Mathematical simulation of heterogeneous detonation of coal dust in oxygen with allowance for the ignition stage

Abstract

A consistent physicomathematical model that describes ignition and detonation combustion of a gas suspension of coal-dust particles is developed. The model is based on the concepts of the two-velocity two-temperature continuum of mechanics of heterogeneous media with allowance for reduced reactions of pyrolysis, combustion of volatiles, and combustion of the coke residue. The model is verified with the use of available experimental data on the dependence of the detonation velocity on the initial concentration of the discrete phase and the dependence of the ignition delay on the Mach number of the incident shock wave. An analysis of ignition of the gas suspension of bituminous coal in shock waves shows that the stage of ignition proceeds under conditions of both temperature and velocity nonequilibrium. The influence of particle heating due to stagnation temperature on devolatilization dynamics and ignition delay is established. Examples of computed flow structures behind shock and detonation waves with allowance for the ignition stage are presented.

Mathematical Modeling of Dispersed Condensed Substance Ignition by Local Energy Source

“…It is known a numerical and an experimental research results of heat and mass transfer processes at single carbon particle or gas-coal dust mixture ignition in air flow heated to high temperatures [16][17][18][19]. But there is no information about ignition characteristics even for widely used dispersed combustible substances at packed state by small-size local energy source with limit heat content.…”

Mathematical modeling of heterogeneous detonation in gas suspensions of aluminum and coal-dust particles

“…A detailed description of the model, which is a generalization of the model developed in [4], can be found in [9]. It should be noted here that the ignition and combustion stages in the model [9] are described by identical equations, but the expressions for the quantities determining the changes in mass of the species are different. The accommodation coefficients determining the fraction of heat spent on particle heating are also different.…”

“…The reaction constants were borrowed from [12][13][14][15] for a similar type of coal. Figure 1a shows the calculated ignition delays for several particle concentrations [9] (solid curves) and the experimental data [6] (points). Note that the results are accurately presented in a semi-logarithmic scale by straight lines, which reflects the Arrhenius character of the ignition process.…”

“…Note that the results are accurately presented in a semi-logarithmic scale by straight lines, which reflects the Arrhenius character of the ignition process. It was also found [9] that the dynamics of emission and combustion of volatiles determines the breakdown of thermal equilibrium in the particle. Thus, bituminized coal was found to have a mixed (homogeneous-heterogeneous) type of ignition in accordance with the classification developed in [16].…”

“…The calculated and experimental data are compared in Fig. 1b: the solid and dashed curves are the results calculated for 50-and 25-μm particles, respectively; λ * = (ρ 30 + ρ 20 )/ρ 10 ; the subscripts refer to the [9] and experiments [6]; (b) detonation velocity u0; the solid and dashed curves show the results calculated for particles 50 and 25 μm in size, respectively; the points are the experimental data [3].…”