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Simulation Methods for Fire Suppression Process
inside Engine Core and APU Compartments Boeing Commercial Airplanes Group Seattle, Washington, , USA Jaesoo Lee The Fourth Triennial International Aircraft Fire and Cabin Safety Research Conference Lisbon Conference Center, Portugal November 15-18, 2004
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Acknowledgment FAA Tech Center: Boeing:
D. Ingerson: Nacelle Fire Simulator Test Data Boeing: C. Roseburg: Thermodynamic Properties of Agents A. Nazir: Hflowx Modification D. Lackas, J. Petkus: Certification Test Data M. Dunn: Engine Cooling Airflow Data D. Dummeyer: APU FireX Test Data M. Grueneis, R. Moody, B. Hsiao: Mesh Generation Acknowledgment This is an outline of my presentation. I will first talk about the background of this simulation work. Next, I will talk about the introduction and the objective of the simulation method developed, which will be followed by: the simulation methods of approach, including analysis method for FireX system analysis method to predict concentration distribution inside compartments. After that, I will show you some of the results of the validation analyses. And I will present the conclusions made based on the research so far and the future activity.
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Outline Introduction / Background Engine Fire Suppression Process
Simulation Methods: FireX System Agent Concentration Distribution Example Applications: FAA Nacelle Fire Simulator APU Compartment Engine Core Compartment Conclusions Future Activities Outline This is an outline of my presentation. I will first talk about the background of this simulation work. Next, I will talk about the introduction and the objective of the simulation method developed, which will be followed by: the simulation methods of approach, including analysis method for FireX system analysis method to predict concentration distribution inside compartments. After that, I will show you some of the results of the validation analyses. And I will present the conclusions made based on the research so far and the future activity.
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Engine Fire / Overheat Detection and Fire Extinguishing
Engine Fire Switch fireX agent Thermal Sensors Aural / Visual Warnings J. Lee, This slide shows the sequence of engine fire extinguishment. When a fire breaks out inside engine core compartment due to overheated parts and fuel or oil leaks, the thermal sensors detect the fire and then transmits warning signals to flight deck inside a cockpit. Based on correct judgement, pilot turns on the engine fire switch to discharge the fire extinguishing agent from storage bottle to engine. The distribution of agent from storage bottle to engine should be as fast as possible. The agent concentration level should be sufficiently high to put out fire. The agent flow pressure at the exit of the injection nozzles should be high enough to spread the firex agent over the entire compartment cavity.
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Environmental and Physical Properties
(Halon 1301 and Alternate FireX Agents) Chemical Formula CF3Br CF3CHF CF3I CH2CBrCF3 Ozone Depletion Potential Molecular Weight Global Warming Potential Critical Temperature, ºF Atmospheric Lifetime, years Liquid Density at 77 ºF, lb/ft Boiling Point, ºF Heat of Vaporization, Btu/lb Vapor Pressure at 77 ºF, psia Halon HFC CF3I BTP Properties
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Probe Locations inside
Certification Requirement (Engines and APUs) If Halon 1301 (CF3Br) is used as the fire extinguishing agent, the minimum agent concentration is 6 % by volume for a minimum of 0.5 seconds for all 12 concentration probe locations, simultaneously (FAA AC ). Range of Concentration Histories %V/V Time 6.0 ½ sec min. conc. history max. conc. history 1 2 3 4 5 6 7 8 11 9 12 10 Probe Locations inside APU Compartment Injection Nozzle
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Technology Status and Need
No Analysis Tool to Simulate the Entire Fire Suppression Process for Engines and APUs. FireX System can be Over-Designed (Heavy, Excess Discharge of Agent to Environment) or Under-Designed. Installation of Injection Nozzles: Many Ground Tests to meet FAA Requirements. Time-Consuming and Costly. Need an Analytical Tool for Performance Design of FireX Systems: Engine Nacelles / APUs of Commercial, Military Airplanes, Helicopters. Reduces Cost of Design / Certification by ~50 Percent. Technology Ready for Halon Replacement.
