Ignition improvers for aqueous ammonia as marine fuel

The potential of three molecules NH₄NO₂, H₂O₂ and O₃ to ignite aqueous solutions of ammonia (25% by mass) as fuel, was investigated using chemical kinetic simulations at conditions representative of a two-stroke marine diesel engine. The purpose was to address two of the most prominent issues with making ammonia a practical fuel for marine applications: the difficulty of igniting ammonia, and the safety concerns regarding its volatility and toxicity. The ignition simulations carried out to this end used a two-zone reactor model of the engine, representing the ignition zone into which fuel was injected, and the bulk cylinder gases, respectively. The results suggested that all three ignition improving molecules were able to ignite aqueous ammonia reliably and at high combustion efficiency with acceptable levels of NO, N₂O and NH₃ emissions. Among the three fuel formulations investigated, H₂O₂ as 12% aqueous solution by mass, promised the lowest emissions of NO and N₂O in the exhaust gases. This ignition improver in aqueous solution added in a mole fraction of 0.15 to a mole fraction of 0.85 aqueous ammonia having an ammonia fraction of 25% by mass promised to be the most practical solution, since it is stable and can be stored safely in a separate tank until injected into the engine.