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Dynamics of Triple-flames in Ignition of Turbulent Dual Fuel Mixture: a Direct Numerical Simulation Study

Jin, T; Luo, KH; Wang, X; Luo, K; Fan, J; (2018) Dynamics of Triple-flames in Ignition of Turbulent Dual Fuel Mixture: a Direct Numerical Simulation Study. Proceedings of the Combustion Institute 10.1016/j.proci.2018.09.018. (In press).

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Abstract

Pilot-ignited dual fuel combustion involves a complex transition between the pilot fuel autoignition and the premixed-like phase of combustion, which is challenging for experimental measurement and numerical modelling, and not sufficiently explored. To further understand the fundamentals of the dual fuel ignition processes, the transient ignition and subsequent flame development in a turbulent dimethyl ether (DME)/methane-air mixing layer under diesel engine-relevant conditions are studied by direct numerical simulations (DNS). Results indicate that combustion is initiated by a two-stage autoignition that involves both low-temperature and high-temperature chemistry. The first stage autoignition is initiated at the stoichiometric mixture, and then the ignition front propagates against the mixture fraction gradient into rich mixtures and eventually forms a diffusively-supported cool flame. The second stage ignition kernels are spatially distributed around the most reactive mixture fraction with a low scalar dissipation rate. Multiple triple flames are established and propagate along the stoichiometric mixture, which is proven to play an essential role in the flame developing process. The edge flames gradually get close to each other with their branches eventually connected. It is the leading lean premixed branch that initiates the steady propagating methane-air flame. The time required for the initiation of steady flame is substantially shorter than the autoignition delay time of the methane-air mixture under the same thermochemical condition. Temporal evolution of the displacement speed at the flame front is also investigated to clarify the propagation characteristics of the combustion waves. Cool flame and propagation of triple flames are also identified in this study, which are novel features of the pilot-ignited dual fuel combustion.

Type: Article
Title: Dynamics of Triple-flames in Ignition of Turbulent Dual Fuel Mixture: a Direct Numerical Simulation Study
DOI: 10.1016/j.proci.2018.09.018
Publisher version: https://doi.org/110.1016/j.proci.2018.09.018
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Dual-fuel combustion, Autoignition, Low-temperature combustion, Triple flame, Direct numerical simulation
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: http://discovery.ucl.ac.uk/id/eprint/10058868
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