An integrated 0D/1D/3D numerical framework to predict performance, emissions, knock and heat transfer in ICEs fueled with NH3–H2 mixtures: The conversion of a marine Diesel engine as case study

In the maritime transportation, e-fuels represent a valid alternative to fossil energy sources, in order to accomplish the European Union goals in terms of climate neutrality. Among the e-fuels, the ammonia-hydrogen mixtures can play a leading role, as the combination of the two allows to exploit the advantages of each one, simultaneously compensating their gaps. The main goal of the present publication is the proposal of a robust numerical framework based on 0D, 1D and 3D tools for CFD analyses of internal combustion engines fueled with ammonia-hydrogen mixtures. The 1D engine model provides boundary conditions for the multi-dimensional investigations and estimates the overall engine performance. 3D in-cylinder detailed analyses are proficiently used to predict combustion efficiency (via the well-established G-equation model supported by laminar flame speed correlations for both ammonia and hydrogen) and emissions (with a detailed chemistry based approach). Heat transfer and knock tendency are evaluated as well, by in-house developed models. As for the 0D/1D chemical kinetics calculations, firstly they support 3D analyses (for example via the generation of ignition delay time tables). Moreover, they allow insights on aspects such as NOx formation, to individuate mixture qualities able to strongly reduce the emissions. The present paper offers also indications for designers on the effectiveness of NH3–H2 as valid substitutes of traditional fuels in marine applications. In fact, the proposed framework is preliminary tested to convert an existing marine Diesel engine to ammonia-hydrogen mixtures. Different proportions (among the two fuels) are investigated, included pure ammonia and pure hydrogen and the NH3–H2 80mol%-20mol% mixture is selected as the best compromise. Thanks to both the anti-knock quality of the ammonia and the (limited) addition of hydrogen as combustion enhancer, the engine supplied with NH3–H2 mixtures is able to operate free of knock and keep the same performance as the original one. Simultaneously (neglecting the presence of lubricant oil in the combustion chamber) unburned hydrocarbons, carbon monoxide and carbon dioxide are eliminated. Still in comparison with the Diesel version, the heat transfer is similar, the NOx formation is much greater and the engine range (here evaluated in terms of working hours) noticeably reduces.