Design Exploration of Insert-Free Micro-Thermophotovoltaic Ammonia-Hydrogen Radial-Combustor

Micro-thermophotovoltaic systems are promising compact power-generation platforms for low-power applications, but their combustor performance is strongly constrained by coupled requirements of high radiative efficiency, uniform emitter temperature, low pressure drop, and fuel-flexible combustion. This study presents a systematic parametric investigation of an insert-free radial micro-combustor for ammonia–hydrogen MTPV applications using two-dimensional axisymmetric simulations incorporating a previously validated CFD framework, a published NH3/H2 kinetic mechanism benchmarked against experimental data, conjugate heat transfer, and surface-to-surface radiation. The effects of key geometric parameters, including radial expansion ratio, emitter thickness, channel width, and adiabatic section length, are evaluated under a hydrogen baseline condition to isolate geometric influences. The selected configuration is subsequently investigated with ammonia–hydrogen fuel blends to assess fuel-flexibility and thermal management characteristics. The results reveal that the performance improvement is governed not by an isolated geometric effect, but by the coupled interaction among radial-flow redistribution, residence-time control, solid-wall heat redistribution, flame stabilization, and emitter-temperature regulation. The selected configuration within the investigated design matrix achieves a combustor-level radiative efficiency of 55.4%, while maintaining a maximum solid temperature below the material constraint and improving emitter-temperature uniformity. A first-order radiation-to-electricity estimate based on an assumed effective TPV conversion factor is provided only for contextual comparison with previous MTPV combustor studies; it is not a device-specific prediction or a normalized system-level fuel-to-electricity efficiency. The results demonstrate the potential of insert-free radial micro-combustors as compact thermal conversion platforms for application-specific low-power MTPV systems, where thermal management, fuel flexibility, and mechanical simplicity are important design considerations.