Interaction of the combustion front of methane-air mixture at low pressures with obstacles of cylindrical shape

Abstract

It was experimentally observed that the front of a propagating flame of a well-mixed diluted methane-oxygen mixture at 298 K and 100–300 Torr does not form von Karman vortex shedding behind the obstacle of cylindrical shape of 30–50 mm in diameter, including a perforated cylinder; however, the instability under the same conditions occurs in the flow of hot products. In the perforated cylinder, the occurrence of local primary ignition centers on its inner surface is observed. In the mathematical modeling, the main observed features of the flame front propagation were taken into account: the chain branched mechanism of gaseous combustion and the absence of vortex shedding behind the obstacle at flame propagation. It was shown that a qualitative model of compressible dimensionless non-reactive/reactive Navier–Stokes equations in low Mach number approximation yields both the mode of the emergence of von Karman instability in chemically inert gas and the absence of the instability in the mode of flame propagation in a reacting flow. The model computations confirmed the occurrence of local primary ignition centers on the inner surface of the obstacle.

Keywords

• Methane combustion
• Instability
• Von Karman vortex street
• Obstacle of cylindrical shape
• Mathematical model