The role of instabilities on ignition of unsteady hydrogen jets flowing into an oxidizer

The current study is a series of experiments designed to examine the role of turbulent instabilities on the ignition process of pressurized hydrogen jets which are released into oxidizer environments. The experiments were conducted in a shock tube where hydrogen gas is shock-accelerated into a partly confined oxygen environment across a perforated plate. Although the considered scenario differs from most practical applications where high pressure hydrogen is released into air, the results may be applicable toward cases where hydrogen leaks are shock assisted through holes in fuel cell membranes. Schlieren visualization permitted the reconstruction of the gas dynamic evolution of the release while time resolved self-luminosity records permitted us to record whether ignition was achieved. Despite the presence of confinement in the experiments, the ignition limits determined experimentally were found to be relatively agreeable with trends predicted by a previously developed 1-D numerical model (Maxwell and Radulescu, 2011), which assumes a release into an unconfined environments. However, the role of confinement in the experiments not only influence ignition at lower limits compared to the 1-D ignition model, but was also found to promote turbulent mixing through shock reflections and flow instabilities. Turbulent mixing thus influences how the ignition spots interact to ignite the entire jet.

► Ignition limits depend on the strength of shock and size of release hole.
► Confining geometry also has influence on ignition limits of hydrogen jet releases.
► Reflected shocks influence turbulent mixing and how ignition spots ignite the jet.
► Turbulent instabilities leads to increased mixing rates and enhanced combustion.