Ignitability and mixing of Under Expanded Hydrogen Jets

1. Ignitability and mixing of Under Expanded Hydrogen Jets Adam Ruggles Isaac Ekoto Combustion Research Facility, Sandia National Laboratories, Livermore, CA, USA ICHS Technical Seminar 14th September, 2011

2. Simple Engineering solution to Determine Ignitability Compressible flow replaced with a ‘Notional Nozzle’ Downstream part of leak behaves as an atmospheric jet Ignitability described by the ‘Flammability Factor’

3. Notional Nozzles Øm ρm Pm Um Tm ØT ρT PT UT TT Replace compressible shock structures with an atmospheric equivalent

4. Atmospheric Jets Obey self similarity laws. Mean and rms scalar fields can easily be reconstructed. mean scalar rms scalar 4th order polynomial curve Gaussian curve Normalised rms concentration Normalised mean concentration Non dimensional Radial Coordinate Non dimensional Radial Coordinate Richards and Pitts, 1993

5. Flammability Factor Equal to the integral of the mole fraction PDF between the flammable limits. 1 UFL Can also be calculated using mean and rms values with an intermittency model. Probability LFL 0 1 0 Mol fraction (xi) Birch et al, 1981

6. Simple Engineering solution to Determine Ignitability Compressible flow replaced with a ‘Notional Nozzle’ Downstream part of leak behaves as an atmospheric jet Ignitability described by the ‘Flammability Factor’

7. Simple Engineering solution to Determine Ignitability Compressible flow replaced with a ‘Notional Nozzle’ Downstream part of leak behaves as an atmospheric jet Ignitability described by the ‘Flammability Factor’ Can it be applied to Hydrogen?

8. High Pressure H2 delivery system Ø127mm 345mm Nozzle profiles adapted from ASME MFC-3M-2004 Stagnation temperature and pressure monitored for feedback control Stagnation Chamber (up to 60:1 supply pressure)

9. High Pressure H2 delivery system Pr = 10 Ø = 1.5mm

10. Reconstructing the downstream Scalar field

11. Reconstructing the downstream Scalar field Centreline unmixedness = 0.222 Jet spreading rate = 0.111 Virtual origin = 7.14mm Mean Centreline decay rate = Virtual origin =

12. Reconstructing the downstream Scalar field Mean Centreline decay rate (K) = 0.105 (Lit. Value) Virtual origin = 24.74mm Gives metric to assess Nozzle models rε, ideal = 0.438mm Richards and Pitts, 1993

13. Reconstructing the downstream Scalar field Richards and Pitts, 1993

14. Predicting the Flammability Factor Schefer et al, 2011

15. Predicting the Flammability Factor

16. Using Notional Nozzle models to predict effective radius and gas density Combined with Abel Nobel rε, ideal = 0.438mm

17. Using Notional Nozzle models to predict the 10% ignitability contour

18. Using Notional Nozzle models to predict the 10% ignitability contour

19. Simple Engineering solution to Determine Ignitability Dependent upon model accuracy Needs to determine virtual origins Compressible flow replaced with a ‘Notional Nozzle’ Downstream part of leak behaves as an atmospheric jet Ignitability described by the ‘Flammability Factor’ Couple very well

20. What is Happening at the Nozzle? Mach Disc Ø = 1.3mm

21. What is Happening at the Nozzle? Is air and H2 mixing outside of Mach Disc? Do Notional Nozzle models require an air entrainment aspect?

22. Jet Light up Boundary Kernel never gives sustained flame Kernel always gives sustained flame Local Extinction Flame Speed Vs Flow Speed Turbulent Time scale Vs Chemical Time scale Birch et al, 1981 Schefer et al, 2011 Swain et al , 2007

23. Ongoing work Be able to predict virtual origins looking at compressible shear layers Improve thermodynamic values using better equation of state Nozzle model development Develop insight/model into Jet light up boundaries Ascertain why no H2 flow with Ø1mm nozzle can have a sustained flame Ignitability

24. Ignitability and mixing of Under Expanded Hydrogen Jets Adam Ruggles Isaac Ekoto Combustion Research Facility, Sandia National Laboratories, Livermore, CA, USA ICHS Technical Seminar 14th September, 2011