Second Law Analysis of Hydrogen-Enriched Methane-Air Flames

A theoretical-numerical analysis based on the Second law of thermodynamics is used for laminar H2-enriched CH4-air flames. The analysis is based on computing the various entropy generation terms in reacting flow field. The objective is to examine the effect of flame configuration and fuel type on entropy generation and the Second law efficiency. A comprehensive, time-dependent computational model, which employs a detailed description of chemistry and transport, is used to simulate the transient ignition and flame propagation in a two-dimensional reacting flow field. Because this propagating flame exhibits a triple flame structure containing premixed and nonpremixed reaction zones, one-dimensional propagating premixed flames and counterflow nonpremixed flames are also analyzed and compared with two-dimensional propagating triple flames. For latter flames, the triple point exhibits the maximum entropy generation, indicating that this point is characterized by high chemical reactivity, and large temperature and mass fraction gradients. The volumetric entropy generation is the highest in the two premixed reaction zones, and the lowest in the nonpremixed reaction zone. In the premixed zones, the volumetric entropy generation due to chemical reaction is the highest, followed by heat conduction, and then mixing. The converse is true for the nonpremixed zone. However, the integrated entropy generation rate indicate