FLUID DISPENSING AND DISPERSION 

Jiann C. Yang 

Building and Fire Research Laboratory 

National Institute of Standards and Technology (NIST) 

MS 8662, Gaithersburg, MD 20899 USA 

Jiann.yang@nist.gov

and 

David R. Keyser 

Naval Air Systems Command (retired) 

Patuxent River, MD 20670 USA 

now 

SURVICE ENGINEERING Co. 

P.O. Box 900, Lexington Park, MD 20653 

dave.keyser@survice.com 

INTRODUCTION 

This paper is a condensed version of a chapter in the forthcoming Next Generation Program 

(NGP) final report edited by the authors. It summarizes the research conducted during the NGP 

program on fluid dispensing and dispersion within aircraft engine nacelles by various principal 

investigators, including the authors. 

Fire-suppression systems for protecting aircraft engines typically consist of a suppressant storage 

bottle(s), a piping system connecting the bottle(s) to the discharge port(s), and the discharge 

nozzle(s). In some cases, nozzles are not used; the fluid simply discharges from the pipe-end. 

Fluid dispensing addresses the multi-component, two-phase flow of the fire suppressant through 

the piping before it is discharged. Fluid dispensing includes the initial conditions for agent 

discharge that affect the subsequent dispersion of the suppressant. The fluid dispensing aspects 

will be discussed in the Fluid Storage and Fluid Transport through Piping sections. The aspects 

of fluid storage are related to the determination of the thermodynamic state of the fluid in the 

bottle and the sizing of the bottle required to accommodate sufficient agent required for fire 

suppression without compromising the bottle’s structural integrity. The discussion of fluid 

transport through piping describes the flow of fire suppressant through various piping 

configurations (straight pipes, bends, tees, etc.). The two-phase computer code was derived from 

a code widely used in the nuclear industries. This program was benchmarked against transient 

experimental data available in the literature as well as experiments conducted in the NGP. 

Bench-scale and full-scale experiments and computer modeling were used to determine fluid 

dispersion. If the suppressant is a gas, then dispersion may not be an issue because the gas 

usually will be dispersed easily throughout the protected space. If a superheated liquid agent is 

released, flashing will occur which also facilitates dispersion. Halon 1301 is such an example. 

Because of its flashing characteristics and rapid evaporation, the dispersion of halon 1301 in an 

enclosure, even cluttered with obstacles, usually poses no difficulties. If the suppressant has a 

high normal boiling point, or it is released at temperatures below its normal boiling point, liquid 

1
droplets will be atomized at the discharge nozzle. The actual droplet size-distribution delivered 

to the fire will be different from the initial distribution at the nozzle. After liquid droplets form, 

depending on their number density and ballistics (even before they arrive at the fire zone), 

droplet-droplet and droplet-surface interaction often occurs in the highly-cluttered environment 

of the nacelle. These processes may alter the initial droplet size and velocity distributions 

significantly. The presence of high-speed airflow can also affect the droplet size and velocity. If 

the dispersing spray impacts a solid obstacle, pooling, dripping, splitting, splashing, or shattering 

of the droplets will result. Dripping and pooling retain the liquid on the nacelle’s bottom 

surface; cutting or splitting of the impacting droplet at the edge of the surface may result in 

smaller droplets, as can splashing and shattering. The surface temperature also plays a role in the 

droplet-surface interaction. 

Serious fires in aircraft engine nacelles, sufficient to terminate a mission, usually involve liquid 

fuel − either jet fuel or hydraulic fluid supplied by a leak in its supply system. There are two 

primary types of fire: spray or pool. Fuel sprays occur when a pressurized line develops a 

relatively small orifice, caused by battle or other damage, which results in a misting or atomized 

discharge of droplets. Fuel from larger openings in pressurized lines may flow over the hot 

surfaces and ignite there, or end up in pools below the engine contained by aircraft structure or 

other clutter. The typical sources of ignition are: electrical sparking or hot surfaces. Because 

aircraft engines produce and reject large amount of heat, many large hot surfaces exist on the 

outside of the engine. The air required to maintain combustion is furnished by flow from the 

atmosphere for which the original purpose is to cool the engine. 

