Experimental investigation of combustion and heat transfer in a direct injection spark ignition (DISI) engine through instantaneous combustion chamber surface temperature measurements

摘要

An experimental study was performed to provide the combustion and in-cylinder heat transfer characteristics resulting from different injection strategies in a direct injection spark ignition (DISI) engine. Fast response thermocouples were embedded inin the piston top and cylinder head surface to measure instantaneous combustion chamber surface temperature and heat flux, thus providing critical information about the combustion characteristics and a thorough understanding of the heat transfer process. Two distinctive operating modes, homogeneous and stratified, were considered and their effect on combustion and heat transfer in a DISI engine was investigated. The results show the stratified operating mode yielded higher spatial variations of heat flux than the homogenous operating mode. This behavior is directly caused by the main features of stratified combustion, i.e. vigorous burning of a close-to-stoichiometric mixture near the spark plug, and cool, extremely lean mixture at the periphery. The cooling effect of the spray impinging on the piston bowl surface when the fuel is injected late in compression could be detected, too. Comparison between the calculated global heat fluxes and measured local heat fluxes were performed in order to assess the behavior of classic heat transfer models. Comparisons between the global and local heat fluxes provide additional insight into spatial variations, as well as indications about the suitability of different classic models for investigations of the heat transfer aspect of DISI engines. The general observation indicates that special consideration is required when applying classic heat transfer correlations to stratified DISI operation.