PERFORMANCE DATA ON COLD TEMPERATURE DISPERSION OF CFJ 

Jiann C. Yang, Thoma\ G. Cleary, and Michelle K. Donnelly 

National Institute of Standard\ & Technology 

INTRODUCTION 

Tritluoroiodomethane (CF3I) has been proposed as a potential replacement for Halon 1301 in 

aircraft engine nacelle and dry bay fire protection applications [I, 21. The potential use of CFjI 

in fuel tank ullage inerting has also been considered recently [3J. Before CFiI can be considered 

as a potential drop-in replacement. several operational issues need to he addressed or re-examined. The proposed work is intended to examine one important aspect related to the application of 

CFiI: cold temperature discharge of CFiI into a suh-zero environment. 

Table 1 lists some of the physical properties of CFII and CFjBr. Since CF31 has a normal boiling 

point of-22 "C, the dispersion of CFJ into air at temperatures down to -40 "C may not be as 

effective as halon 1301 which has a normal boiling point of -57.8 "C. Although discharge of 

cold CF3I (chilled to about -40 "C) into a compartment at ambient room temperature has been 

examined at NIST [2], the discharge of cold CF31 into a cold compartment has not been performed, or at least has not been documented in open literature. In order to assure that there is no 

substantial deterioration in dispersion performance of CFil under cold temperature applications. 

discharge tests in a simulated fire compartment at the lowest temperatures expected in servicc 

should be conducted. 

TABLE I. SELECTED PHYSICAL PROPERTIES OF CFiI AND CF3BR [2]. 

Agent Molecular weight Th T, p, P, MI 

(kpimoll ("CI ("Ci (MPa) (keirn' i (hJikf) 

CF3I 0. I Yh -22.0 122.0 4.04 87 I 106 

CF7Br 0.144 -57.8 67.0 4.02 145 Ill 

T,, is the normal boiling point: T, is the critical temperature; P, is the critical pressure: p, is the 

critical density: AH is the latent heat of vaporization at T,]. 

An example is used to illustrate the importance of studying the discharge and dispcrsion of CFJ 

in a suh-zero environment. Consider a 3 L container with 4.5 kg of CFd pressurized with nitrogen to 4.12 MPa (600 psia) at 22 "C, If this container with agent is cooled down to 40 "C, the 

final pressure of the container is estimated to be 2.8 MPa using the computer code (PROFISSY) 

developed by the National Institute of Standards and Technology [2]. Assuming the discharge of 

the liquid agent from the container is an isentropic process from the initial container pressure to 

atmospheric pressure, the final states of the agent can he calculated using the computer code 

(FISSYCS), which is a derivative of PROFISSY [2]. Table 2 tabulates the calculated results. 

Comparing the two initial conditions, the liquid fraction (the percent of agent/nitrogen mixture 

still remained in liquid phase after the isentropic expansion process) is substantially higher at 

Halon Options Icchnical Working Conlcrcnce 2-4 May 2000 I75 
-40 OC. Such a high liquid fraction should have a significant effect on the subsequent 

evaporation and dispersion of the agenthitrogen mixture. 

Irrespective of the break-up mechanisms, the liquid core from the discharge nozzle will be disintegrated subsequently into small droplets. At 22 "C, the liquid droplets rapidly evaporate into 

vapor, thus facilitating the agent dispersion. However, at 40 "C, the liquid droplets evaporate 

slowly, and a two-phase (droplet-gas) flow persists longer, thus hindering the effective dispersion 

of agent droplets especially when baffles are present. This point is further illustrated in Figure 1, 

which shows the calculated evaporation time as a function of ambient temperature for three 

initial droplet diameters when the ambient agent mass fraction is zero. The evaporation time was 

calculated using the classical d2-law for droplet evaporation [e.g., 41. For simplicity and illustrative purposes, neat CF31 droplets were used in the calculations. When the ambient agent mass 

fraction is not zero, the evaporation time of an agent droplet is longer because of the reduction in 

the concentration gradient for mass transfer. Figure 2 shows the effect of ambient CF,I mass 

fraction on the evaporation time of a 100 pn droplet. A mass fraction of 0.316 corresponds to 

twice the cup-burner value (mole fraction of 0.032 [I]) of CFJ Note that in an actual discharge, 

the agent droplets will not be evaporating at zero ambient agent mass fraction. 

