Investigations on the Start-Up Process of a DISI Engine

Understanding the processes regarding fuel injection, vaporization and combustion during cold start is very important in order to reduce the HC-emission of gasoline engines. To learn more about the cold engine start-up process an experimental study on a 4.2 liter eight cylinder engine with gasoline direct injection was carried out. Parameters such as injection and ignition timing as well as the injection quantity were varied to get information about their effect on the combustion process and speed rise.

Especially during engine run-up it is important to investigate every subsequent combustion. Therefore the engine was equipped with high pressure indication in each cylinder. The transient pressures and the instantaneous crankshaft speed of the engine were recorded by means of an indication system. Additionally a fast response flame ionization detector (FRFID) was applied to measure the transient HC-emissions during the first cycles of the engine. The pressures of every single cylinder were evaluated in terms of pressure maximum and mean effective pressure. Furthermore the speed signal was analyzed in terms of its increase per ignition. To get additional information about the combustion quality the emission of unburned hydrocarbons was analyzed.

Based on these measurements the optimal parameter setting for every subsequent ignition during the engine start-up was derived.