An Experimental Investigation on Combustion and Emissions of a Hydrogen Enriched Ammonia–Diesel Dual Fuel Engine at a Medium Load Condition

Abstract As a carbon-free hydrogen carrier, ammonia is easy to store, handle, and distribute compared to hydrogen itself. Switching from diesel to green ammonia in heavy-duty compression ignition engines dominating the power generation of freight transportation industry has the potential to reduce greenhouse gas (GHG) emissions. However, due to the low flame speed and presence of fuel-bound nitrogen, ammonia combustion may result in certain unburned ammonia slip and nitrous oxide (N2O) emissions, which offsets its zero-carbon advantage in applications. In this paper, an investigation on the influence of hydrogen blending on ammonia slip and emissions of nitrogen oxide (NO), N2O, and GHG in a heavy-duty ammonia–diesel dual fuel engine is experimentally conducted at a medium engine load, various hydrogen blending ratios, and different gaseous fuel energy fractions. The results reveal that hydrogen blending does help significantly reduce ammonia slip. However, hydrogen blending does not help reduce N2O emissions at relatively lower gaseous fuel energy fractions that result in lower equivalence ratio for hydrogen/ammonia mixture but does help reduce N2O emissions at relatively larger gaseous fuel energy fractions. As a result, hydrogen blending does not help reduce GHG emissions at relatively lower gaseous fuel energy fractions, but does help at higher gaseous fuel energy fractions. Blending of a small amount of hydrogen significantly improves engine efficiency, but the effect of further increasing hydrogen blending ratio on engine efficiency is insignificant. A side effect of hydrogen blending is that it increases NO emissions since it not only increases combustion temperature but also promotes the NO formation via fuel route during ammonia combustion.