Experimental and theoretical observations on DDT in smooth narrow channels

Abstract

A combined experimental and theoretical study of deflagration-to-detonation transition (DDT) in smooth narrow channels is presented. Some of the distinguishing features characterizing the late stages of DDT are shown to be qualitatively captured by a simple one-dimensional scalar equation. Inspection of the structure and stability of the traveling wave solutions found in the model, and comparison with experimental observations, suggest a possible mechanism responsible for front acceleration and transition to detonation.

Flame acceleration and detonation onset in narrow channels: Simultaneous schlieren visualization

“…The spatial distribution of DO seems to be a function of dilution and may be the result of the different flow structures that develop before transition, we note however that a larger data set may plausibly change the distributions obtained; we are currently performing additional tests to verify this statement. These observations provide further evidence of the role played by walls on DO, most probably through the formation of favorable thermal gradients [51,52] due to friction induced heating within the hydrodynamic boundary layer [23,25,53]. The formation of ignition centers within corners was conclusively confirmed by our results in line with recent experiments [26]; the spatial distributions measured do not therefore seem to be facility dependent.…”

“…Note that the formation of a preheated zone is not a sufficient condition for DO as shock induced preheating alone does not reduce significantly the induction delay time [48]. However, recent theoretical work [49], and an experimentally informed simulation [50] revealed the crucial role of compressibility and the importance of the late stages of 21 FA in the potential development of very strong shocks in close proximity to the flame front than subsequently leads to DO. as long as the size of the gap is of the order of or larger than the laminar thermal flame thickness of the mixture, δ t .…”

“…However, to the best of our knowledge, this reasonable but rather strong assumption is not supported by experimental evidence. Further experimental, numerical and theoretical contributions were made subsequently attempting to clarify the role of boundary layer, viscous heating, compressibility, unsteadiness and strong flow gradients [19][20][21][22][23][24][25]. Whether these effects are essential to DDT or merely aiding mechanisms remains largely unknown.…”

Heat and momentum losses in $${\text {H}}_{2}$$–$${\text {O}}_{2}$$–$${\text {N}}_{2}/{\textrm{Ar}}$$ detonations: on the existence of set-valued solutions with detailed thermochemistry

“…The applicability of the latter models or even simpler scalar analogs to deflagration-to-detonation transition (DDT) had not previously been suggested nor explored until Melguizo-Gavilanes et al [26] pointed out that the transition between the aforementioned traveling wave solutions bears striking similarities with what is typically observed during DDT experiments in narrow channels.…”