American Motors AMC modern era inline six on stand at Rambler Ranch

A petrol engine (gasoline engine in American and Canadian English) is an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

designed to run on

petrol Gasoline (North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When formul ...

(gasoline). Petrol engines can often be adapted to also run on fuels such as

liquefied petroleum gas Liquefied petroleum gas, also referred to as liquid petroleum gas (LPG or LP gas), is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, Butane, ''n''-butane and isobutane. It can also contain some ...

and ethanol blends (such as '' E10'' and '' E85''). They may be designed to run on petrol with a higher

octane rating An octane rating, or octane number, is a standard measure of a liquid fuel, fuel's ability to withstand Compression ratio, compression in an internal combustion engine without causing engine knocking. The higher the octane number, the more compres ...

, as sold at

petrol stations A filling station (also known as a gas station [] or petrol station []) is a facility that sells fuel and engine lubricants for motor vehicles. The most common fuels sold are gasoline (or petrol) and diesel fuel. Fuel dispensers are used to ...

. Most petrol engines use

spark ignition A spark-ignition engine (SI 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, ...

, unlike

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

s which run on

diesel fuel Diesel fuel, also called diesel oil, heavy oil (historically) or simply diesel, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a re ...

and typically use compression ignition. Another key difference to diesel engines is that petrol engines typically have a lower

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

History

The first practical petrol engine was built in 1876 in Germany by

Nicolaus August Otto Nicolaus August Otto (10 June 1832 – 26 January 1891) was a German engineer who successfully developed the compressed charge internal combustion engine which ran on petroleum gas and led to the modern internal combustion engine. The Associ ...

and

Eugen Langen Carl Eugen Langen (9 October 1833 in Cologne – 2 October 1895 in Elsdorf) was a German entrepreneur, engineer and inventor, involved in the development of the petrol engine and the Wuppertal Suspension Railway. In 1857 he worked in his fathe ...

, although there had been earlier attempts by

Étienne Lenoir Jean Joseph Étienne Lenoir, also known as Jean J. Lenoir (12 January 1822 – 4 August 1900), was a Belgian-French engineer who invented the internal combustion engine in 1858. Prior designs for such engines were patented as early as 1807 (De ...

in 1860, Siegfried Marcus in 1864 and George Brayton in 1873.

Design

Thermodynamic cycle

Most petrol engines use either the four-stroke

Otto cycle An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. The Otto cycle is a description of what happ ...

or the

two-stroke cycle A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston, one up and one down, in one revolution of the crankshaft in contrast to a four-stroke engine which re ...

. Petrol engines have also been produced using the Miller cycle and

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

Layout

Most petrol-powered piston engines are

straight engine The straight engine (also called inline engine) is a configuration of multi-cylinder piston engine where all of the cylinders are arranged in a single row, rather than radially or in two or more cylinder banks. Design A straight engine is eas ...

s or

V engine A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder ...

s. However,

flat engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, ...

W engine A W engine is a type of piston engine where three or four cylinder banks share the same crankshaft, resembling the letter "W" when viewed from the front. W engines with three banks of cylinders are also called "broad arrow" engines, due to thei ...

s and other layouts are sometimes used. Wankel engines are classified by the number of rotors used.

Compression ratio

Cooling

Petrol engines are either

air-cooled Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. Air-cooled designs are far simpler than their liquid-cooled ...

water-cooled Cooling tower and water discharge of a nuclear power plant Water cooling is a method of heat removal from components and industrial equipment. Evaporative cooling using water is often more efficient than air cooling. Water is inexpensive and no ...

Ignition

Petrol engines use

High voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...

for the spark this may be provided by a

magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

or an

ignition coil An ignition coil is used in the ignition system of a spark-ignition engine to transform the battery voltage to the much higher voltages required to operate the spark plug(s). The spark plugs then use this burst of high-voltage electricity to ig ...

. In modern car engines, the

ignition timing In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need ...

is managed by an electronic

Engine Control Unit An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...

. 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.

Primer

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 A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Ventu ...

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 Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

. Typically, petrol engines have a

thermodynamic efficiency In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For a he ...

of about 20-30% (approximately half that of some diesel engines).

Applications

Applications of petrol engines include

automobile A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, peopl ...

motorcycle A motorcycle (motorbike, bike; uni (if one-wheeled); trike (if three-wheeled); quad (if four-wheeled)) is a lightweight private 1-to-2 passenger personal motor vehicle Steering, steered by a Motorcycle handlebar, handlebar from a saddle-style ...

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

motorboat A motorboat or powerboat is a boat that is exclusively powered by an engine; faster examples may be called "speedboats". Some motorboats are fitted with inboard engines, others have an outboard motor installed on the rear, containing the inter ...

s and

small engine A small engine is the general term for a wide range of small-displacement, low-powered internal combustion engines used to power lawn mowers, generators, concrete mixers and many other machines that require independent power sources. These engin ...

s (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.

References

{{Authority control 1876 introductions Internal combustion piston engines Gasoline engines German inventions