Ammonia-hydrogen blends combustion in turbulent high temperature co-flow

Abstract

In response to the stringent vehicle emission regulations, ammonia, with its potential as a carbon-free alternative fuel for reducing carbon emissions, faces application challenges due to higher ignition energy requirements and lower flame stability. Adding hydrogen is one of the effective ways to improve combustion performance of pure ammonia. This study focuses on the auto-ignition characteristics and jet flame stability of ammonia-hydrogen fuel blends under various conditions, such as different injection pressures, co-flow velocities, co-flow temperatures, and hydrogen blending ratios, employing a controllable active thermal atmosphere burner. Hydrogen addition increases flame brightness, area, and crinkly morphology due to enhanced NH2 production and higher combustion temperatures. The flame length increases together to the hydrogen ratio and the co-flow temperature, and it has been verified that it is primarily governed by jet momentum. Above 1073 K of co-flow temperature, the heat transfer becomes dominant for auto-ignition, reducing the effect of hydrogen presence. Combustion efficiency improves for higher co-flow temperatures, while hydrogen enhances propagation until a threshold is reached for XH2 = 20 %, beyond which a sensible increment in propagation cannot be detected. When the injection pressure augments, the flame is enlarged but auto-ignition can be hindered. Hydrogen addition reduces fluctuations, ensuring optimal stability for XH2 = 20 %