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Simulation of Fire Extinguishing Process
Complex Geometries Uncertainties in Airflow Sources Complicated Flow Physics: Two-Phase Agent Jet Flow Droplet Formation / Break-up Droplet Interaction with Solid Surfaces Two-Phase CFD Problems Coupled Transport Phenomena Long Analysis Cycle Time Challenges: Storage Bottle FireX Agent Liquid- / Gas-Phase FireX Agent / N2 Distribution Pipe Injection Nozzles Compartment Vented air Non-Pressurized Engine Core Air/Agent Mixture Gas
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Elements of the Simulation Process
FireX System Analysis CFD Mesh Generation Engine Core Compartment Geometry CFD Analysis for Concentration Propagation Initial Vented Airflow Distribution Post-Processing Histories
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Unsteady Analysis of Agent Injection Process
Storage Bottle Distribution Pipe Multiple Injection Nozzles Agent Mass, Bottle (P, T, Vol), Distribution Pipes, Nozzle Size Hflowx Unsteady BCs at Injection Nozzles ŵ (t)liquid ŵ (t)vapor P (t)mixture T (t)mixture
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Validation Analysis of Hflowx
Agent Types: ICHEM = 1 (Halon 1301) = 2 (HFC-125) = 3 (CF3I) Validation Analysis of Hflowx FLOW SPLIT 9/32”ID ORIFICE 55/8” TUBE NOZZLES STORAGE BOTTLE Halon Mass = 5.2 lbm Bottle Volume = 219 In3 Charge Pressure = 720 psig Test Temperature = 100 ºF
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Predicted Agent Discharge Characteristics
FireX System Conditions Agent Mass: 22 lbm Bottle Volume: 800 In3 Charge Press.: 825 psia Test Temp.: 10 F Pipe Diameter: 0.75 In Pipe Length: 80 Ft Two-Phase Vapor / Liquid Mixture Jet Liquid-Phase Agents Vapor-Phase Agents
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Species Conservation Eq.
CFD Modeling of Agent Injection / Conc. Propagation Process • Mass Continuity Eq. Momentum Eqs. Energy Eq. Species Conservation Eq. Turbulence Model Eqs. Species Transport Eq. Air / Agent Gas Mixture Eulerian Description Liquid Agent Droplets Mass Transport Eq. (Evaporation) Momentum Transport Eqs. (Trajectories) Energy Transport Eq. (Heat Transfer) Lagrangian Description 2 - Way Coupling Injector nozzle
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CFD Input Data / Solution Control
Unsteady Vented Airflows: Pre-Cooler Air, Bleed Air Turbine Cooling Air, Leaks Unsteady Agent Injection at Nozzles: Vapor-Phase Flow Liquid-Phase Flow Droplet Size Two-Phase Flow Velocities Droplet Break-up Model. Droplet-Solid Surface Interaction. Non-Slip / Thermal BCs on Surfaces. Thermodynamic Properties of Agent. Variable Time Steps Agent Injection Concentration Propagation yes Buoyancy Effect All Transport Eqs. Under-Relaxation Scheme Double-Precision Calculation Precision 2nd –Order Upwind Discretization Schemes SIMPLE Pressure-Velocity Coupling 30 ~60 Iterations per time-step 2nd–Order Implicit Time-Marching Eff. Conditions Solution Controls
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Volumetric Concentration
av = fh / [fh + (1 - fh) (Mh/Ma)] where, fh = Predicted Mass Fraction of Agent Mh = Mol. Weight of Agent Vapor Ma = Mol. Weight of Air av = Volumetric Concentration v, %V/V time, sec
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Validation Application - Case 1
(FAA Nacelle Fire Simulator) Axial View Vertical Center Plane Pool Fire Test Pan Exhaust Gas Pipe Engine Core Flanges Fuel Nozzles Injection and Orifices airflow gas
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Halon 1301 Concentration Histories
Vented Airflow: Unsteady Airflow Rate: (2.2 steady-state) Temperature: °F FireX Condition: Halon 1301 Mass: 5.2 lbm Bottle Volume: 219 in3 Bottle Charge: psi, 100 °F Discharge Temp.: °F Predicted Measured 4 Probes (12, 3, 6, 9 o’clocks) (4:30, 7:30, 12, 6 o’clocks) 12 Probe Locations
