Thermodynamic and chemical kinetic characteristics of NTC turnover states

Weiqi Ji, Peng Zhao, Xin He, Chung King Law

Research output: Contribution to conferencePaper

Abstract

This work investigates the thermodynamic and chemical kinetic behavior of the upper and lower turnover states of the Negative-temperature Coefficient (NTC) regime, in which the ignition delay exhibits a local maximum and then a local minimum with increasing temperature. It is shown that the ignition delays vary Arrheniusly with the temperature, while the pressure can also be correlated Arrheniusly with temperature for both turnover states. These two behaviors have been investigated using detailed mechanisms for typical n-alkanes exhibiting NTC, namely n-butane, n-heptane and iso-octane. Further theoretical analyses demonstrate that the upper turnover states result from the competition between the low-temperature chain branching reactions and the decomposition of the intermediate species, which corresponds to a critical value, α, of the ratio of OH production from low-temperature chemistry, and that the pressure dependence of the ignition delay mainly results from the H2O2 decomposition reaction. It is further shown that, for the lower turnover state the first and second stage delays are approximately equal and the change of the second-stage ignition delay due to both pressure and temperature variation is balanced, with the change of the first-stage ignition delay due to its temperature sensitivity. Analytical expressions are derived and are shown to well reproduce the lower turnover states. These thermodynamic and kinetic insights related to both turnover states also achieve quantitative agreement with the literature experimental data of n-heptane ignition delay time.

Original languageEnglish (US)
StatePublished - Jan 1 2016
Event2016 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, ESSCI 2016 - Princeton, United States
Duration: Mar 13 2016Mar 16 2016

Other

Other2016 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, ESSCI 2016
CountryUnited States
CityPrinceton
Period3/13/163/16/16

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Physical and Theoretical Chemistry
  • Chemical Engineering(all)

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  • Cite this

    Ji, W., Zhao, P., He, X., & Law, C. K. (2016). Thermodynamic and chemical kinetic characteristics of NTC turnover states. Paper presented at 2016 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, ESSCI 2016, Princeton, United States.