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ABSTRACT
There are few studies of flame propagation and the initiation of detonation for blended mixtures. In this article, an experimental study is conducted to investigate the acceleration of a flame in stoichiometric methane/hydrogen/oxygen (CH4/H2/O2) mixtures in millimeter-scale smooth tubes. In the 1.0- and 1.5-mm tubes, there is no flame acceleration or detonation initiation. The flame propagates at a speed of several m/s. This may occur because of the heat loss on a non-adiabatic wall and the condensation of water vapor. When the molar fraction of CH4 in a 3.0-mm tube is larger than 0.3, detonation is initiated. The early stage of flame propagation is divided into propagation at a constant velocity, deceleration, and exponential acceleration. An increase in the molar fraction of CH4 induces a pulsating propagation of a flame.
Funding
The authors gratefully acknowledge the financial support by the Ministry of Science and Technology (MOST 100-2623-E-006-015-D).
Nomenclature
| d | = | tube diameter |
| L | = | length of a tube |
| Pi | = | initial pressure of CH4 or H2 |
| t | = | time |
| Vf | = | flame propagation speed |
| Vf* | = | normalized flame propagation speed |
| VL | = | laminar burning velocity |
| Vsf | = | spatial flame speed |
| Vt | = | terminal flame speed |
| XDDT | = | distance for the initiation of detonation |
| Xt | = | location of the flame tip |
| λ | = | width of the detonation cell |
| σ | = | expansion ratio |
| χ | = | molar fraction of CH4 |