Self-ignition of hydrogen-nitrogen mixtures during high-pressure release into air

•The hydrogen and hydrogen mixtures self-ignition is promoted by the tube length and the burst pressure.•5% N2 addition increases (1.15-2.12) the burst pressure necessary for ignition.•10% N2 addition increases (1.8-2.85) the burst pressure necessary for ignition.•Simulations showed that specific sequence of 3 ignition spots is necessary for the sustained combustion after leaving the tube.

This paper demonstrates experimental and numerical study on spontaneous ignition of H2-N2 mixtures during high-pressure release into air through the tubes of various diameters and lengths. The mixtures included 5% and 10% (vol.) N2 addition to hydrogen being at initial pressure in range of 4.3-15.9 MPa. As a point of reference pure hydrogen release experiments were performed with use of the same experimental stand, experimental procedure and extension tubes. The results showed that N2 addition may increase the initial pressure necessary to self-ignite the mixture as much as 2.12 or 2.85 - times for 5% and 10% N2 addition, respectively. Additionally, simulations were performed with use of Cantera code (0-D) based on the ideal shock tube assumption and with the modified KIVA3V code (2-D) to establish the main factors responsible for ignition and sustained combustion during the release.