The most likely region for fires in engine nacelles is the long, narrow, annular space between the 

engine core and the outer aerodynamic skin. A large number of components are located within 

this region resulting in a complex, cluttered geometry. The nacelle design typically includes 

ventilation, either via an external scoop or other source, to both cool the engine and avoid the 

build-up of flammable mixtures. In general, this engineered airflow has sufficient momentum to 

dominate the buoyancy produced by burning, and the dynamics of a fire within a typical nacelle 

are dominated by the designed airflow. 

Presently, suppression system-proving tests are performed on the ground using airflows which 

replicate flight conditions. Test fixtures, such as the Aircraft Engine Nacelle Fire Test Simulator 

(AEN) at Wright-Patterson AFB (WPAFB) in Dayton Ohio and the Ground Test Nacelle 

Simulator at Patuxent River NAS (Naval Air Station), have been constructed to represent fullscale geometries typical of aircraft nacelles. Extensive sets of experiments and live-fire tests 

with varying degrees of complex internal geometry have been conducted to evaluate the 

performance of suppression systems and new agents. These tests and experiments have provided 

significant insight into the essential features of successful systems and serve as the bases for 

present acceptance tests. However, the results from these tests, particularly when fire 

extinguishment (as opposed to merely the concentration of agent) is the criterion, are often 

difficult to understand given the lack of a detailed, well-characterized flow field. 

Adding to the difficulty in extinguishing fires in nacelles, especially in flight, is their cluttered 

interiors, as shown in Figure 1. These bluff bodies create many “flame-holders” and 

recirculating zones into which the suppressive agents have difficulty penetrating. In the case of 

2
fires in flammable liquid in the bottom of the nacelle, the pool fire is often temporarily 

suppressed by an agent, but rapidly flares up again after the agent is exhausted. The re-ignition 

of the liquid pool is probably caused by continuing vaporization from the pool near adjacent hot 

surfaces having temperature above the ignition point in spite of the suppression. 

In addition, a phenomenon, termed accelerated burning, was witnessed in this test program 

which resulted from too-slow injection of insufficient agent to suppress the fires. It is believed 

that the injection transient served to facilitate mixing of fuel vapor and air leading to a more 

intense fire than if nothing had been done. 

Figure 1. Typical aircraft engine nacelle clutter. 

FLUID STORAGE 

When the suppressant is a fluid, it is stored in a pressure vessel. In most applications, the release 

or discharge of its contents depends on the initial and transient pressure within the ullage. For a 

pure fluid, the ullage will be at the vapor pressure of the fluid at the prevailing temperature. If 

the applications are limited to room temperature or above, fluids with high vapor pressures at 

room temperature may be released at an adequate rate. However, such a discharge becomes 

problematic at very low temperatures such as those typical of the upper atmosphere. The 

conventional way to alleviate this problem is to use a suppressant gas (e.g., nitrogen) to raise the 

pressure above the vapor pressure of the fluid. Alternatively, the so-called hybrid system, which 

uses a solid propellant gas generator (SPGG), upon activation provides the pressure to drive the 

fluid out of the bottle. The hybrid system will not be discussed here; the focus of this section is 

on pure fluid pressurized with a suppressant gas. 

The thermodynamic state of the fluid in the bottle not only determines the initial conditions for 

discharge in case of a fire, but it also provides data for the structural design of size and strength 

of the bottle at elevated temperatures. 

The bottle pressure is a complex function of ambient temperature because of the temperaturedependence of the fluid’s vapor pressure, the partial pressure of the added nitrogen in the ullage, 

and its solubility in the fluid. For halon 1301, the pressure-to-temperature relationship and the 

solubility of nitrogen have been characterized well. Unfortunately, for many potential 

replacement fluids, such relationships and solubility data do not exist. 

3
The thermodynamic state of the storage container can be determined by an appropriate equation 

of state applicable to mixtures (fluid and pressurized gas) with empirically determined binary 

interaction coefficients [1]. Other thermodynamic frameworks have also been used [2]. In the 

following, the development of a computer code, named PROFISSY (acronym for PRoperties Of 

FIre Suppression SYstems) [3], to calculate the thermodynamic state in the bottle will be 

discussed. 

