EXPERIMENTAL STUDY OF PREMIXED LEAN COMBUSTION IN OPPOSING JETS

Abstract

Using the opposing jets configuration, the velocity fields and extinction conditions for premixed lean combustion has been studied experimentally. This geometry is created by arranging two identical axisymmetric burners face to face, forming an axisymmetric stagnation flow. In this flow geometry, two symmetrical flames are stabilized near to the stagnation plane which lies at the center of the twin flames and can be considered as an adiabatic surface. This configuration minimized downstream heat loss and increased the measurement access to the reaction zones. An experimental rig was built to establish this flow configuration. Aspects of the project include general observations of the behaviour of opposing jets configuration in both non-reacting and reacting case, and particular attention is given to the flame near extinction. Investigations performed on propane-air flames with equivalence ratios ranging from 0.7 to 0.9, and incident turbulence intensities ranging from 0.2 to 1.5 m/s. Both laminar and turbulent flames produced by this apparatus are disc-like, and the flame brush oriented perpendicular to axis of the jets. The coin-shaped flame geometry can be observed in laminar case when nozzle to nozzle separation is small. It is found that these flames can be forced to extinguish close to the stagnation surface under certain conditions, and this extinction limit to the flame is studied. The global extinction of the combustion is found to be related to the total stretch rate applied to the flames. There is a linear relationship between nozzle separation and velocity function V? when the extinction data points are away from the asymptotic velocity value at flame extinction. The approach to the current project is mainly based on the research work done by Kostiuk et al.(1989,1991,1993). It is found that some of results are similar to his findings, and some of them disagree with his experimental observations. Comparisons with existing literature, especially that of Kostiuk et al. (1989, 1991, 1993), confirms several of the reported findings, although a number of experimental observations and their interpretation do differ.