Apetrol engine (gasoline engine in American and Canadian English) is aninternal combustion engine designed to run onpetrol (gasoline). Petrol engines can often be adapted to also run on fuels such asliquefied petroleum gas andethanol blends (such asE10 andE85). They may be designed to run on petrol with a higheroctane rating, as sold atpetrol stations.
Most petrol engines usespark ignition, unlikediesel engines which run ondiesel fuel and typically use compression ignition. Another key difference to diesel engines is that petrol engines typically have a lowercompression ratio.[1][2][3]
The first practical petrol engine was built in 1876 in Germany byNicolaus August Otto andEugen Langen, although there had been earlier attempts byÉtienne Lenoir in 1860,Siegfried Marcus in 1864 andGeorge Brayton in 1873.[4]
Most petrol engines use either the four-strokeOtto cycle or thetwo-stroke cycle.[5][6][7] Petrol engines have also been produced using theMiller cycle andAtkinson cycle.[8][9][10][11]
Most petrol-powered piston engines arestraight engines orV engines. However,flat engines,W engines andother layouts are sometimes used.
Wankel engines are classified by the number of rotors used.
Petrol engines are eitherair-cooled orwater-cooled.
Petrol engines usespark ignition.High voltage for the spark this may be provided by amagneto or anignition coil. In modern car engines, theignition timing is managed by an electronicEngine Control Unit. Ignition modules can also function as a rev limiter in some cases to prevent overrevving and the consequences of it, such as valve float and connecting rod failure.
Primers may be used to help start the engine. They can draw fuel from fuel tanks and vaporize fuel directly into piston cylinders. Engines are difficult to start during cold weather, and the fuel primer helps because otherwise there will not be enough heat available to vaporize the fuel in thecarburetor.[12]
The power output of small- and medium-sized petrol engines (along with equivalent engines using other fuels) is usually measured inkilowatts orhorsepower.
Typically, petrol engines have athermodynamic efficiency of about 20-30% (approximately half that of some diesel engines).[13]
Applications of petrol engines includeautomobiles,motorcycles,aircraft,motorboats andsmall engines (such as lawn mowers, chainsaws and portable generators). Petrol engines have also been used as "pony engines", a type of engine used to start a larger, stationary diesel engine.
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