TWO FRONT OF COMBUSTION AROUND FUEL PARTICLE IN HYBRID ATMOSPHERE

Analytic solution of the problem of stationary spherically symmetric double-front diffusion combustion around a particle boiling fuel (with infinite density to ensure the stationarity of combustion) in a hybrid atmosphere was derived. Under the hybrid atmosphere was understood to be a mixture of air and combustible gas, present in a quantity smaller than the lower concentration limit of the flat flame propagation through gas-air mixture (LELg). The nearest to particle flame front (A) has the same nature as the single diffusion flame front around the particle burning in clean air (Varshavsky, 1945). In the second flame front (B) there is a stable diffusion combustion of gas-air mixture. Main assumptions facilitate the representation of results in analytical form, was to neglect the influence of gravity, heat loss by radiation, the real thickness of the diffusion flame, the dependence of the thermophysical parameters on the temperature. It was assumed that the temperature of the flame at the limit of diffusion combustion in front B coincides with the temperature of the flat flame in the gasair mixture at LELg. The Lewis number equal to 1 for all components of the gas phase apart from the combustible gas, in which this parameter (Le3) can take different values. The results are illustrated on two variants of the original data. In the first variant, all combustible gaseous components identical to typical hydrocarbon (ethane). The difference between the second variant of the modeling from the first variant was only the fuel gas for which diffusion capacity, LELg and the burning temperature, borrowed from hydrogen. Dependencies of the size and temperature of the diffusion flames on the content of combustible gas in the air and the particle radius shown in the graphic form for both versions. The geometric similarity of the fields of temperature distribution in space was absent for particles with radius of the order of and less than 20 ,m. As in the case of unstable stationary diffusion flame in a homogeneous combustible mixture (Zeldovich, 1944) when Le3 > 1 in the area bounded by the front surface B, it was noted superadiabatic temperature. The stationary solution of the task was absent when the concentration of combustible gas exceeds LELg
Le3. The function of the temperature distribution in the space between the fronts Aand B linearly increased with the increase of the content of combustible gas. The last rule was used for the quantitative explanation of the dependence of the lower concentration limits of flame propagation in dispersive component (ÍÊÏÐs) on the content of combustible gas in the turbulent hybrid dust – combustible gas-air mixture, including an explanation of the particular case, when the combustible gas is hydrogen. Due to the lack of a theory of turbulent combustion of dust-air mixture in this application used reasonable assumptions and known experimental dependence ÍÊÏÐs of dust-air mixture on the initial temperature.