First-stage ignition delay in the negative temperature coefficient behavior: Experiment and simulation

Peng Zhang, Weiqi Ji, Tanjin He, Xin He, Zhi Wang, Bin Yang, Chung King Law

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The existence of the first-stage ignition delay (FID) negative temperature coefficient (NTC) behavior was confirmed by rapid compression machine experiments using iso-octane and methyl-cyclohexane. The first-stage NTC behavior of iso-octane is observed in the temperature range 757-782K under 20bar and φ=1. For methyl-cyclohexane, the observed first-stage NTC temperature range is 750-785K under 15bar and φ=0.5. In further iso-octane experiments, the FID is found to be sensitive to the O2 concentration and insensitive to the dilution gas and fuel concentrations. The effects of the FID and its NTC behavior on the total ignition delay NTC were analyzed using a detailed n-heptane mechanism. The contributions to the total ignition delay NTC from the reduced second-stage initial temperature, pressure, and less reactive species pool, together with the NTC of FID were discussed quantitatively. For the first-stage NTC behavior, five competing reactions were identified as being important based on sensitivity analysis, reaction pathway analysis, and simplified mechanism method. They are the backward reaction of second O2 addition, RO2 ⇔ alkene+HO2, QOOH ⇔ cyclic-ether+OH, QOOH ⇔ alkene+HO2, and the beta scission reaction of the alkyl radical. Their competition with the low-temperature branching channel finally leads to the first-stage NTC behavior.

Original languageEnglish (US)
Pages (from-to)14-23
Number of pages10
JournalCombustion and Flame
StatePublished - May 1 2016

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Chemical Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology
  • General Physics and Astronomy


  • First-stage ignition
  • Low-temperature mechanism
  • Negative temperature coefficient
  • Rapid compression machine


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