Particle size influence on the aluminum combustion dynamics in 1-m³ chamber

Introduction. The results of a standard study of the explosibility of aluminum air suspensions (AAS) can contribute to the development of AAS combustion physics. In particular, a complex of information about the polydispersity and of the AAS low explosion limit values in a 1-m³ chamber made it possible to determine the maximum particle size of the explosive fraction of a polydisperse sample d^*_m,t ≈ 40–50 µm (Poletaev, 2014). In the present work, a relationship is established between the AAS combustion dynamics in a 1-m³ chamber and persion. The dispersity of sample particles is described by the mass-average particle size of its explosive fraction (d^*₅₀), in contrast to the works of other researchers who use the mass-average size of all particles (d₅₀).

Initial data. Known information about the dispersity and explosion parameters of 15 aluminum samples studied in a 1-m³ chamber was used. The continuous particle size distribution functions necessary for calculating d^*₅₀ were represented by the Rosin – Rammler distributions filling the gaps between the discrete data of the sieve analysis of the samples.

Combustion dynamics. The dynamics of AAS turbulent combustion in a 1-m³ chamber is represented by the maximum air suspension burn-up rate U_b. U_b was calculated using the formula (Kumar, 1992) intended for gas-air mixtures by substituting the AAS explosion parameters into this formula.

Results and its discussion. A plot of the d^*₅₀ U_b complex versus d^*₅₀  is shown. The average value of the complex (≈ 33 µm·m/s) is constant in the range 10 ≤ d^*₅₀  ≤ 35 µm. The latter is typical for the product of the particle size and the normal velocity of the laminar flame in AAS (Ben Moussa, 2017) and indicates the similarity of the effect of particle dispersion on the dynamics of turbulent and laminar combustion of AAS.

Conclusions. The dispersion of an explosive polydisperse aluminum sample is determined by the average particle size of the explosive fraction of the sample d^*₅₀. The similarity of the combustion patterns indicates a relationship between the mechanisms of laminar and turbulent flame propagation in AAS.

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