A single fuel port and direct injected low temperature combustion strategy to reduce regulated pollutants from a light-duty diesel engine

Abstract

Low temperature combustion (LTC) recently received considerable attention due to its potential to simultaneously reduce oxides of nitrogen (NOx) and soot emissions from diesel engines and high thermal efficiency benefits. However, lack of ignition timing control, narrow engine operating load range, high unburned hydrocarbon (UHC), and carbon monoxide (CO) emissions are significant shortcomings in LTC. A homogeneous charge with direct injection (HCDI) strategy is proposed in this study to address these shortcomings. HCDI is a single-fuel LTC strategy that includes port and direct diesel fuel injection. The direct-injected diesel provides better control over ignition timing, and a wider engine operating load range could be achieved in HCDI. However, NOx emissions are significantly higher in HCDI than conventional diesel combustion (CDC). A novel water vapour induction system using ultrasonic atomizers is proposed to address this shortcoming. The experiments were conducted in a modified single-cylinder light-duty diesel engine operated in HCDI mode. A high-pressure port and direct fuel injection systems are installed in the metallic engine (engine with factory configuration) to achieve HCDI. Ultrasonic atomizers installed closer to the intake port generated the water vapour for NOx control. The premixed ratio and direct-injected diesel fuel timings are optimized to achieve maximum thermal efficiency at each load condition. The results obtained with and without water vapour induction in HCDI are compared to examine the NOx reduction potential. Further, the results obtained in HCDI with water vapour induction are compared with CDC with production settings to examine engine performance improvement and emission reduction. The results show improved thermal efficiency with reduced NOx emissions with water vapour induction in HCDI. HCDI resulted in higher thermal efficiency than CDC, with a maximum increase of 20.3 % and a 27.1 % reduction in NOx emissions at 3.5 bar IMEP. However, at a higher load condition of 5.7 bar IMEP, the thermal efficiency is reduced with higher soot emissions in HCDI. Direct-injected fuel pressure was increased, and injection timings were optimized to address this shortcoming. The soot emissions were reduced by 89.2 %, with a slight increase in thermal efficiency. The unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions were reduced significantly in HCDI compared to CDC, with a maximum reduction of 95.9 % and 40.7 %, respectively. Overall, the proposed novel HCDI with water vapour induction is a promising LTC strategy for diesel engines that helps achieve a wider operating load range, higher thermal efficiency and lower regulated pollutants.