The Combustion Characteristics of n-Heptane Fueled HCCI Engine Operation With Gaseous Fuels Admission

The effects of the introduction of the gaseous fuels, methane, hydrogen and carbon monoxide into the intake of a variable compression ratio n-heptane fuelled HCCI, CFR engine were investigated. The variations in some of the key combustion and operational parameters were determined experimentally. These included cylinder pressure and its rise rate temporal developments, autoignition timing, combustion durations for both the low and high temperature reaction regions, COV values for IMEP and maximum cylinder pressure, and the incidence of knock and its intensity. In parallel with the experimental investigation, results of a numerical simulation of the processes involved obtained by employing a KIVA based approach while incorporating sufficiently detailed chemical kinetics are presented. It was found that supplementing n-heptane HCCI with gaseous fuels could inhibit the low temperature combustion region and delay to varying extents the high temperature combustion region. Methane admission produced lengthening of the delay to autoignition and extended the combustion durations. It is suggested that supplementing the liquid fuel with methane may be a means for controlling the combustion process of a liquid fuelled HCCI engine while obtaining higher power and acceptable levels of emissions without producing unacceptably heavy knock. However, the addition of hydrogen or carbon monoxide could not reduce the intensity of knock while improving power output.