Effect of ammonia addition on laminar burning velocity of CH4/H2 premixed flames at high pressure and temperature conditions

Abstract

Global emissions of nearly 30% stem from fossil fuel combustion for long-distance transportation vehicles. Therefore, investigations on newer alternatives for clean and green fuels is desired in pursuance of net-zero carbon emissions by 2050. Given this contemplation, the current study aims at studying the effect of ammonia addition, a carbon-free fuel, on laminar burning velocity of CH4/H2 fuel blends at high-pressure and high-temperature conditions utilizing the high-pressure diverging-channel method. The NH3 varies from 0% to 30% in the CH4/H2 fuel blend by volume. With regard to adiabatic flame temperature, this NH3/CH4/H2 mixture is comparable to pure CH4-air mixtures, but with a reduction in carbon emissions of about 26.6%. The research involves conducting measurements at high temperatures between 300 K and 750 K, pressures between 1 atm and 5 atm, and equivalence ratios between ϕ = 0.7 and 1.4. When the pressure is 5 atm, the obtained burning velocities of NH3/CH4/H2 blends are analogous to that of CH4-air mixtures. The temperature exponent, α, does not change when the NH3 fraction or pressure changes, but at high temperatures there is a slight shift in the pressure exponent, β. The experimental results suggest that the Okafor and Li kinetic models align well with the measurements made in the current work up to 5 atm, while the Reduced GRI Mech 3.0 mechanism overestimates the burning velocity values. Additionally, an increase in NH3 fraction and pressure results in a decrease in burning velocity and NO formation due to the presence of NHi (i = 0–2) radicals. Overall, this study convincingly demonstrates the viability of NH3/CH4/H2-air mixtures as a practical alternative to reduce carbon emissions.