Low Pressure Extrapolations for Soot Oxidation Rates

摘要

The carbon oxidation rates of Nagle and Strickland-Constable are routinelyapplied in the flame community to determine 500 oxidation by molecular oxygen. These rates were experimentally determined at temperatures from 1000 to 2000 C (1273 to 2273 K) and at oxygen partial pressures from 0.1 to 0.6 atm and then curve fit. For typical laboratory flames, oxygen partial pressures may be significantly lower than 0.1 atm. Frequently, researchers will extrapolate the Nagle, Strickland-Constable (hereafter referred to as NSC) curve fits to these lower oxygen partial pressures to determine the molecular oxygen contribution to the overall soot oxidation rate. It is shown that the NSC curve fits exhibit nonphysical behavior at pressures 0.05 atm (depending on the temperature). This behavior is revealed when the oxidation rates are transformed to collision efficiencies. At at fixed temperature, the oxidation rate drops faster than the collision rate as the pressure is reduced. At typical flame conditions, extrapolation of the NSC curve fits yields collision efficiencies that may be an order of magnitude too low.