Hydrogen flame behavior in constant volume bomb at sub-zero temperature

Storing hydrogen in liquid form increases its volumetric energy density, which facilitates transportation. If the confinement system of a hydrogen cryogenic tank fails, the liquid hydrogen (LH2) will vaporize and form low-temperature gaseous hydrogen (GH2). To prevent industrial risk during the storage and transportation of LH2 it is essential to characterize the flammable properties of a GH2-air cloud at low temperature. In particular, the flammability limits must be determined to ensure that the concentration of GH₂ remains below the level that could potentially lead to an explosion. Another fundamental property is the unstretch laminar burning velocity (LBV), which is intrinsic to the chemistry driving the flame propagation. Its determination has two major implications: (i) A comparison with the prediction of LBV from a kinetic model allows one to evaluate the reliability of different mechanisms (which are typically not designed to operate at low temperatures). (ii) LBV serves as a design criterion in numerous engineering applications and numerical models.
At present, only flammability limits for upward propagating flames in a tube are available (Karim et al. 1984), while laminar burning velocity (Ghosh et al. 2022) were measured within a burner for GH2-air at low temperature.
This study focus on the behavior of lean H2 mixture with air close to flammability limits as a function of temperature. We were able to design and operate a visually accessible constant volume combustion vessel to measure the impact of sub-zero temperature on flame structure. Our result highlight the influence of the mode of energy deposit on flammability limits by comparing 2 methods of arc ignition. Flame structure and over-pressure inside the vessel was recorded and showed for the first time how instabilities are impacted by the initial temperature.