Fundamentals of Pressure Trace Analysis for Gasoline Engines with Homogeneous Charge Compression Ignition 2010-01-2182

Regarding further development of gasoline engines several new technologies are investigated in order to diminish pollutant emissions and particularly fuel consumption. The Homogeneous Charge Compression Ignition (HCCI) seems to be a promising way to reach these targets. Therefore, in the past years there had been a lot of experimental efforts in this field of combustion system engineering. Negative valve overlap with pilot injection before pumping top dead center (PTDC) and an “intermediate” compression and combustion during PTDC, followed by the main injection after PTDC, is one way to realize and to proper control a HCCI operation.

For conventional CI and SI combustion the pressure trace analysis (PTA) is a powerful and widely used tool to analyse, understand and optimize the combustion process. With the first law of thermodynamics and some model assumptions regarding heat transfer and gas properties the burn rate is calculated by a pressure trace analysis from a given indicated cylinder pressure. For a HCCI engine with negative valve overlap, pilot injection and PTDC combustion a pressure trace analysis would be a very interesting tool to analyse the combustions during PTDC and FTDC, and to investigate the reaction of these two combustions on injection timings and other engine parameters. But, pressure trace analysis of such an engine is quite challenging.

A one-cylinder research engine was investigated with such a pressure trace analysis. The main focus was on the combustion during the PTDC. This intermediate combustion was clearly and reasonably indicated by the burn rate. The influence of varying pilot injection timings on the burn rate of the PTDC “intermediate” combustion will be presented.

The specifics of pressure trace analysis on HCCI engines will be discussed in detail. The authors recommend using different approaches for heat transfer during the high-pressure part of the cycle, the gas-exchange and during the negative valve overlap. To analyse the PTDC combustion the pressure trace analysis has to be combined with a gas exchange analysis. The fundamentals of gas exchange analysis will be described. It has to be stated that using small valve lifts the measured flow coefficients of the inlet and exhaust ports have to be often adjusted.

At last, the possibility to analyse the PTDC combustion is a mandatory step towards a burn rate simulation model for gasoline HCCI engines.