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

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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’

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Notional Nozzles Replace compressible shock structures with an atmospheric equivalent ØTØT ρ T P T U T T T ØmØm ρ m P m U m T m

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

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

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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’

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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?

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High Pressure H 2 delivery system Ø127mm 345mm Stagnation Chamber (up to 60:1 supply pressure) Stagnation temperature and pressure monitored for feedback control Nozzle profiles adapted from ASME MFC-3M-2004

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High Pressure H 2 delivery system Pr = 10 Ø = 1.5mm

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Reconstructing the downstream Scalar field

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Centreline unmixedness = 0.222 Jet spreading rate = 0.111 Virtual origin = 7.14mm Mean Centreline decay rate = Virtual origin =

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

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Reconstructing the downstream Scalar field Richards and Pitts, 1993

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Predicting the Flammability Factor Schefer et al, 2011

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Predicting the Flammability Factor

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Using Notional Nozzle models to predict effective radius and gas density ModelEffective nozzle radius (mm) Jet density (Kg/m 3 ) r ε (mm)r ε /r ε, ideal Birch et al (1984)1.800.08050.4751.084 Ewan and Moodie (1986)1.700.09710.4921.123 Yuceil and Otugen (2002)1.150.13910.3990.911 Birch et al (1987)1.500.08050.3960.904 Harstad and Bellan (2006)2.700.08370.7261.658 r ε, ideal = 0.438mm Combined with Abel Nobel

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Using Notional Nozzle models to predict the 10% ignitability contour

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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’ Couple very well Dependent upon model accuracy Needs to determine virtual origins

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

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What is Happening at the Nozzle? Is air and H 2 mixing outside of Mach Disc? Do Notional Nozzle models require an air entrainment aspect?

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

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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 H 2 flow with Ø1mm nozzle can have a sustained flame Ignitability

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

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