Gasoline (or petrol) engine is a type of engine which is used for automobiles and small mobile vehicles such as lawnmowers or motorcycles. The most common engine of this type is a four stroke cycle internal combustion engine that burns gasoline (American usage) or petrol (British usage). Burning is initiated by an ignition system that fires a high voltage spark through a field-replaceable airgap called a "sparkplug."
In practice, almost all parts of the high voltage system are designed to be replaced in the field. A classic car has a set of "points," usually in the distributor housing. These open and close once for each cylinder. The points drive battery current through the primary winding of a step-up transformer, the "spark coil." The output of the spark coil is then distributed through a set of rotating mechanical contacts called the "distributor." Constant arcing in the points and distributor eventually cause them to wear, and need replacement. In more modern engines, the points or the entire distributor are often replaced by an electronic circuit. More rarely, in a few European engines, the distributor is sometimes replaced by a spark coil for each cylinder.
One crucial component in older and smaller engines is the carburetor, which mixes the gasoline with air. Carburetors are fluidic and mechanical computors that meter the fuel and mix it with the air in precise proportions. Classic carburetors measure spark advance by measuring the difference in pressure between the outside and inside of the carburetor. The degree of throttle advance is also measured. The air temperature is measured to make the measure richer in the cold, because the air is denser, and contains more oxygen per unit of volume. It would be nice to measure the engine's exhaust for carbon monoxide or unburned hydrocarbons to see how well the carburetor is working.
In more modern engines, a small electronic computer measures these parameters, and controls one or more electric injectors , which can be in the intake throat, commonly called throttle-body injection or in the individual intake runners, commonly called port fuel injection. Almost all new cars now use electronic fuel injection because it allows the engine computer to precisely regulate the fuel air mixture which increases energy efficiency and reduces pollution.
More exotic mixing, with heaters and ultrasonic mixers, is known to further improve efficiency. Most manufacturers don't bother.