Impact of Splitting n-Dodecane Pilot Injection on Ammonia RCCI Engine 2023-24-0076

The increased interest in ammonia as a hydrogen carrier and a carbon-free fuel for combustion applications continues to present several challenges to address. Moreover, the high auto-ignition temperature (925 K) for ammonia limits its use in compression ignition engines because excessively high compression ratio are required. One way to retrofit diesel engine is to help the ignition by injecting a pilot injection of reactive fuel, like diesel or biodiesel. In this study, the ammonia engine ignited by a dodecane pilot injection is investigated with a maximum ammonia energy share (until 98.5%). The effect of split diesel injection strategy in two-steps under medium load operating conditions is studied as a function of ammonia/air equivalence ratio. Splitting this injection reduces NO_X, CO, UHC and unburnt NH₃ emissions at the exhaust, even it remains above the recommended emissions limit, especially at stoichiometric or slightly rich ammonia/air mixture. Not evident tendencies can be drawn about the improvement of GHG reduction (i.e. N₂O and CO₂) by splitting the diesel pilot injection. However, a strategy when the pre and the main injections being set closer to TDC, proves to be the best configuration due to the improvement of the combustion process, with a minimum diesel energy amount.