Heat-release rates accompanying the nonisothermaloxidation of organic compounds

Heat-release rates in propane oxidation have been evaluated by direct measurements ofself-heating of the reactants in a well-stirred reactor. By using a very fine thermocouple (1.25×10^-3 cm diam) with suitably rapid response, the temperature excess has been followed through slow reaction and oscillatory cool flames. Nonisothermal characteristics under well-stirred conditions have been plotted on a P-T_oignition diagram. Three principal regions are defined: there is a closed zone of undamped oscillations bounded on the low-temperature side by slow reaction and on the high-temperature side by highly damped oscillations. The latter give way to a monotonic approach to the steady state (similar to slow reaction) at still higher temperatures. No hot ignitions have been studied in this work. Heat-release rates at a steady state are related to temperature excesses through the heatlossproperties of the reactor. Three independent methods have been used to evaluate the heat-transfer coefficient for our reactor, giving a mean value of 85 Watts ^oK^-1 m^-2. For propane oxidation, heat-release rates have been plotted for different initial pressures, as a function of the steady-state reacting-gas temperature. With increasing temperature, the rates rise to maxima and then fall to minimum values with a very strong negative dependence on temperature. Undamped oscillations are associated with the positive temperature-dependent zone of each rate curve, but these become highly damped as the heat-release rate passes throught its maximum and then decreases.