Performance and emission analysis of ammonia-ethanol and ammonia-methane dual-fuel combustion in a spark-ignition engine: An optical study

In light of the pressing need to address climate change, it is imperative to take immediate action to reduce conventional hydrocarbon fuel demand. In pursuit of achieving decarbonization goals, it has become apparent that modern internal combustion engines need to adopt either carbon–neutral fuels or fuels with lower hydrocarbon content. To this end, there are several options available including alternatives such as ammonia (NH₃), hydrogen (H₂), methane (CH₄), methanol (CH₃OH), and ethanol (C₂H₅OH). These fuels offer the potential to be produced in a manner that is either carbon–neutral (the latter two) or entirely free of carbon emissions (the former two), making them an ideal choice for powering advanced IC engines with minimum climate impact. The use of ammonia as a fuel has the potential to significantly reduce the demand for conventional fuels and decrease the emission of harmful pollutants like CO, CO₂, particulates, and unburned hydrocarbons during combustion. However, as a combustion fuel, it poses several challenges, including a low burning velocity, narrow flammability range, and instabilities arising during the combustion process. This study compared the two different dual fuel approaches, mixing ammonia-ethanol and ammonia-methane, and investigated their effect on engine performance and emissions. The experiments were conducted on a light-duty, single-cylinder, and spark-ignition four-stroke engine with an optically accessible cylinder head equipped with a port-fuel injection system. The results show that blending ethanol and methane with ammonia significantly improves its combustion characteristics due to the higher flame speed of the added components. Ammonia-ethanol blends produced reduced combustion duration, lower combustion instability, and higher engine efficiency compared to ammonia-methane blends due to the higher flame speed of ethanol. Additionally, ammonia-ethanol blends also produced higher NO_x and CO₂ emissions due to the higher in-cylinder temperature and lower H/C ratio. The study also applied high-speed natural flame luminosity imaging to observe the flame propagation speed for various fuel blending cases. The results found that ammonia-ethanol blends produced higher flame propagation speed than ammonia-methane blends.