Performance and emissions of a high-speed marine dual-fuel engine operating with methanol-water blends as a fuel

Dual-fuel (DF) operation with methanol-diesel allows to reduce CO2 emissions, increase efficiency and decrease NOx and soot. This paper describes the experimental results with methanol-water (MeOH-W) blends as a fuel, and has three objectives: (1) whether water acts as a knock suppressant, enabling higher diesel substitution ratios, (2) if water can be a measure to control engine-out NOx emissions given its cooling effect, and (3) to test the effect on brake thermal efficiency (BTE) of a blend of 90% methanol and 10% water by weight, which is interesting from a methanol fuel production cost perspective. Experiments were conducted on a dual-fuel marine Volvo Penta engine with methanol/water weight by weight shares of 50%/50% (MeOH-50), 64%/36% (MeOH-64), 90%/ 10% (MeOH-90) and 100%/0% (pure methanol, MeOH-100). A maximal increase in BTE of 3.3% and 4.9% were observed when going from respectively MeOH-100 and diesel-only operation to MeOH-50. The maximum methanol energy fraction (MEF) was obtained with pure methanol, equal to 76%, and decreased with increasing water content. NOx emissions decreased with pure methanol compared to diesel-only operation, and further decreased with increasing water content. It is concluded that MeOH-90 does not harm the BTE of the tested dual-fuel engine; and that MeOH-50 and MeOH-64 were able to reach IMO Tier III NOx legislation, but at the same time score worse for greenhouse gas reduction potential as less diesel can be substituted by methanol with these blends.