### Abstract

We investigated the local flame speed of a two-dimensional, methane-air triple flame in a rectangular burner. The velocity fields and the concentration profiles were measured with particle image velocimetry and the Rayleigh scattering method, respectively. There was a requisite combination of initial velocity and initial concentration gradient for consistency of the local concentration gradient at the leading edge of the flame. In these cases, the flame curvatures were also consistent. Accordingly, the burning velocity, defined as local flow velocity at the triple point, was determined by the flame curvature. The burning velocity increased with increasing flame curvature, when the curvature was near zero. After that, the burning velocity decreased with increasing curvature. The peak value thus exceeded the adiabatic one-dimensional laminar burning velocity. Comparing the effects of the measured flame stretch rate on the flow strain κ_{s} and flame curvature κ_{c}, κ_{s} is larger and increases more rapidly than κ_{c} for flame curvatures satisfying 1/R_{f} < 250 m^{-1} and then becomes constant while κ_{c} still increases for 250 m^{-1} < 1/Rf, so that κ_{c} becomes much larger than κ_{s}. There is also a peak in burning velocity at roughly the transition in flame curvature specified above. Therefore, the burning velocity for a low concentration gradient correlates with the flame stretch rate.

Original language | English |
---|---|

Pages (from-to) | 893-899 |

Number of pages | 7 |

Journal | Proceedings of the Combustion Institute |

Volume | 31 I |

DOIs | |

Publication status | Published - 2007 |

Externally published | Yes |

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### Keywords

- Burning velocity
- Concentration gradient
- Flame curvature
- Flame stretch rate
- Triple flame

### ASJC Scopus subject areas

- Automotive Engineering

### Cite this

*Proceedings of the Combustion Institute*,

*31 I*, 893-899. https://doi.org/10.1016/j.proci.2006.08.068

**Burning velocity of triple flames with gentle concentration gradient.** / Hirota, Mitsutomo; Yokomori, Takeshi; Yasuda, Kyouhei; Nagai, Yoshitaka; Mizomoto, Masahiko; Masuya, Goro.

Research output: Contribution to journal › Article

*Proceedings of the Combustion Institute*, vol. 31 I, pp. 893-899. https://doi.org/10.1016/j.proci.2006.08.068

}

TY - JOUR

T1 - Burning velocity of triple flames with gentle concentration gradient

AU - Hirota, Mitsutomo

AU - Yokomori, Takeshi

AU - Yasuda, Kyouhei

AU - Nagai, Yoshitaka

AU - Mizomoto, Masahiko

AU - Masuya, Goro

PY - 2007

Y1 - 2007

N2 - We investigated the local flame speed of a two-dimensional, methane-air triple flame in a rectangular burner. The velocity fields and the concentration profiles were measured with particle image velocimetry and the Rayleigh scattering method, respectively. There was a requisite combination of initial velocity and initial concentration gradient for consistency of the local concentration gradient at the leading edge of the flame. In these cases, the flame curvatures were also consistent. Accordingly, the burning velocity, defined as local flow velocity at the triple point, was determined by the flame curvature. The burning velocity increased with increasing flame curvature, when the curvature was near zero. After that, the burning velocity decreased with increasing curvature. The peak value thus exceeded the adiabatic one-dimensional laminar burning velocity. Comparing the effects of the measured flame stretch rate on the flow strain κs and flame curvature κc, κs is larger and increases more rapidly than κc for flame curvatures satisfying 1/Rf < 250 m-1 and then becomes constant while κc still increases for 250 m-1 < 1/Rf, so that κc becomes much larger than κs. There is also a peak in burning velocity at roughly the transition in flame curvature specified above. Therefore, the burning velocity for a low concentration gradient correlates with the flame stretch rate.

AB - We investigated the local flame speed of a two-dimensional, methane-air triple flame in a rectangular burner. The velocity fields and the concentration profiles were measured with particle image velocimetry and the Rayleigh scattering method, respectively. There was a requisite combination of initial velocity and initial concentration gradient for consistency of the local concentration gradient at the leading edge of the flame. In these cases, the flame curvatures were also consistent. Accordingly, the burning velocity, defined as local flow velocity at the triple point, was determined by the flame curvature. The burning velocity increased with increasing flame curvature, when the curvature was near zero. After that, the burning velocity decreased with increasing curvature. The peak value thus exceeded the adiabatic one-dimensional laminar burning velocity. Comparing the effects of the measured flame stretch rate on the flow strain κs and flame curvature κc, κs is larger and increases more rapidly than κc for flame curvatures satisfying 1/Rf < 250 m-1 and then becomes constant while κc still increases for 250 m-1 < 1/Rf, so that κc becomes much larger than κs. There is also a peak in burning velocity at roughly the transition in flame curvature specified above. Therefore, the burning velocity for a low concentration gradient correlates with the flame stretch rate.

KW - Burning velocity

KW - Concentration gradient

KW - Flame curvature

KW - Flame stretch rate

KW - Triple flame

UR - http://www.scopus.com/inward/record.url?scp=34548715410&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=34548715410&partnerID=8YFLogxK

U2 - 10.1016/j.proci.2006.08.068

DO - 10.1016/j.proci.2006.08.068

M3 - Article

VL - 31 I

SP - 893

EP - 899

JO - Proceedings of the Combustion Institute

JF - Proceedings of the Combustion Institute

SN - 1540-7489

ER -