Recent progresses in research on liquid ammonia spray and combustion: A review

As climate change intensifies, the global push for de-carbonization highlights the urgent need for carbon-free fuels. Ammonia (NH3), with zero carbon emissions and a notable ability as a hydrogen carrier (17.8 % by weight), has emerged as a promising candidate for a net-zero economy. Over the past decade, substantial research has been devoted to the combustion of gaseous ammonia. However, liquid ammonia has several key advantages over gaseous ammonia, including high energy density, cost efficiency, system simplicity, and a high octane number. Despite these benefits, challenges such as high NOx emissions, low combustion stability, significant latent heat, and susceptibility to flash boiling necessitate further exploration. This article comprehensively reviews the current state of research on liquid ammonia as a fuel, covering experimental and numerical efforts regarding fundamental fuel properties, spray characteristics, flame stabilization, combustion performance, and emissions. By systematically summarizing the recent advancements in liquid ammonia spraying and combustion, this review aims to serve as a cornerstone for future experimental and numerical studies and industrial applications, providing a reference for the research and utilization of liquid ammonia combustion.