| 1. |
- Akkerman, V., et al.
(författare)
-
Mechanism of fast flame acceleration in cylindrical tubes with obstacles
- 2009
-
Ingår i: Fall Meeting of the Eastern States Section of the Combustion Institute 2009; College Park; United States; 18 October 2009 through 21 October 2009. - 9781615676682 ; , s. 301-307
-
Konferensbidrag (refereegranskat)abstract
- The physical mechanism of fast flame acceleration in tubes with obstacles is explained by recognizing that delayed burning between the obstacles creates a powerful jet flow which drives the acceleration. It is demonstrated theoretically and computationally that this mechanism is unlimited in time and independent of the Reynolds number, and it is much stronger and qualitatively different from the classical Shelkin mechanism of flame acceleration due to wall friction. As long as the gas compression is weak, the flame accelerates exponentially, with an enormous acceleration rate. We present formulae describing evolution of the flame tip, as well as its velocity and acceleration rate. Furthermore, it is shown that flames accelerate noticeably stronger in the axisymmetric cylindrical geometry as compared to the planar one.
|
|
| 2. |
|
|
| 3. |
- Valiev, D.M., et al.
(författare)
-
Stage of quasi-steady propagation in premixed flame acceleration in narrow channels
- 2013
-
Ingår i: 8th US National Combustion Meeting 2013. - : Western States Section/Combustion Institute. - 9781627488426 ; , s. 947-956
-
Konferensbidrag (refereegranskat)abstract
- The present work investigates the spontaneous acceleration of premixed flames in micro-channels in the process of deflagration-to-detonation transition. It has recently been shown experimentally [Wu et al., Proc. Combust. Inst. 31 (2007) 2429], computationally [Valiev et al., Phys. Rev. E 80 (2009) 036317] and analytically [Bychkov et al., Phys. Rev. E 81 (2010) 026309] that the flame acceleration undergoes a number of stages from an initial exponential regime to quasi-steady fast deflagration. The present work focuses on the final saturation stages in the process of flame acceleration, during which the flame propagates with supersonic velocity with respect to the tube wall. It is shown that an intermediate stage with quasi-steady velocity noticeably below the Chapman-Jouguet deflagration speed may be observed during the acceleration process. The intermediate stage is followed by additional flame acceleration and subsequent saturation to the Chapman-Jouguet deflagration regime. We explain the intermediate stage by the combined effects of gas pre-compression ahead of the flame front and the hydraulic resistance. We estimate the first quasi-steady saturation velocity theoretically and compare it with the numerical results. Numerical simulation shows that, in agreement with the theoretical prediction, heating due to viscous stress at the wall is minor before the flame reaches the first quasi-steady stage and is prevailing afterwards. The additional acceleration is related to viscous heating at the channel walls, being of key importance at the final stages. The possibility of explosion triggering is also demonstrated.
|
|
