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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 NOX 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%.

Alternative fuels are of great interest since they can be refined from renewable feedstocks, and their emission levels can be lower than those of conventional fueled engines. Despite the fact that alternative fuels are not currently widely used in vehicular applications, using these kinds of fuels is definitely inevitable in the future. In this paper, a computer code is developed in Matlab environment and then its results are validated with experimental data. This simulated engine model could be used as an appropriate mean to investigate the performance and emission of a given SI engine fueled by alternative fuels including hydrogen, propane, methane, ethanol and methanol. Also, the superior of alternative fuels is shown by comparing the performance and emissions of alternative fueled engines to those in conventional fueled engines.