Diesels known for their power handling capabilities acquired the title workhorse engines. Diesels may reside in heavy-duty trucks, buses, tractors, and trains, not to mention large ships, bulldozers, cranes, and other construction equipment. Gasoline engines might dwell in the typical passenger vehicle, lawn equipment and recreational vehicles.

There are basically 2 types of popular engines used in the world today:

1. Petrol engines
2. Diesel engines

Petrol fuel is injected as an air/fuel mixture into the combustion chamber and ignited by the spark from spark plugs. Diesel fuel is pressurized and injected into the combustion chamber through a fuel injector nozzle, just when the air in the chamber has been subjected to high pressure that it is hot enough to ignite the fuel spontaneously.

Traditional fuel injection systems for diesel engines are designed with the objective to secure acceptable fuel spray characteristics during the combustion process at all load conditions. Incorrect injection causes reduced efficiency and increased emission of harmful species.. Among the advantages claimed with respect to the common rail concept are injection rate shaping, variable timing and duration of the injection, in addition to variable injection pressure, enabling high injection pressure even at low engine loads. Medium speed diesel engines are different from the automotive diesel engines, especially in that the majority of them operate at constant load and speed most of the time, and the advantages of the more complicated common rail system may not be justified. The common rail injection system is not capable of supplying all possible rate shapes, and rate shaping is mostly restricted to delivering a pre injection prior to the main injection. When the rate of injection is the key to an effective combustion process, it is vital to determine how the 4 rate of injection from the common rail system compares to the rate of injection from a traditional injection system. 

The common rail is a modular system, and can therefore be easily adapted for different engines.Besides acting as fuel accumulator, the fuel rail also distributes fuel to the injectors. The function of the high pressure accumulator is to maintain the fuel at high pressure. In so doing accumulator volume has to dampen pressure fluctuations caused by fuel pulses delivered by the fuel pump and the fuel injection cycles. This ensures that, when the injector opens the injection pressure remains constant.