Engine performance and emissions from a fumigated hydrogen/ammonia compression ignition engine with a hydrogen peroxide pilot

The study investigates, numerically, the potential use of introducing aqueous H2O2 as an ignition promoter in a statistically homogeneous NH3/H-2 fuelled, medium speed (1250 rpm), 4-stroke, 1.3 litre cylinder displacement, mildly boosted CI engine with a compression ratio of 17.6:1. The H-2 is considered to be produced on-board from ammonia cracking. An extensive campaign is undertaken using the commercial stochastic reactor model, SRM Engine Suite, which allowed the modelling of temporal, temperature and spatial stratification in the cylinder. The engine performance, combustion phasing, maximum pressure rise rate and emissions (NOx, N2O and unreacted NH3) are investigated in view of: (i) the share of molecular hydrogen in the initial NH3/H-2 mixture from 10 to 40 percent; (ii) the mass of aqueous H2O2 introduced from 0.1 to 16 mg; (iii) the start of injection (-10 to +6 CAD aTDC) and duration of injection (1, 4 and 8 CAD); (iv) the amount of exhaust gas recirculation (up to 30 percent by mass); (v) the share of energy from the H2O2 in the aqueous solution mixture at less than 0.5 percent of that in the main fuel; (vi) engine load corresponding to a variation in the equivalence ratio from 0.32 to 1.2 by changing the mass of the NH3/H-2 mixture in the combustion chamber. A wide range of loads (evaluated against the engine's rated power when operated with diesel and at its rated boost levels) can be achieved (44%-93%) with the energy share of H2O2 being as little as equivalent to 2.7% vol% that of the main fuel, ammonia, which is introduced into the cylinder. This implies that the required storage volume of the H2O2 is low, at a few percent that of the main ammonia tank. NOx emissions peak between phi=0.6-0.65 and rapidly decrease as the equivalence ratio increases or decreases reaching values marginally above the Tier III standard at high loads (>90%) while ammonia slip and N2O emissions are generally extremely low (10(-12) mg for NH3 and < 0.01 mg/kWh for N2O).