Optimization of Laval nozzle structure for gas mixture of NH3–O2 combustion products and CO2–H2O by response surface methodology

Ammonia is a promising alternative fuel, and the nozzle plays a critical role as a core component in ammonia-fueled hypersonic propulsion systems. This study combines response surface methodology (RSM) with computational fluid dynamics (CFD) simulations to optimize the geometric configuration and combustion performance of the ammonia-fueled Laval nozzle. The RSM is adopted for optimizing the thrust by adjusting the nozzle's geometric parameters and the inlet parameters of the Laval nozzle. The CFD's results demonstrate that the quadratic effect of the throat radius and the interaction between the inlet and throat radii are critical for thrust optimization. The response surface models have demonstrated significant potential in enhancing nozzle thrust. The thrust is increased by 2% through adjusting the geometric parameter of the nozzle. Optimizing inlet parameters indicates that higher inlet temperatures (1073.15 K) and higher oxygen concentrations (12%) enhance the chemical kinetics efficiency of ammonia combustion, thereby improving the conversion of thermal energy into kinetic energy. The thrust increased by 37% under the optimal inlet parameters obtained through response surface optimization. The effectiveness of RSM in multi-variable optimization is verified, and the mechanism of multi-parameter coupling effects on hypersonic ammonia combustion dynamics is revealed.