Stabilization of Flames

One of the most characteristic features of flame propagation is the existence of flammability limits. For any given fuel-oxidizer mixture, there exists a range of compositions, which usually centers about the 

At higher pressures, the composition limit appears to be experimentally independent of the dimensions of the equipment and has been widely considered to be a property of an adiabatically propagating mixture (Bl). This type of limit has been referred to as a fundamental limit. The demonstration of the existence of such a limit is an exceedingly difficult task. Since all flames radiate some of their thermal energy, it is impossible to stabilize a flame without losses to the surroundings. However, most flame gases are very poor radiators, and, since the residence time of the gases in the reaction zone of a flame is quite small, flames have been observed which come quite close to the adiabatic flame temperature (F14). 

A flame will remain stationary only if the flow velocity perpendicular to the flame front is exactly equal to the burning velocity. However, this condition needs to be met only for a limited region over a flame front. For other regions it is possible for the flame front to be inclined to the flow at an angle such that the component of the velocity perpendicular to the front is equal to the flow velocity. The limited region over which the 

Recent work on spatial stabilization has been directed towards the production of one-dimensional flames (Fll, P10). These may be either flat, cylindrical, or spherical. The primary purpose of such flames has been to measure velocities accurately and to provide a flame that can be described by a one-dimensional theory. The measurement of temperature and composition profiles is meaningful, of course, only in a flame in which the geometry is known. One-dimensional geometry greatly reduces the labor required to analyze such profiles in order to study kinetics. 

The preceding remarks all apply to a steadily propagating one-dimensional detonation. It is a relatively simple task to solve the algebraic equation for the over-all steady-state motion. The differential equations for the structure may be solved in the steady state, but the task is tedious and, in addition, detailed knowledge of reaction rates needed in the equation is not available. It is not too difficult to solve the time-dependent over-all equation if a burning velocity for the flame as a function of temperature and pressure is assumed (J4). It is not practicable to solve the time-dependent equations which govern the structure of the wave with any certainty because of the lack of kinetic information, in addition to the mathematical difficulty. The acceleration of the slowly moving flame front as it sends forward pressure waves which coalesce into shock waves that eventually are coupled to a zone of reaction to form a detonation wave has been observed experimentally (LI, L2). 

---

The types of obstacles used in stabilization of flames in high-speed flows could be rods, vee gutters, toroids, disks, strips, etc. But in choosing the... 

The preliminary results obtained show that the initiation limits for polydispersed mixtures and stability of flame propagation strongly depend on inhomogeneity of particles (droplets) concentration distribution typical for the majority of practical cases wherein the ignition and combustion of polydispersed mixtures take place. Thus to ensure stable ignition and combustion characteristics... 

The other stabilizer of flames is cold surfaces. These act to lower in the region of the surface and thus create a stable edge to the flame at the wall of the burner. This occurs both by thermally quenching the reaction near the surface and by quenching free radicals by adsorption on the surfaces, which stops the combustion reactions. 

Stabilization of flame-retarded polypropylene requires attention to detail, which include performance requirements, cost constraints, and coadditive interactions. Improvements to traditional additive performances often fall short of requirements. Therefore, the focus is shifting to the full formulation components, often with new chemistry types. System compatibility is a key concept. Next-generation systems will be more worker and environmentally friendly as the polypropylene industry displaces both commodity and engineering resins at ever harsher requirements. 

---