The common rail injector system is used in gasoline direct injection for modern two and four-stroke gasoline-run engines, but is more popularly used in diesel engines; in gasoline engines, the gasoline is pressurized and injected into the combustion chamber in each cylinder by the common rail fuel line. In diesel engines the high pressure fuel rail line feeds individual solenoid valves. Newer common rail diesel systems now use piezoelectric injectors (injectors that can generate an electric field when mechanical stress is applied to them) which results in increased precision and higher pressure. The common rail system was first developed by Robert Huber in Switzerland in the 1960’s and was then further developed by Dr. Marco Ganser. The first time that the common rail system was successfully used was in Japan in the 1990s by Dr. Shohei Itoh and Masahiko Miyaki who developed the system for use in heavy duty vehicles and first mounted it on a Hino Rising Ranger truck which was sold in 1995.

In 1997 use of the common rail system was extended to passenger cars and used in the Alfa Romeo 156 and then the Mercedes-Benz C 220 CDI. In more recent times the common rail system has been used in trains, boats, and even submarines. The common rail system works by storing a reservoir of high pressure fuel in a high pressure pump; when the fuel injectors are activated, a hydraulic valve is opened and fuel is sprayed into the cylinders at high pressure by the common rail. However, generating the pressure and injecting it are two separate occurrences; the high pressure pump creates pressure in the rail independently of the engine speed and the quantity of fuel that is being injected. The fuel is then fed through pipes to the injectors which in turn injects the required amount of fuel into the combustion chambers.

The Electronic Diesel Control (EDC) controls the pressure in the rail, the intervals at which fuel is injected, and how long fuel is injected each time; while the engine control unit (ECU) is responsible for opening each injector to receive fuel from the common rail. Many auto companies, especially European ones now make and use common rail fuel injector systems, all with different names; a few of these companies are: Daimler Chrysler, General Motors, Fiat, Mitsubishi, Hyundai, Ford, Toyota, Nissan, Land Rover, BMW and several others; in more recent times Honda has also developed their own version of the common rail system.