Comparison of the Performance and Operation Limits of an S.I. Engine Fueled with Neat Ammonia and Hydrogen-Ammonia Blends

Nowadays, the interest in carbon free fuels for internal combustion engines has increased due to the high levels of CO2 in the atmosphere. In particular, ammonia can be used either as a neat fuel, either as an energy carrier for hydrogen production. Adding hydrogen to ammonia is important in order to improve the combustion characteristics of this fuel, like the laminar flame speed. In this paper, the authors investigated the operation limits of a light duty spark ignition engine fueled by neat ammonia and by an ammonia-hydrogen blend (85% of ammonia by volume). The whole maps of the engine powered by the considered fuel mixtures have been obtained by means of 1-D simulations taking into account several operating constraints. The addition of hydrogen to ammonia extends the exploitable region of the engine. In particular, if the engine is powered by neat ammonia, the maximum reachable engine speed is 3000 rpm, while considering the blend, it can be extended up to 5000 rpm. At low load operations the blend still allows to explore a wider region with respect to pure ammonia. Finally, up to 3000 rpm, the engine fueled with the ammonia-hydrogen blend can be properly regulated.