Experimental Investigations on the Effects of Multiple Injections in Reactivity-Controlled Compression Ignition in a Light-Duty Engine Operated with Gasoline/Diesel

Reactivity-Controlled Compression Ignition (RCCI) is a promising low-temperature combustion (LTC) strategy to mitigate the oxides of nitrogen (NO_x) and soot emissions. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are much higher in RCCI compared to the conventional diesel combustion (CDC). In this present work, multiple injections of the direct-injected (DI) diesel fuel are explored as a potential method to reduce the high HC and CO emissions. Although significant research works have been done in the past on RCCI combustion in different engine types, investigations on small air-cooled diesel engines are very limited. In the present work, a production light-duty air-cooled diesel engine is modified to run in RCCI, with diesel as the high-reactivity fuel and gasoline as the low-reactivity fuel. Before modifications, the engine is run in CDC with production settings. In RCCI, experiments are initially performed with single-pulse DI. The DI fuel timings and the port injected-to-total fuel ratio are optimized at each load conditions, using a suitable controller to achieve maximum brake thermal efficiency (BTE). The results obtained from single-injection RCCI show near-zero nitric oxide (NO) and soot emissions, but significantly higher HC and CO emissions compared to CDC. The experiments are then performed with multiple injections of DI fuel in RCCI. The pilot injection timing and the port injected-to-total fuel ratio are optimized at each load conditions to achieve low HC and CO emissions. The effects of the split ratio between the pilot and main injection pulses are also studied. The engine performance and emissions with multiple injections RCCI are compared with those of single-injection RCCI and CDC. The results obtained show that the HC and CO emissions are reduced in multiple-injection RCCI at all the load conditions with a maximum reduction of 49% without any significant change in NO and soot emissions. The engine BTE with single and multiple injections in RCCI remained almost the same.