PROFISSY was developed to help bottle designers or users to estimate temperature-pressure 

characteristics of their contents. The program also predicts whether a liquid-full condition would 

occur at elevated temperatures for a given initial fill, defined as the amount of liquid divided by 

the vessel volume. When thermal expansion of the initial liquid fills the vessel completely as the 

vessel is heated, the internal pressure of the vessel will rise sharply at elevated temperatures [2]. 

The current PROFISSY code, running on a PC, supports thermodynamic state calculations for 

halon 1301, FC218, CF3I, HFC125, and HFC227ea. Experimental data have been obtained to 

compare to the code’s predictions for these fluids [4]. In general, the predictions were found to 

be within +10 % or less of the measurements. The code can be extended to include other fluids 

with added nitrogen. 

FLUID TRANSPORT THROUGH PIPING 

A key technical approach in the present program was utilization of advancements made in other 

applications that deal with multi-phase flows. In particular, the highly sophisticated computer 

codes that have been developed for thermal-hydraulic analyses of nuclear power systems have all 

the characteristics required for fire-suppressant systems. These include models that account for 

relative slip between liquid and vapor phases, thermodynamic nonequilibrium between the 

phases, changes in two-phase flow regimes, choked flows, and transport of noncondensable 

gases. Such codes are also structured for numerical analysis of fast transients, well capable of 

the transients anticipated for suppressant systems. 

As stated above, the current halon-delivery systems generally consist of a pressurized vessel 

connected to the delivery locations by a piping manifold. The suppressant fluid is maintained in 

a liquid state by the pressurization of the system, usually up to several MPa. The system is 

activated by a quick-opening valve in response to either an automatic or manual trigger which 

then expels the suppressant through the piping. This system must deliver all the fluid to the 

discharge locations very quickly, generally within 0.1 s to 10 s. 

Since halon and its potential replacement fluids are in a vapor state at standard pressure and 

temperature, at the discharge location the fluid will be a two-phase mixture of superheated liquid 

and vapor in thermal nonequilibria. Also, because of the large pressure difference between the 

source and the downstream exit, continuous flashing is anticipated as the fluid travels through 

the piping, and two-phase choked flow may occur at various locations inside the manifold. 

Hence, to predict the performance of the delivery system accurately, a computer code must be a 

transient, nonequilibrium, two-phase code. The short delivery times require fairly high flows, 

which tend to promote homogeneous two-phase flow, i.e., little slip. However, in imbalanced 

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piping networks, with side tees and other fittings, some separated flow may occur (stratified 

flows, slug/plug flow, etc.). Hence the code should be able to predict slip between phases and 

the corresponding effect on pressure losses, which can be important when separated flow 

encounters a directional change, such as at a side tee. The ability to predict the transport of 

noncondensable gas is also important. The fluid, pressurized with a gas, is initially saturated 

with the gas. During the delivery and as the system depressurizes, the added gas comes out of 

solution and expands, and this evolution must be included. One additional requirement is that 

the code should be useful for estimating the transient hydrodynamic loads on the piping. Thus 

the momentum equations need to be sufficiently detailed to estimate the unbalanced force in 

piping sections between elbows and other fittings. 

The code is based on a one-dimensional, two-fluid model of two-phase flow. In this model, 

separate conservation equations are written for the liquid and gas phases for mass, momentum 

and energy. Constitutive relationships are specified for interphase transport of mass, momentum 

and energy. Heat transfer between the fluid and passive structures such as pipe walls are 

modeled. The program also contains built-in models for wall friction and two-phase critical 

flow. The transport of noncondensable gas in the system, namely the nitrogen gas, as well as the 

nitrogen released from solution during the agent’s discharge, is modeled via separate mass 

conservation equations, with constitutive relations to specify the rate of gas release. The 

conservation equations are solved using a semi-implicit numerical method, with user-supplied 

boundary and initial conditions. 

The program was deliberately made flexible in terms of types of fluids and piping layout. The 

current version of the program allows the user to select any one of five fluids – water, 

halon 1301, CO2, HFC-227ea or HFC-125. Modules are available in the program with which the 

user can model a delivery system, including one or more supply tanks and a combination of 

piping networks. The user can also model valves in the system, with specified valve opening 

times if needed. 

