Motor Common Rail

The diesel engine fuel system must ensure that fuel is delivered to the cylinders at the correct point in the engine cycle, in the right amount and in the correct in order for the engine to function correctly at a given engine working condition.

To ensure tough legislations are met, the rate at which fuel is injected and the number of injections per cycle must be tailored to suit the entire range of speeds and loads that the engine will experience.

One successful technology currently being used, which provides us with the control and flexibility, is common rail, as shown in Figure One. It is consist of a container, mounted on the engine that holds fuel at high pressures. A high-pressure pump, pressure sensor and regulating valve (all electronically controlled) maintain the correct pressure in the rail. The rail is ‘common’ because all of the fuel injectors are connected directly to it by high-pressure pipes and share the high-pressure fuel that it holds. When a fuel injection is required, the injector opens for a controlled amount and time allowing a known quantity of fuel to be delivered into the cylinder at the desired rate.


The common rail replaces the PLN (Pump-Line-Nozzle) system currently used on the 4&6 cylinder 1100VistaC engines. A major advantage of the common rail in comparison to the PLN is that the pressure is controlled independently of the pump, allowing for better performance at low engine speeds.

Another benefit is that Multi-shot injection strategies, which help reduce emissions at certain engine conditions, are much more easily produced on the common rail than using a PLN system, as the common rail can more accurately control small quantities of fuel.

Common rail also helps to decrease fuelling variations between cylinders, as all the injector fuel lines are fed directly from the common rail, therefore held at the same pressure, which further increases the fuelling control.