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The effects of cooled EGR on combustion and emission characteristics in HCCI operation region was investigated on a single-cylinder diesel engine, which is fitted with port injection of DME and methanol. The results indicate that EGR rate can enlarge controlled HCCI operating region, but it has little effect on the maximum load of HCCI engine fuelled with DME/methanol dual-fuels. With the increase of EGR rate, the main combustion ignition timing (MCIT) delays, the main combustion duration (MCD) prolongs, and the peak cylinder pressure and the peak rate of heat release decreases. Compared with EGR, DME percentage has an opposite effect on HCCI combustion characteristics. The increase of indicated thermal efficiency is a combined effect of EGR rate and DME percentage. Both HC and CO emissions ascend with EGR rate increasing, and decrease with DME percentage increasing. In normal combustion, NOX emissions are near zero.

The effects of Exhaust Gas Recirculation (EGR) and octane number of PRF fuel on combustion and emission characteristics in HCCI operation were investigated. The results show that EGR could delay the ignition timing, slow down the combustion reaction rate, reduce the pressure and average temperature in cylinder and extend the operation region into large load mode. With the increase of the fuel/air equivalence ratio or the fuel octane number (ON), the effect of EGR on combustion efficiency improves. With the increase of EGR rate, the combustion efficiency decreases. The optimum indicated thermal efficiency of different octane number fuels appears in the region of high EGR rate and large fuel/air equivalence ratio, which is next to the boundary of knocking. In the region of high EGR rate, HC emissions rise up sharply as the EGR rate increases. With the increase of octane number, this tendency becomes more obvious.