The code-development effort included an experimental task to obtain data needed to assess the 

code. The experimental program utilized a discharge loop using several suppressants. Major 

flow parameters which have not been measured heretofore were measured successfully. These 

include measurements of instantaneous discharge rates, fluid temperatures, and void fractions at 

various locations along a discharge pipe [5]. 

Such a discharge is a highly transient process, generally lasting from less than a second to a few 

seconds. The program was benchmarked against transient experimental data available in the 

literature, as well as experiments conducted as a part of this project, on the discharge of HFC227 and HFC-125 in a specially prepared discharge loop. The present experiments lasted from 

1.5 s to 6 s. In addition to transient pressures at various points, these experiments also measured 

parameters such as the transient mass discharge, fluid temperatures, and the void fraction near 

the exit. These are the first dynamic measurements of mass flows, fluid temperatures, and void 

fractions using suppressants. These new data allowed a more comprehensive assessment of the 

computer program than was possible with previous experimental data. The results of the 

assessment showed that the program is capable of predicting the performance of various delivery 

systems with several fluids. 

5
FLUID DISPERSION IN HIGHLY-CLUTTERED NACELLES 

The release and transport of an agent into an engine nacelle is sensitive to local geometrical 

features or “clutter” that are difficult to resolve numerically without using an excessively large 

CFD (Computational Fluid Dynamics) grid. Examples include wire bundles or hydraulic lines. 

Capturing these features in a grid will result in extremely small time steps for accurate numerical 

simulations of the agent’s release and its subsequent suppression or extinguishment of the fire. 

An alternative is to use a sub-grid scale model to represent the macroscopic effects of these small 

features using reasonably sized CFD grid-cells. This approach permits faster and more efficient 

iterative simulations of the nacelle and its fire-suppression design during the aircraft’s conceptual 

and preliminary design phases—thereby reducing the time and cost of final qualification testing 

of the system. 

The research effort focused on the development of sub-grid scale models for CFD and the 

experimental validation of these models using data obtained from flow measurements around 

simulated clutter packages and a simplified quarter-scale nacelle simulator with well-defined 

boundary conditions and suppressant dispersion and fire test data from a full-scale nacelle 

simulator. In addition, the dispersion of high-boiling point agents and low-temperature 

dispersion were also examined. 

Quarter-Scale Nacelle Simulations and Tests 

Quarter-scale experiments (to allow access of appropriate diagnostics guided by pretest 

calculations) were performed at WPAFB [6]. Flow conditions were scaled to match the 

Reynolds numbers in the extensive set of experiments performed in the AEN facility as part of 

the Halon Alternatives Program. Calculations were performed using both the CFD-ACE code (a 

commercial computational fluid dynamics model with a body-fitted coordinate grid) and the 

VULCAN code (which is a CFD fire-field model using a Cartesian grid and for which sub-grid 

scale models were developed) and then were compared with experimental data at multiple crosssections within the flow field. 

Transport around Clutter and Recirculation Zones 

Experiments were conducted to quantify velocity, turbulent intensity, and drag on various bluffbody shapes in a low-speed, highly turbulent wind tunnel. The experimental data were obtained 

using thermal anemometry and were intended to validate CFD codes. Circular cylinders (single 

and in tandem), spheres (single and tandem), a simulated wire bundle, a structural rib, and a 

cubic arrangement of spheres with cylindrical connectors were tested from 1 m/s to 10 m/s in a 

free-stream turbulence intensity of approximately 10 %. A circular cylinder was also tested in 

laminar flow at a turbulence intensity of 0.6 % for comparison with published data. Drag 

measurements were estimated using a momentum-deficit approach. The results show higher 

turbulence behind the bluff body when compared to the same configuration in a laminar flow 

field. Also, the drag coefficients were lower than the same configurations in laminar flow. 

6
The flow in an aircraft engine bay is low speed and highly turbulent. The data from these tests 

were used to develop a sub-grid-scale model to account for the effects of small objects in the 

engine bay that are difficult to resolve using a CFD mesh. The data were collected using a single 

thermal anemometry probe traversed upstream and downstream of sixteen configurations. The 

data were analyzed to obtain mean velocity, turbulent intensity, and drag coefficient. In addition, 

the data history was analyzed to gage the Strouhal number of the bluff-body wake. 

