Combustion multi-phase

Nekrasov, E. A., Tkachenko, V. N., and 2Jakirov, A. E, Diffusive combustion of multicomponent gasless systems forming multi-phase peroducts. Combust. Sci. Tech., 91,207 (1993). 

In contrast to the combustion of gases, the combustion process of condensed substances and, in particular, of polymer substances, has a multi-phase character. Each stage of the initial transformation of a substance correlates with a corresponding value (combustion wave) with specific physical and chemical properties (state of aggregation, temperature range, concentration of the reacting substances, kinetic parameters of the reaction etc.). 

The central thesis of the theory of the non-steady combustion of powders and explosives developed by Ya.B. in this article is the assumption of rapid readjustability of the gas phase of combustion compared to thermal changes in the condensed phase, which allows us to consider the gas phase as quasi-steady. This fundamental property of burning condensed materials allows us not only to significantly simplify the solution of the problem by reducing it to an analysis of the non-steady temperature distribution in the surface layer of the condensed material, but also not to carry out a detailed analysis of the complex structure of the combustion zone above the material (the multi-stage character of the chemical transformation, thermal decomposition, and gasification of the dispersed particles of condensed material and other processes). 

Such questions are answered empirically all too often. A more fundamental approach is needed. In the area of gas-phase kinetics, the developments in the chemistry of large sets of elementary reactions and diffusion in multi-component mixtures in a combustion context are now finding applications in chemical engineering, as mentioned above. In the area of gas-solid reactions, the information flow will be in the opposite direction. A need exists... 

The glycine/nitrate process (GNP) is a self-combustion method using glycine as fuel and the nitrates of metal components of the material to be synthesized as oxidant, which can prepare a high specific surface powder with single phase composition in very short time. It is especially appropriate for the fabrication of multi-component system such as doped perovskite compounds [11]. Moreover, this process is easily operated and cost-effective. 

Nine compositions with the diamond concentration of 3, 5, 7, 9, 10, 12, 15, 20, 25 mass % were mixed with the charge Ti-C-Mo to produce multi-layered semi-products. The ready mixtures were placed layer-by-layer into a pressform in the following order diamondless layer weighing 25,5 g 3 mass % diamond layer, weighing 10 g 5 % layer -10 g 7 % layer - 10 g 9 % layer - 9,9 g 12 % layer - 9,9 g. After densification pellets were obtained 48 mm in diameter with the thickness of the layers 5.0, 2.0, 2.0, 2.0, 2.0, 2.0 mm correspondently. Multilayered pellets with the diamond concentration from layer to layer as much as 0, 5, 10, 15, 20, 25 % mass were prepared similarly. The final pellet was placed into a reactional mold. An SHS reaction was initiated from the lateral face of the cylindrical pellet by a tungsten spiral. After accomplishment of the combustion reaction and propagation of the combustion synthesis wave, the hot SHS-products were compacted in a hydraulic press at P > 400 MPa for no more than 10 s. The time of exposure to pressure was chosen dependent on the combustion temperature and reology of the products, e.g., on their plasticity and the amount of the liquid phase formed. Usually this time is 0.5 -4 2 sec. SHS-products were cooled at the room temperature. 

Some studies, such as Fujima et al., concentrate on one aspect of this multi-faceted problem [105]. For example, they set out to show the relationship between sulfur capture, particle concentration, and firing conditions. Boyd and Friedman, on the other hand, summarize the effect of many process variables on combustion performance [107]. The final DOE report concerning the NUCLA experimental program concludes that radial gas mixing is poor Gas samples withdrawn across the radius of the reactor at two heights 7 m apart had similar concentration profiles [106]. They also found that secondary air had little effect on gas phase hydrodynamics... 

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