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%. Advancing the
SOI by two crank angle degrees (CAD) can reduce soot emission by up to 16%. To
address NOX 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 NOX. A combination of pre- and
post-injection strategies was studied, and this case resulted in 31.2% and 38%
reductions in NOX 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.