Full-Scale Nacelle Modeling and Testing 

The NAVAIR’s full-scale ‘Iron Bird’ nacelle at NAS Patuxent River, Maryland, which generates 

conditions typical of an advanced tactical aircraft, was used for this effort. Figure 2 shows the 

fire test simulator. The nacelle is roughly 3.18 m long. The width and height vary significantly 

along the length, but are contained within a region 1.45 m high and 1.15 m wide. The simulator 

is designed for testing at one flight condition, traveling at 0.55 Mach number at sea level. 

Figure 2. Ground Test Nacelle ‘Iron Bird’ Simulator. 

The VULCAN code was used to perform full-scale nacelle modeling. The fire-suppression 

model for VULCAN is based on a critical Damköhler number (the ratio of the mixing or flow 

time to the chemical time) for extinction. For Damköhler numbers smaller than a critical value, 

the flame will be extinguished. Chemical time-scales for suppression were obtained using 

perfectly-stirred reactor (PSR) calculations with detailed chemistry to determine the PSR mixing 

time that corresponds to extinction. Combustion in VULCAN is modeled using the eddydissipation concept (EDC) − a distribution of PSRs that relate the fuel-consumption rate to the 

fluid-mixing rate, the latter obtained from turbulent time-scales. Radiative thermal losses and 

losses to the walls, while included in VULCAN, are neglected in the suppression model because 

the magnitude of these losses is dependent on the heat flux through the wall, which is unknown. 

Estimates indicate that heat losses to obstructions are significant here and tend to increase the 

chemical time-scale. 

7
The ground simulator was outfitted with a set of four suppressant nozzles that were found to be 

sufficient to suppress a fire when 3.2 kg of suppressant was discharged. Numerical simulations 

have been conducted for suppressant injection through these nozzles into the nacelle (in the 

absence of a fire) to obtain information on the distribution through the nacelle [7]. The 

suppressant was assumed to enter the nacelle in the vapor phase or to vaporize very rapidly 

relative to other time-scales. The suppressant’s mass flux for each nozzle was assumed to be 

proportional to the nozzle area. 

As a measure of sufficient distribution in the nacelle, the portion of the nacelle volume for which 

the suppressant’s mass-fraction exceeds 30 % has been used for characterization. Even with 

low-intensity mixing, this amount generally is sufficient for extinction and represents a 

conservative estimate of suppressibility. The failure to fill the nacelle completely does not 

indicate that suppression will not occur, but rather reduces the confidence in suppression. If the 

turbulent mixing in the nacelle were sufficient to create homogeneity, the mass fraction 

throughout the nacelle would exceed 0.3 for all of the scenarios simulated. Clearly, 

inhomogeneities arising from imperfect mixing are significant. 

Simulations were also conducted to ascertain the effect of removing a single suppressant nozzle, 

while keeping the overall mass of injected suppressant constant at 3.2 kg injected uniformly over 

3 s. For these conditions, the nacelle volume in which the fraction exceeds 0.3 was evaluated. 

These results were compared to those shown for all four nozzles functioning; the nacelle was 

completely filled, according to this criterion, for the range of flows considered. The simulation 

results indicate that depending on nozzle location, the removal of one nozzle results in no, little, 

or significant effect on suppressant distribution throughout the nacelle. 

Pool fires stabilized behind obstructions have been identified as among the most challenging 

fires to suppress [8, 9]. Obstructions such as structural ribs provide a region of recirculating 

flow that suppressant is relatively slow to penetrate where hot products help stabilize the flame. 

In certain scenarios, such as those described in [7, 10, 11] the concentration must be maintained 

at an elevated level in the flow past the stabilization region for a substantial period to ensure that 

adequate suppressant penetrates the stabilized region. 

Several pool-fire configurations and locations within the nacelle were used in the simulations. 

The calculated results indicate that pool fires at certain locations are difficult to stabilize because 

of the peculiar circulation. The surface areas of the largest possible pools in each section were 

measured in the ground-test simulator. Similar pool areas have been used in the simulations. 

