International Conference on Hydrogen Safety 19-21 October 2015, Yokohama, Japan Design recommendations for on-board hydrogen storage: plane jet releases and a variable aperture pressure relief device D. Yates, D. Makarov, V. Molkov Hydrogen Safety Engineering and Research Centre, University of Ulster

Introduction Thermally Activated Pressure Relief Devices Low fire resistance of bare hydrogen fuel tanks remains an unresolved technological safety issue for hydrogen-powered vehicles To avoid catastrophic failure of tank in a fire, tanks are outfitted with a thermally activated pressure relief device (TPRD) - current typical orifice diameter is about 5 mm A release from 70 MPa storage tank from such TPRD produces a flame of up to 15 m long and separation distance to "no harm" criteria of 70oC of about 50 m, and would destroy a typical garage in less than one second from overpressure PRD release from CNG bus, courtesy of Peter Jensen, Atlanta, Georgia

Introduction Presentation outline Jet flame model validation: Round jets Plane jets Ongoing research Variable aperture TPRD study: Blow-down problem Proposed TPRD design Fixed aperture comparison PRD release from Malek (2006)

Plane Jet Fires Previous work Mogi and Horiguchi (J.Loss Prev. Process Ind. 2009): Lf reduced from 2.5m to 1.0m with 1 mm eq. diameter plane nozzle (AR=12.8), inlet pressure 400 bar Makarov and Molkov (IJHE, 2014) modelled plane nozzle flows using 2 stage approach employed by Xu et al. (ICHS 2013) Combustion in first (compressible) stage was not accounted and combustion in near-to-nozzle field on jet fire was not studied AR 1 (round nozzle) AR 12.8 Mogi (exp) 2.5 m 1.0 m Ulster (CFD) 2.3-2.5 m (1300-1500 K) 0.8-1.0 m (1300-1500 K)

Plane Jet Fires Numerical approach 1 mm round nozzle 3.2x0.25 mm plane nozzle Present calculation domain continues two-stage model approach using the mesh by Makarov: 1mm round nozzle AR 12.8 plane nozzle (same cross-section area) 40 MPa H2 pressure-inlet Near field: Spalart-Allmaras model / laminar finite-rate chemistry Far field: RNG k-ε / Eddy- Dissipation Concept

Plane Jets Near field jet behaviour Axis switching Present study: SA model (reacting) Previous study: k-ε model (non-reacting) AR 1 AR 12.8

Round jet fire, 40 MPa, 1 mm nozzle Plane Jet Fires Far field results Round jet fire, 40 MPa, 1 mm nozzle AR 1 AR 12.8 Mogi (exp) 2.5 m 1.0 m Makarov (simulations) 2.3 m Present simulations 2.7 m 1.2 m AR 12.8 plane jet, minor axis Left: Yates (2013) Right: Makarov, Molkov (2009)

Fan jet computational domain TPRD designs Fan jet computational domain

Variable Aperture TPRD

Variable Aperture TPRD Investigated Design

Variable Aperture TPRD (VAPRD) Motivation for Study TPRDs form powerful, transient jet fires when H2 released from high pressure storage Tamura: TPRD release has potential to cause TPRD activations in other cars in close proximity Recent tests have demonstrated increased fire resistance using intumescent paint (above 2 hrs) Existing spring-loaded TPRD designs have valve seat that opens higher with increasing upstream pressure – no real protection against initial transient release Rolander, et al. (2003)

VAPRD Calculation Domain A constant-mass flow TPRD serves two purposes Confine harm effect distance to chosen value Reduce blow-down time by achieving consistent mass flow rate compared to fixed- aperture TPRD VAPRD proposed which closes against spring loading with high upstream pressure, opening as pressure drops Constant nozzle size gives predictable mass flow rate (flame length) when pressure downstream of throttle is known Above: investigated VAPRD design. Below: calculation domain.

VAPRD Results (1/2) Results obtained by examining fixed nozzle placements and varying inlet pressure until target mass flow rate obtained (3.8 g H2/s) Linear relationship observed between inlet pressure and mass flow rate for each fixed throttle location Relationship between throttle location and force on valve also linear, so this system could be built using simple springs (k=57.8 N/mm) Above: Pressure vs. mass flow rate. Below: force on valve v. displacement.

VAPRD Results (2/2) Blow-down performance to 1 MPa improved significantly over other nozzles that have either same diameter or same initial mass flow rate (70 MPa, 114 L) Ø=1 mm: Lf=3.04m (maximum) tb-d= 688 s (11 min) Ø=0.38 mm: Lf=1m tb-d=4782 s (1 hr 20 min) VAPRD throttles initial mass flow rate: Lf =1m tb-d=1274 s (21 min) Blow-down curves from 70 MPa initial pressure for different nozzles.

Conclusions Acknowledgments Plane jets: Model validated within 10% of experiment Flame length reduced by 60% using AR 12.8 plane jet Fan jet further reduces flame length Variable aperture TPRD study Flame length confined to 1m with 1mm orifice, 70 MPa release Blow-down time increased to 21 min Simple spring system could be used to construct this design H2FC SUPERGEN Hub – project financers Acknowledgments

Afterword Hydrogen has potential as an energy carrier to provide CO2-free energy if and only if it is sustainably sourced and after extensive investment in infrastructure and research Ongoing and increasingly devastating effects of climate change require immediate and collective action that cannot wait for future technological or infrastructure advances CH4 is more than 20 times as potent a greenhouse gas contributor as CO2; positive feedback loop with surface temperature accelerates methane release rate (Yvon-Derecher, Nature 2014) Animal agriculture, not transportation, is the dominant source of anthropogenic greenhouse gas emissions (18% of CO2, 35% of CH4, and 65% of N2O), accounting for up to 51% of total global GHG emissions (UNFAO, Goodland) Goodland, 2009