Exploring direct injection strategies for improved combustion efficiency and emissions reduction in dual-fueled RCCI/compressed natural gas engine: A experimental survey

The dwindling reserves of conventional fuels have spurred research into alternative options for diesel engine, particularly given diesel's widespread use in global public transportation. Environmental concerns, notably regarding oxide of nitrogen (NOx), and smoke necessitate a shift toward alternative fuels. Diesel's partial replacement with compressed natural gas in CI engines has shown promise in mitigating smoke and NOx emissions. The Present research utilized an RCCI engine, and employed combinations of Diesel+CNG dual-fuel to analyze how direct injection techniques affect performance, emission, and combustion features. Under full load conditions sans exhaust gas recirculation (EGR) 6 ms and 8 ms CNG yielded superior brake thermal efficiency (BTE) of 30.5% and 29.5% surpassing diesel's 26%, although excessive CNG induction disrupted combustion, reducing efficiency, and introducing EGR, particularly at 10% enhanced BTE, with 6 ms CNG achieving a peak of 32.5%, slightly lower at 15% EGR with 30.9%. Diesel engine showcased diminishing brake-specific fuel consumption values with CNG supplementation, further mitigated by increased CNG concentrations and EGR rates. Peak combustion pressure decreased in the RCCI engine, with promising results seen at 6 ms CNG, comparable to pure diesel. EGR introduced pressure fluctuations, signifying a dilution effect on combustion, while the net heat release rate displayed increasing trends for CNG, stabilizing with EGR. NOx emissions, peaking in diesel engine, showed reductions with 6 ms CNG, further diminished with EGR implementation.