The pools were assumed to be filled with JP-8, and the evaporation rate was based on heat 

feedback to the pool. In general, it is difficult to predict the thermal feedback to a pool from a 

fire, because these fires are partially advected beyond the pools by the convective flows in the 

nacelle. It is particularly difficult to determine the evaporation rates without measurements. The 

uncertainty of the evaporation rate may be as high as 50 %. Suppression was predicted for all 

pool fires in the nacelle using a specified four-nozzle configuration and 3.2 kg of suppressant 

when this mass was injected over three or four seconds. 

To examine the effect of varying the mass of suppressant injected and the rate of injection, a 

series of additional simulations for fires in a specified pool configuration were conducted. It is 

8
noteworthy that the mass of suppressant injected plays little role in determining the occurrence of 

suppression here. There will be a lower bound in terms of suppressant mass injected over a short 

period, although this has not been identified here. More significant in practice is the duration 

over which suppressant will act to inhibit reignition and allow cooling of heated surfaces. Thus 

the requirements are likely to be dictated by a combination of the rate required to flood the 

compartment with a high enough concentration and the mass required to maintain that 

concentration to inhibit potential reignition sources. 

Suppression is sensitive to heat flux from the fire to the pool. If the heat flux and, hence, the fuel 

evaporation are reduced by 50 %, suppression is substantially easier for the cases considered. 

Similar results are expected if the fuel is cold or if there are substantial heat losses through the 

nacelle under the pool. While relatively high engine temperatures are expected during 

operations, temperatures during ground tests may be such that reduced evaporation is 

experienced. 

The capping of various nozzles caused large-scale inhomogeneities that left certain regions with 

little suppressant. A series of simulations was conducted where one nozzle was assumed to 

remain capped. To examine the effects of these inhomgeneities for the majority of these 

simulations, the flow from each of the other nozzles was maintained at previous values when all 

nozzles were open, giving a reduced rate for the sum of the three remaining nozzles and an 

increased duration of injection. For fires in the extreme forward and aft pools, the removal of 

various nozzles did not alter the predicted suppression. 

As the rate of injection was reduced to a third or more, many volumetric regions of the nacelle 

did not have sufficient suppressant for all fires. This was caused by inhomogeneities in the 

concentration, since the average concentrations in the nacelle were sufficient to suppress all fires. 

Suppression also failed as the rate of injection was reduced to one third or more. Sensitivity 

studies in these simulations disclosed that the pool vaporization is very sensitive to temperature, 

heat losses, details of the geometry, and the momentum associated with injection. 

The model-validation experiments described above and others for studying fire-suppression of 

obstruction-stabilized flames were conducted in roughly square wind tunnels. In aircraft engine 

nacelles, the width-to-height aspect ratio tends to be large. The characteristic dimensions 

identified are obstructions on the order of 5 cm in height in wide channels on the order of 10 cm 

to 30 cm. In each of these simulations, the inlet velocity was 5 m/s, the turbulent intensity was 

10 %, and the turbulent length-scale was 0.025 m. Pool sizes were narrow relative to the channel 

width. Simulations indicate that dilatation from a pool fire behind a rib induces secondary 

recirculation sweeping the fire outward and along the ribs transverse to the flow. Observation of 

these flow-fields indicates that they may reduce the suppressant penetration into certain portions 

of the flame-stabilized region. However, within aircraft, structural supports and clutter are 

observed to be oriented in both transverse and longitudinal directions. The consequences of 

longerons (streamwise obstructions) were examined by adding longerons just outside of the pool. 

It was observed that the longerons do not prevent spread of the fire beyond the ribs. Massfraction profiles in the recirculation zone indicate, however, that longerons do affect the flow, 

because rate of transport of agent is greater with ribs than without. Further, the time to suppress 

the fire is reduced. If longerons reduce the time required to suppress a fire, a series of 

9
experiments in high-aspect-ratio wind tunnels could be conducted. If the experiments were 

consistent with the simulations, then both the potential of reduced suppressibility caused by 

dilatation and the possibility that longitudinal clutter ameliorates it become considerations in 

design. 

