Effects of nitrogen addition on the shock-induced ignition of high-pressure hydrogen release through a rectangular tube of 400 mm in length

This paper reports on the nitrogen addition effects on the self-ignition of high-pressure hydrogen leakage. It reveals that the intensity of produced incident shock decreases with more nitrogen addition, unbeneficial for self ignition occurrence. Besides, nitrogen addition in hydrogen significantly reduces self-ignition possibilities inside the tube and self-sustained jet flame formation outside the tube. There exists a certain critical threshold of shock overpressure of about 1 MPa for self-ignition occurrence at different nitrogen additions. In our experiments, the impurity gases (N-2, CO, CH4) reduce the self-ignition possibilities in the same order as it reduces the shock intensity, namely, the effect of N-2 is similar to that of CO, larger than that of the same volume of CH4. It suggests that the decrease of binary mixture self-ignition can be mostly explained by the reduction of shock intensity, and the decrease effect enhances with fuel molecular weight. Furthermore, nitrogen addition inhibits the flame development and propagation inside the tube. Nitrogen-weaken ignited flame barely survives during the expansion outside the tube or is soon extinguished inside the tube with more nitrogen addition. Moreover, the flame has a rapid flame length growth rate of 1-2 mm/mu s in the initial stage, but the expanding velocity becomes lower to 0-1 mm/mu s after a period of spread. Accordingly, a mechanism of the self-ignition process for highpressure hydrogen release is proposed for cases with 0%-7.5% nitrogen addition.

Automated summary

This paper investigates the effects of nitrogen addition on self-ignition of high-pressure hydrogen leakage, showing that an increase in nitrogen addition reduces the likelihood of self-ignition events and external tube flame formation, with a critical threshold for overpressure. Impurity gases have a similar impact on self-ignition possibilities as they do on shock intensity, with the reduction in self-ignition primarily attributed to the decrease in shock intensity and enhanced with higher fuel molecular weight. Additionally, nitrogen addition inhibits flame development and propagation inside the tube, with ignited flames barely surviving expansion outside the tube.