Fire Suppression Simulation Study

Kshitij (KD) Deshmukh, Ph.D.

Automatic Fire Extinguishing Systems (AFES)

Protect against fuel fires inside military and commercial vehicles (air,

land, and sea)

– Occupant areas

– Cargo areas

– Engine compartments

– Landing gear bays

Background

Designing the system is difficult

– Nozzle type, placement, suppressant concentration

– Especially in a cluttered volume

Simulation is a cost-saving tool to evaluate and optimize the design before

test & build

STAR-CCM+ is uniquely suited for this simulation:

– Complicated geometries

– Complex multiphase physics

– Fuel combustion

– Suppression chemistry

– Generation and transport of toxic gases

– Other crew survivability criteria

Why model Fire Suppression Systems?

Effective fire suppression agents are mostly HFC

HFC materials have high Global Warming Potential (GWP) & Ozone

depletion potential (ODP) - thousands of times that of carbon dioxide

Fire Suppression Simulation study

– To test out concept agents without expensive testing and experiments

– To optimize agent bottle location to maximize suppression efficacy

– To minimize delivery dosage of agent concentration for suppression to keep

adverse effects below lowest acceptable level

– To simulate actual vehicle and tactical scenarios using exploratory test box

simulation setup and experimental test data

Fire Suppression Simulation Study

5 suppression agents simulated over 4 years

Only FM200+SBC discussed here

FM200 = C3HF7 (liquid) & SBC = NaHCO3 (solid)

Geometry: Exploratory test box

Mesh 158K Cells, Walls @ 130 F

Ref. Fire Extinguishing Agents for Protection of Occupied Spaces in Military Ground Vehicles,

Steven E. Hodges, Steven J. McCormick, Fire Technology, Volume 49, Issue 2 , pp 379-394

Physics Models

• Start at fire detection

• Model fireball build up

• Model for small time past discharge

Transient Analysis

• K-epsilon

• Realizable wall functions

• Segregated solver

Turbulence Model

• Two-way coupling

• Evaporation for liquid droplets

• Devolatilization & combustion of solids

Lagrangian Physics

• Liquid spray using droplet distribution

• Auto flash

• Continuous injection

Liquid Fuel Injection

Physics Models

• Mimic release from pressurized bottle

• Both liquid and vapor phase

• Discharge tapers with falling pressure

Suppressant Discharge

• Hybrid EBU w/ finite rate kinetics

• 14 species & 12 reactions reduced set

• Soot as transported scalar

Combustion Model

• Catalytic & non-catalytic effects

• Success criteria = thermal + chemical

• Acid gases monitored

Suppression Mechanisms

• Participating media DOM S4

• User-coded absorption coefficient

• WSGG model for CO2, H2O & Soot

Radiation Model

Fire Suppression animation # 1

Fire Suppression animation # 2

Crew Survivability Criteria

Parameter RequirementConsidered in

CFD?

Fire suppression Extinguish all flames w/o reflash

Skin burns < 2nd degree burns over 10 sec

Overpressure < 11.6 psi

Agent concentration Below adverse effect level

Acid gases

(HF + HBr + 2 COF2)< 746 ppm over 5 minutes

Oxygen level > 16%

Discharge noise Below hearing protection limit ×

Discharge forces Not to exceed 8g ×

Exploratory test box results comparison

Setup tailored to capture successful suppression

rather than suppression failure

Criteria Above Design conc. Below design conc.

Experiment CFD Experiment CFD

Overall PASS PASS FAIL FAIL

Extinguish all flames YES YES YES NO

HF acid (PPM) < 20 47 3975 N/A

COF2 acid (PPM) <20 97 1550 N/A

O2 levels 17.4% 18.0% 16.5% N/A

Application to Nozzle design

Nozzle configurations

I II

I II

Discharge patterns: Fire Ball (red), SBC (yellow), FM200 (Blue)

Challenge:

– Fire suppression system design is challenging due to demanding requirements,

cluttered environments, and complex physics.

– Development efforts include many design / test / fail / repeat cycles.

Solution:

– CFD-based simulation of the fire suppression event predicts whether the design

will meet suppression success criteria.

– STAR-CCM+ is unique in having this capability in a general-purpose CFD tool.

Impact:

– Reduction in time and cost by evaluating and optimizing on virtual designs prior

to test.

– Minimal development effort due to commercial, off-the-shelf CFD tool.

– Improved occupant survivability in case of a fire.

Summary

Fire Suppression Modeling using Computational Fluid Dynamics,

Vamshi M. Korivi, Bradley A. Williams, Steven J. McCormick, Kshitij Deshmukh,

2014 NDIA Ground Vehicle Systems Engineering & Technology (GVSETS) Symposium,

Novi, MI, 14th August 2014, http://ww2.esd.org/gvsets/