Effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane

Haisheng Di, Xin He, Peng Zhang, Zhi Wang, Margaret S. Wooldridge, Chung King Law, Cuiping Wang, Shijin Shuai, Jianxin Wang

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Abstract

Experimental and numerical studies have been performed on the thermal and chemical effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane. Experiments were conducted using a recently developed rapid compression machine in the temperature range of 600-850K. Three buffer gases were studied including nitrogen (N2), argon (Ar), and a mixture of Ar and carbon dioxide (CO2) at a mole ratio of 65.1%/34.9%. Iso-octane was studied at 20bar, φ=1, and a dilution level of buffer gas to O2 of 3.76:1 (mole ratio). n-Heptane was studied at 9bar, φ=1, and a dilution level of buffer gas to O2 of 5.63:1 (mole ratio). For experiments where two-stage ignition was observed, the buffer gas composition had no impact on the first-stage ignition time but, as expected, it caused differences in the total heat release, pressure and temperature rise after the first-stage ignition. As a consequence, significant differences were observed for the total ignition delay time as a function of the buffer gas composition, with up to 40% and 42.5% faster total ignition time for iso-octane and n-heptane, respectively, by using Ar instead of N2. The chemical effects of the buffer gas composition were studied experimentally by comparing the results of the N2 and Ar/CO2 (65.1%/34.9%) mixtures, recognizing that while the Ar/CO2 mixture has the same heat capacity as N2, its predicted combined third-body collision efficiency is about 76% higher than N2. The experimental results showed negligible chemical effects on the first-stage and total ignition delay times. Numerical simulations were carried out over a wider range of temperatures for pure N2, Ar, and CO2 as buffer gases. Results showed that thermal effects are very pronounced and dominated at the negative temperature coefficient and two-stage ignition conditions, which is consistent with the experimental results and previous studies in the literature. However, the simulation results also showed at temperatures higher than 850K, the chemical effects of CO2 became more important than the thermal effects.

Original languageEnglish (US)
Pages (from-to)2531-2538
Number of pages8
JournalCombustion and Flame
Volume161
Issue number10
DOIs
StatePublished - Oct 2014

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Physics and Astronomy(all)

Keywords

  • Buffer gas
  • Ignition delay time
  • Iso-octane
  • N-Heptane
  • Rapid compression machine

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  • Cite this

    Di, H., He, X., Zhang, P., Wang, Z., Wooldridge, M. S., Law, C. K., Wang, C., Shuai, S., & Wang, J. (2014). Effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane. Combustion and Flame, 161(10), 2531-2538. https://doi.org/10.1016/j.combustflame.2014.04.014