the fuel/oxidiser mixture are ignited has a direct effect on the fuel/oxidiser mixture are ignited has a direct effect on the efficiency and output of the ICE. For a typical 4 stroke efficiency and output of the ICE. For a typical 4 stroke automobile engine, the burning mixture has to reach its automobile engine, the burning mixture has to reach its maximum pressure when the maximum pressure when the crankshaftcrankshaft is 90 degrees after is 90 degrees after TDCTDC. The speed of the flame front is directly affected by . The speed of the flame front is directly affected by compression ratiocompression ratio, , fuel mixturefuel mixture temperature and temperature and octaneoctane or or cetanecetane rating of the rating of the fuelfuel. Modern ignition systems are . Modern ignition systems are designed to ignite the mixture at the right time to ensure designed to ignite the mixture at the right time to ensure the flame front doesn't contact the decending the flame front doesn't contact the decending piston crownpiston crown. . If the flame front contacts the piston, If the flame front contacts the piston, pinkingpinking or or knockingknocking results. Leaner mixtures and lower mixture pressures burn results. Leaner mixtures and lower mixture pressures burn more slowly requiring more advanced more slowly requiring more advanced ignition timingignition timing. Today . Today most engines use an most engines use an electricalelectrical or or compression heatingcompression heating system for ignition. However system for ignition. However outside flameoutside flame and and hot-tubehot-tube systems have been used historically. systems have been used historically. NikolaNikola Tesla Tesla gained gained one of the first patents on the mechanical ignition system one of the first patents on the mechanical ignition system with with U.S. Patent 609250U.S. Patent 609250

FuelFuel systems systems

• Fuels burn faster, and more completely when they have lots of Fuels burn faster, and more completely when they have lots of surface area in contact with oxygen. In order for an engine to surface area in contact with oxygen. In order for an engine to workwork efficiently the efficiently the fuelfuel must be vaporized into the incoming must be vaporized into the incoming airair in what is in what is commonly referred to as a commonly referred to as a fuelfuel airair mixture. There are two commonly mixture. There are two commonly used methods of vaporizing used methods of vaporizing fuelfuel into the into the airair, one is the , one is the carburetorcarburetor and the other is and the other is fuelfuel injection. injection.

• Often for simpler reciprocating engines a carburetor is used to Often for simpler reciprocating engines a carburetor is used to supply supply fuelfuel into the cylinder. However, exact control of the correct into the cylinder. However, exact control of the correct amount of amount of fuelfuel supplied to the engine is impossible. Carburetors are supplied to the engine is impossible. Carburetors are the current most widespread the current most widespread fuelfuel mixing device used in lawnmowers mixing device used in lawnmowers and other small engine applications. Prior to the mid-1980s and other small engine applications. Prior to the mid-1980s carburetors were also common in automobiles.carburetors were also common in automobiles.

• Larger gasoline engines such as used in automobiles have mostly Larger gasoline engines such as used in automobiles have mostly moved to moved to fuelfuel injection systems (see injection systems (see Gasoline Direct InjectionGasoline Direct Injection). ). Diesel enginesDiesel engines always use always use fuelfuel injection. injection.

• LPG engines use a mix of LPG engines use a mix of fuelfuel injection systems and closed loop injection systems and closed loop carburetors.carburetors.

• Other internal combustion engines like Other internal combustion engines like jet enginesjet engines use burners, and use burners, and rocket engines use various different ideas including impinging jets, rocket engines use various different ideas including impinging jets, gas/liquid shear, preburners and many other ideas.gas/liquid shear, preburners and many other ideas.

• Intake. Intake. During the intake stroke, the During the intake stroke, the piston moves downward, drawing a piston moves downward, drawing a fresh charge of vaporized fuel/air fresh charge of vaporized fuel/air mixture.  The illustrated engine mixture.  The illustrated engine features a 'poppet' intake valve features a 'poppet' intake valve which is drawn open by the vacuum which is drawn open by the vacuum produced by the intake stroke.  Some produced by the intake stroke.  Some early engines worked this way, early engines worked this way, however most modern engines however most modern engines incorporate an extra cam/lifter incorporate an extra cam/lifter arrangement as seen on the arrangement as seen on the exhaustexhaust valve.  The valve.  The exhaustexhaust valve is held shut valve is held shut by a spring (not illustrated here).by a spring (not illustrated here).

• Compression.Compression. As As the piston rises the the piston rises the poppet valve is poppet valve is forced shut by the forced shut by the increased cylinder increased cylinder pressure.  Flywheel pressure.  Flywheel momentum drives momentum drives the piston upward, the piston upward, compressing the compressing the fuel/air mixture.fuel/air mixture.

• Power.Power. At the top At the top of the compression of the compression stroke the spark stroke the spark plug fires, igniting plug fires, igniting the compressed the compressed fuelfuel.  As the .  As the fuelfuel burns it expands, burns it expands, driving the piston driving the piston downward.downward.

• ExhaustExhaust.. At the bottom of the power At the bottom of the power stroke, the stroke, the exhaustexhaust valve is opened valve is opened by the cam/lifter mechanism.  The by the cam/lifter mechanism.  The upward stroke of the piston drives upward stroke of the piston drives the exhausted the exhausted fuelfuel out of the cylinder out of the cylinder

• Intake.Intake.  The fuel/air   The fuel/air mixture is first drawn mixture is first drawn into the crankcase by into the crankcase by the vacuum created the vacuum created during the upward during the upward stroke of the piston.  stroke of the piston.  The illustrated engine The illustrated engine features a poppet intake features a poppet intake valve, however many valve, however many engines use a rotary engines use a rotary value incorporated into value incorporated into the crankshaft.the crankshaft.

• Transfer/Exhaust.Transfer/Exhaust. Toward Toward the end of the stroke, the the end of the stroke, the piston exposes the intake piston exposes the intake port, allowing the port, allowing the compressed fuel/air mixture compressed fuel/air mixture in the crankcase to escape in the crankcase to escape around the piston into the around the piston into the main cylinder.  This expels main cylinder.  This expels the the exhaustexhaust gasses out the gasses out the exhaustexhaust port, usually port, usually located on the opposite located on the opposite side of the cylinder.  side of the cylinder.  Unfortunately, some of the Unfortunately, some of the fresh fresh fuelfuel mixture is usually mixture is usually expelled as well. expelled as well.

• Compression.Compression. The The piston then rises, piston then rises, driven by flywheel driven by flywheel momentum, and momentum, and compresses the compresses the fuelfuel mixture.  (At the mixture.  (At the same time, another same time, another intake stroke is intake stroke is happening beneath happening beneath the piston).  the piston).  

• Power.Power. At the top At the top of the stroke the of the stroke the spark plug ignites spark plug ignites the fuel mixture. the fuel mixture. The burning fuel The burning fuel expands, driving expands, driving the piston the piston downward, to downward, to complete the cycle.complete the cycle.

• Detailed DescriptionDetailed Description

• Fuel and oxygen are injected Fuel and oxygen are injected

• Fuel and oxygen are compressed and Fuel and oxygen are compressed and ignited ignited

• Fuel combusts and piston is pushed Fuel combusts and piston is pushed downwards downwards

• Exhaust is removed Exhaust is removed