Releases And Jet Flames Of Room-temperature And Cryogenic Compressed Hydrogen

Energy shortages and environmental pollution are becoming increasingly serious due to global industrialization.Hydrogen is a promising alternative fuel that has the advantages of a wide variety of sources,cleanliness and efficiency.However,hydrogen is a flammable gas that has a wide flammability range in air.Therefore,hydrogen safety is an important topic for hydrogen applications.Potential accident scenarios include hydrogen releases and combustions whose conditions must be well understood for emergency response teams and safety codes and standards development.This study experimentally,numerically and analytically modeled releases and jet flames of room-temperature and cryogenic compressed hydrogen.Steady and transient release experimental systems were built in the room-temperature compressed hydrogen facility in the Karlsruhe Institute of Technology(KIT)in Germany.The steady release experiments measured the hydrogen jet velocity and concentration distributions and the visible jet flame lengths with the experimental data then used to validate the numerical models.Then,the numerical models were used to model steady horizontal jet flames for various stagnation pressures and nozzle diameters.The visible flame length data was then correlated as a function of the stagnation pressure and nozzle diameter.The jet trajectory was then modeled for jet flames bending upward due to buoyancy.The trajectories,the trajectory temperature distributions and the radial temperature distributions were predicted and fit with correlations.The numerical results were then used to develop a statistical regression model for horizontal high pressure hydrogen jet flames.The mathematical model can quickly and accurately predict the horizontal jet flame temperature fields,which will significantly improve the calculation efficiencies of engineering applications.The transient release experiments measured the pressure drops in the storage tank with a thermodynamic model then developed based on the Van der Waals equation of state to predict the stagnation parameters,outlet velocities and flow rates during releases.Then,the hydrogen was ignited at the centerline during releases.The turbulent jet flames were visualized using a background-oriented Schlieren(BOS)system.The flame spread velocities were analyzed for various initial pressures,nozzle diameters and ignition positions.The flame development processes after delayed ignition were also modeled to study the effects of the eddy dissipation model(EDM)coefficients on the predictions.The results showed that the predicted flame propagation speed increases as the coefficient B1 in the EDM combustion model increases.The predictions with the proper model coefficient agree well with the experimental data.The experimental and modeling results provide scientific basises for revealing the temporal and spatial hydrogen fire evolutions,and provide new ideas for improving the combustion model accuracy.Cryogenic compressed hydrogen releases and jet flames were numerically modeled based on experimental data provided by the Sandia National Laboratories.The predicted concentrations,temperatures and velocity distributions follow self-preservation laws.The visible jet flame lengths of cryogenic compressed hydrogen jets were longer than those of room-temperature hydrogen jets with the same mass flow rate.The visible jet flame length was then correlated as a function of the mass flow rate.The temperature distributions in horizontal cryogenic jet flames were also predicted with the results showing that the maximum temperature along the flame trajectory is closer to the nozzle than in room-temperature hydrogen jets.The radial temperature distributions are shown to be similar to those of room-temperature hydrogen jet flames.The results can provide scientific basises for developing the cryogenic hydrogen safety codes.