Entropy production and thermodynamics exergy investigation on an ammonia-methane fueled micro-combustor with porous medium for thermophotovoltaic applications

Abstract

As conventional fossil fuel is depleting, ammonia has attracted extensive attention as a renewable fuel, which could be made from water, air, and sun. There is current interest in burning ammonia in macro, meso, and micro-combustors. The present work is concerned with the numerical investigations of the entropy production, thermodynamic exergy performance from ammonia/methane-fueled micro-combustors with a single-channel inlet and double-channel outlet (SIDO) in the presence and absence of a porous media (PM). For this, a 3D time-domain model is developed. With the model being validated with experimental data available in the literature, it is then applied to examine the effects of 1) equivalence ratio (Φ), 2) inlet velocity (Vin), 3) blending/mixing ratio (Φb) between the methane and ammonia, and 4) PM porosity (σ). In comparison with the combustion system without PM, the application of PM is found to lead to a significant improvement on thermal performances, as Vin is varied. It is found that there is a substantial 37.5% reduction in the standard deviation of the combustor outer wall temperature ST,W at Vin = 2.0 m/s. The optimal thermal performance is achieved, as Φ = 0.9. However, nitrogen oxide emission is shown to be decreased, as Φ is increased. As the entropy production is concerned, the σ of PM is shown to exhibit a notable influence. A higher porosity gives rise to a lower entropy production within the PM. The lowest entropy production resulting from heat conduction is shown to be achieved, when σ = 0.8. By implementing PM, the exergy efficiency (ηexergy) is found to be increased by 23.9% at Vin = 2.0 m/s. In general, the present investigation shed physical insights on the entropy production and thermodynamic exergy performances of ammonia/methane-fueled micro-combustion systems with and without PM.

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