The effect of concentration gradient on overpressure hazards and flame behavior of gas explosion in a vessel-duct connected device

•The concentration gradient distribution of gas in the vessel-duct connected device is achieved, and explosion experiments are conducted.•With constant CI, the peak overpressure and the maximum flame speed initially increased and then decreased with increased CP.•The study investigates the propagation of gas explosion shock waves, flames, and gas flow in a connected device with varying concentration gradients.•The concentration gradient in the connected device has a dual influence mechanism on the gas explosion process. Gas leaks often lead to the formation of CH4-air mixtures with concentration gradients in confined spaces. These gradients differ significantly from uniform premixed conditions and have a significant impact on the development process and propagation of explosions, which has not been extensively studied in previous research. This paper first analyzes the variations in the propagation characteristics of overpressure and flame under different concentration gradients by conducting explosion tests using a vessel-duct connected device. A numerical model was developed and used to simulate the propagation of gas explosion under varied concentration gradients. The influence and mechanism of concentration gradient on gas explosion propagation is finally discussed. Results show that with a constant concentration inside the vessel (CI), the peak explosion overpressure and flame speed in the connected device initially increase and then decrease with the continuous increase of the concentration in the propagation duct (Cp). The highest recorded explosion overpressure and flame speed were observed at the concentration gradient levels of CI = 9.5 % and CP = 8 %, resulting in values of 0.65 MPa and 500 m/s, respectively. The simulation and experimental results indicate that the gas concentration gradient distribution in the connected device has a dual impact mechanism on the explosion process. The specific impact on the explosion process is determined by the coupling of the concentration inside the vessel (CI) and the concentration inside the duct (CP). The research enriches the theory of gas explosion under the conditions of concentration gradients in connected spaces, providing valuable references for explosion-proof design in all industries related to connected spaces.