Impact of Water Injection on Emission Formation in an HVO-fuelled NRMM Engine

Water injection in diesel engines is a well-known method of lowering combustion temperatures and thus reducing nitrogen oxide (NOx) emissions. In this study, the influence of water injection in hydrogenated vegetable oil (HVO) operation on NOx formation, particulate emissions and ignition delay is analysed in comparison to diesel operation. Both the fuel (HVO) and the water injection system were designed as ‘drop-in’ solutions that enable rapid implementation to reduce emissions, even in existing vehicle fleets. The standard engine control unit of the John Deere JD4045 engine was therefore used for the tests. A single water nozzle was installed downstream the charge air cooler to integrate a water injection system. The three operating points of interest were: (1) low speed and high load without exhaust gas recirculation (EGR), (2) high EGR rates at low speed and medium load and (3) the engine's ‘sweet spot’ regarding the emission-tradeoff at high speed and high load. The focus of the study is on the formation of nitrogen oxides (NOₓ) and particulate matter (PM), analyzing the particle mass and particle size distribution as well as ignition and combustion behaviour. The effects of varying the mass flow of the water injection and charge air temperature were investigated at all operating points. A comparative analysis between diesel and HVO operation shows the differences in emission behaviour and the effects of water injection. The results provide insight into the potential of retrofit water injection to reduce NOₓ emissions by up to 40%, especially in combination with the renewable fuel HVO. However, a slight increase in particulate emissions was observed, which requires further analysis of particulate mass and size distribution to analyse possible trade-offs. These findings might contribute to the promotion of sustainable and low-emission solutions for NRMM applications in the existing and upcoming fleet.