Analysis of entropy generation and exergy efficiency of a micro-combustor with a passive exhaust gas recirculation channel

Abstract

In this study, the performance of a micro-combustor with an exhaust gas recirculation (EGR) channel was analyzed based on the second law of thermodynamics. Effects of the inlet velocity (Vin), equivalence ratio (ϕ), separating wall length (L1) and nozzle diameter (din) on entropy generation and exergy efficiency of the micro-combustor were investigated. In general, chemical reaction contributes most to the total exergy destruction (>60%), followed by heat conduction, mass diffusion, and viscous dissipation. Meanwhile, all parts of the entropy generation rate increase with the increase of Vin and ϕ. However, the entropy generation rates caused by chemical reaction and heat conduction decrease with the increase of L1. The entropy generation rates due to chemical reaction and heat conduction show opposite variation trends respect to din. An increase of Vin and ϕ results in higher exergy destruction and exergy loss of the micro-combustor, the largest exergy destruction and exergy loss are 3.06 W and 5.94 W under Vin=200 m/s and ϕ =1.0, respectively. While a longer separating plate length leads to a decrease in the exergy destruction and exergy loss. Exergy destruction and exergy loss change a little with din and their values are around 1.6 W and 3.4 W, respectively. Exergy efficiency of the micro-combustor increases with the increase of Vin and L1, but exhibits a non-monotonic variation with ϕ. A maximum exergy efficiency of 51.3% is achieved at Vin=200 m/s under ϕ =1.0, din=0.20 mm and L1=4 mm. In addition, the exergy efficiency decreases from 38.5% to 37.5% as din increases from 0.20 mm to 0.30 mm under the same mass flow rate.