The dependence of NTC behavior on the equivalence ratio and nitrogen fraction in cool flame region

Abstract

Using propane (which issues a cool flame at low temperature oxidation) as the archetype of the higher alkanes, comprehensive computational research, with detailed mechanisms and theoretical analysis, was implemented to investigate the controlling points of the cool flame region and the negative temperature coefficient (NTC) behavior. It found that the temperatures of the two turnover points steadily decreased with the increase of equivalence ratio. The pressures of the upper turnover points decreased more when the equivalence ratios were less than 2.0, but the pressures of the lower turnover points showed no notable decrease. With an increase in the nitrogen fraction, the explosion limit curve shifted to the high-pressure region. However, the temperature variations of the turnover points were relatively small, and the dependence of the NTC degree on the equivalence ratio and the nitrogen molar fraction was derived. The slope of the NTC line showed a power law dependence on the equivalence ratio and was almost unrelated to the nitrogen ratio. To elucidate the key control mechanism, sensitivity analyses of the turnover points were performed.