Petrol engine

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Side view of a circa-1970 AMC 232 automotive engine American Motors AMC modern era inline six on stand at Rambler Ranch.jpg
Side view of a circa-1970 AMC 232 automotive engine

A petrol engine (gasoline engine in American and Canadian English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as E10 and E85).


Most petrol engines use spark ignition, unlike diesel engines which typically use compression ignition. Another key difference to diesel engines is that petrol engines typically have a lower compression ratio.


The first practical petrol engine was built in 1876 in Germany by Nicolaus August Otto, although there had been earlier attempts by Étienne Lenoir in 1860, Siegfried Marcus in 1864 and George Brayton in 1876.[ citation needed ]


Thermodynamic cycle

Animation of an Otto cycle engine 4StrokeEngine Ortho 3D Small.gif
Animation of an Otto cycle engine

Most petrol engines use either the four-stroke Otto cycle or the two-stroke cycle. [1] [2] [3] Petrol engines have also been produced using the Miller cycle and Atkinson cycle. [4] [5] [6] [7]


Most petrol-powered piston engines are straight engines or V engines. However, flat engines, W engines and other layouts are sometimes used.

Wankel engines are classified by the number of rotors used.

Compression ratio


Petrol engines are either air-cooled or water-cooled.


Petrol engines use spark ignition. High voltage for the spark this may be provided by a magneto or an ignition coil. In modern car engines, the ignition timing is managed by an electronic Engine 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 the carburetor. [8]

Power output and efficiency

The power output of small- and medium-sized petrol engines (along with equivalent engines using other fuels) is usually measured in kilowatts or horsepower.

Typically, petrol engines have a thermodynamic efficiency of about 20-30% (approximately half that of some diesel engines). [9]


Applications of petrol engines include automobiles, motorcycles, aircraft, motorboats and small 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.

See also

Related Research Articles

<span class="mw-page-title-main">Compression ratio</span> Ratio of the volume of a combustion chamber from its largest capacity to its smallest capacity

The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.

<span class="mw-page-title-main">Diesel cycle</span> Engine combustion process

The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it, fuel is ignited by heat generated during the compression of air in the combustion chamber, into which fuel is then injected. This is in contrast to igniting the fuel-air mixture with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines are used in aircraft, automobiles, power generation, diesel–electric locomotives, and both surface ships and submarines.

<span class="mw-page-title-main">Reciprocating engine</span> Engine utilising one or more reciprocating pistons

A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the Stirling engine for niche applications. Internal combustion engines are further classified in two ways: either a spark-ignition (SI) engine, where the spark plug initiates the combustion; or a compression-ignition (CI) engine, where the air within the cylinder is compressed, thus heating it, so that the heated air ignites fuel that is injected then or earlier.

<span class="mw-page-title-main">Miller cycle</span> Thermodynamic cycle

In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. Patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel. It uses a supercharger to offset the performance loss of the Atkinson cycle.

A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.

<span class="mw-page-title-main">Four-stroke engine</span> Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
<span class="mw-page-title-main">Atkinson cycle</span> Thermodynamic cycle

The Atkinson-cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density.

<span class="mw-page-title-main">Gasoline direct injection</span> Mixture formation system

Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct from manifold injection systems, which inject fuel into the intake manifold.

<span class="mw-page-title-main">Otto engine</span> Large stationary single-cylinder internal combustion four-stroke engine

The Otto engine was a large stationary single-cylinder internal combustion four-stroke engine designed by the German Nicolaus Otto. It was a low-RPM machine, and only fired every other stroke due to the Otto cycle, also designed by Otto.

Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction produces heat that can be transformed into work in a heat engine.

A spark-ignition engine is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, typically diesel engines, where the heat generated from compression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.

hot-bulb engine Internal combustion engine

The hot-bulb engine is a type of internal combustion engine in which fuel ignites by coming in contact with a red-hot metal surface inside a bulb, followed by the introduction of air (oxygen) compressed into the hot-bulb chamber by the rising piston. There is some ignition when the fuel is introduced, but it quickly uses up the available oxygen in the bulb. Vigorous ignition takes place only when sufficient oxygen is supplied to the hot-bulb chamber on the compression stroke of the engine.

<span class="mw-page-title-main">Model engine</span>

A model engine is a small internal combustion engine typically used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight, control line aircraft, or ground-running tether car model.

Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines-

  1. Internal combustion and
  2. External combustion engines.

The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. Claimed advantages may include increased fuel efficiency, reduced mechanical complexity, and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes.

<span class="mw-page-title-main">Liquidpiston</span> US engine manufacturer

LiquidPiston is the developer and manufacturer of a pistonless rotary engine called the X-engine, located in Bloomfield, Connecticut.

<span class="mw-page-title-main">Hesselman engine</span>

The Hesselman engine is a hybrid between a petrol engine and a diesel engine. It was designed and introduced in 1925 by Swedish engineer Jonas Hesselman.

Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.

<span class="mw-page-title-main">Petrol-paraffin engine</span>

A petrol-paraffin engine, TVO engine or gasoline-kerosene engine is an old-fashioned type of dual-fuel internal combustion engine with spark-ignition, designed to start on petrol (gasoline) and then to switch to run on paraffin (kerosene) once the engine is warm. The grade of paraffin used is known as tractor vaporising oil in the UK.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.


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  2. "What is Two Stroke Engine?- Types, And Working". Engineering Choice. 12 November 2020. Retrieved 14 August 2022.
  3. "Two Stroke Engine - Internal Combustion Engines (IC) - Automobile Magazine". MotorTrend. 16 December 2009. Retrieved 14 August 2022.
  4. "How does a Miller-cycle engine work?". HowStuffWorks. 1 April 2000. Retrieved 14 August 2022.
  5. "Mazda 2.3L Miller-cycle DOHC V-6". WardsAuto. 1 January 1998. Retrieved 14 August 2022.
  6. "Why does Toyota use Atkinson cycle engines?". Toyota UK Magazine. 14 January 2015. Retrieved 14 August 2022.
  7. "Engine Types: Atkinson Cycle vs Otto vs Miller". EngineHoist. 4 April 2016. Retrieved 9 June 2023.
  8. "Chapter 7: Aircraft Systems". Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C ed.). Federal Aviation Administration. 2023-07-17. p. 25.
  9. "Toyota Gasoline Engine Achieves Thermal Efficiency Of 38 Percent". Green Car Reports. Retrieved 2017-10-07.