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Research Article

Effect of Initial Reactant Temperature on Flame Speeds in Aluminum Dust Suspensions

ORCID Icon, , ORCID Icon, ORCID Icon & ORCID Icon
Pages 1513-1526 | Received 13 May 2020, Accepted 03 Sep 2020, Published online: 12 Oct 2020
 

ABSTRACT

Measurements of how the flame speed in suspensions of metal fuels depends on the initial temperature of the unburned mixture are important for understanding the role of mixture preheat by radiation heat transfer. This preheat can be an important stabilization mechanism for metal dust flames in energetic devices. A newly constructed counter-flow flat-flame metal dust burner allows for the measurement of burning velocities in aluminum-air suspensions preheated to temperatures up to 524 K using Particle Image Velocimetry (PIV). The experimental method was verified by measuring and comparing burning velocities in preheated methane-air mixtures at different fuel-oxygen equivalence ratios with previous experimental data and theoretical predictions. Whereas the flame speed in methane-air mixtures increases by 2.75 times with an increase in temperature to about 524 K, the flame speed in aluminum-air mixtures increases by less than 2 times over the same temperature interval. The independence of the adiabatic flame temperature of aluminum-air flames on the initial temperature of the mixture suggests practically constant reaction rates either for kinetically- or diffusion-controlled aluminum combustion. Thus, the observed moderate dependence of the aluminum-air flame speed on mixture initial temperature can be explained by a cumulative effect of the increased heat diffusivity, decrease in the amount of heat required to reach the particle ignition temperature, and increased flame sensitivity to preheat due to discrete source effects discussed in recent flame models.

Additional information

Funding

Support for this work was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de Recherche du Québec-Nature et Technologies (FRQ-NT), the Canadian Space Agency (CSA) and Tata Steel.

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