Effect of oxidizer dilution on thermophotovoltaic performance of premixed ammonia/hydrogen/air combustion in radial micro-combustor

Abstract

Present research deals with the combustion characteristics, thermal performance, and emissions analyses of a radial micro-combustor for thermo-photovoltaic application. Simulations are carried out for premixed ammonia/hydrogen/air combustion with different inlet velocities and air dilution levels with N2. Influences of input parameters on the thermal performance of micro-combustor, the total energy conversion efficiency of the micro thermo-photovoltaic system, OH distribution, recirculation zone characteristics, flame blowout limits and NOx-N2O emissions are examined. The results imply that elevating inlet velocity in the studied range enhances the uniformity factor of temperature distribution in the fluid and solid domains. The maximum value of the total energy conversion efficiency was obtained to be 8.2 % corresponding to the 6.6 W of output electric power. On the other hand, the present results showed that a higher dilution level of air (up to 84 % N2 on volume basis) results in a significant increase in temperature distribution uniformity and consequently a decrease in mean temperature and total thermo-photovoltaic efficiency. Moreover, such increment in dilution level results in higher N2O emission at lower velocities and consequently a significant decrease in NOx emission level up to 58 %. Finally, reaction pathway analysis showed that the main NO production pathway remains unchanged in NH3 → NH2 → HNO → NO route with increasing inlet velocity and dilution level.