Effect of a side-mounted cavity resonator tube on deflagration to detonation transition in lean acetylene-oxygen mixtures in a confined system

Abstract

The deflagration to detonation transition (DDT) in acetylene–oxygen mixtures is experimentally investigated in a 1.5 m long, 80 mm inner diameter tube to quantify the influence of initial pressure, equivalence ratio, and geometric modification on the transition length. Tests are conducted over initial pressures of 0.3–1.5 bar and equivalence ratios ϕ = 0.4–1.6. Acetylene–oxygen is selected owing to its high detonation sensitivity, which enables DDT studies at relatively low initial pressures (0.3–1.0 bar) and lean equivalence ratios (ϕ = 0.4–0.6), where conventional hydrocarbon fuels typically fail to transition. Under lean and low pressure conditions, the deflagration phase is markedly prolonged, with run-up distances extending to about 1.5 m for P₀ = 0.5 bar and ϕ = 0.5 in the clean tube configuration. To mitigate this, a small diameter cavity resonator tube (CRT) is introduced within the deflagration region downstream of the ignition source. The CRT modifies the local combustion dynamics by enhancing flame acceleration and triggering a localized cavity induced detonation mechanism, thereby significantly reducing the DDT run-up distance to 0.5 m. This mechanism is active primarily during the transition phase and has limited influence once a fully developed detonation is established. The results demonstrate that targeted geometric modifications, combined with controlled initial conditions, provide a passive strategy to manipulate flame acceleration and DDT dynamics in large diameter confined reactive systems, with direct relevance to detonation based propulsion devices.