Several North American utilities are planning to blend hydrogen into gas grids, as a short-term way of addressing the scalable demand for hydrogen and as a long-term decarbonization strategy for ‘difficult-to-electrify’ end uses. This study documents the impact of 0–30% hydrogen blends by volume on the performance, emissions, and safety of unadjusted equipment in a simulated use environment, focusing on prevalent partially premixed combustion designs. Following a thorough literature review, the authors describe three sets of results: operating standard and “ultra-low NOx” burners from common heating equipment in “simulators” with hydrogen/methane blends up to 30% by volume, in situ testing of the same heating equipment, and field sampling of a wider range of equipment with 0–10% hydrogen/natural gas blends at a utility-owned training facility. The equipment was successfully operated with up to 30% hydrogen-blended fuels, with limited visual changes to flames, and key trends emerged: (a) a decrease in the input rate from 0 to 30% H2 up to 11%, often in excess of the Wobbe Index-based predictions; (b) NOx and CO emissions are flat or decline (air-free or energy-adjusted basis) with increasing hydrogen blending; and (c) a minor decrease (1.2%) or increase (0.9%) in efficiency from 0 to 30% hydrogen blends for standard versus ultra-low NOx-type water heaters, respectively.

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A high‐pressure and temperature cyclohexane pyrolysis shock tube study was completed with the goal of extending the experimental cyclohexane pyrolysis data to pressures relevant to current and future combustors and to investigate whether ring contraction products observed in high‐pressure, supercritical phase cyclohexane and cycloalkane pyrolysis experiments can form at matching, and higher, pressures in the gas phase. The experiments in the current work were completed over a range of 950–1650 K and at nominal pressures of 40, 100, and 200 bar. No alkylcyclopentanes, possible ring contraction products, were observed to form under the conditions of the current study. The production of methylenecyclopentane and 1,3‐cyclopentadiene, and the other three cyclic species quantified: cyclohexene, benzene, and toluene, increased significantly with a substantial increase in the initial fuel concentration. Two sets of experimental data obtained at 200 bar were compared with a literature and laboratory‐generated model. Both models had difficulty capturing the propadiene and propyne profiles, and the literature model significantly overestimated the benzene observed in the set of experiments completed with the more dilute fuel mixture. The literature model was able to better predict propadiene, propyne, and benzene product profiles in the 200 bar set of experiments, which used a higher concentration of fuel in the test gas. These results suggest that despite both cyclohexane and benzene being well‐studied and important species in combustion chemistry, their reaction pathways and reaction rates would benefit from further refinement.

This work is a continuation of a previous study (IMECE2019-11449) which sought to explore the feasibility and means of successfully modeling the hydrogen fast filling process of cylinders lined with phase change material (PCM) entirely in CFD software. The first focus of this work was to address the simplistic approach of how the liner temperature was modelled in the previous study. Previously, the entire liner was assigned a single temperature which was obtained and updated through the lumped heat capacity method. This meant that the hotter gas at the end of the cylinder opposite the inlet was in contact with a liner at a temperature lower than could realistically be expected. This was remedied by splitting the liner into four sections. Two sections were used for the curved portions at each end of the cylinder, and the straight wall section was split into two. Each section had its temperature independently calculated through the lumped heat capacity method. A temperature difference on the order of a ten degrees Celsius was observed between the different sections of the liner prior to latent heating beginning. The mass averaged temperature of the hydrogen inside the cylinder obtained with the sectioned wall case matched that obtained with the single wall temperature almost exactly, less than a degree difference. Despite the unexpected findings of the average hydrogen temperature not changing much when the wall is split into sections, this approach was still taken with all the cases completed in this study. The liner could be split into a greater amount of sections than four, but this was considered unnecessary due to the findings regarding the overall hydrogen temperature. Four sections were considered adequate and used to model the temperature gradient along the wall or liner. The effect of gravity on the filling process was also explored based on the orientation of the cylinder. This required completing three-dimensional simulations to accurately simulate buoyancy driven flow in horizontally mounted cylinders. All the simulations were completed with ANSYS Fluent 2019 R1 without the use of additional software to handle the heat transfer involving the PCM. All simulations were completed with the coupled pressure-based solver and K-Omega SST turbulence model. The gas properties were obtained from tables generated from NIST properties (REFPROP) available within ANSYS Fluent to limit the amount of error in the accumulated mass within the cylinder due to inaccurate gas properties. The initial conditions for the gas and liner temperatures were 25°C and 100 bar for the gas pressure. A constant mass flow rate of 0.02174 kg/s at a temperature 0°C were used as the initial conditions for the inlet hydrogen gas.