Hydrogen–oxygen torch igniters are widely used to promote ignition and flame holding during high-speed propulsion. However, the coupled internal reaction flow and solid heat conduction processes that govern their thermal limits remain insufficiently quantified. We developed a conjugate framework that couples a one-dimensional plug-flow reactor for gas-phase H \(_2\) /O \(_2\) chemistry with an axisymmetric transient heat conduction model of a noncooled copper micro-rocket torch. The inner/outer wall boundary conditions account for gas-to-wall convection, external natural convection, and radiation. The solver was verified against the analytical solution for an infinitely long cylinder with convective cooling, yielding a small and decaying RMSE ( \(\sim 10^{-2}\) – \(10^{-3}\) ), which supports the fidelity of temporal/spatial discretization and boundary implementation. Simulations at \(\phi =1.14\) show post-ignition chamber temperatures near \(3100~\textrm{K}\) and near-exit temperatures that decrease with increasing internal heat-transfer coefficient \(h_{\textrm{inner}}\) [50–500 W/(m \(^2 \cdot\) K)] from \(\approx 3180\) to \(2930~\textrm{K}\) . A comparison with the wall thermocouple data at 3 and 6 cm from the tip indicates \(h_{\textrm{inner}}\approx 100\) –200 W/(m \(^2 \cdot\) K), which is consistent with the Nusselt-based estimates for nominally laminar flow (Re \(_d\approx 1690\) ). Despite strong internal heating, the torch temperature-rise rate remained \(<4\) K/s and diminished over time, implying thermal robustness for at least 15 s of operation under the present conditions. The gas-phase radiation inside the chamber is negligible because of the small \(p_{\mathrm {H_2O}}L\) , whereas the external radiation becomes comparable to natural convection near \(\sim 600\) K and must be included in the design. The framework enables quantitative assessment of gas–wall coupling and provides actionable guidance for selecting operating windows and material/thickness choices to balance ignition strength against structural heating in scramjet and liquid/hybrid-rocket torch igniters.
