Experimental Investigation On Control Strategies Of Diesel Low Temperature Premixed Combustion

Diesel low temperature premixed combustion has been paid attention by more andmore researchers since it has the potential to achieve premixed homogeneous mixture inthe cylinder which can result in simultaneously reduction of NOxand soot emission.Optimized injection strategies and using EGR to lower the combustion temperature hasbeen an indispensable approach for realizing low temperature premixed combustion. Theeffects of EGR and injection strategies including injection timing, pilot injection, postinjection, interval between injections, injection pressure on low temperature premixedcombustion and conventional diesel combustion were investigated in a heavy-dutycommon rail diesel engine.The investigation of the influence of EGR, injection timing and injection pressure oncombustion and emissions of low temperature premixed combustion mode were carriedout using single injection strategy. The results were compared with those obtained inconventional diesel combustion. The investigation showed that with the combination ofmoderate EGR and retarded injection timing, low temperature premixed combustion modecan be achieved in low load. Compared to conventional diesel combustion, in lowtemperature premixed combustion mode, the peak cylinder pressure and peak pressure riserate significantly decreased, the ignition delay was extended largely, the combustionduration reduced. NOxand smoke emission can be substantially improved but CO and fuelconsumption became worse. Higher injection pressure can increase the degree of premixedcombustion, weaken the mixing-controlled combustion and advance the start ofcombustion. The ignition delay, combustion duration and CA50with a higher injectionpressure were shorter. Smoke and CO as well as the fuel consumption can be improved atthe same time under higher injection pressure.Multiple injection strategies were studied in order to further optimize the combustionand reduce the emissions of low temperature premixed combustion mode. The results showed that larger pilot-main interval and smaller pilot quantities were better indecreasing the peak pressure rise rate. Pilot injection had a slightly effect on NOxemissionand negative effect on smoke emission. No matter what the engine load is, smallerpilot-main interval had fewer penalties to HC and CO emission. Conversely, larger pilotquantities deteriorated HC and CO less under low load when compared to moderate andhigh load. The pilot injection influenced the fuel consumption slightly. Post injection had alittle bad effect on NOx. Smaller main-post interval and larger post quantities showed abetter effect on improving smoke, CO and fuel consumption. The smoke and CO emissioncan be significantly reduced when using two pilot+post injection strategy with a slightlynegative effect on NOxand fuel consumption keeping nearly constant.