Review of dual-fuel combustion in the compression-ignition engine: Spray, combustion, and emission

Increasing global demand for transport energy and concerns regarding diesel engine emissions have motivated alternative fuels for the internal combustion (IC) engine. Numerous researchers have investigated alternative fuels in the diesel engines’ dual-fuel mode to improve the emission profiles and energy consumption for transportation and distribution activities. In this review, the engine performance, combustion, and emission characteristics of alternative fuels (hydrogen, natural gas, biodiesel) in dual-fuel mode in compression ignition (CI) engines are thoroughly analyzed. Due to different fuel properties in a dual-fuel mode, the size distribution of spray droplets, and consequent mixing with ambient air, generally improve the brake specific energy consumption (BSEC) compared to the baseline diesel mode. However, the performance of the dual-fuel engine based on brake thermal efficiency (BTE) and volumetric efficiency remains significantly lower. The dual-fuel combustion mode in an engine significantly increases the in-cylinder pressure and the heat release rate and extends the ignition delay. The emission characteristics indicated a trade-off between nitrogen oxides and hydrocarbon emissions, and reduced nitrogen oxides, particulate matter, and smoke were influenced by engine load, blend ratio, and injection timing. However, the dual-fuel engine shows a significant increase in hydrocarbons (HC) and carbon monoxide (CO) emissions (up to several times) compared to a normal diesel engine.