Sensitivity of flame structure and flame speed in numerical simulations of laminar aluminum dust counterflow flames

Aluminum dust counterflow flames are investigated numerically using a two-stage model including the effects of interphase heat transfer, phase change, heterogeneous surface reaction (HSR), oxide cap growth, homogeneous combustion and radiation. The numerical model is first validated by simulating the aluminum dust counterflow flames of McGill University [Julien et al., 2017]. The results show that the particle velocity profile is consistent with the experimental results, and the error in the gas phase velocity caused by the use of aluminum particles as tracers in the experiment is analyzed. Then, further validation is conducted by comparison of the flame speed, and the predicted results agree well with the measurements. The flame structure of the aluminum dust counterflow flame is analyzed, and intermediate product (AlO) is observed to present a discrete distribution in space due to the nature of heterogeneous combustion. Different terms in the particle energy equation are analyzed, and the results indicate that the HSR plays an important role in the late preheating stage, while the interphase heat transfer dominates the rest of the conversion process. Under the assumption of unity Lewis number, the interphase heat/mass transfer models are found to have a great impact on the flame for a particle size smaller than 10 µm. With increasing particle sizes, the flame speed decreases, and most particles with a diameter of 12 µm cannot be fully burnt in the flame under the studied conditions. The effect of the strain rate on the flames is investigated with different particle sizes and unstretched reference flame speeds are obtained by linear extrapolation of the predicted results. Finally, a sensitivity analysis of the parameters of the heterogeneous surface reaction model is conducted.