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Initial Airflow Pattern
Validation Application - Case 2 (APU Compartment) Surface Mesh Side View Top View t = 0.30 sec after injection Initial Airflow Pattern The picture on the upper left, which was generated using the developed CFD mesh, shows some important parts including the injector nozzle. The 777/APU has one agent storage bottle with the volume of 536 cubic inches which carries 14 lbm of Halon charged with Nitrogen at 600 psi. The two-phase Halon liquid/vapor jet flow at the injector nozzle was predicted using the HFLOW. The nozzle injects the Halon liquid/vapor mixture over approximately 0.5 second period. The mass fraction of liquid-phase Halon was approximately 95 percent. Using the Halon flow conditions at the nozzle as the boundary condition and the airflow condition at 3 second after the engine shutdown as the initial condition, the time-dependent concentration distribution inside the compartment should be analyzed using the Fluent CFD code for approx. 10 second period. The separately analyzed initial air temperature was 125 ºF. The predicted Halon concentration distribution at 0.06 second after the Halon injection are shown by the iso-concentration contours on the right-side of the vufoil.
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Halon 1301 Concentration Histories
2 3 4 5 6 7 8 11 9 12 10 Probe Locations Agent Injection: Halon Mass: lbm Charge Pressure: 600 psi Bottle Vol.: In3 Vent Air: Initial avg. Air Temp.: ºF Transient Vented airflow Measured Predicted
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Validation Application - Case 3
(Engine Core Compartment) Surface Mesh Airflow Streamlines Halon 1301 Flow: Mass (CBrF3) = 22 lbm Bottle Volume = 800 in3 P (Charge) = 825 psia Vented Airflow: Flow Rate = lbm/sec t = 0.13 s t = 3.70 s t = 7.10 s
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Analysis Types / Cycle Times
♣ : CPU time depends on: Total simulation time; Size of CFD mesh; No. of injection nozzles; No. of droplet sizes; No. of droplet starting locations per nozzle; No. of computer processors; Convergence criteria, etc. 1 Injection Nozzle ~1 Wk ORIGIN 3800 (6 cpus) 0.32 Mcells ~0.5 Day (4 cpus) < 1 Min. SGI Octane2 400 MHz Remarks Analysis Time♣ Computer Platform Unsteady Agent Injection / Concentration Distribution Steady- State Initial Airflow Distribution FireX System Types
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Key Factors for Improved Simulations
Analysis Domain based on Fire Suppression Process. Advanced Flow Physics Models: - Two-Phase Agent Jet Flow - Droplet Interaction with Solid Surfaces Accurate Airflow / Agent Jet Flow Boundary Conditions. Refined CFD Mesh including Details of Important Geometry. Accurate Property Correlations of Agents.
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Conclusions Simulation Methods for Fire Suppression Process inside
Aircraft Propulsion Systems have been Developed. The Capabilities of the Methods have been Demonstrated by Simulating the FireX Tests of Engines and APUs. Predicted Concentration Histories are well Correlated with Measured Data. The Simulation Methods need to be Improved for More Accurate Prediction of Concentration Histories.
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Future Activities Continuous Improvement of
the Developed Methods to Enhance Applicability and Practicality. Support the Design and Installation of FireX System for Commercial, Military Airplanes, Helicopters, and for Halon Replacements. Complement of the FAA Certification Tests. 7E7 Dreamliner
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