Pyrolysis rates

MAKEFIRE models the growth, steady state, and decay phases of the each fuel element in the compartment. It consists of routines that create and edit fire files that specify the fire heat release rate and fuel pyrolysis rate as a function of time. 

Another contributing mechanism is the direct cooling of hot propellant surface by contact with the injected fluid. The fluid should cause the decomposing surface to reduce its pyrolysis rate to a point where combustion cannot be sustained. In addition, the presence of water on the surface would obstruct heat transfer from the gas-phase reaction zones to the solid surface, thus augmenting the cooling of the surface. Proponents of these two approaches have correlated the injection data on the basis of mass of fluid required per unit area of surface, but theoretical justifications for the use of this particular correlating parameter have not been presented. 

Figure 3. The mass pyrolysis rate, kg/sec, predicted by FIRST ...

On Figure 3 is shown (------------) the mass pyrolysis rate used in... 

The increase in char yield, the decrease in exothermicity, and the delay of the peak oxidative-pyrolysis rate by the zinc... 

Thermogravimetric analysis (TGA) measures cellulose pyrolytic mass loss rates and activation parameters. The technique is relatively simple, straightforward and fast, but it does have disadvantages. One disadvantage is that determination of the kinetic rate constants from TGA data is dependent on the interpretation/analysis technique used. Another disadvantage of TGA is that the rate of mass loss is probably not equivalent to the cellulose pyrolysis rate. 

Thermogravimetric analysis (TGA) has often been used to determine pyrolysis rates and activation energies (Ea). The technique is relatively fast, simple and convenient, and many experimental variables can be quickly examined. However for cellulose, as with most polymers, the kinetics of mass loss can be extremely complex (8 ) and isothermal experiments are often needed to separate and identify temperature effects (9. Also, the rate of mass loss should not be assumed to be related to the pyrolysis kinetic rate ( 6 ) since multiple competing reactions which result in different mass losses occur. Finally, kinetic rate values obtained from TGA can be dependent on the technique used to analyze the data. 

Cellulose crystallinity has been shown to affect pyrolysis rates and Ea s (2,26,27). The initial low temperature decomposition is reported to occur first in the amorphous region (5,26,27). Also,... 

Table I. Comparison of Cellulose Pyrolysis Rates (Rates of Weight Loss) Rnalyzed by Differential Methods for Control...

Table II. Activation Parameters for Pyrolysis (Rate of Weight Loss) for Untreated Cellulose Samples Based on Data in Table I...

The slope of the volatile = f(final temperature) curve in Figure 1 amounts to volatile increments at particular temperature steps, and is a measure of the pyrolysis rate. The slopes have been obtained by differentiating the volatile curve of Figure 1 for drafting Figure 2. For example, volatiles at 200"C equal 4.6%, and 7.7% at 220"C that is a 3.1% increment in the 20"C step and amounts to a... 

The evidence suggests that temperature is the major parameter governing the extent to which a given fuel will soot under a particular flame condition or combustion process. As emphasized earlier, increasing the temperature under premixed fuel-air conditions decreases soot production, whereas the opposite is true for diffusion flames. The main effect of varying pressure must be manifested through its effect on the system temperature. Fuel pyrolysis rates are a... 

The presence of halogen additives substantially increases the tendency of all fuels to soot under diffusion flame conditions [69], The presence of H atoms increases the soot pyrolysis rate because the abstraction reaction of H + RH is much faster than R + RH, where R is a hydrocarbon radical. Halogenated compounds added to fuels generate halogen atoms (X) at modest temperatures. The important point is that X + RH abstraction is faster than H + RH, so that the halogen functions as a homogeneous catalyst through the system... 

The pyrolysis rate is also a function of the heat flux from different heat sources during the course of the batch combustion. 

Table 1. Pyrolysis of Silica-Iimnobilized Ph(CHj)jPh at 375°C Influence of Surface Composifion on Pyrolysis Rate...

The condensed phase mechanism was explained taking into account the decrease of the pyrolysis rate of polypropylene BiCl3 could catalyze the condensation between chloroparaffin and polypropylene by addition to chain end double bonds (Equation 4.25) formed either in reaction (Equation 4.22) or in chain scission occurring during volatilization of polypropylene 31... 

Figures 15.8 and 15.9 illustrate examples of how cone calorimeter data can be used in the development of flame-retarded materials. PA 66-GF without Pred showed typical fire behavior for noncharring polymers containing inorganic glass fiber as inert filler,69 when high external heat flux is applied. The shape of the HRR curve is divided in two different parts. In the beginning, the surface layer pyrolysis shows a sharp peak, followed by a reduced pyrolysis rate when the pyrolysis zone is covered by the glass fiber network residue layer. When Pred was added, the PA 66-GF samples were transformed into carbonaceous char-forming materials, which led to a...

Predicted Surface Temperature History in the Cone for TGA Obtained Pyrolysis Rate... 

The basic assumption inherent to heat transfer limited pyrolysis models is that heat transfer rates, rather than decomposition kinetics, control the pyrolysis rate. Consequently, thermal decomposition kinetics do not come into play, other than indirectly through specification of Tp. This approximation is often justified on the basis of high activation energies typical of condensed-phase pyrolysis reactions, i.e., the reaction rate is very small below Tj, but then increases rapidly with temperature in the vicinity of Tp owing to the Arrhenius nature, and the high activation energy, of the pyrolysis reaction. 

In kinetically limited models, the pyrolysis rate is no longer calculated solely from a heat balance at the pyrolysis front. Instead, the rate at which the condensed-phase is volatilized depends on its temperature. This gives a local volumetric reaction rate (kg/m3-s) by assuming that all volatiles escape instantaneously to the exterior gas-phase with no internal resistance, the fuel mass flux is obtained by integrating this volumetric reaction rate in depth. One consequence is that the pyrolysis reaction is distributed spatially rather than confined to a thin front as with heat transfer limited models and the thickness of the pyrolysis front is controlled by decomposition kinetics and heat transfer rates. For a pyrolysis reaction with high activation energy or for very high heat transfer rates, the pyrolysis zone becomes thin, and kinetically limited models tend toward heat transfer limited models. 

TABLE 1. Mass of the soot (g/g Mg2Ni) formed at various temperatures of C2H4 pyrolysis (rate of volume flow of feeding gases 40 cm3/min) and Ar H2 ratios... 

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