Primary flame

Fig. 1. The postulated flame stmcture for an AP composite propellant, showing A, the primary flame, where gases are from AP decomposition and fuel pyrolysis, the temperature is presumably the propellant flame temperature, and heat transfer is three-dimensional followed by B, the final diffusion flame, where gases are O2 from the AP flame reacting with products from fuel pyrolysis, the temperature is the propellant flame temperature, and heat transfer is three-dimensional and C, the AP monopropellant flame where gases are products from the AP surface decomposition, the temperature is the adiabatic flame temperature for pure AP, and heat transfer is approximately one-dimensional. AP = ammonium perchlorate.

Antimony Oxide as a Primary Flame Retardant. Antimony oxide behaves as a condensed-phase flame retardant in cellulosic materials (2). It can be appHed by impregnating a fabric with a soluble antimony salt followed by a second treatment that precipitates antimony oxide in the fibers. When the treated fabric is exposed to a flame, the oxide reacts with the hydroxyl groups of the cellulose (qv) causing them to decompose endothermically. The decomposition products, water and char, cool the flame reactions while slowing the production and volatilization of flammable decomposition products (see Flaa retardants for textiles). 

The vapor cloud of evaporated droplets bums like a diffusion flame in the turbulent state rather than as individual droplets. In the core of the spray, where droplets are evaporating, a rich mixture exists and soot formation occurs. Surrounding this core is a rich mixture zone where CO production is high and a flame front exists. Air entrainment completes the combustion, oxidizing CO to CO2 and burning the soot. Soot bumup releases radiant energy and controls flame emissivity. The relatively slow rate of soot burning compared with the rate of oxidation of CO and unbumed hydrocarbons leads to smoke formation. This model of a diffusion-controlled primary flame zone makes it possible to relate fuel chemistry to the behavior of fuels in combustors (7). 

The behavior of rich mixtures is compHcated by the entrainment of air at the burner port that sustains combustion of hot combustion products of the primary flame near the port. The blowoff velocity is found to increase continuously with ( ), or richer mixtures are more stable with respect to blowoff. They also have a lesser tendency toward flashback. Hence, a Bunsen flame has more latitude for stable operation if the primary mixture is rich. For this... 

A good example of the many successftil DfE Partnerships is the Furniture Flame Retard-ancy Partnerhip. Pentabromodiphenylether (PentaBDE) was the primary flame retardant used in low density, flexible polyurethane furniture foam. Due to concerns over its use and the fact that the chemical was found widespread in the environment and in human tissue and breast milk, PentaBDE was voluntarily phased out of production by US manufacturers in January 2004. The industry needed alternatives in order to meet furniture flame retardancy requirements, but did not have the human and environmental health and safety information needed in order to compare the alternatives. DfE worked with the furniture manufacturers, foam manufacturers, and flame-retardant chemical suppliers along with governmental and environmental groups to evaluate possible alternatives. 

For the primary flame reaction steam and oxygen are fed to the reactor at the following rates ... 

As a result of the cooling effect of the steam in the primary flame zone of the combustion chamber, it results in a reduction in the emission of noxious oxides of nitrogen, NO , from the cycle. 

A number of conclusions can be drawn from this first detailed analysis of NO production in methane-air diffusion flames by techniques of RRA. It is found that all production mechanisms have rates dependent on the peak flame temperature T°. The production rates for the thermal and nitrous oxide mechanisms increase sufficiently rapidly with T° that they are calculated by AEA after the peak flame temperature, and superequilibrium radical mole fractions are obtained from the RRA analysis of the primary flame structure. The flame temperature depends on the temperature of the fuel and oxidizer streams and... 

Fig.l2.n Definition of the primary flame and the secondary flame of a rocket plume. 

