Experimental study of the HCCI combustion through the use of minor oxidizing chemical species

To reduce the fuel consumption, CO2 emissions and pollutant emissions while keep improving thermal efficiency of engines, alternative combustion modes are being investigated as good candidates to replace spark-ignited and diesel engines. In particular, Homogeneous Charge Compression Ignition (HCCI) engines have proven their potential to meet these requirements. However, despite of these advantages, several challenges remain to be addressed prior to the widespread implementation of HCCI engines. Among them, the control of the overall combustion process in such an engine over the full operating range is still considered as the main challenge to overcome. The present work introduces the use of oxidizing chemical species seeded in the intake system as a robust control technique for HCCI combustion process. In particular, ozone was examined due to its strong oxidizing characteristics. Moreover, ozone can be easily produced on-board a real vehicle from the intake oxygen thanks to small ozone generators, but can also lead to the production of NOx. Investigations were carried out using a single-cylinder HCCI engine and kinetics computation analysis. The two main objectives of this work are: (1) Evaluate the potential of using ozone generator to control the HCCI combustion. Along these lines, the interaction between NOx and ozone was investigated for isooctane as fuel and a real time control of the HCCI combustion was implemented and successfully tested. (2) Compare the influence of ozone on the combustion of isooctane and alternative fuels. Methane-based fuels (methane/propane and methane/hydrogen mixtures) and alcohols (methanol, ethanol, n-butanol) were selected due to their higher resistance to autoignition and their different chemical structure.