Effects of split injection and exhaust gas recirculation strategies on combustion and emissions characteristics in a modern V6 diesel engine

摘要

The thesis presents investigations of advanced combustion strategies in a modern V6 diesel engine fuelled with mineral diesel and Tallow Methyl Ester (TME)-diesel blends, in order to meet future emissions legislation. One of the main objectives of this research is to improve fuel consumption whilst minimising engine emissions through the combined effects of injection strategy (fuel injection pressure, dwell period, pilot fuel quantity) and cooled Exhaust Gas Recirculation (EGR) on a modern V6 common rail direct injection diesel engine. In the case of using EGR (49–52%) at 1500 rpm and 10% of engine peak torque, by increasing the fuel injection pressure from 300 to 800 bar, engine thermal efficiency increased from 16.5 to 19.1% and 17.1 to 19.7%, BSFC decreased by 13.5% and 13.2%, smoke level decreased by 74.3% and 70.1% and NOx emissions increased by 69.6% and 68.0%, respectively for a short (5 CAD) and a long (40 CAD) dwell period. In addition, the study of a variation of pilot fuel quantities (0.8–3.0 mg/stroke) with a fixed dwell period (5 CAD) at two different fuel injection pressures (250 bar and 800 bar) shows that the smaller pilot quantity with the higher fuel injection pressure can be considered as an enhanced strategy to control engine performance and emissions simultaneously. Therefore, the combination of higher injection pressure, longer dwell, smaller pilot quantity and the use of EGR could potentially improve fuel consumption and minimise engine emissions. The use of TME-diesel blends results in lower engine thermal efficiency and higher fuel consumption and NOx emissions. In the case of 1500 rpm and 25% of engine peak torque, the combustion of TME10 and TME30 reduced the engine thermal efficiency from iii 35.3 to 33.7% and 35.3 to 33.2% and increased the BSFC by 4.9% and 6.5%, respectively. At the same engine condition, the combustion of TME-diesel blends increased NOx emissions by 1.8% and 10.0% and reduced CO by 0.9% and 1.8%, THCs by 18.0% and 23.9 %, smoke by 30% and 51.7% for TME10 and TME30 respectively. However, the engine thermal efficiency, BSFC and NOx emissions could be improved with the application of the combined effect of injection strategy (fuel injection pressure, dwell period, pilot fuel quantity) and EGR as shown in the first phase of this study.