Numerical study on laminar burning velocity and ignition delay time of ammonia flame with hydrogen addition

Abstract

This study focuses on the application of NH3 as a carbon-free alternative fuel in internal combustion devices. The two key parameters for fuel combustion, namely, laminar burning velocity and ignition delay time of the NH3 flame at various H2 blending levels, are numerically investigated. Results show that the selected modified Dagaut-Kéromnès mechanism is acceptable and repeatable for calculating the burning velocity and ignition delay time of NH3-air flame at various H2 addition conditions. H2 addition increases the reactivity of NH3 combustion at all conditions and enhances the burning velocity. This enhancement is mainly due to chemical effect caused by the reduction in chemical activation energy and the transport effect resulting from the high mobility of H2. Furthermore, an increase in pressure and H2 addition ratios can significantly decrease the ignition delay time of NH3 mixtures and promote NH3 ignition. The enhancement of H2 addition on NH3 ignition and laminar burning velocity is mainly attributed to the contribution of the three following reactions: O + H2 = OH + H, H + O2 = OH + O, and H2 + OH = H2O + H. These reactions can significantly increase the concentration of free radicals and accelerate the peak of radicals.