Overview of Autoignition and Flame Propagation Properties for Ammonia Combustion

Abstract

With the increasingly stringent ${\mathrm{CO}}_2$ emission, next-generation propulsion systems with chemical reaction combustion involved need to operate with carbon-free fuels, such as ammonia or hydrogen. During the past few decades, intensive research has been conducted on ammonia combustion, which is growingly regarded as a potential alternative fuel to be applied in gas turbines for power generation and aviation propulsion systems to reduce the ${\mathrm{CO}}_2$ footprint and increase carbon-free fuel flexibility. Two major technical challenges with applying such fuel in practical engines are poor ignition and flame propagation behaviors. The present work provides a technical review by presenting state-of-the-art advances in ammonia combustion science and technology by clarifying the fundamental combustion properties and the corresponding enhancement strategies. Experimental techniques applied to measuring the ignition delay time are first introduced and overviewed, along with passive and active means to accelerate them. Then, the laminar burning velocities of ammonia-based dual-fuel combustion at varying operating conditions and their temperature and pressure dependences are described. This is followed by the spin-off applications of ammonia-fueled detonation engines. Finally, we show the prospects and challenges of ammonia combustion and suggest critical topics in aerospace and power generation applications that could benefit from further investigations.