Download files
Abstract
Gasoline compression ignition (GCI) engines promise a significant reduction in NOx and smoke emissions while maintaining high efficiency of diesel engines. This thesis implemented triple injection strategy, exhaust gas recirculation (EGR) and intake air e-boosting with an aim to further improve GCI combustion. The engine performance and emissions results obtained from a single-cylinder common-rail diesel engine were analysed with a specific interest in how each of these key parameters impacts the in-cylinder pressure, heat release rate, combustion phasing, efficiency and engine-out emissions. From the systematic tests of triple injection strategy, GCI combustion showed high sensitivity to the second/third injection proportion and timing. Increased charge premixing and advanced combustion phasing was found with increased 2nd injection proportion or advanced 3rd injection timing placed at mid-to-late crank angle and near-TDC, respectively. However, the increased in-cylinder pressure and apparent heat release rate (aHRR) resulted in higher NOx emissions. This was resolved using advanced 2nd injection timing, which led to higher mixture homogeneity and thus lower peak in-cylinder pressure and aHRR for decreased NOx, smoke and noise emissions. To further reduce NOx emissions, EGR was tested in the 0 to 16% range. In consideration of lower power output with the use of EGR, a supercharger driven by an electric motor (i.e. e-booster) was also used for up to 130 kPa (absolute) intake air pressure. The results indicated that higher EGR ratio causes reduced in-cylinder pressure and aHRR to achieve significant NOx and noise emissions reduction. However, it suffered from reduced engine efficiency and increased smoke/uHC/CO emissions. This was recovered using e-boosting due to higher intake air pressure and thus reduced pumping loss and increased in-cylinder pressure. At the same time, the reduced ignition delay time caused lower peak aHRR, which in turn further reduced NOx emissions. The resulting NOx reduction due to the combined use of EGR and e-boosting was very significant as the e-boosting successfully reduced uHC and CO emissions back to no EGR level.