Impact of Ethane Enrichment on Diesel-Methane Dual-Fuel Combustion

Over the past few years, the growing concerns about global warming and efforts to reduce engine-out emissions have made the dual-fuel (DF) engines more popular in marine and power industries. The use of natural gas as an alternative fuel in DF engines has both the environmental and economic advantages over the conventional diesel combustion. However, the misfire phenomenon at lean conditions limits the operating range of DF combustion and causes emissions of unburned hydrocarbon (UHC) and unburned methane (methane-slip) in the environment. The greenhouse effect of methane is considered 28 times greater than CO₂ over a 100-year perspective, which raises concerns for the governments and marine engine manufacturers. In efforts to reduce the UHC and methane-slip from DF engines, this study discusses ethane enrichment of diesel-methane DF combustion in a full-metal single-cylinder research engine under lean condition (λ_GFB = ~2.0) while keeping the total-fuel energy rather constant. The 99.9% pure methane is enriched with ethane in such a way that three gaseous-fuel blends of 0-20% ethane concentration could be achieved. The substitution rate of gaseous fuel blend (methane + ethane) is 97%, which is ignited by a small pilot diesel (3% of total energy). The conditions at top-dead-center (TDC) are kept constant in all experiments i.e. motored peak pressure of 60 bar and T_TDC = 835 K. Moreover, engine speed (ω) of 1500 rpm is utilized during the experiments to explore the effect of ethane enrichment on engine-out emissions and combustion characteristics. The results show that adding ethane into the gaseous-fuel blend decreases the ignition delay time (IDT) and improves overall combustion that leads to a significant decrease in UHC and methane-slip. Furthermore, coefficient of variability of IMEP (COV_IMEP) decreases about 53% by enriching pure methane with 20% ethane.