Combustion intensification

However, in this paper Ya.B. went further and considered the chemical kinetics. He determined the limit of intensification of diffusion combustion, which is related to the finite chemical reaction rate and the cooling of the reaction zone, for an excessive increase of the supply of fuel and oxidizer. If the temperature in the reaction zone decreases in comparison with the maximum possible value by an amount approximately equal to the characteristic temperature interval (calculated from the activation energy of the reaction), then the diffusion flame is extinguished. The maximum intensity of diffusion combustion, as Ya.B. showed, corresponds to the combustion intensity in a laminar flame of a premixed stoichiometric combustible mixture. 

Returning from dimensionless variables to the conventional dimensional unburned fuel concentration c, temperature T, chemical reaction rate k, and time t, we rewrite the conditions of extinction at the limit of extinction due to intensification of combustion (disruption of combustion when the jet velocity is increased and r is decreased—adiabatic extinction) ... 

For laminar combustion on the basis of this investigation we are able to go further and determine the limits of intensification of combustion which result in the fact that for a large fuel and oxygen supply rate to the flame surface, the chemical reaction rate proves to be insufficient. 

The feasibility limit of intensification of combustion of non-premixed gases was found, and is dependent on the limiting rate of the chemical reaction. In order of magnitude this limit is close to the combustion rate of the stoichiometric mixture. 

For a sufficient increase in the braking and heat transfer time we may imagine that the slowest reactions, e.g., combustion of dusts, will keep up with the detonation wave and can lead to detonation. Large losses in mixtures in which the detonation velocity is larger turn out to be related to intensification of the turbulent heat transfer and braking for an increase in the velocity proportional to D. 

It is clear that intensifying combustion is just to shorten the time needed for complete combustion tb. It can be seen from Eq. (8.13) that tb is positively proportional to the square of the radius of the droplet, rp. Therefore the most effective measure for the intensification of combustion is full atomization of the liquid fuel to increase its dispersity, i.e. reducing the size of the droplet. For heavier oils fine atomization is of more importance because of their large densities /, as can be predicted by Eq. (8.13). 

The next important step in the elucidation of the role of the thermal factor in the mechanism of the phenomena in question was studying the effect of the sample size on the characteristics of the autowave process. Can the self-sustained wave regime of conversion be made impossible by intensification of heat release at the expense of a decrease in the diameter of a cylindrical sample containing the reactant mixtures By analogy with combustion physics, the question of a critical sample size has been raised. 

This example can be applied to a broad class of catalytic reactions but it is much more obvious for partial oxidation reactions where secondary reactions (total combustion) result in a dramatic decrease of selectivity. This is the case with methanol decomposition and methane conversion, where the intensification of gas-phase catalytic operations in micro- or nanochannels clearly appears. 

Kolodziej A, Lojewska J. Short-channel structured reactor for catalytic combustion Design and evaluation. Chemical Engineering and Processing Process Intensification 2007 46 637-648. 

The foregoing indicates that the ideal process characteristic for the application of intensification is that the reaction or phase change kinetics should be as fast as possible. If we regard the H2/O2 rocket motor as a chanical reactor, its performance is very definitely limited by heat and mass transfer considerations. Nevertheless the very fast combustion kinetics allows residence times of several milliseconds and... 

It has been shown within the fiamewoik of strange (anomalous) diffusion conception that instantaneous jumps ( Levy s flights ) of combustion front from one region of polymeric material into another increase sharply this material flammability. Distanee between nanofiller particles decreasing reduces such jumps intensity, increasing thereby material flame-resistance. The fractal time of combustion enhancement results in Levy s flights intensification and vice versa. 

K.I. Shchelkin, Intensification of weak shock waves by a cellular flame. Combust. Explos. Shockwaves 2(2), 20-21 (1966)... 

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