To examine the dispersion of CF31 in a cold environment, a new experimental facility will be 

designed and built. The experimental apparatus, the test matrix, and the test procedure to 

conduct the proposed discharge tests at sub-zero temperature are described in detail below. 

TABLE 2. LIQUID FRACTION OF CF?I/Nz MIXTURE AFTER ISENTROPIC 

EXPANSION TO 0.101 mpa. 

Initial conditions Liquid fraction (%) 

4. I2 MPa, 22 OC 

2.8 MPa. - 40 "C 

70 

90 

PROPOSED EXPERIMENTAL APPARATUS AND TEST PROCEDURE 

The proposed experimental apparatus will be a simulated engine nacelle with airflow and with an 

annulus cross-sectional area and length scalable to a real nacelle. Figure 3 is a schematic of the 

proposed experimental fixture, which consists of a compartment with baffles, an agent release 

port, observation windows, and sampling ports. The compartment has a configuration and 

dimensions commensurate with a typical engine nacelle. The annulus has an inside diameter of 

-0.5 m and an outside diameter of -1 m, resulting in a cross-sectional area of -0.59 m2. The 

length (-2 m) of the compartment is comparable to the distance between the agent injection port 

and the downstream end of a typical engine nacelle. The compartment is made of stainless steel 

sheet metal. 

The entire test facility will be placed inside a large environmental chamber. Agent discharge 

experiments will be conducted at the lowest achievable temperature (-40 "C) in the environmental chamber. Thermocouples will be placed on several locations inside the simulator to ensure 

176 Halon Options Technical Working Conference 2-4 May Zoo0 
---_- -_-- 00 ''''11/~~1~/1~1,/,,1,,,,11,,,,,,,, 

230 240 250 260 270 280 290 300 

Ambient temperature (K) 

Figure 1. Evaporation time of a CFiI droplet as a function of ambient 

temperature when the ambient agent mass fraction is zero. 

230 240 250 260 270 280 290 300 

Ambient temperature (K) 

Figure 2. Effect of ambient agent mass fraction on the evaporation time 

of a 100 pm CFiI droplet at various ambient temperatures. 

H:don Oplionh Technical Working C~nlcrcnuc 2-4 May 2000 I77 
Video Camera Video camera 

Environmental chamber 

fmm 

A" 

blower - ! 

. 

Sample cylinder -2m Sample cylinder 

__ -~ --H 

Figure 3. Proposed experimental apparatus for cold temperature agent dispersion. 

thermal equilibrium with the compartment environment before a test is performed. Air flow 

through the compartment will be provided by a variable-speed blower. 

The observations of the extinction of several tell-tale gaseous jet flames placed strategically at 

several locations in the compartment with video cameras will be used to assess qualitatively how 

well the agent is dispersed. These flames, which will be lit (possibly remotely) immediately 

before the discharge of CF31, are used as markers to detect the amval of the agent to these 

locations. Extinction of a flame indicates the presence of sufficient agent concentration at that 

location. In addition, samples will be collected for -0.5 s immediately after agent discharge at 

locations close to the tell-tale flames using evacuated sample cylinders and subsequently analyzed for CF31 using an FTIR. The integrated temporal CFJ concentration measurements will be 

used to evaluate the uniformity of the agent dispersion in the compartment. 

Experiments using pure nitrogen will also be conducted to separate the effect of the pressurization gas (nitrogen) on flame extinction alone. If the flames cannot be extinguished by pure 

nitrogen, then one can infer that the extinguishment of these small flames is due to the presence 

of the agent. Baseline suppression performance will also be established using a room temperature environment. 

