Affordable Access

Numerical analysis of entropy generation in an annular microcombustor using multistep kinetics

Authors
Journal
Applied Thermal Engineering
1359-4311
Publisher
Elsevier
Publication Date
Volume
52
Issue
2
Identifiers
DOI: 10.1016/j.applthermaleng.2012.12.021
Keywords
  • Entropy Generation
  • Microcombustion
  • Multistep Kinetics
  • Lean Flame
  • Hydrogen
Disciplines
  • Physics

Abstract

Abstract Entropy generation by combustion and additional irreversibility due to heat loss was studied numerically for a premixed flame based microcombustor. Detailed axisymmetric reactive flow model employing a 21 step–9 species reaction mechanism for hydrogen–air mixture was considered. The analysis identified reactions contributing most of the entropy generated in combustion. These reactions are removed from thermodynamic equilibrium in the low temperature region between 400 and 700 K of the flame and a combination of their high affinity and low temperature induces entropy generation in this region. Single step kinetics and a reduced scheme neglecting HO2 is consequently incapable of accurately calculating the entropy generation and second law performance. Overall entropy generation rates increased from lean to rich mixtures in the range ф = 0.5–1.4 and were dominated by combustion reactions. Characterization of combustor performance in terms of second law efficiency showed that availability reduction by wall heat losses and combustion irreversibility were of the same order for stoichiometric and both decreased for rich flames. On the other hand, near-quenching fuel lean flames (ф≤0.75) suffered mostly from combustion irreversibility. These trends caused the minimum efficiency (maximum thermodynamic irreversibility) point to locate near stoichiometric fuel–air composition.

There are no comments yet on this publication. Be the first to share your thoughts.