VULCAN was used to predict the results of the fire tests. Table 1 shows a condensation of all 

tests for which simulations were available. The primary observations therein include whether or 

not the fire was extinguished, the model’s predictions, the period of injection of the agent, and an 

estimate of the observed times-to-extinguish versus the predictions. These latter comparisons 

required a bit of interpretive judgment unique to each simulation to decide when extinction was 

complete. Similarly, while the injection period for the actual fire-test data was acquired, the link 

between the recording video and the data-acquisition system had failed, unbeknownst to the test 

engineers. Consequently, the synchronization of the visual data to the agent-injection transient 

was not available during post-processing. The time of extinction was clearly observable with an 

uncertainty of ± 0.1 s, but the initiation of mixing the agent could be observed only by a sudden 

increase in the intensity of the fire. The uncertainty of this observation is estimated to be ± 2 s.

Table 1. Comparison of Fire Test Results and Pretest Simulations. 

Test Fire Test Fire Test VULCAN 

Test number Time to extinguish (s) Agent injection, Rise time (s) Time to extinguish (s) 

2 Out in 1.3 s 6.8 1.1 (estimated) 

3 & 12 Accelerated Burning 10.0 Marginal out 

5 Out in 5.2 s 7.0 1.9 (estimated) 

6 Out, no data No data 1.9 (estimated) 

7 Out in 4.4 s 9.5 Out 

8 Out >6.3 s 4.4 1.9 (estimated) 

9 Out in 4.85 s 5.0 n/av 

10 & 11 Out in 2.3 s 9.6 n/av 

13 Out in 11.2 s 6.5 Not out 

14 Not out 10.4 Not out 

15 Out in 28.9 s 7.2 3.4 (estimated) 

16 Not out 9.3 Not Out 

17 Not out 10.8 Not out 

18 Out in 6.0 s 5.6 1.5 (estimated) 

23 Not out 13.8 N/A 

24 Out in 3.9 s 3.8 N/A 

25 Out in 1.8 s 2.4 N/A 

Dispersion of Agents with High Boiling Points 

As part of a halon replacement research program, new high-boiling-point chemical suppressants 

have been identified. These agents would discharge in a liquid state, breaking into liquid 

droplets, and then be entrained within the flow passing through the nacelle, impinging on various 

10
objects prior to reaching the fire. The goal of this research was to enhance the fundamental 

knowledge of interactions of sprays with clutter. To this end, this program focused on the ability 

of water sprays to pass through a series of cylindrical obstacles, representing generic clutter, 

while moving in a turbulent co-flow. Results indicated that the amount of suppressant captured 

by the clutter was directly related to the stream-wise spacing of the clutter and co-flow air speed 

at the clutter location. A low-speed flow facility with the test section’s air speed ranging from 

0 m/s to 12.0 m/s was modified for the current program. The major components of this facility 

include an inlet contraction, a turbulence generator, a test section, a clutter section, and the return 

and separation plenum. The results of this work provide valuable insight into the transport of 

liquid agents through nacelles and provide essential data to develop sub-models to aid in the 

design of fire-suppression systems for aircraft [12]. 

Low Temperature Agent Discharge 

To assure that there is no substantial deterioration in dispersion or performance of agents at 

temperatures below their normal boiling points, tests in a simulated aircraft engine nacelle were 

conducted. CF3I (with normal boiling point of −22 oC) was used as a surrogate for the study. 

These discharge tests were performed at −40 oC. The experimental apparatus, (called Extremely 

Low-temperature Environment For Aircraft Nacelle Testing, ELEFANT) consisted of a 

simulated engine nacelle with baffles, an agent release port, four observation windows, and two 

measurement ports. To achieve an operating temperature of –40 °C, the entire facility was 

placed inside an environmental test chamber, and the cold experiments were conducted inside the 

chamber. Discharge tests at room temperature were also conducted inside the chamber with the 

refrigeration unit turned off to establish baselines for comparisons. 

