Experimental and numerical analysis of ammonia/hydrogen combustion under artificial exhaust gas recirculation

This paper investigates the potential of exhaust gas recirculation in hydrogen/ammonia mixtures. The effects of artificial exhaust gas recirculation were evaluated on flame morphology and unstretched laminar burning velocities experimentally, while the flame stability and NO emissions were simulated using previous kinetic models. The experiments and numerical simulations were performed for various equivalence ratios, initial temperatures, pressures, exhaust gas recirculation rates, and compositions. Results show that recirculation of exhaust gases can enhance flame stability by diminishing the hydrodynamic instabilities while negatively affecting the flame laminar burning velocities. This negative impact, which is more sensible at nonstoichiometric conditions, reduces the flame speed between 19% and 58% based on the flue gas content of the combustible mixture. Despite this reduction, recirculating the exhaust gases can considerably reduce the high NO emissions of hydrogen/ammonia/air mixtures. Indeed, adding flue gases can decrease the maximum NO concentrations up to 45% at near stoichiometric conditions. The effects are even more significant in fuel-rich mode, diminishing the NO emissions up to 84% at an equivalence ratio of 1.3. Finally, these evaluations support the idea of exhaust gas recirculation application for using hydrogen/ammonia blends as a clean fuel while considering the expenses of burning rate reduction.