Double-pulse diesel injection strategy on combustion performance and emission characteristics of turbocharged multi-cylinder CRDI dual-fuel diesel engine fueled with gasoline/diesel and ethanol/diesel

Rising environmental regulations and increasing fossil fuel costs have intensified the search for sustainable and renewable fuel alternatives. The associated well-to-tank and tank-to-wheel emissions from fuel production, transportation, and end-use further highlight the need for cleaner energy sources. Compared to spark ignition engines, compression ignition engines are more durable and have superior thermal efficiency. Due to the autoignition of heterogeneous mixtures, diesel engines have significant issues with high amounts of nitrogen oxide and particulate matter emissions. The present work focuses on the utilization of low-reactivity gasoline/ethanol in a turbocharged multi-cylinder common rail direct injection engine operating in conventional dual-fuel mode. In the first phase, the engine was operated with pure diesel injection timing of 23° bTDC as reference across four brake mean effective pressure (BMEP) loading percentages: 25%, 50%, 75%, and 100%, corresponding to low load at 3 bar, a mid load at 6.1 bar, a mid-high load at 9.07 bar, and a high load at 11.43 bar. In the second phase, port-injected gasoline and direct-injected diesel fuel were supplied using a double-pulse injection strategy: 30° pilot/5° main injection as (S1) and 40° pilot/10° main injection as (S2). In the third phase, an ethanol PFI/diesel double-pulse diesel injection (DPI) strategy was employed to evaluate combustion characteristics, including in-cylinder pressure, net heat release rate, rate of pressure rise, mean gas temperature, and cumulative heat release rate. Engine performance parameters, including brake power (BP), brake thermal efficiency (BTE), and indicated thermal efficiency, along with regulated emissions such as carbon dioxide (CO 2 ), carbon monoxide (CO), unburned hydrocarbons, and nitrogen oxides (NO x ), were also evaluated. Results reveal that port-injected low-reactivity fuels enhanced mixture homogeneity and increased the premixed energy share compared to baseline diesel operation. Overall, nitrogen oxide (NO x ) emissions for GPI/DDI under low and mid load operating conditions decreased by 89.94% and 29.50% compared to EPI/DDI. When the load rises from mid to high load, the EPI/DDI has enhanced differences of 8.63%, a 149.14% reduction compared to GPI/DDI. Smoke opacity decreased significantly by 10.75% at high load, attributed to ethanol’s high oxygen content.