Effect of Methane Substitution with Hydrogen in a Dual-Fuel Diesel/Methane Engine with Late Pilot Injection Strategy

Hydrogen is recognized as a promising energy vector for the decarbonization of energy production. Besides the undoubted benefits, its utilization poses some technological challenges in the generation, transportation, storage and utilization phases, which must be carefully assessed. The aim of this work is to assess the effect of methane substitution with hydrogen in a dual-fuel diesel/methane engine on fuel conversion efficiency and pollutant emission levels. Therefore, an extensive experimental campaign has been designed in which a hydrogen/methane mixture with variable composition is ignited with a pilot injection of diesel fuel. The engine was operated in naturally aspirated or supercharged conditions, and conventional or alternative combustion strategies were implemented, spanning a pilot injection timing over a broad range of values. The results show that the effect of a variation in H2 percentage of up to 20% strongly depends on air intake pressure and pilot injection timing. In particular, engine efficiency and HC and CO emissions are penalized as H2 percentage increases; however, this penalty can be mitigated in naturally aspirated conditions if a late pilot SOI strategy is adopted. In terms of NOx, a reduction is observed as H2 percentage increases. Late SOIs determine the lowest levels of NOx emissions in both naturally aspirated and supercharged conditions.