Abstract
This study investigated engine efficiency and emissions at low load dual-fuel diesel-natural gas (NG) engine operation, which has a higher sensitivity to NG composition. 40% of the diesel fuel energy was partially substituted with gas blends containing methane, ethane, and propane. NG was delivered inside the intake manifold by low-pressure gas injectors. Results showed that blends with ethane and propane reduced the net global warming potential by ∼5% compared to pure methane, at constant fuel energy content, with the reduction primarily linked to differences in exhaust hydrocarbon composition. No statistically significant impact on the brake mean effective pressure was found. The changes in gas composition created up to a 10% increase in carbon monoxide concentrations in the exhaust, as an earlier combustion phasing increased the fraction of premixed NG trapped in the combustion chamber’s crevices. Also, a 20% reduction in specific methane, ethane, and propane emissions was achieved for mixtures with 10% propane addition. Propane addition enhanced combustion efficiency and methane oxidation compared to ethane addition. The reduction of methane, ethane, and propane mass fraction in the exhaust correlated with their auto-ignition temperatures and laminar flame speeds, with ethane and propane oxidizing significantly better than methane. Finally, the results imply the emission composition of diesel-NG dual-fuel operation was more sensitive than engine power output to the change in NG fuel composition.
