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Homogeneous charge compression ignition (HCCI) combined with high compression ratio is an effective way to improve engines’ thermal efficiency. However, the severe thermodynamic conditions at high load may induce knocking combustion thus damage the engine body. In this study, advanced compression ignition knocking characteristics were parametrically investigated through RCM experiments and simulation analysis. First, the knocking characteristics were optically investigated. The experimental results show that there even exists detonation when the knock occurs thus the combustion chamber is damaged. Considering both safety and costs, the effects of different initial conditions were numerically investigated and the results show that knocking characteristics is more related to initial pressure other than initial temperature. The initial pressure has a great influence on peak pressure and knock intensity while the initial temperature on knock onset.

Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO2 emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions.

Nowadays the strong knocking combustion involving destructive pressure wave or shock wave has become the main bottleneck for highly boosted engines when pursuing high thermal efficiency. However, its fundamental mechanism is still not fully understood. In this study, synchronization measurements through simultaneous pressure acquisition and high-speed direct photography were performed to comparatively investigate the strong knocking combustion of iso-octane and propane in a rapid compression machine with flat piston design. The pressure characteristics and visualized images of autoignition and reaction wave propagation were compared, and the correlations between thermodynamic trajectories and mixture reactivity progress were analyzed. The results show that iso-octane behaves a greater propensity to strong knocking combustion than propane at similar target pressures.