Experimental Study on Flash Boiling of Ammonia Fuel Sprays – A Potential Alternative Fuel

The current transportation fuels have been one of the biggest contributors towards climate change and greenhouse gas emissions. The use of carbon-free fuels has constantly been endorsed through legislations in order to limit the global greenhouse gas emissions. In this regard, ammonia is seen as a potential alternative fuel, because of its carbon-free nature, higher octane number and as hydrogen carrier. Furthermore, many leading maritime companies are doing enormous research and planning projects to utilize ammonia as their future carbon-free fuel by 2050. Flash boiling phenomenon can significantly improve combustion by enhancing the spray breakup process and ammonia possessing low boiling point, has a considerable potential for flash boiling. However, present literature is missing abundant research data on superheated ammonia sprays. Therefore, this research work aims to optically investigate the behavior of ammonia sprays under different conditions of fuel temperatures for varying chamber pressures. This work probes overall ammonia spray geometry at engine relevant conditions and compare the results with gasoline sprays. A multi-hole solenoid gasoline injector is used to inject fuels into a constant volume spray chamber and fuel sprays are investigated using optical z-type schlieren imaging technique. Higher fuel temperatures are achieved by installing a heater coil on the injector tip with a sleeve in between to avoid possible heat transfer losses. The experimental results show significant effect of superheating on ammonia and gasoline sprays. The liquid and vapor phase are clearly characterized upon flash boiling, resulting in decreased spray tip penetration and areas compared to ambient fuel temperature conditions. The results also show differences between the overall spray geometries of both fuels, and that ammonia sprays are more sensitive to chamber pressure as compared to gasoline.