Composition and Injection Angle Effects on Combustion of an NH3/H2/N2 Jet in an Air Crossflow

This study explores the combined effects of fuel composition and injection angle on the combustion behavior of an NH3/H2/N2 jet in an air crossflow by means of high-fidelity Large Eddy Simulations (LESs). Four distinct fuel mixtures derived from ammonia partial decomposition, with hydrogen concentrations ranging from 15% to 60% by volume, are injected at angles of 90 degrees and 75 degrees relative to the crossflow, and at operating conditions frequently encountered in micro-gas turbines. The influence of strain on peak flame temperature and NO formation in non-premixed, counter-flow laminar flames is first examined. Then, the instantaneous flow features of each configuration are analyzed focusing on key turbulent structures, and time-averaged spatial distributions of temperature and NO in the reacting region are provided. In addition, statistical analysis on the formation pathways of NO and H2 is performed, revealing unexpected trends: in particular, the lowest hydrogen content flame yields higher temperatures and NO production due to the enhancement of the ammonia-to-hydrogen conversion chemical mechanism, thus promoting flame stability. As the hydrogen concentration increases, this conversion decreases, leading to lower NO emissions and unburned fuel, particularly at the 75 degrees injection angle. Flames with a 90 degrees injection angle exhibit a more pronounced high-temperature recirculation zone, further driving NO production compared with the 75 degrees cases. These findings provide valuable insights into optimizing ammonia-hydrogen fuel blends for high-efficiency, low-emission combustion in gas turbines and other applications, highlighting the need for a careful balance between fuel composition and injection angle.