Influence of Nozzle Hole Geometry, Rail Pressure and Pre-Injection on Injection, Vaporisation and Combustion in a Single-Cylinder Transparent Passenger Car Common Rail Engine

The application of exhaust gas aftertreatment systems is currently discussed to be the most suitable solution to significantly reduce soot and nitrogen oxide emissions of modern diesel engines. Nevertheless, an improvement of the engine combustion process reducing the raw emissions must be seen in combination with such systems or as a replacement.

In this study, the influence of nozzle geometry, rail pressure and pre-injection on injection, vaporisation and combustion was analysed in a transparent single-cylinder diesel engine equipped with a common rail injection system by means of optical measurement techniques. The results show that a high-speed fuel intake into the combustion bowl, in combination with high rail pressures, forces the injection jets to break-up close to the wall of the combustion bowl. The engine swirl and the influence of the wall improve the mixture formation. Homogeneous regions are built over extended parts of the combustion bowl, where the combustion takes place with less diffusion flames reducing the soot emissions. Additionally, also advantages for the nitrogen oxide emissions can be expected, since homogeneous regions generate less temperature peaks in the combustion bowl.