Ammonia as fuel for future diesel engines

Ammonia (NH3) is one of the important ways for diesel engines to achieve carbon neutrality. Ammonia’s energy density by volume is nearly double that of liquid hydrogen, making it easier to ship and distribute. Ammonia has a well-developed infrastructure and can also be used as a hydrogen energy carrier. However, it was discovered that using pure ammonia as fuel was impracticable, prompting researchers to create concepts for dual-fuel systems or innovative combustion techniques. Therefore, a detailed literature review was conducted on applying ammonia in diesel engines. Firstly, the development of ammonia as a fuel, green ammonia production, ammonia’s physicochemical characteristics, and challenges were discussed. Then, using ammonia as fuel in a dual-fuel compression ignition engine was emphasized, with secondary fuels such as diesel, dimethyl ether, hydrogen, and other alternative fuels. Advanced injection strategies help improve engine combustion performance and reduce emissions. Due to the low flame velocity, long quenching distance, and fuel-bound nitrogen of ammonia, there are high levels of NOx and unburned NH3 in the exhaust, which makes it necessary to use after-treatment systems downstream. The NH3-H2 homogeneous charge compression ignition mode and ammonia cracking are also presented.