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DDT induction distance measurements for methane/hydrogen/ oxygen mixtures
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DOI：10.1016/j.combustflame.2026.115040.png)
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Abstract
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A fast-flame was produced by passing a detonation wave through a perforated plate with 3.2 mm holes in a 7.6 cm inner-diameter polycarbonate tube. The flame velocity immediately after the perforated plate was in the range of 0.5 to 0.6 the Chapman-Jouguet detonation velocity based on initial conditions. The distance from the perforated plate to the deflagration-to-detonation transition (DDT) location, i.e., the DDT induction distance, was measured for different stoichiometric methane/hydrogen/oxygen mixtures with methane/hydrogen blends from 100% methane to 100% hydrogen (the mixture reactivity varied via the initial pressure). The DDT induction distance was found to be shortest for the 100% methane mixture and no DDT occurred before the endplate for the 100% hydrogen mixture, up to a maximum test pressure of 35 kPa. For intermediate blends the DDT induction distance increased with increased fuel hydrogen-content. High-speed visualization identified three DDT mechanisms that directly correlated with the DDT induction distance. For the shortest DDT induction distance, the detonation initiated from a hot spot at the main flame front; whereas, for the largest DDT induction distance the flame initially decelerated and then accelerated following the formation of an inverted hollow cone-shaped flame where detonation initiation occurred at the mouth of the cone near the wall. For intermediate DDT induction distances detonation initiation occurred due to the acceleration of a secondary flame that formed between the flame-front and the lead shock wave.
Keywords:
Detonation
DDT
Fast flame
Explosion
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