Experimental Investigations on the Effects of Injector Orientation in a Diesel-Gasoline-Fuelled Premixed Charge Compression Ignition Engine

Premixed charge compression ignition (PCCI) presents a promising alternative to conventional diesel combustion (CDC), substantially reducing pollutant levels by lowering the local in-cylinder temperature and enhancing fuel-air mixing. A significant challenge in PCCI is controlling the initiation of combustion, along with a narrow operating load range due to early ignition and knocking combustion at the higher load when using high-reactivity diesel fuel. This poses an obstacle to successfully implementing the PCCI combustion mode engine. In the present study, experimental investigations are carried out in a light-duty diesel engine in PCCI mode using three fuel blends, 0% (G0D100), 10% (G10D90) and 20% (G20D80) gasoline in diesel on a volume basis, and exhaust gas recirculation (EGR) and water vapor as charge diluents. A common rail direct injection (CRDi) system replaces the existing mechanical fuel injection, and the compression ratio is decreased from 17.5 to 15 to achieve the PCCI combustion mode. The initial parametric investigations indicated that early direct injection and high fuel injection pressure confined the load range to 30% of the rated load in PCCI combustion with diesel fuel. However, with diesel and EGR, the load range is extended up to 60% of the rated load, with increased HC and CO emissions. The engine's cylinder head is modified to accommodate a vertical injector configuration, and diesel is replaced with diesel-gasoline blends to address these shortcomings. Experiments were conducted using a modified cylinder head at a constant rated speed of 1500 rpm with varying load conditions at the optimized injection timing in PCCI combustion mode to analyze the effect of injector orientation and diesel-gasoline fuel blends using EGR and water vapor charge diluents. The results show that the diesel-gasoline blend extends the ignition delay and the fuel-air mixing time between the end of fuel injection and the start of combustion. With the G20D80 blend, using EGR and water vapor as the charge diluents, the engine operating load range extends to 74% of the rated load. The NOx and soot emissions are reduced compared to CDC; HC and CO emissions are lower at low and higher at high loads. The G20D80 blend using EGR alone as charge diluent leads to load extending up to 73.4% of the rated load. Emissions of NOx and soot are lower compared to CDC. Also, HC and CO emissions are reduced by 60% and 23%, respectively, at higher loads and 23% and 29% at low loads compared to using both EGR and water vapor as charge diluents.