Piotr Wolański Warsaw University of Technology, Warsaw, Poland

Nearly 40 years ago in Chorzow Chemical Plant “Azoty” explosion of synthesis gas killed four workers. Explosion happened during failure of high pressure gas installation in which mixture of hydrogen and nitrogen (3H 2 – N 2 ), used for synthesis of ammonia, was at high pressure (about 300 bar) and high temperature (about C). Since during expansion gas is cool down and selfignition temperature was far above initial temperature, search for external ignition source was started. No such source was found, so we were asked to explain the reason. This was motivation to initiate research to found real reason for ignition.

Hydrogen fueled car and refueling station at Tocho Gas in Japan.

L [mm]D [mm] xxx 65x 75x 95xx Lengths and diameters of the tube tested in the research

Pressures and signal from photodiode courses. Extension tube length 45 mm, extension tube diameter 25 mm, initial hydrogen pressure equal to 7.6 MPa

Direct pictures of the hydrogen outflow, extension tube length 45 mm, extension tube diameter 32 mm, initial hydrogen pressure equal to 6.2 MPa. Frame rate f/s, shutter 1/ s.

Direct pictures of the hydrogen outflow, extension tube length 65 mm, extension tube diameter 10 mm, initial hydrogen pressure equal to 7.4 MPa. Frame rate f/s, shutter 1/ s.

Results of the experiments as a function of pressure and length of the tube. Tube diameter equal to 10 mm.

Critical value of the hydrogen pressure required for ignition as a function of length of the tube. Tube diameter equal to 10 mm.

Results of the experiments as a function of pressure and diameter of the tube. Tube length equal to 95 mm.

Number of tests as a function of pressure range and length of the extension tube

Reconstruction of the experimental facility. Initial conditions 1. High pressure hydrogen - red region on the left hand side of the membrane.

Reconstruction of the experimental facility. Initial conditions 2. High pressure hydrogen - red region on the left hand side of the membrane.

Comparison of experimental and numerical results. 2 nd order upwind, explicit. Left - 2 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, explicit. Left - 2 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, explicit. Left - 2 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, explicit. Left - 2 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, explicit. Left - 2 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, explicit. Left - 2 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

Comparison of experimental and numerical results. 2 nd order upwind, implicit. Left – 1 initial conditions, temperatura distribution (80 bar initial pressure). Right – direct pictures from experiment (76 bar H2 initial pressure) 50 mm

It was first time shown nearly 40ty years ago that outflow of the high pressure combustible gas can be a source of ignition. Ignition can be obtained both in incident as well as in reflected shock wave. In case of reflected shock wave, which might be more often case in reality, parameters of outflowing gas which can initiate explosion are even lower. In case of reflected wave, geometry (such as cavities) which might focus reflected shock, might additionally lower ignition parameters. 

Also spilled fuel on surface can be potential source of ignition. In this case even outflow of air or even inert gas can initiate combustion and possible explosion. So, research on this direction must be continued to evaluate more accurately conditions which will lead to ignition during outflow of gas from the high pressure installation.

 Hydrogen ignition takes place behind the contact surface of the wave generated by hydrogen outflowing from high pressure installation, due to mixing of air heated by created shock wave with expanding hydrogen.  Geometry of the extension tube significantly influences ignition process during outflow of the high pressure hydrogen.

 Ignition process shows stochastic behavior, since it depends very much on random processes associated with opening of the diaphragm (membrane).  The results of the experimental tests and numerical simulations show that geometry of the extension tube and the process of the diaphragm opening have a significant influence on the presence of the hydrogen ignition and the flame propagation. 

More research is necessary to explain complicated nature of this phenomenon.

THANK YOU FOR YOUR ATTENSION!