Numerical analysis and optimization of combustion and emissions in an ammonia-diesel dual-fuel engine using an ammonia direct injection strategy

To reduce greenhouse gases in accordance with stringent emission regulations, interest in ammonia, a carbon-free fuel, is increasing in the heavy-duty engine industry. Pre-mixed ammonia-diesel dual-fuel combustion showed better results than diesel combustion in efficiency and greenhouse gas emissions, but NO and unburned NH3 levels were significant. Therefore, a liquid ammonia direct injection strategy should be considered, and that requires detailed combustion and emission formation process analyses. Therefore, in this study, a numerical analysis of the direct injection ammonia-diesel combustion process was conducted, and an optimal injection strategy was sought. Compensating for the slow flame speed of ammonia by supplying additional momentum to the ammonia through direct injection could improve combustion characteristics. Furthermore, NO removal could be promoted by widening the thermal DeNOx reaction region compared to that in pre-mixed ammonia-diesel combustion. At injection timing was −7 CAD for the ammonia injection and −15 to −10 CAD for the diesel injection, the efficiency increased by 8 %, NO emissions were reduced by up to 13.5 %, and GHG emissions were reduced by about 91 % compared with diesel alone. In addition, unburned ammonia was reduced to least 58.4 ppm, a significant improvement over pre-mixed ammonia combustion. •Direct injection of ammonia reduces the effects of slow flame propagation.•Ammonia direct injection can improve NO emissions over pre-mixed combustion.•Applicable ammonia energy fraction limit was 97 % with ammonia direct injection.•Improving in efficiency, NOx, and GHG compared to diesel using ammonia direct injection.