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

A petrol engine (gasoline engine in American 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 co ...

designed to run on

petrol Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...

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

liquefied petroleum gas Liquefied petroleum gas (LPG or LP gas) is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, propylene, butylene, isobutane and n-butane. LPG is used as a fuel gas in heating appliances, cookin ...

and ethanol blends (such as ''E10'' and ''E85''). Most petrol engines use spark ignition, unlike

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-cal ...

s which 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 volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...

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 hap ...

or the two-stroke cycle. Petrol engines have also been produced using the Miller cycle and Atkinson cycle.

Layout

Most petrol-powered piston engines are

straight engine The straight or inline engine is an internal combustion engine with all cylinders aligned in one row and having no offset. Usually found in four, six and eight cylinder configurations, they have been used in automobiles, locomotives and aircraf ...

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, ...

s, W engines 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. In all combustion engines, a great percentage of the heat ge ...

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 n ...

Ignition

Petrol engines use spark ignition.

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 ...

current for the spark may be provided by a magneto or an

ignition coil An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. So ...

. In modern car engines the ignition timing is managed by an electronic

Engine Control Unit An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by ...

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 The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James W ...

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

Applications

Applications of petrol engines include

automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle Steering, steered by a Motorcycle handlebar, handlebar. Motorcycle design varies greatly to suit a range of different purposes: Long-distance ...

aircraft An 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 by using the Lift (force), dynamic lift of an airfoil, or in ...

, motorboats and small engines (such as lawn mowers, chainsaws and portable generators).

History

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.

References

{{Authority control Internal combustion piston engines Gasoline engines