Abstract

The structure and dynamics of laminar nonpremixed dimethyl ether (DME)/air coflow flames were investigated at elevated temperatures and pressures. Computations with detailed chemistry were performed for DME and heated coflow air at 30 atm with uniform but sinusoidally oscillating inlet velocities. A normalized displacement velocity was defined to differentiate flame propagation from autoignition, and this definition was validated against the steady cases previously studied by Deng et al. (Combust. Flame, 162, 2015). In the oscillating reacting flow, transition between a multibrachial autoignition front and a tribrachial flame occurs periodically. However, unlike the harmonic velocity oscillation, the combustion mode transition is hysteretic. The oscillation cycle starts with the largest inlet velocity, with the multibrachial thermal structure, located downstream, being governed by autoignition chemistry. As flow velocity decreases, the autoignition front moves upstream and transitions to a tribrachial flame near the lower velocity limit, similar to the steady flow, since autoignition chemistry becomes weaker with decreasing upstream residence time. As the flow velocity increases again, the tribrachial flame is convected downstream, and, ultimately, due to radical and heat accumulation in time, autoignition eventually occurs and becomes the dominant pathway. The finite induction time for autoignition results in the hysteretic behavior during the decreasing- and increasing-velocity cycles.

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

    Deng, S., Zhao, P., Mueller, M. E., & Law, C. K. (2016). Autoignited DME/air coflow flames in oscillating flows. Paper presented at 2016 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, ESSCI 2016, Princeton, United States.