Research paper Some aspects of stabilization and structure of laminar premixed hydrogen-air ﬂames in a microchannel Swarup Y. Jejurkar * , D.P. Mishra Combustion Laboratory, Department of Aerospace Engineering, Indian Institute of Technology Kanpur 208 016 India highlights graphical abstract  homogeneous ignition of ﬂame by continuous ignition mechanism.  thermal diffusion of H 2 at the leading edge affects ﬂame structure.  twin-peaked heat release proﬁle for rich ﬂame.  unravels role of OH in reaction ki- netics of rich ﬂame. article info Article history: Received 24 February 2015 Accepted 20 May 2015 Available online 30 May 2015 Keywords: Hydrogen Flame structure Microcombustion Thermal diffusion abstract In the present paper, ﬂame stabilization and structure are investigated numerically for non-adiabatic hydrogen-air ﬂames at different equivalence ratios and inlet velocities. A cylindrical microcombustor in which combustion occurs in the annular region between two concentric tubes is investigated. The inner hollow tube contains static nitrogen gas and this combination acts as a thermal reservoir that stores and recirculates heat to the incoming mixture. Investigations are carried out using detailed nu- merical model incorporating two-dimensional transport, thermal radiation, multi-step kinetics, and conjugate heat transfer. Flame is sustained by the continuous ignition mechanism activated by an un- interrupted temperature ﬁeld between gas mixture and wall developing at steady state. Heat losses from ﬂame resulted in a crossover temperature higher than that of the lean-limit and stoichiometric free ﬂames due to slow radical build-up. Thermal diffusion of hydrogen is shown to be responsible for enhancing the burning intensity of leading edge. Diffusion and reaction kinetics at the ﬂame tip result in twin-peaked heat release rate distribution, most prominently for fuel rich ﬂame (f ¼ 1.7). © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Microcombustion is a potential power source for miniature devices. However, issues such as ﬂame stabilization [1e3], ﬂame- wall interaction [4], and reaction kinetics [5] in these devices need to be handled for successful operation. Increased ﬂame-wall thermal coupling in a narrow passage affects reaction kinetics [5]. Branching by H 2 þ O ¼ H þ OH and H þ O 2 ¼ O þ OH dominates propagation by HO 2 þ H ¼ 2OH in lean (f ¼ 0:5) hydrogen ﬂame at microscale [5]. Kagan and Sivashinsky [6] used reaction-diffusion model of two-dimensional (2D) ﬂame stabilized at the junction of hot and cold sides to study the effects of radiation losses on tip opening for Lewis number (Le ¼ a=D) equal to 0.5. More fuel leaked from tip and burnt as diffusion ﬂame near the ruptured tip as heat losses and inlet velocity increased. Conduction losses played no role * Corresponding author. Tel.: þ91 512 259 7125. E-mail addresses: ﬂowdyna@gmail.com (S.Y. Jejurkar), mishra@iitk.ac.in (D.P. Mishra). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2015.05.053 1359-4311/© 2015 Elsevier Ltd. All rights reserved. Applied Thermal Engineering 87 (2015) 539e546