Fire risk on high-pressure full composite cylinders for automotive applications

1. Fire risk on high-pressure full composite cylinders for automotive applications ICHS4, San Francisco, Sept. 12-14th, 2011Ruban, S.1, Heudier, L.2, Jamois, D.2, Proust, C.2, Bourhy-Weber, C.1 ,Jallais, S.1,Kremer-Knobloch, K.3, Maugy C.3, Villalonga, S.41Air Liquide R&D, CRCD, Jouy en Josas, France 2 INERIS, Verneuil-en-Halatte, France3 PSA PEUGEOT CITROEN, Carrières-sous-Poissy, France4 CEA, Le Ripault, Monts, France

2. Context Gravimetric capacity Cost Volumetric capacity The high-pressure (70 MPa/10.1 kpsi) fully wrapped epoxy resin/carbon fiber composite cylinder is currently the preferred option for fuel cell electric vehicle Epoxy resin/carbon fiber composites cylinder • Light weight • Excellent mechanical performance • High capacity of H2 storage • Good chemical and electrical resistance Cylinder connector Cylinder connector H2 vehicle refilling station Fire safety strategy: preventing the cylinder from bursting Epoxy resin/carbon fiber composite wall (a few cm) Releasing hydrogen through a thermal pressure release device (TPRD) and/or using a thermal protection Epoxy resin/carbon fiber composite wall (few cm) Liner: H2 tightness (a few mm) Liner: H2 tightness (feu mm)

3. Suzuki, IEA Task 19 – SAE 2006-01-0129 Bonfire Test in INERIS, 2009 OBJECTIVE: DESIGN FOR SAFETY • TPRD Design: size of orifice and delay to opening avoiding cylinder burst • Current TPRD orifice diameter: 3.6 to 6 mm => 11 to 18 m initial flame length • Safe H2 release through TPRD • Reduce the H2 flow-rate released though TPRD or allow a longer release duration in order to decrease the flame length TPRD H2 DYNETEK 700b TPRD H2 CIRCLE SEAL 700b • Increase knowledge on behavior of cylinder in fire without TPRD • Current standard drafts (ISO/DIS 15869.3, CGH2R-12b, SAE J2579) and regulations (EC 79/2009) define testing for fire impact on cylinders equipped with TPRD • Current tests do not allow the proper design of the TPRD orifice and opening delay or thermal protection • Tests • Evaluation of the duration of cylinder resistance in fire, depending on initial pressure in the cylinder • Influence of partial fire • Validation of a smaller release rate through a TPRD

4. Time (s) Test conditions – Assessment of the net flux received by a metallic cylinder in this bonfire • Experimental set-up • Gallery: 80 m long, 3 meters high, 10 m3/s ventilation to extract fumes • Bonfire: Heptane pan (0.6 x 1.2 m2), protected with baffles, 5.71 L/min consumption • Cylinder characteristics • Steel cylinder sealed at both ends • Diam: 330 mm, Length 900 mm, Thickness 12 mm • Filled with air, pressure measurement • Results • Themal load is reproducible and not constant with time • Heat flux reached a maximum of 120 kW/m2 after 200 seconds • The heat flux then decreased as the outside wall temperature increased INERIS Test Gallery Steel cylinder over the pan Bonfire in the gallery

5. Bonfire tests on composite cylinders • Composite cylinder: 70 Mpa, 36L, 34 kg, type IV, design coefficient: 3 • Experimental set-up • Cylinder pressured with Helium at 700 bar, 350 bar or 175 bar • Cylinder engulfed in fire or partially in fire (one half protected by a thermal shield) • No venting or venting with a 0.5 mm orifice opening 90 s after the start of the fire • 5 Thermocouples (type IV – 1mm) positioned on the cylinder and one place 50 mm under the cylinder • Pressure inside the storage monitored Global bonfire test Partial bonfire test

6. Results • No pressure increase inside the composite cylinder during the first 3 minutes • Bursting delays are of the same order of magnitude as found by Weyandt (6 to 12 min for cylinders type III and IV, 72 L and 88 L , 35 MPa) • The pressure increase before cylinder rupture or leak is at the most 12.5% after 11 minutes of fire (and was null before the opening of the release valve in test N°5) • The storage does not burst for an initial pressure of 178 bar or for an initial pressure of 701 bar with a gas release through a 0.5 mm orifice after 1 min 30 s. • Slight pressure drop (factor 0.98) at the beginning due to the cooling of the gas after the filling procedure

7. Temperatures measured at cylinder surface vary between 500 and 900°C • Temperatures measured in the flame (TC6) were above 600°C after only a few seconds • For the partial fire test TC6 was placed in the immediate vicinity of the thermal shield explaining low temperature • Norm requirements: • Comply with ISO_DIS15869 (At least one thermocouple on the cylinder indicates a minimum temperature of 590 °C and is maintained for the remaining duration of the test as required in bonfire specification). • draft SAE J2579 : 800°C required was not systematically reached. Global bonfire test Partial bonfire test

8. Influence of the fire engulfing conditions • Under global fire conditions, the storage bursts one minute later than under partial fire conditions. • Given the number of test involved (only one per condition) we can not rely on this unexpected result • Burst delay seems not to depend significantly on the size of the surface impacted by the fire, even if this size is divided by a factor of 2

9. Influence of initial pressure Global bonfire test • The higher the initial pressure, the shorter the resistance time • For initial pressure under 178 bar, the gas leaks through the composite laminate and the cylinder does not burst Composite after fire Leak test after fire

10. Controlled release • The 178 bar test gives a pressure/time threshold for the composite cylinder corresponding to the maximum pressure reached during the test : 200 bar and 11 minutes. • To avoid a burst, a TPRD should detect the high temperature and allow the release of H2 to decrease the cylinder pressure down to 200 bar in less than 11 minutes. • A 0.5 mm TPRD orifice opening at 90 s prevented the cylinder from bursting • Difference between the theoretical release and measured release (with or without fire) may be due to the temperature decrease in the cylinder induced by depressurization or to the reel orifice size being slightly different as specified (e.g. 0.6 mm) • Theoretical release modeled as an isentropic release and sonic flow of ideal gas

11. CONCLUSION • The resistance time of a composite cylinder is of the same order of magnitude for a localized fire (where only half of the cylinder is exposed to fire) and for a global bonfire. • The cylinder as a whole needs to be protected from localized fire impact, possibly achieved by a thermal protection. • The release of hydrogen through an orifice with a diameter of 0.5 mm and opening at 90 seconds prevented the studied 36 L cylinder from bursting. • This diameter represents a decreased factor of 10 compared to current practice, allowing the flame length and consequently the safety distance in case of fire to be decreased by the same factor. • In order to be safer in case of TPRD release, one can adapt the design of the TPRD to the characteristics of the cylinder. • Reducing the orifice diameter, we also reduce the safety margin to avoid burst, so we have to accurately design the storage protections.

12. Acknowledgements • To ANR (French National Research Agency) for its financial support through Plan d’Action National sur l’Hydrogène et les piles à combustibles program (project HYPE ref ANR07 PANH006) • To INERIS (Institut National de l’Environnement Industriel et des Risques) for the tests performed and their continuous support

13. Thank you! Sidonie Ruban sidonie.ruban@airliquide.com