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A numerical study has been performed to investigate the soot emission from a high-speed single-cylinder direct injection diesel engine. It was shown that the current KIVA CFD code with the standard evaporation model could predict the experimental trend, where at a low speed running condition a higher smoke reading is reached when increasing the injector protrusion into the piston chamber and conversely a lower smoke reading was recorded for the same change in injector protrusion at a high running speed condition. Evidence of inappropriate air/fuel mixing was seen via rates of heat release analyses, especially in the high-speed conditions. Efforts to reduce this discrepancy by way of improvements to the KIVA breakup and evaporation models were made. Results of the modified models showed improvements in the vapor dispersion of the atomizing liquid jet, thus affecting the mixing rates and predicted smoke emissions.

An experimental study has been carried out on a single-cylinder pressure-charged engine with a near quiescent combustion system. An improvement in the NOx/BSFC trade-off was achieved by two different approaches, namely exhaust gas recirculation and pilot injection. Without EGR, a reference EUI-200 system with 1900 bar peak injection pressure gave a low soot particulate level of 0.013 g/bhp h over a simulation of the US FTP cycle. The results with EGR show how higher levels of EGR can be used at more advanced injection timings to give substantially improved NOx versus BSFC results compared with timing retard alone. It was possible to reduce the NOx from 4.85 to 3.6 g/bhp h for no increase in BSFC over the simulated US FTP cycle and with a total calculated particulate of 0.075 g/bhph. The results with electronically-controlled pilot injection show improvements in NOx versus BSFC, lower NOx before HC increase with retard, or reduced combustion noise at certain test modes.