Ammonia as a clean energy for internal combustion engines: A review and preliminary CFD investigation

The emissions from internal combustion engines (ICEs) contribute to climate change, air pollution, and pose risk to human health. This review is the first part of a research study that aims to employ computational fluid dynamics (CFD) to develop a clean and efficient combustion strategy focussing on ammonia as an alternative fuel. This article discusses background related to ammonia economy, safety, and its impact on the environment and human health. Combustion characteristics of ammonia are analysed in this article. The review explores various techniques such as blended and dual fuels that are employed to optimize the ignition, including developments in recent ammonia commercial engines. It discusses challenges for minimizing nitrogen-based emissions and also delves into investigations of hydrogen generation through ammonia decomposition, with a focus on microwave heating as an efficient method. Literatures on CFD models tailored to ICEs are also examined. The methodologies of CFD model and techno-economic approach of ammonia decomposition by microwave heating are described. Key findings referred that nearly 4% of ammonia production currently utilizes sustainable sources. Hydrogen with selective catalytic reduction reduces the temperature of reaction to below 200 °C and produces water vapour as a byproduct. Ammonia decomposition by microwave heating occurs at temperatures 100–200 °C lower than conventional methods. Moreover, the localized ammonia decomposition by microwave heating for hydrogen production proves to be 4.5% more efficient than hydrogen storage for transportation. The preliminary CFD investigation from this study suggests the feasibility of using ammonia as a carbon-free fuel for spark ignition ICEs. Compared to methane (CH₄) combustion, ammonia shows a 2.5% increase in thermal efficiency and approximately 40% reduction in NOx emissions. This study lays the groundwork for future exploration of ammonia and hydrogen as potential cornerstone for cleaner and more sustainable ICEs.