Fig. 12.11 shows the structure of a rocket plume generated downstream of a rocket nozzle. The plume consists of a primary flame and a secondary flame.Fil The primary flame is generated by the exhaust combustion gas from the rocket motor without any effect of the ambient atmosphere. The primary flame is composed of oblique shock waves and expansion waves as a result of interaction with the ambient pressure. The structure is dependent on the expansion ratio of the nozzle, as described in Appendix C. Therefore, no diffusional mixing with ambient air occurs in the primary flame. The secondary flame is generated by mixing of the exhaust gas from the nozzle with the ambient air. The dimensions of the secondary flame are dependent not only on the combustion gas expelled from the exhaust nozzle, but also on the expansion ratio of the nozzle. A nitropolymer propellant composed of nc(0-466), ng(0-369), dep(0104), ec(0 029), and pbst(0.032) is used as a reference propellant to determine the effect of plume suppression. The burning rate characteristics of the propellants are shown in Fig. 6-31. Since the nitropolymer propellant is fuel-rich, the exhaust gas forms a combustible gaseous mixture with the ambient air. This gaseous mixture is ignited and afterburning occurs somewhat downstream of the nozzle exit. The major combustion products in the combustion chamber are CO, Hj, CO2, N2, and HjO. The fuel components are CO and H2, the mole fractions of which at the nozzle throat are co(0.47) and iH2(0.24).

Fig. 12.12 shows a typical set of flame photographs of a nitropolymer propellant treated with potassium nitrate. From top to bottom, the photographs represent KNO3 contents of 0.68%, 0.85%, 1.03%, and 1.14%. Each of these experiments was performed under the test conditions of 8.0 MPa chamber pressure and an expansion ratio of 1. Though there is little effect on the primary flame, the secondary flame is clearly reduced by the addition of the suppressant The secondary flame is completely suppressed by the addition of 1.14% KNO3. The nozzle used here is a convergent one, i. e., the nozzle exit is at the throat... 

Fig. 127. Flame from picric acid. The primary flame (relatively small) is visible with the secondary flame above it. The duration of both flames is shown on the scale the primary flame of short duration, the secondary of long duration. The material was fired in a mortar (according to Will [11]).

The primary flame in the form of a dark-red taper is created by inflammable gases escaping from the bore. These gases mix with the air to form an inflammable mixture. If the temperature of the mixture is sufficiently high, it ignites at the end furthest from the muzzle (Fig. 190). 

Fig. 190. Muzzle flame I—primary flame, 2—secondary flame, 5—initiation of the...

Hydrocarbon flames have rapid dissociation reactions within the primary flame zone, leading to a mole-number overshoot, which is followed by a relatively long recombination zone. Important rapid-dissociation reactions include... 

The so-called "secondary or after flame which arises from the combination of reaction products of primary flame (such as of CO) with surrounding oxygpn in the air, is also dangerous. Other causes of ignition include any naked flame present in mine hot or inflamed particles ejected from the expl adiabatic compression of the gas by a shock wave at supersonic velocity general adiabatic compression of a body or pocket of gas electric sparks or sparks produced by drills hitting stones (which are sometimes embedded in coal) (Refs 7b, 7c, 16a, 22 31)... 

In a study of 78 TV sets and 34 personal computers, 78% of the modified polystyrene housings contained PBDEs, 16% PBBs, and 3% l,2-bis-(tribromo-phenoxy)ethane. Composed samples of this material with PBDEs and PBBs as flame retardants already contained traces of PBDFs and PBDDs. When PBBs were used as flame retardant, the levels of these impurities increased during the recycling process. The formation of these PBDFs and PBDDs from the primary flame retardants, should also be considered when assessing the toxic properties of PBBs and PBDEs [25]. 

The interpretation of the gas phase kinetic mechanism for <<1 is as follows. In the reaction B + M C -i- M, species-M can be interpreted as representing a pool of unspecified chain carriers whose concentration is negligibly small compared to that of B and C and spatially constant (i.e., steady-state approximation). Species-B is an intermediate, representative of species like NO2, HONO, and CH2O in NC/NG and HMX/RDX. Species-C is interpreted kinetically as products formed by the primary flame, such as NO, CO, and H2O. The process... 

K, is important for determining regression rate (only the primary stage is shown in Fig. 11). In the primary flame species like NO2, MONO, and CH2O which evolve from the surface as decomposition products are converted to NO, CO, and H2O, with a significant liberation of chemical energy, Qg. The secondary... 

Burning rate and primary flame length scale... 

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