Prospects and Challenges of Green Ammonia as an Alternate Fuel for Internal Combustion Engines

Humans contemporarily depend on fossil fuels for most of their energy needs which however is depleting at an alarming rate, forcing researchers to search for alternate and sustainable ways. The potential of ammonia and hydrogen as carbon-free fuels in energy systems is very promising. Hydrogen is the cleanest fuel presently available. The use of hydrogen in internal combustion engines, however, is constrained due to its low density, shorter flame-quenching distance, and complex storage and infrastructure. Ammonia is a hydrogen energy carrier (17.65% hydrogen by weight) with high hydrogen energy density, and it has a well-established storage/transportation infrastructure, and thus has the potential to mitigate the challenges faced due to hydrogen storage, distribution, and infrastructure drawback. Green ammonia produced from renewable sources can also contribute to carbon-neutrality targets. Using ammonia as a single fuel in an internal combustion engine faces several challenges due to its high auto-ignition temperature (~930 K), low flame velocity, slow chemical kinetics, and high unburnt ammonia emissions. Ammonia utilization in IC engines could be improved by enhancing the fuel quality, incorporating physical modifications in the engines (compression ratio, fuel injection strategies, etc.). This chapter discusses the key aspects of conventional and green ammonia production, highlighting the world energy outlook and a detailed literature study on the engine characteristics and challenges for ammonia-fueled engines with a due note on strategies for improving ammonia utilization and the possible enormous impact on various energy sector segments.