Effect of Injection Parameters on the Premixed Charge Compression Ignition Combustion in a Small-Bore Light Duty Diesel Engine – A CFD Study

Premixed charged compression ignition (PCCI) is a promising low temperature combustion strategy for achieving simultaneous reduction of oxides of nitrogen (NOx) and soot emissions in diesel engines. However, early direct injection results in significant penalty in fuel economy, high unburned hydrocarbon (HC) and carbon monoxide (CO) emissions, especially in small-bore diesel engines. In the present work computational fluid dynamic investigations are carried out in a small-bore diesel engine using a commercial CFD software, CONVERGE. The computational models are validated with experimental results at two different load conditions, 20% and 40% of rated load. The validated models are used to carry out parametric investigations on the effects of fuel injection parameters, namely start of fuel injection timing, injection pressure and spray cone angle on PCCI combustion. The fuel-air equivalence ratio, temperature and emission contours are used to get more insight into the effect of fuel injection parameters on the combustion process to reduce the spray wall wetting and the high HC and CO emissions. The results obtained show reduction in the NOx and soot emissions with advanced injection timings from 20 deg to 50 deg. CA bTDC with a penalty in the HC and CO emissions as well as indicated thermal efficiency. Increasing injection pressure from 300 to 900 bar resulted in higher HC and CO emissions at both the loads due to increased spray wall impingement. A narrow spray cone angle of 88 deg. results in significant reduction in the HC and CO emissions by up to 77% and 80%, respectively compared to a wider cone angle of 148 deg. at low load condition. At high load, using a narrow spray angle resulted in increase in the CO and soot emissions with only minor reduction in HC emissions due to poor air utilization in the current small-bore engine.