Feasibility study of hydrogen-ammonia synergistic combustion in scramjets across broad Mach ranges

Ammonia shows advantages over hydrocarbon fuels for high-Mach scramjet engines, including superior cooling capacity and carbon-free combustion. However, its operation at lower Mach numbers remains challenging. Here, we successfully demonstrate ammonia-hydrogen ignition at Mach 3 and sustained combustion at Mach 6, confirming the feasibility of hydrogen-ammonia synergistic supersonic combustion. Compared to hydrogen combustion, ammonia addition at low Mach numbers does not alter flame paths but increases flame establishment times by 57.1% upstream and 100% downstream. Both global flame establishment and cavity ignition times are longer under the upstream scheme. At high Mach numbers, two distinct combustion modes are observed. Upstream hydrogen injection ignites more ammonia and produces more intense combustion than downstream injection. These results demonstrate the feasibility of ammonia-fueled scramjets operating across a broad Mach range.