Ammonia Combustion with Ignition Improvement Measures in a High-Speed Marine Application

<div class="section abstract"><div class="htmlview paragraph">Ammonia (NH₃) has gained significant attention as a zero-carbon fuel which is capable of supporting global decarbonization goals, especially in the maritime transportation and power generation sectors. Its hydrogen density, storage feasibility, established production methods, and transportation infrastructure are key benefits which contribute to its potential both as a hydrogen carrier and as a direct fuel.</div><div class="htmlview paragraph">The study investigates the combustion characteristics and emission profiles of ammonia on a spark ignited 2.13L single cylinder engine with the goal of evaluating ammonia as a single fuel. This displacement is representative of the typical cylinder displacement of small to mid-size engines for marine applications on sportfishing boats and as auxiliary power units. Challenges to consider for ammonia combustion are its high ignition energy requirement and low laminar flame velocity. Several methods were employed to compensate for these properties such as increasing compression ratio, the use of a passive pre-chamber spark plugs, and the use of hydrogen in a dual fuel set-up.</div><div class="htmlview paragraph">The experimental results demonstrate stable combustion of 100 % ammonia under homogenous stoichiometric condition. NO_X emissions reach typical levels of SI engines, around 8 – 12 g/kWh. Meanwhile, a certain level of NH₃ emissions are unavoidable and require a customized exhaust aftertreatment. Up to 45 % indicated efficiency have been reached. The evaluation of the combustion enhancement techniques shows clearly that the higher CR, the use of a pre-chamber spark plug as well as the addition of a small hydrogen share all significantly reduce the burn delay and speed up the combustion considerably. Moreover, the NH₃/NO_X ratio in the exhaust gas is directly affected by these techniques which have relevance for the operation of an SCR aftertreatment system.</div></div>