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Show Mixtures with Volatility Differentials OUf interest in volatility differences arises from the following question: if we blend a heavily chlorinated hydrocarbon with a conventional hydrocarbon fuel, should the hydrocarbon fuel be more or less volatile than the chlorinated hydrocarbon? Figure 8 shows typical burning rate profiles of mixtures of 85% C2H2C4 and the alkanes heptane (C7H16), nonane, dodecane (C12H26), and hexadecane. The curves for the less volatile additives (C12H26 and C16H34) have the greatest slopes. The burning rate constants for these mixtures are plotted in Figure 9 along with the rates for pure alkanes. We see that mixture burning rate increases with decreasing volatility of the additive. This interesting and practically significant result is caused by two factors. First, a less volatile additive has a higher boiling point, and hence tends to heat the C2H2C4 component to a higher temperature. This increases the gasification rate. Second, since C2H2Cl4 is more volatile, it is preferentially gasified in the early part of the droplet lifetime. Thus, in the latter part of the droplet lifetime when extinction could occur, the C2H2C4 concentration in the droplet has been reduced enough to delay extinction. Our sampling data confinns that the C2H2Cl4 concentration decreases during the droplet lifetime for the hexadecane additive, increases for the heptane additive, and remains constant for the nonane additive. The final point to note is that when the additive is more volatile than C2H2C4, as in the case of heptane, burning is inhibited. 4. PRACflCAL IMPLICATIONS The following practical implications can be inferred from the present study: (i) A heavily chlorinated hydrocarbon droplet can be burned with the addition of only a small quantity of regular hydrocarbon fuel. This result is obtained from equal volatility mixtures and therefore its application is not restricted to droplet combustion, i.e., may apply to other diffusion flames. (ii) Droplet combustion of a mixture is facilitated when the hydrocarbon fuel additive is less volatile than the chlorinated hydrocarbon. Improving the combustion of a single chlorinated droplet through this blending strategy is a technique that may apply to large scale incinerators in which, according to Mulholland et al. (1986), oversize, rogue droplets escape the spray interior and bum singly. 4 |