Effects of Injection Parameters and Injection Strategy on Emissions and Performance of a Two-Stroke Opposed-Piston Diesel Engine

Abstract

Modern two-stroke opposed-piston (OP2S) engines offer high efficiency and high power-to-weight ratio compared to conventional four-stroke (4S) engines. Oil consumption and high emissions are usually attributed to 2S engines. However, it is claimed that these drawbacks are well addressed in the modern OP2S engines. In this paper, a three-dimensional computational fluid dynamics (3D-CFD) model for combustion in an OP2S diesel engine was developed and validated against experimental data. The effects of injection parameters, such as the number of nozzles, spray angle, injector’s angle, injection pressure, and the start of injection (SOI), on emissions and performance, were investigated. By rotating one of the injectors by 45 degrees around its axis, it was found that NO_X emission decreased by 20% and gross thermal efficiency (GTE) improved by 0.9%. In the case of injection pressure studies, by increasing the injection pressure up to 1600 bar, soot emission reduced by 7.7%. Advancing the SOI by two crank angle degrees (CAD) can reduce soot emission by up to 16%. To address NO_X and soot emissions as primary drawbacks of conventional diesel engines, post- and pre-injection strategies were also studied. In the post-injection study, soot reduced by 30%, and the results of the pre-injection case showed a 37% reduction in NO_X. A combination of pre- and post-injection strategies was studied, and this case resulted in 31.2% and 38% reductions in NO_X and soot emissions, respectively. Finally, the emissions and performance of the OP2S diesel engine were compared with the experimental results of two conventional 4S diesel engines. The OP2S produces 3.5% and 6.5% higher GTE than heavy-duty (HD) and light-duty (LD) 4S engines. The OP2S also has lower fuel consumption and CO₂ by about 15.5% and 10.5%, respectively, compared to the HD4S.