Results of Reactivity Mapping Studies through the Negative TemperatureCoefficient Region of Propane at Pressures from 5 to 15 atm

摘要

A pressurized flow reactor (PFR) has been constructed for kinetic studies ofhomogeneous gas-phase hydrocarbon oxidation in the low to intermediate temperature regimes. The design of the flow reactor provides the ability to study gas-phase kinetics free from transport effects and temperature gradients at pressures up to 20 atm. A series of experiments designed to map the reactivity of hydrocarbon/air mixtures over a range of temperatures (600-900 K) and pressures (5-14 atm) has been conducted on the PFR using propane/air mixtures. These mapping experiments examine the effect of pressure on the overall tendency of hydrocarbons to oxidize by using carbon monoxide measurements as an indicator of the degree of oxidation or autoignition tendency. The reactivity mapping technique using CO concentration has been validated by comparison of results with detailed species measurements. The mapping results indicate a narrow temperature range extending from 640 to 770 K in which the rate of hydrocarbon oxidation reaches a peak and then diminishes. This behavior is consistent with negative temperature coefficient (NTC) behavior, where low-temperature oxidation nearly stops as temperature is increased above a threshold value corresponding to the transition to intermediate temperature oxidation. The temperature range over which NTC behavior occurs is observed to shift to higher temperatures and to broaden as pressure is increased. NTC region broadening is indicated by a shift of the starting temperature to lower temperatures, and a shift of the ending temperature to higher temperatures as the pressure is increased.