Abstract Ammonia is a promising carbon-free fuel alternative, offering higher energy density and easier storage compared to liquid hydrogen. This study presents experimental measurements of the laminar flame speed for an NH3:H2:N2 mixture with a 40:45:15 volume ratio at elevated pressures. Experiments were conducted at Texas A&M University, employing high-speed schlieren photography to capture spherical flame propagation. Flame stretch effects were accounted for to determine unstretched laminar burning velocities over equivalence ratios ranging from 0.7 to 1.4 at pressures of 1 to 4 atm and an initial temperature of 298 K. At 1 and 2 atm, with air as the oxidizer, peak laminar flame speeds were 42.5 and 34.1 cm/s at F=1.1. Leaner mixtures at these conditions exhibited cellular instabilities. To mitigate these instabilities at 3 and 4 atm, the oxidizer was replaced with a 1:6 O2:He mixture, resulting in increased peak laminar flame speeds of 54.6 and 48.7 cm/s at F=1.1, respectively. Comparative experiments using a Bunsen flame at 1 atm with PLIF imaging of OH revealed flame speeds approximately 10 cm/s slower than those of spherically propagating flames. Experimental results were compared with predictions from four chemical kinetics models, identifying discrepancies and emphasizing areas for refinement.
Costa et al. (Mon,) studied this question.