A Numerical Study on Key Thermal Parameters and NOx Emissions of a Hydrogen-Fueled Double-Channel Outlet Micro Cylindrical Combustor Employing a Heat-Recirculating Configuration for Thermophotovoltaic Applications

The current study proposes a novel design configuration of a hydrogen-fueled micro cylindrical combustor. The newly developed design consists of a single-channel inlet and a double-channel outlet with a heat-recirculating structure aimed at enhancing the heat transfer mechanism from the combustion to the walls. Investigations are conducted using three-dimensional numerical simulation means, and emphasis is placed on assessing the effects of the novel design structure on key thermal parameters and nitrogen oxide (NOx) emissions. The numerical modeling approach is first validated against the experimental and numerical data available in the literature. A parametric study is then conducted by means of varying the length and width of the heat-recirculating channel, inlet velocity, and inlet equivalence ratio. The findings revealed that the novel design configuration significantly improves thermal performance and curtails NOx emissions in comparison with those of the conventional structure. For example, the proposed design leads the radiation efficiency to increase by roughly 10%. The increase in the width of the preheating channel yields further optimization by boosting the heat transfer process from the flame to the walls. Elevating the inlet velocity exhibits a pronounced increase in the mean wall temperature and a more uniform distribution of the wall temperature. However, the exhaust gas temperature increases with increasing inlet velocity, leading to a reduction in the exergy and radiation efficiencies. The equivalence ratio of unity optimizes key thermal parameters, as the lean and rich conditions suffer from low hydrogen and oxygen contents, respectively.