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In this study, the characteristics and the advantages on engine performance of the reformed molecule HCCI (RM-HCCI) combustion fueled with gasoline were investigated by exergy analysis. The processes of fuel reforming and the closed portion of the engine cycle were simulated integrated with chemical kinetics mechanism at varied compression ratio (CR) and constant speed conditions. Results showed the fuel reforming under high temperature and oxygen-free condition by the exhaust heat recovery and electric heating assistance could drive gasoline to transform to the small-molecule gas fuels, meanwhile enhanced the chemical exergy of the fuel. The reformed fuel contributed to extending ignition delay, so less dilution required in RM-HCCI engine when expanding high load compared with gasoline HCCI engine. Thus, RM-HCCI engine could achieve higher load than gasoline HCCI engine, with the improvements by 12%, 26%, and 31% at CR17, CR19, and CR21, respectively.

To explore the exergy loss of engine combustion process, entropy generations were numerically analyzed through detailed chemical kinetics. It revealed that the reformed fuel with simpler molecular tended to produce lower combustion irreversibility. Furthermore, a promising high efficiency RM- HCCI (Reformed molecule HCCI) combustion principle was proposed. In a RM-HCCI engine, hydrocarbon fuels were reformed into small molecule fuels under high temperature and low/no oxygen atmosphere before injection into the cylinder when the exhaust gas enthalpy to a certain extent was recovered, further improving the engine efficiency. The second law efficiency (η2nd) of a RM-HCCI combustion with a CR of 10 can be increased from 36.78% to 45.47% by coordination of multiple control parameters, and to 67.79% by raising CR from 10 to 100.