Integrated 2D two-phase flow simulation with porous media model for 98% hydrogen peroxide monopropellant thruster

High-concentration hydrogen peroxide monopropellant thrusters are promising candidates for green space propulsion applications. However, numerical simulation remains challenging due to the strong coupling of gas-liquid two-phase flow, chemical decomposition, and heat transfer within the catalyst bed, which often leads to severe convergence difficulties in multi-dimensional full-component simulations. In this work, a decoupled stepwise reaction model is proposed for an integrated 98% hydrogen peroxide monopropellant thruster. The model separates liquid-phase evaporation from subsequent decomposition, and kinetic parameters are calibrated through visualized drop tests. Based on this model, a two-dimensional axisymmetric full-component numerical framework is established by coupling the Volume of Fluid method with a porous media model. The numerical model is validated against hot-fire test data at a mass flow rate of 422 g/s (33.6 g cm−2 s−1). Predicted chamber pressure, temperature, and thrust agree well with experimental measurements, with relative deviations below 3%, 1.12%, and 1.14%, respectively. The simulation captures key internal flow features, including intense upstream phase change, downstream radial gas mixing, and high-temperature zones consistent with injector distribution. In addition, the simulation accurately captures pressure evolution across the injector, porous media, distributor, and nozzle. Furthermore, catalyst activity decay is investigated, revealing a nonlinear degradation in thruster performance. The catalyst aging tolerance threshold of approximately 20% is identified, beyond which liquid breakthrough occurs and thrust decreases to 70.5% (420 N) at an activity decay factor of 1.3. This study provides a validated and efficient numerical framework for performance prediction and design optimization of hydrogen peroxide monopropellant thrusters.