Impact of ethane enrichment on diesel-methane dual-fuel combustion 2020-01-0305
Over the past few years, the growing concerns about global warming and efforts to reduce the 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 CH4 (methane-slip) in the environment. The greenhouse effect of CH4 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 CH4-slip from DF engines, this study discusses ethane enrichment of diesel-methane DF combustion in a full-metal single-cylinder research engine at a constant load of approx. 12 bar IMEP under lean condition (λCH4 = 2.0) with a small pilot diesel (3% of total injected energy). The conditions at top-dead-center (TDC) are kept constant in all experiments i.e. motored peak pressure of 60 bar and TTDC = 835 K. Moreover, two engine speeds (ω) of 950 rpm and 1500 rpm have been utilized during the experiments to explore the effect of engine speed on engine-out emissions and combustion performance. The gaseous fuel (99.9% pure methane) is enriched with ethane in such a way that the main fuel (methane + ethane) substitution rate is 97% at the constant load point. The results show that adding ethane into the charge decreases the ignition delay time and improves overall combustion that leads to a significant decrease in UHC and CH4-slip. Furthermore, DF combustion shows higher pressure-rise rate at lower engine speed (ω = 950 rpm) compared to higher engine speed (ω = 1500 rpm).
Zeeshan Ahmad, Ossi Kaario, Qiang Cheng, Martti Larmi