The Evolution and Structure of Ignited High-pressure Cryogenic Hydrogen Jets

The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen at cryogenic conditions. Understanding the potential hazard arising from leaks in high-pressure cryogenic storage is needed to improve hydrogen safety. The manuscript reports a series of numerical simulations with detailed chemistry for the transient evolution of ignited high-pressure cryogenic hydrogen jets. The study aims to gain insight of the ignition processes, flame structures and dynamics associated with the transient flame evolution. Numerical simulations were firstly conducted for an unignited jet released under the same cryogenic temperature of 80 K and pressure of 200 bar as the considered ignited jets. The predicted hydrogen concentrations were found to be in good agreement with the experimental measurements. The results informed the subsequent simulations of the ignited jets involving four different ignition locations. The predicted time series snapshots of temperature, hydrogen mass fraction and the flame index are analyzed to study the transient evolution and structure of the flame. The results show that a diffusion combustion layer is developed along the outer boundary of the jet and a side diffusion flame is formed for the near-field ignition. For the far-field ignition, an envelope flame is observed. The flame structure contains a diffusion flame on the outer edge and a premixed flame inside the jet. Due to the complex interactions between turbulence, fuel-air mixing at cryogenic temperature and chemical reactions, localized spontaneous ignition and transient flame extinguishment are observed. The predictions also captured the experimentally observed deflagration waves in the far-field ignited jets.