Common rail fuel injection arrangement.Common rail is a type of fuel injection system in use on diesel engines.

Older systems used a mechanical injection pump (either rotary or in-line) to generate high pressure for each injector which caused the unit to inject fuel-oil into the combustion chamber.

With the common rail system, a pump pressurises a rail of fuel which is common to each injector. In other words, each injector is connected to this rail, which contains fuel-oil under high pressure. When it is time for a particular injector to fire, a signal from the ECU lifts the needle in the injector. This causes fuel from the rail, under very high pressure, to be injected into the combustion chamber.

NEVER open injector pipes on modern common rail systems. Conventional mechanical systems such using inline or rotary pumps have injection pressures in the region of 120 bar. Modern common rail systems operate on pressures in the region of 1,800 bar. If you are in any doubt whatsoever about the type of system you are working on, LEAVE IT ALONE, and check with your instructor, a supervisor, or a more experienced work colleague.

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