Combustion hysteresis and vaporization interaction of two burning droplets with different sizes

The multiple-path on combustion hysteresis and vaporization interactive factor of two droplets in a high-temperature flow stream with mutual interaction is numerically analyzed, to recognize the droplets burning situation in sprays. The conservation equations of mass, momentum, energy, and species in the gas-phase are solved by utilizing a body-fitted technique in association with curvilinear coordinate system. By increasing the ambient temperature from lower to higher value and then reversing, the obtained results illustrate that the hysteresis effect of the two-droplet system can be classified into four different types, depending intrinsically upon the droplet size ratio. As a whole, as the droplet size ratio decreases, the hysteresis effect will be contributed from the leading droplet to the trailing one. Within this transition, the effect can be induced by both of the leading and trailing droplets such as the droplet size ratio of 0.5. This results in a double-hysteresis effect being characterized. Accordingly, an extensive demonstration on combustion hysteresis effect is conducted. On the other hand, the droplet interactive factor is taken into consideration to account for the vaporization rate of a convective droplet influenced by droplet mutual interaction. The results elucidate that, no matter what the upper- or lower-branch is the droplet's vaporization rate is always suppressed by the interaction in the lower and the higher ambient temperatures. However, under certain conditions with moderate ambient temperature, such as a flame is stabilized between droplets and the droplet size ratio is not very large, unlike the stationary many-droplet systems, the existence of the leading droplet is conducive to vaporization of the trailing one. Therefore, a more realistic insight for burning droplet in sprays is outlined.