Given the simulated nacelle volume, the amount of agent required for a fixed injection period 

(-0.5 s for typical nacelle applications) can be estimated using the generic nacelle modeling 

results in Gann [2]. The preparation of CFjUdissolved nitrogen mixtures follows the procedure 

as described in Gann [2]. The release of the agent can be achieved using one of the several 

mechanisms (e.g., a Marotta valve or a squib). Agent injection time will be tailored using an 

178 Halon Options Technical Working Conference 2-4 May 2000 
orifice plate at the exit of the valve. Table 3 lists the proposed experimental matrix. Two 

representative air flows (-I kg/s and -0.3 kg/s) will be used in the tests. 

TABLE 3. PROPOSED EXPERIMENTAL MATRIX FOR COLD TEMPERATURE 

AGENT DISPERSION. ~~ ~~~ ~~~ ~-~ ~~~ -~~ ~- ~- ~~ ~ ~~ ~~~ ~~~~ ~~.~ ~~~~~~ 

Initial conditions of vessel Conditions of vessel Conditions in 

before discharge simulated fir? compartment ~~ ~~ ~~~~ ~~ (half filled) ~~~ ~~ ~~ ~~ ~ ~~~ ~~~ ~~ ~~ - - ~- 

22"Cand4.12MPa 40 "C at prevailing P" 22 "C 

22 "C and 4. I2 MPa 

22 "C and 4.12 MPa 

22 "C and 2.15 MPa 

22 "C and 2.75 MPa 

40 "C at prevailing 

40 "C at prevailing f" 

40 "C at prevailing P' 

~ 40 "C 

22 "C (baseline) 

22 "C 

- 40 "C 

22 "C and 4.12 MPd 

22 "C and 2.75 MPa 22 "C and 2.75 MPa ~~~ ~~~ ~ ~~ ~~~~~ ~~ ~~ ~ ~~~~ ~~ ~~~ 

*Dry ice will be used to chill the vessel. 

Tests will he performed in an environmental chamber. Q 

The deliverahles of the proposed research will be the performance data on CFiI dispersion in a 

clustered compartment at 40 "C. The results from the CFJ dispersion tests under 40 "C will 

determine if CFiI can be effectively dispersed in an engine nacelle under temperature well below 

its normal boiling point. 

ACKNOWLEDGMENTS 

This research is part of the Department of Defense's Next Generation Fire Suppression 

Technology Program (NGP), funded by the DoD Strategic Environmental Research and 

Development Program (SERDP). 

REFERENCES 

1. Grosshandler, W.L.. Gam, R.G., and Pitts, W.M. (eds.), Ei~~luution oj'Alternati1.e In-Fliglzr 

Fire Snppres.sun~.s,for Full-Scale Tcstiny in Sinzuluted Airrruft Engine Nocelles und Dry 

Buys, NIST SP 861, US Department ot'Conimerce. Washington, DC, April 1994. 

2. Gann R.G. (ed.), Fire Supprmsion System Perforrnunre ofAlternutive A,gents in Aircrufi 

Engine und Dry Buy Luhoru/ory Simulutions, NIST SP-890: Vol. I. Chapter 8, U.S. 

Department of Commerce, Washington, DC, November 1995. 

3. Van Horn, S.R., and Vitali, J.A., "Fuel Inertion Live Munitions Testing Using CF31," 

Proceedinys, Halon Options Technical Working Conference, Albuquerque, NM, pp. 428- 

435, 1999. 

4. Chin, J.S., and Lefebvre, A.H., "Steady-State Evaporation Characteristics of Hydrocarbon 

Fuel Drops,"AlAA.l., 21, 1437.1443, 1983. 

Halon Options Technical Working Conlerencc 2-4 May 3lXJO I79