Dispersion of Under-expanded Hydrogen-methane Blended Jets through a Circular Orifice

Blending hydrogen into natural gas and using existing natural gas infrastructure provides energy storage, greenhouse gas emission reduction from combustion, and other benefits as the world transitions to a hydrogen economy. Though this seems to be a simple and attractive technique, there is a dearth of existing safety codes and standards and understanding the safety implications is warranted before implementation. In this paper, we present some preliminary findings on the dispersion characteristics of hydrogen-methane blends performed under controlled conditions inside a laboratory. Experiments were performed at two different upstream pressures of 5 and 10 bar as the blends dispersed into air through a 1 mm diameter orifice. Blends of 25, 50, and 75 vol-% hydrogen in methane were tested. Spatially resolved Raman signals from hydrogen, methane and nitrogen were acquired simultaneously at 10 Hz using separate ICCD cameras from which the individual concentrations and jet boundaries could be determined. Finally, a comparison between dispersion characteristics of blended fuel jets with pure hydrogen and pure methane jets was made.