Effect of pilot fuel quantity and fuel injection pressure on combustion, performance and emission characteristics of an automotive diesel engine

Abstract

The work presented here experimentally investigates the effect of pilot quantity (PQ) on combustion, performance and emission characteristics of an automotive diesel engine. All the experiments were performed at max torque speed of the test engine (1600 rpm) and 75 % of full engine load. Three PQs under consideration are 10 %, 20 % and 30 % of total fuel mass per cycle while maintaining the fixed pilot as well as main injection timings. The minimum PQ (10 %) considered in the study was found sufficient to enhance the in-cylinder thermodynamic conditions before main injection starts. Also, fuel injection pressure (FIP) was maintained constant at 500 bar initially. Obtained results showed that the pilot injection mode with 30 % PQ reduced nitrogen oxide (NO) emission as well as brake specific fuel consumption (BSFC) by 21.87 % and 1.46 % respectively compared to reference single injection mode while smoke emissions were increased by 77.64 %. In order to curb this negative effect of higher smoke emissions offered by pilot injection, FIP was increased from 500 bar to 700 bar and similar experiments were repeated. The experimental results demonstrated that higher FIP significantly reduced smoke emissions as well as fuel consumption under all the considered pilot injection modes with acceptable rise of NO emission which was still considerably lower than reference single injection mode. For e.g., when FIP was increased from 500 bar to 700 bar in case of pilot injection mode with 30 % PQ, smoke emissions and BSFC were reduced by 26.40 % and 2.14 % respectively, while NO emission was increased by 6.30 %. Therefore, it can be said that combination of pilot injection and high FIP leads to overall improvement in performance and emission characteristics of the test engine.