The burning rate

Experimental Determination of the Burning Rate. Experimental determinations of the burning rate are made with the closed tomb for gun propellants and the strand burner for rocket propellants. The closed bomb is essentially a heavy-wahed cylinder capable of withstanding pressures to 689 MPa (100,000 psi). It is equipped with a piezoelectric pressure gauge and the associated apparatus requited to measure the total chamber pressure, which is directly related to the force of the propellant. It also measures the rate of pressure rise as a function of pressure which can then be related to the linear burning rate of the propellant via its geometry. Other devices, such as the Dynagun and the Hi—Low bomb, have also been developed for the measurement of gun propellant performance. 

Specific Tests. Federal (United States) Motor Vehicle Safety Standard (MVSS) 302 is used to measure the burning behavior of materials used in automobile interiors. A specimen is mounted horizontally and ignited for 15 seconds. The burning rate should be below 10 cm /min. The test specimen is 35.5 X 10.1 cm by the actual thickness (up to 1.3 cm). Automakers typically impose more severe criteria than the 10 cm /min in the standard. 

Paper. Citric acid is added to the pulp slurry prior to bleaching to sequester metal ions and prevent discoloration (208—211). Citrates are used in cigarette paper to control the burning rate to match that for tobacco. 

The burning rate of the droplet (kg/s), and its rate of change of radius ate related by ... 

The convective gas flow around a burning particle affects its burning rate. It has been postulated that in the absence of convection, the burning rate is independent of pressure. Forced convection, on the other hand, is befleved to increase the burning rate. 

The fuels consumed in the fire were treated wood, penta, and creosote (coal tars). Both are considered combustible liquids, with flash points above 160° F (CC). Vapor conditions within the headspaces of tanks can, however, reach explosive conditions, and the introduction of an ignition source resulted in spontaneous combustion. Under ideal conditions, creosote burns similar to crude oil, and in standard lab burn tests, has an average burn rate of 4 mm/min. There is no data on the burn rate of penta however, its vapors would have likely burned at much slower rates and a series of complex chemical transformations would have occurred. 

Hydrocarbons. Addn of metallo-org compds lowers the burning rate of TeNMe/hydrocarbon mixts to the point where they are useful mono-propints (Ref 27)... 

Obviously the pressure dependence of the burning rate in Taylor s expts with porous PETN is much greater than linear... 

Uses. At a level of 1%, anhyd Co perchlorate was found to increase the burning rate of a pro-plnt formulation from 0.07 to 0.12 inches/... 

Burning Rate. Samples were compressed into Plexiglas tubes 7mm in diam and the burning rate vs press measured. At 1 atm it was found to be ca lg/sqcm-sec and at lOOatm 27g/sqcm-sec (Refs 19 20)... 

With regard to pro pints, brisance, power and detonation velocity are not tested. It is, however, necessary to determine the burning rate, press developed on burning, vol of gas evolved, calorific value, thermal stability, etc. If one is... 

VasU ev (Ref 36) impacted various explosives with steel plates and followed events with a framing camera. PA at 1,59g/cc impacted with a 3-mm thick steel plate at 430m/sec showed only deflagration and no expins. Initially the burning rate was low but reached 600m/sec in about 65 microseconds after impact C. Potential Hazards. The main danger of accidental expln of PA appears to be in fires. There appears to be uncertainty if explns result if PA bums out of contact with metals. On p 494, Urbanski (Ref 35) states ... 

Shock waves from primers, quite often referred to as brisance or the brisant effect , may cause rupture of propint grains (Refs 19 20). This effect is accentuated at low temps, at which condition the NC grains become more brittle and subject to fracture- This effectively results in the burning of much smaller proplnt particles, radically increasing the burning rate. This then produces very high gun chamber pressures, which have been known to cause guns to expld... 

Modification of the burning rates, pressure exponents, and temp coefficients of burning rate of the fluorocarbon composites has been accomplished with copper, lead, tin, sodium, ammonium and potassium fluoborates sodium, potassium, lithium, lead, copper and calcium fluorides potassium and ammonium dichromate lead and zinc stearate cesium carbonate potassium and ammonium sulfate copper chromite oxides of magnesium, copper and manganese boron zinc dust and carbon black (Ref 75)... 

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