Numerical study on geometric parameter optimization of wall-cooled hydrothermal combustion reactor

Abstract

A wall-cooled reactor (WCR) for hydrothermal combustion was modeled using the supercritical water diluted flamelet generated manifolds (SCWD-FGM) model for geometric optimization. The effects of four key geometric parameters on reactor performance were systematically analyzed using a one-factor-at-a-time (OFAT) approach. Results indicate that increasing the fuel nozzle inner diameter weakens fuel–oxidizer mixing and reduces reaction intensity while enhancing wall cooling; increasing the fuel nozzle recess depth improves flame stability but raises the oxidizer nozzle inner wall temperature; increasing the cooling water layer thickness has little effect on combustion but strengthens wall protection; and adding additional cooling water injection stages lowers downstream wall temperature while slightly increasing upstream temperature. Based on these insights, a sensitivity-guided coordinate search method was applied to optimize the baseline configuration. The optimized configuration slightly increases the axial distance for 99 % hydrogen conversion by 0.2 mm, but substantially reduces the oxidizer nozzle inner wall temperature by 536 °C and the reactor inner wall temperature by 4 °C. The enlarged geometry increases material consumption by over 70 %, but it reduces the peak temperatures of critical components and broadens the range of feasible structural materials, thereby markedly enhancing operational safety and structural robustness under supercritical conditions.