Dispersion, Ignition and Combustion Characteristics of Low-pressure Hydrogen-Methane Blends

In this paper, we study the dispersion, ignition and flame characteristics of blended jets of hydrogen and methane (as a proxy for natural gas) at near-atmospheric pressure for a fixed volumetric flow rate, which mimics the scenario of a small-scale unintended leak. A reduction in flame height is observed with increasing hydrogen concentration. A laser is tightly focused to generate a spark with sufficient energy to ignite the fuel. The light-up boundary, defined as the delineating location at which a spark ignites into a jet flame or extinguishes, is determined as a contour. The light-up boundary increases in both width and length as the hydrogen content increases up to 75% hydrogen, at which point the axial ignition boundary decreases slightly for pure hydrogen relative to 75% hydrogen. Ignition probability, a key parameter regarding safety, is computed at various axial locations and is also shown to be higher near the nozzle as well as non-zero at further downstream locations as the hydrogen content in the blend increases. Planar laser Raman scattering is used in separate experiments to determine the concentration of both fuel species. Mean fuel concentrations well below the lower flammability limit are both within the light-up boundary and have non-zero ignition probabilities.