Fuel injection

Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines.

All compression-ignition engines (e.g. diesel engines), and many spark-ignition engines (i.e. petrol (gasoline) engines, such as Otto or Wankel), use fuel injection of one kind or another. Mass-produced diesel engines for passenger cars (such as the Mercedes-Benz OM 138) became available in the late 1930s and early 1940s, being the first fuel-injected engines for passenger car use. In passenger car petrol engines, fuel injection was introduced in the early 1950s and gradually gained prevalence until it had largely replaced carburettors by the early 1990s. The primary difference between carburetion and fuel injection is that fuel injection atomizes the fuel through a small nozzle under high pressure, while carburetion relies on suction created by intake air accelerated through a Venturi tube to draw fuel into the airstream.

The term fuel injection is vague and comprises various distinct systems with fundamentally different functional principles. The only thing all fuel injection systems have in common is the absence of carburetion.

There are two main functional principles of mixture formation systems for internal combustion engines: internal and external. A fuel injection system that uses external mixture formation is called a manifold injection system. There exist two types of manifold injection systems: multi-point (or port) and single-point (or throttle body) injection.

Internal mixture formation systems can be separated into several different varieties of direct and indirect injection, the most common being the common-rail injection, a variety of direct injection. The term electronic fuel injection refers to any fuel injection system controlled by an engine control unit.

The fundamental functions of a fuel injection system are described in the following sections. In some systems, a single component performs multiple functions.

Fuel injection is operated by spraying pressurised fuel into the engine. Therefore a device to pressurise the fuel is needed, such as a fuel pump.

The system must determine the appropriate amount of fuel to be supplied and control the fuel flow to supply this amount.