Quenching, flame propagation

Flame quenching. Flame propagation is suppressed if the flammable mixture is held in a narrow space. There is a minimum diameter for apparatus used for determination of flammability limits. Below this diameter the flammable range measurements are narrower and inaccurate. 

Elame Arrester A flame arrester is a device permeable to gas flow but impermeable to any flame. It quenches the flame and cools the products sufficiently to prevent reignition at arrester outlet. Arresters are used to prevent a flame propagating into the system from outside (such as via a tank vent) or one part of the system to another (such as through connected piping). 

The location and energy level of an ignition source has a profound effect on flame propagation and the ability of a DDA to quench the flame. 

In order to ensure the reliability of a flame arrester (ability to quench a propagating flame or withstand a stationary flame) a number of factors must be taken into consideration as follows ... 

Over the years, this concept was refined in several ways. A scale dependency was modeled by the introduction of scale-dependent quenching of combustion. The first stage of the process was simulated by quasi-laminar flame propagation. In addition, three-dimensional versions of the code were developed (Hjertager 1985 Bakke 1986 Bakke and Hjertager 1987). Satisfactory agreement with experimental data was obtained. 

Quenching process of a flat hmit flame, propagating downward from the open end of the tube in mixture with 2.20% CjHg observed by schlieren system with superimposed direct photography. Square tube 125 mm x 125 mm x 500mm. Time interval between frames 0.3 s. 

Flame Propagation in Narrow Channels and Mechanism of Its Quenching.102... 

As the quenching distance for flames propagating in different mixtures was often important for industrial applications, experimental methods to measure this quantity were developed. The most frequently used ones were... 

For a while till now, our research group has been involved in studies of the properties of limit flames. Most of the results reported in this chapter were obtained for propane flames, under normal atmospheric conditions, in 300 mm long channels, with a square cross-section. The experimental procedure was described previously [25]. A flame propagating through a stationary mixture in a quenching tube or quenching channel can be characterized by the parameters defined in Figure 6.1.1. 

On the basis of the observations and results so far presented, it is obvious that the properties of limit flames are very different depending on the width of the quenching channel, the equivalence ratio, and the direction of flame propagation. The reasons for this are detailed in the following four sections. 

Jarosinski, J., Podfilipski, J., and Fodemski, T., Properties of flames propagating in propane-air mixtures near flammability and quenching limits. Combust. Sci. Tech., 174 167, 2002. 

The concept of turbulent flame stretch was introduced by Karlovitz long ago in [15]. The turbulent Karlovitz number (Ka) can be defined as the ratio of a turbulent strain rate (s) to a characteristic reaction rate (to), which has been commonly used as a key nondimensional parameter to describe the flame propagation rates and flame quenching by turbulence. For turbulence s >/ />, where the dissipation rate e and u, L and v... 

Flame Propagation in a Rotating Cylindrical Vessel Mechanism of Flame Quenching... 

In Chapter 6.1, A. Gutkowski and J. Jarosinski present results of an experimental and numerical study of flame propagation in narrow channels and the mechanism of quenching due to heat losses. This work takes up again classical studies of the quenching distance. The most characteristic features of limit flames are determined experimentally. 

In Chapter 6.4, J. Chomiak and J. Jarosinski discuss the mechanism of flame propagation and quenching in a rofating cylindrical vessel. They explain the observed phenomenon of quenching in ferms of the formation of fhe so-called Ekman layers, which are responsible for the detachment of flames from the walls and the reduction of fheir width. Reduction of the flame speed with increasing angular velocity of rofation is explained in terms of free convection effects driven by centrifugal acceleration. 

A flame is quenched in a tube when the two mechanisms that permit flame propagation—diffusion of species and of heat—are affected. Tube walls extract heat the smaller the tube, the greater is the surface area to volume ratio within the tube and hence the greater is the volumetric heat loss. Similarly, the smaller the tube, the greater the number of collisions of the active radical species that are destroyed. Since the condition and the material composition of the tube wall affect the rate of destruction of the active species [5], a specific analytical determination of the quenching distance is not feasible. 

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