A comparative study of H₂-air premixed flame in micro combustors with different physical and boundary conditions

Abstract

A numerical study of H₂-air premixed combustion in the micro channels with a detailed chemical reaction mechanism is performed by solving the two-dimensional fully elliptic governing equations of continuity, momentum, energy and species, coupled with the energy equation in the solid wall. A reference case is defined as the combustion in a cylindrical tube with 0.8 mm inner diameter and 8 mm length with a non-slip wall and a uniform velocity profile at the inlet plane. Different physical and boundary conditions have been applied in order to investigate their respective effects on the flame temperature. The conditions studied in the current paper include the combustor size and geometry, inlet velocity profile, axial heat conduction in the solid wall and slip-wall and temperature jump at the gas–solid interface. It is noted that effects of Knudsen number (slip-wall and temperature jump) on the thermal and fluid field are not very significant in a d = 0.4 mm micro combustor. Furthermore, the qualitative effects of Knudsen number on the flame temperature are analysed. The results of this paper indicate that these various boundary and physical conditions have effects on the flame temperature to different extent and should be carefully monitored when applied for different applications.

Keywords:

• micro combustion
• premixed flame
• numerical simulation
• boundary conditions
• flame temperature

Acknowledgments

The authors would like to thank the Computer Center, National University of Singapore (NUS), for providing the computational software Fluent® and the supercomputing workstations. In addition, the authors are very grateful to Mr Wang Junhong of the NUS Computer Center, for his technical support and assistance regarding Fluent®.

Notes

∗Rate constants are given in the form k = A _k T ^{β _k} exp (− E _k /RT)

^†Enhancement factors: H₂O = 20.0.

^‡Enhancement factors: H₂O = 6.0, H = 2.0, H₂ = 3.0.

^§Enhancement factors: H₂O = 21.0, H₂ = 3.3, O₂ = 0.0, N₂ = 0.0.