Experimental Investigations on the Effects of Injector Design and Operating Parameters on PCCI Combustion in a Light-Duty Diesel Engine

Due to increasingly stringent emission regulations, advanced combustion strategies, such as premixed charge compression ignition (PCCI), have emerged promising solutions for achieving low NO_x and soot emissions. However, challenges such as increased unburned hydrocarbon (HC), carbon monoxide (CO) emissions, and a restricted engine operating load range remain unsolved. Since conventional diesel engines are not inherently designed for PCCI operation, re-optimizing engine parameters is essential. The primary objective of this work is to investigate the influence of injector orientation and nozzle spray angle on combustion parameters, performance, and emissions in a PCCI diesel engine. Initial parametric studies revealed that early direct injection combined with high fuel injection pressure limited the PCCI load range to 30% and 60% of the rated capacity with diesel, without and with EGR, respectively, accompanied by higher HC and CO emissions. To address these limitations, the injector orientation is modified from inclined to vertical, increasing the offset from 5 to 9 mm and employing symmetric spray angles along the z-axis. The experiments were conducted at a constant engine speed of 1500 rpm with varying load conditions at optimized timing in PCCI mode to investigate the effect of injector orientation, offset, and spray angle. The results demonstrate two positive aspects: first, the load range extended from 30% to 40% of the rated load with diesel, with improved engine brake thermal efficiency and reduced NO_x emission up to 85.6% compared to conventional diesel combustion (CDC). Second, while using the EGR, the load range extends from 60% to 62.5%, achieving up to 96% NO_x reduction compared to CDC. Although HC and soot increased significantly, a notable decrease in HC was observed at higher loads compared to lower load conditions. According to this study, injector orientation and nozzle spray angle variation are effective strategies for enhancing the performance and extending the operating load range of PCCI engines.