Flame and NO emissions characteristics of NH3/H2/N2 mixed-fuel jet flames with hot co-flow air

Ammonia cracking offers a promising route to enhance combustion activity, yet the coupled effects of fuel composition and thermal conditions on flame behavior and emissions remain unclear. This study integrates experiments and numerical simulations to examine laminar NH 3 /H 2 /N 2 jet flames, with fuel and co-flow air preheated from 293 to 673 K. Reducing the cracking ratio and hot co-flow alter flame color and increases luminosity, attributed to NH 2 * and H 2 O. Flame height decreases with both parameters, but co-flow temperature weakens the cracking ratio's effect. Flammable range widens with temperature, and limiting ammonia concentration rises linearly from 0.8 to 0.9. OH distribution expands and its radial thickness decreases at lower cracking ratios due to flame speed and oxygen consumption effects, while co-flow temperature marginally affects OH distribution. Furthermore, NO emissions decline with reduced ammonia content, but higher co-flow temperature promotes net NO formation by enhancing air-side production without altering fuel-side consumption.