Ammonia Combustion in a High-Speed Marine Application

Ammonia (NH3) has gained significant attention as a zero-carbon fuel which is capable to support global decarbonization goals, especially in the maritime transportation and power generation sectors. Its high hydrogen density, storage feasibility, established production and transportation infrastructure are benefits to be mentioned which leads to a promising candidate as a hydrogen carrier, or as fuel for direct use. This study investigates the combustion characteristics and emission profiles of ammonia on a spark ignited 2.13 L single cylinder engine which represents the typical cylinder displacement of marine applications in sportfishing boats and auxiliary power units. The goal is to evaluate the potential of using ammonia as a single fuel. Considering its high ignition energy requirement and low laminar flame velocity several combustion enhancement techniques were evaluated, such as compression ratio increase, the use of a passive pre-chamber spark-plug and the influence of the addition of hydrogen in a dual fuel setup. The experimental results demonstrate a stable combustion of 100 % ammonia under homogenous stoichiometric condition over a wide operation range of the engine. NOx emission lands on a typical level of SI engines, around 8 – 12 g/kWh. Meanwhile, NH3 emissions are unavoidable and require a specialized exhaust aftertreatment. Up to 45 % indicated efficiency have been reached in the investigated operation range. 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 reduce the burn delay significantly and speed up the combustion remarkably. Moreover, the NH3/NOx ratio in the exhaust gas is directly affected which has a relevance for the operation of a SCR aftertreatment system.