Improvement of exhaust emissions by early injection in multiple stage fuel injection

Multiple staged injection is available to improve of exhaust gas emission and combustion noise. Attached pilot injection, which pilot injection is very close to main injection by using piezo-electronic injector, can be reduce a combustion noise about 5dB compare with single injection without smoke emission increasing. Early injection is also possible to reduce NOx and smoke simultaneously. However, HC and CO emissions are increased in case of early injection due to quench of the fuel impinged to cylinder wall. To reduce the quantity of impinging fuel spray to the cylinder wall, multiple staged injection is performed with very small quantity in each pilot injection. Multiple staged injection can be reduce simultaneously HC, NOx, smoke and fuel consumption.