Needle lift of fuel injector nozzle and pressure curve in the cylinder with pilot injection
1 Combustion pressure in the cylinder
2 Needle lift
3 TDC
4 Needle lift for pilot injection
5 Needle lift for main injection
6 Crank angle
In the case of vehicles with common rail injection systems electrically-controlled pilot injection occurs after a set time prior to the main injection event.
In the case of pilot injection, a small amount of fuel is injected into the cylinder prior to the main injection. Pilot injection results in a gradual increase in the combustion pressure, leading to an improvement in combustion quality.
The small, pilot injection fuel quantity is ignited and heats up the upper part of the cylinder, thereby bringing it into an optimum temperature range (pre-conditioning of the combustion chamber).
This means that the main injection mixture ignites more quickly and the rise in temperature is less abrupt as a result.
This also results in a less abrupt increase in combustion pressure, significantly reducing combustion noise.
Advantage:
โข Continuous build-up of combustion pressure, resulting in reduced combustion noise,
โข Reduction of nitrogen oxides in the exhaust gas.
Note: As pressure generation and injection in common rail systems are separate, it is possible to considerably enhance the range for pilot injection (up to approx. 3000 rpm regardless of engine load). This has led to a decisive improvement in the running characteristics of the engine.