Extinction and Chemiluminescence Measurements of HCCI Mode in Diesel Engine Operating with Late Injection 2008-01-0027
Nowadays HCCI combustion process is revealing the most useful technique for reducing pollutant emission from internal combustion engines. In the present paper, HCCI combustion was realized by means of single late injection at high pressure and heavy EGR, up to 50%. A transparent Direct Injection (DI) diesel engine equipped with high pressure Common Rail (CR) injection system was used. The engine was fed with commercial diesel fuel and ran in continuous mode.
Digital imaging and spectroscopic techniques, with high temporal and spatial resolution, were applied to study the low temperature combustion process. Injection and combustion phases were analysed by digital imaging. Mixing process, autoignition and pollutants formation were investigated by Broadband Ultraviolet - Visible Extinction Spectroscopy (BUVES) and flame emission measurements. Radicals and species such as OH, CH and CO were detected in the combustion chamber. They are of interest in order to study the chemical kinetics of low temperature combustion process. Moreover, fuel distribution and oxidation were studied. Finally, the injection pressure effect on the development of low temperature combustion was analysed.
Liquid and vapour phase of fuel, injected around the top dead centre, were analysed. Extinction due to liquid diesel fuel was observed when the liquid jet reached the bowl rim. Vapour fuel was detected 2° ca after the start of injection and liquid one disappeared. Aromatic compounds due to fuel decomposition were identified. During combustion, bright spots due to non homogeneous charge were detected. They were the source of very low amount of soot detected at the exhaust pipe. Finally, several radicals like HCO, CH and OH were detected. In particular, OH was strongly evident during the whole premixed combustion and dominated the process also beyond the end of the premixed rate of heat release.