Diesel engines use fuel injection pumps to maintain consistency in how diesel fuel travels to the engine. Three basic types of diesel fuel pumps exist: distributor-style, common-rail and unit-pump injection systems. These injection pumps deliver the correct amount of fuel to your engine for the power you want, performing the same work as a gas engine's ignition system and throttle.
Fewer moving parts means simplicity regarding distributor-injection (rotary) pumps. One spinning rotor creates the hydraulic connection to various ports on the distributor head. One plunger meters fuel into the engine. The small pump system with only one plunger shooting fuel into the system distributes all shots equally.
The hallmark of the common-rail injection system centres on separating the pressure and fuel injection functions. A central accumulating rail first stores fuel under high pressure before it delivers that fuel to the fuel injector valves. The system maintains high pressure at all times, producing a clean, fine mist to burn in the combustion chamber. Each common rail cycle allows up to five injections.
Large diesel engines use compact fuel injection designs called unit injectors. The engine applies mechanical force to the unit's pump plunger, creating high pressure that works together with the injector as a single entity to inject diesel fuel to the engine's combustion chamber.