Investigation on gasoline homogeneous charge compression ignition (HCCI) combustion implemented by residual gas trapping combined with intake preheating through waste heat recovery

Homogeneous charge compression ignition (HCCI) combustion achieved by residual gas trapping suffers from the limitation of the low load extension and fuel economy penalties whilst achieved by intake preheating alone is limited by the high intake thermal requirement and waste heat recovery. In the presented research, systematic engine experiments were carried out on a single cylinder engine on the combined use of residual gas trapping and intake preheating to achieve optimized combustion and better fuel conversion efficiency in the HCCI operational range. The effect of different combinations between residual gas trapping and intake preheating on HCCI combustion was explored and analyzed. It was indicated that the implementation transition from residual gas trapping to intake preheating significantly influenced the fuel economy and emissions. The decreased loss resulting from changed valve configuration contributed much more than half of the fuel economy improvement. The variation in emissions depended both on the combustion temperature influenced by dilution charge and the in-cylinder distribution affected by implementation form. It was also demonstrated that the increased benefit became less when the intake temperature further went up. Thus a relatively reasonable compromise between intake thermal demand and engine efficiency could be achieved to optimize the HCCI combustion by combining waste heat recovery and residual gas trapping. Compared to negative valve overlap method alone, the supplementary of intake preheating by waste heat recovery provided 8-12% fuel economy improvement throughout the typical load range of HCCI combustion. Also the low load boundary was effectively extended to 0.8 bar, without suffering excessive increase in CO and HC emissions.