Experimental study on the effect of water port injection on the combustion and emission characteristics of diesel/methane dual-fuel engines

In this study, the effect of water port injection on the combustion and emission characteristics of diesel/methane dual-fuel combustion was studied experimentally. Conventional dual-fuel engine combustion was extended and explored as tri-fuel combustion by introducing a water port injection. The experiments were conducted on a four-cylinder engine at 1600 r/min and low load with a brake mean effective pressure of 0.42 MPa. Six methane substitution ratios (MSRs) (0%, 10%, 20%, 30%, 40%, and 50%) were programmed. At each MSR point, five water-to-diesel in pure diesel mode mass ratios (WDMRs) (0%, 25%, 45%, 65%, and 85%) were arranged. The experimental results indicated that methane addition decreased the combustion intensity and retarded the combustion process of the diesel engine. In addition, methane addition and water port injection prolonged the ignition delay of the diesel engine. The larger the MSR, the longer was the ignition delay for the corresponding WDMR. Similarly, the larger the WDMR, the longer was the ignition delay for the corresponding MSR. For emissions, the number concentration of particles decreased owing to methane addition, whereas it increased owing to water injection. Notably, for the maximum MSR (50%) and WDMR (0.85) utilization, the maximum total number concentration was 94474 #/cm(3), which is much lower than the minimum total number concentration in a pure diesel engine (118549 #/cm(3)). Furthermore, both methane addition and water injection significantly decreased the nitrogen oxide (NOx) emissions; however, they increased the CO and HC emissions. In summary, adding methane coupled with water injection is an effective method to decrease NOx and particle emissions simultaneously.