Burn Rate Description

A number of burn rate models have been developed for MTV by Cudzilo, Kubota, Kuwahara and Koch. 

Kubota s model is based on the assumption that the heat generation with MTV occurs exclusively in the gas phase [8]. Thus, heat transfer from the gas phase to the burning surface, qg s (W mm ), is the determining factor for the burn rate [6-8]  

A similar yet different bum rate model has been applied by Kuwahara et al. [9j. They assumed that 

Unlike Kubota [8], Kuwahara [9] took into account energy-releasing reactions in the condensed phase as well. However, his analytical model requires only burn times and does not need to solve the heat and mass balance equations for this case. 

Q g the enthalpy of fusion of Mg Tf the burning surface temperature To the ambient temperature Qk the conductive heat flux Qp the radiative heat flux and Qj the heat flux from condensed phase reaction. 

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Test specimens for burning rate data were 1.27 x 15.24 x 0.318 cm. Descriptions of burning rate and other flammabiHty characteristics developed from small-scale laboratory testing do not reflect hazards presented by these or any other materials under actual fire conditions. 

The basic assumptions in the following description of the burning rate modelare One-dimensional burning Steady-state burning at a fixed pressure... 

Both above methods can be used not only for detn of combustion limits, but also for detn of burning rates as will be explained further in this description... 

Injector design determines the physicochemical processes occurring in liquid propellant rocket engines. A complete quantitative description of the processes in liquid rockets is impossible because of our limited understanding of chemical reaction mechanisms and rates. The use of similarity principles simplifies the solution of theoretical combustion problems and is described for channel flow with chemical reactions and for diffusion flames over liquid droplets involving two coupled reaction steps. We find the new result that the observed burning rate of a liquid droplet is substantially independent of the relative rates of the coupled reactions. 

A theory for calculation of burning rates for composite propellants is even more difficult to devise because of the intermediate mixing process necessary. Recent experimental work has led to a semitheoretical description of the structure of composite propellant flames (A2, C5, S7, S8). It is possible to vaporize each of the ingredients of a composite propellant by the application of a heat flux. Experimentally it is possible to measure... 

Harvey, "Improved Technique for the Determination of Burning Rate vs Pressure Relationship in Solid Propellants , Allegany Ballistics Laboratory ABL/B-17(l958)(Not used as a source of info) 15)Warren(1958), 90-91 177-8 l6)K.Schriver, Explosivst 1959, 260-2 (Description and drawing of an apparatus for the detn of burning rates of proplnts at constant pressure)... 

The two-dimensional nature of the process initially forced semiempiricism upon theoretical descriptions of erosive burning. The first proposed empirical burning-rate formulas were of the form... 

A two-zone engine simulation, which divides the cylinder volume into burned and unburned regions, each spatially uniform, provides the simplest predictive description. In early work Hirst and Kirsch [155] applied the Shell model to the unburned region and showed that autoignition in a CFR engine could be predicted, and the model used to investigate the factors that influence fuel sensitivity (Section 7.2.3). The burning rate, a... 

A similar approach was applied to study the combustion characteristics of HMX monopropellant. A detailed description of the theoretical formulation and results is available in Ref. 37. Figure 10 shows the pressure sensitivity of the HMX burning rate. Good agreement was obtained with the experimental measurements by Zenin [11] and Atwood et al. [21]. The pressure exponent n in Eq. (34) was about 0.88, with the pre-exponential factor a equal to 0.35 for T, = 293 K. The temperature sensitivity of burning rate defined by Eq. (35) at various pressures is shown in Fig. 11. There were noticeable discrepancies... 

Note 1 ASTM s policy is not to use descriptive terms such as nonflammable, flame retardant, self-extinguishing, non-burning, and similar. According to ASTM, results of any of fire test methods must be described in numbers, such as flame spread index of 75, or flame spread index below 200, or a burning rate of... 

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