An experimental study of inlet water injection combined with high pressure(HP) exhaust gas recirculation(EGR) was conducted on a high pressure common rail heavy-duty diesel engine. The effects of introducing HP EGR and inlet water injection on diesel engine emissions and fuel economy were investigated at all working points of the world harmonized steady-state cycle(WHSC). Based on that

the optimization of the combustion phase at each working point was carried out to obtain an optimal control strategy of coupling inlet water injection with EGR over the WHSC cycle. The results show that

considering both the emissions and fuel economy

the HP-EGR should be introduced at low load conditions and the fuel injection timing should be advanced to obtain a better combustion phase. A small amount of inlet water injection and a proper rate of EGR should be adopted at medium and high load conditions

while the inlet water injection strategy should be adopted at full load. The weighted WHSC results show that the optimized weighted NOx specific emissions can be reduced by 7.71 g/(kW·h)

a reduction of about 45.2%

and the weighted brake specific fuel consumption(BSFC) can be decreased by 1.20 g/(kW·h)

while still maintaining low HC

CO and soot emissions.