CFD study of jet fuel with ammonia - Hydrogen mixtures in a jet engine: Emissions and combustion characteristics analysis

The growth of the aviation industry and the rapid increase in global transportation demand have further emphasized the importance of global efforts to reduce pollutant emissions. In this context, taking strategic and technological steps to lower greenhouse gas emissions in aviation has become inevitable to ensure environmental sustainability and effectively combat climate change. At the centre of these efforts lies the pursuit of environmentally friendly alternatives to hydrocarbon-based aviation fuels. In this study, the impacts of blending alternative fuels such as hydrogen and ammonia with kerosene in a GTM-120 mini gas turbine engine on flame temperature, CO, CO2, and NOX emissions were analysed. In the constant thermal power scenarios, the kerosene ratio was limited to a maximum of 50 %, while the ammonia-hydrogen mixture was applied in varying proportions ranging from 5 % to 45 %. CFD simulations conducted under non-premixed combustion conditions revealed that the introduction of hydrogen increases flame temperature and propagation speed. However, this also negatively affects combustion stability, and CO emissions could not be sufficiently reduced. In contrast, as the proportion of ammonia in the mixture increased, CO emissions decreased significantly, with average values dropping from 0.74 ppm to 0.0158 ppm. Ammonia, being an efficient hydrogen carrier, initially caused an increase in NOX emissions when combined with hydrogen due to the effect of the fuel NOX mechanism. At 50 % kerosene - %45 hydrogen - 5 % ammonia case, NOX emissions reached as high as 344.5 ppm. However, as the ammonia ratio in the fuel mixture increased, the flame temperature decreased, suppressing thermal NOX formation and reducing the average NOX emissions at the outlet to 14.26 ppm. Moreover the addition of ammonia reduced flame speed, which led to a significant decrease in incomplete combustion product CO emissions while increasing the amount of CO2 as a product of complete combustion. At the highest ammonia ratio, CO2 emissions reached up to 3.21 %. In conclusion, ammonia, which is low-cost and easy to store, when used together with hydrogen and kerosene in gas turbine engines, provides significant advantages with respect to emission control and combustion efficiency. This study presents a novel contribution to the literature by comprehensively evaluating the environmental performance and flame temperature of ammonia-hydrogen-kerosene ternary fuel blends under real engine conditions - an area that has mostly been addressed separately in previous studies. Thus, it offers valuable insight for the development of next-generation low-emission fuel strategies in gas turbine engine applications.