Effect of Equivalence Ratio on Combustion Characteristics under Propane-Air Flame Acceleration Conditions

An improved constant-volume combustion bomb (CVCB) with a double-layer perforated plate was employed to investigate the combustion characteristics of propane-air premixed flames at different equivalence ratios (Φ = 0.8-1.25). Combined three-dimensional simulations and high-speed Schlieren imaging were used to analyze the coupled evolution of flame, flow, and pressure fields in confined space. The simulations revealed that before reaching the plate, expansion-induced flow and geometric contraction accelerated the unburned gas through the orifices, while pressure-driven jets near the orifices stretched and wrinkled the flame front, forming a complex flow-combustion structure. Experimentally, three flame development stages were identified: primary jet propagation, secondary jet acceleration, and flame-shock wave coupling. As Φ increased, both flame velocity and combustion intensity rose, and the flame mode transitioned from turbulent to quasi-detonative. Overpressure and high-frequency (4 kHz) filtered pressure analyses showed that both parameters increased with Φ, reaching 3.16 and 0.501 MPa at Φ = 1.25. The enhanced oscillations were attributed to local autoignition near the perforations and spontaneous ignition in the end region. This study clarifies the mechanisms of secondary jet flame acceleration and local autoignition in confined double-plate systems, providing new insight into explosion dynamics and safety control in fuel storage and transportation environments.