The results from the two measurement locations in the nacelle have shown that the dispersion of 

CF3I under the cold condition with the equipment and the discharge nozzle used is not very 

effective, and there is substantial reduction in the agent’s vapor concentration. The situation 

worsens at the location furthest away from the agent-injection port. If the extinguishing 

concentration for the nacelle is designed based on room-temperature test data, the measurements 

indicate that dispersion and performance are likely to deteriorate when the agent is used at a 

temperature lower than its normal boiling point. 

ACKNOWLEDGEMENTS 

This work was supported by the Department of Defense, Strategic Environmental Research and 

Development Program, Next Generation Program; Dr. Richard Gann of NIST is the Program 

Manager. 

REFERENCES 

1. Walas, S.M., Phase Equilibrium in Chemical Engineering, Butterworth, Boston, 1985. 

2. Grosshandler W.L., Gann R.G., and Pitts W.M., eds., Evaluation of Alternative in-Flight Fire 

Suppressants for Full-Scale Testing in Simulated Aircraft Engine Nacelles and Dry Bays, 

NIST SP 861, U.S. Department of Commerce, Washington, DC, 1994. 

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3. Yang, J.C., Cleary, T.G., Vázquez, I., Boyer, C.I., King, M.D., Breuel, B.D., Womeldorf, 

C.A., Grosshandler, W.L., Huber, M.L., Weber, L., and Gmurczyk, G., “Optimization of 

system discharge,” in Gann, R.G., ed., Fire Suppression System Performance of Alternative 

Agents in Aircraft Engine and Dry Bay Laboratory Simulations, NIST SP 890: vol. I, U.S. 

Department of Commerce, Washington, DC, November 1995. 

4. Yang, J.C., Huber, M.L., Vázquez, I., Boyer, C.I., and Weber, L., “Measured and Predicted 

Thermodynamics Properties of Selected Halon Alternative/Nitrogen Mixtures,” International 

Journal of Refrigeration, 20, 96-105, 1997. 

5. Tuzla, K., Palmer, T., Chen, J.C., Sundaram, R.K., and Yeung, W.-S., “Development of 

Computer Program for Fire Suppressant Fluid Flow,” Report number ITF 2000-1, Vols. I and 

II, Institute of Thermo-Fluid Engineering & Science, Lehigh University, Bethlehem, PA, 

September 2000. 

6. Black, A.R., Suo-Anttila, J.M., Gritzo, L.A., Disimile, P.J., and Tucker, J.R., Numerical 

Predictions and Experimental Results of Air Flow in a Smooth Quarter-Scale Nacelle, 

Sandia National Laboratories Report SAND2002-1319, Albuquerque, New Mexico, 2002. 

7. Keyser, D.R. and Hewson, J.C., “Fire Suppressant Distribution in an Engine Nacelle,” 

Proceedings of the Halon Options Technical Working Conference, Albuquerque, New 

Mexico, 2004. 

8 Hirst, R., Farenden, P.J., and Simmons, R.F., “The Extinction of Fires in Aircraft Jet Engines 

– Part I, Small-Scale Simulation of Fires,” Fire Technology 12, 266-275, 1976. 

9. Hirst, R., Farenden, P.J., and Simmons, R.F., “The Extinction of Fires in Aircraft Jet Engines 

– Part II, Full-Scale Fires,” Fire Technology 13, 59-67, 1977. 

10. Hewson, J.C., Tieszen, S.R., Sundberg, W.D., and Desjardin, P.E., “CFD Modeling of Fire 

Suppression and Its Role in Optimizing Suppressant Distribution,” Proceedings of the Halon 

Options Technical Conference, Albuquerque, New Mexico, 2003. 

11. Hamins, A., Cleary T., Borthwick, P., Gorchkov, N., McGrattan, K., Forney, G., and 

Grosshandler, W., “Suppression of Engine Nacelle Fires,” in Gann, R.G., ed., Fire 

Suppression System Performance of Alternative Agents in Aircraft Engine and Dry Bay 

Laboratory Simulations, NIST SP 890: vol. II, U.S. Department of Commerce, Washongton, 

DC, 1995. 

12. Presser, C., Widmann, J.F., and Papadopoulos, G., “Liquid Agent Transport around Solid 

Obstacles,” Proceedings of the Halon Options Technical Conference, Albuquerque, New 

Mexico, 2002. 

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