Exhaust gas recirculation (EGR) has a great influence on the combustion characteristics of homogenous charge compression ignition (HCCI) engine. An experimental study was conducted on the EGR technology in an optimized kinetic process (OKP) HCCI engine. The results show that EGR can retard the combustion phase and reduce the combustion reaction rate in the OKP HCCI engine. EGR could be utilized for HCCI load expansion. EGR could improve indicated mean effective pressure. Different EGR rate should be optimized in different engine load. There are differences on temperature and air charge between cylinders in multi-cylinder engine, which will lead to different characteristics in cycle-to-cycle variation. Cycle-to-cycle variation will increase as EGR rate increases, and so will cylinder-to-cylinder variation.

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