The effect of carbon dioxide on the deflagration of hydrogen-ammonia mixed gases

Abstract

Hydrogen-ammonia mixed fuel is a current research hotspot. Experimental studies were conducted to investigate the effect of CO₂ on the deflagration of hydrogen-ammonia mixed gases, and the impact of CO₂ on the deflagration flame characteristics under varying equivalence ratios was analyzed. The inhibition mechanism of CO₂ was analyzed using CHEMKIN software. The results showed that CO₂ has an inhibitory effect on the deflagration of hydrogen-ammonia mixed gases. With the addition of CO₂, the disturbance effect of pressure waves generated by deflagration on the flame is reducted, thereby inhibiting the formation of tulip-shaped flames. Meanwhile, the inhibitory effect on flame propagation speed appeared mainly during oscillation. When the equivalence ratio is 0.87, adding 15% CO₂ resulted in a 62.8% decrease in the average flame propagation speed during the stable period and an 86.3% decrease during the oscillation period. Additionally, the decreasing trend of laminar burning velocity was consistent with the decreasing trend of average flame propagation speed. Further analysis of species composition, laminar flame sensitivity coefficients, and radical concentrations revealed that in hydrogen-ammonia mixed gases, CO₂ inhibits the reaction by promoting the consumption of O₂, H·, and NH₂·. Moreover, the variations in NH₂· aligns closely with the fluctuation in flame propagation speed observed in hydrogen-ammonia mixed gas. The findings can provide valuable references for the safe design and engineering application of hydrogen-ammonia mixed-fuel vehicles.