Edinburgh Napier University

  The study investigates, numerically, the potential use of introducing aqueous HO as an ignition promoter in a statistically homogeneous NH/H 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 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, NO and unreacted NH) are investigated in view of: (i) the share of molecular hydrogen in the initial NH/H mixture from 10 to 40 percent; (ii) the mass of aqueous HO 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 HO 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 NH/H 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 HO 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 HO is low, at a few percent that of the main ammonia tank. NOx emissions peak between .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 NO emissions are generally extremely low (10−12 mg for NH and 0.01 mg/kWh for NO).