Intermediate Reynolds number flat plate boundary layer flows over catalytic surfaces for “micro”-combustion applications

Abstract

The reactive, flat plate, boundary layer flow of close-to-stoichiometric, combusting methane–air mixtures over small size Pt plates was studied experimentally for the range of intermediate Reynolds numbers that pertain to micro-combustion applications. The emphasis was on detecting combustion features that differentiate this flow from similar flows that have been studied extensively of leaner mixtures at higher Reynolds numbers. Surface temperature was measured with infrared thermography and was correlated to reactant concentration profiles that were acquired with gas chromatography/mass spectroscopy. Additionally, particle image velocimetry was used in order to investigate the streamwise and transverse velocity profiles along the reacting plate. It was established that combustion took place in three subsequent phases: in the immediate vicinity of the leading edge of the flat plates, a first phase of combustion was established with high surface temperature (>1200 °C), intense fuel depletion and product formation, and maximum streamwise and transverse velocities. This was followed by a second, relatively long phase, where temperature leveled out to an intermediate value, product formation and reactant depletion slowed, and velocities were further reduced. In a third phase, combustion was completed and the surface temperature was reduced to the temperature of the free–stream mixture. The flow field differs significantly from the classical flat plate boundary layer with strong transverse velocities due primarily to chemistry. It is suggested that phase I combustion can be used for burner miniaturization through boundary layer interruption.