Spectroscopic Studies of Inhibited 

Opposed Flow Propane/Air Flames 

by Reed R. Skaggs, Robert G. Daniel, 

Andrzej W. Miziolek, Kevin L. McNesby, 

Valeri I. Babushok, Wing Tsang, and Mitchell D. Smooke 

February 2001 

20010307 137 

Approved for public release; distribution is unlimited. 
The findings in tbis report are not to be construed as an official 

Department of the Army position unless so designated by other 

authorized documents. 

Citation of manufacturer’s or trade names does not constitute an 

official endorsement or approval of the use thereof. 

Destroy this report when it is no longer needed. Do not return 

it to the origiuator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

AIU-TR-2388 February 2001 

Spectroscopic Studies of Inhibited 

Opposed Flow Propane/Air Flames 

Reed R. Skaggs, Robert G. Daniel, ,Andrzej W. Miziolek, and 

Kevin L. McNesby 

Weapons and Materials Research Directorate, ARL 

Valeri I. Babushok and Wing Tsang 

National Institute of Standards and Technology 

Mitchell D. Smooke 

Yale University 

Approved for public release; distribution is unlimited. 
Abstract 

Planar laser induced fluorescence (PLIF) and laser induced fluorescence are used to 

measure relative OH concentration profiles and maximum flame temperatures in an 

atmospheric pressure, opposed flow, propane (C$H&ir flame. Flame inhibiting agents 

CFsBr, Nz, Fe(CO)s, FM-200, FE-36, DMMP, and PN were added to the flame, and relative 

OH concentration profiles and peak flame temperatures were measured as each flame 

approached extinction. The measured OH profiles illustrate that adding N2, FM-ZOO, and FE36 to the flame produced smaller changes in OH concentrations relative to C&Br, implying 

these agents have chemical inhibition capacities less than CFsBr. However, adding DMMP 

and Fe(C0)5 to the flame demonstrated chemical inhibition capabilities greater than CKBr, 

with larger changes in OH concentrations; similar trends are observed for peak flame 

temperatures. CF3Br, PN, DMMP, and Fe(C0)5 have temperature values (1600-1800 K) that 

are lower than the uninhibited flame peak temperature (2200 K). OH profile widths were 

measured in the uninhibited flame and in each inhibited flame with inhibitor addition at 50% of 

determined extinction concentrations. Profile widths for CF3Br, PN, DMMP, and Fe(CO)s 

were at least 20% less than the uninhibited flame. Numerical modeling of a stoichiometric, 

premixed, &Ha/air flame inhibited by DMMP, Fe(C0)5, CFjBr, and N2 indicated DMMP and 

Fe(CO)s have greater decreases in burning velocities and OH relative to CFsBr. 
Acknowledgments 

The authors would like to thank Anthony Hamins (NIST) for burner fabrication. This work 

was supported by the Next Generation Fire Suppression Technology Program under the auspices 

of the U.S. Army TACOM (Steve McCormick). Finally, R. Skaggs would like to acknowledge 

financial support from the U.S. Army Research Laboratory through an American Society for 

Engineering Education Postdoctoral Fellowship. 

. . . 

111 
iv 
Table of Contents 

1. 

2 

3. 

4. 

5. 

6. 

7. 

Acknowledgments .................................................................................................... 

List of Figures ........................................................................................................... 

List of Tables ............................................................................................................ 

Introduction .............................................................................................................. 

Background .............................................................................................................. 

Experimental ............................................................................................................ 

Results ....................................................................................................................... 

Numerical Modeling ................................................................................................ 

Conclusion ................................................................................................................ 

References.. ............................................................................................................... 

Distribution List ....................................................................................................... 

Report Documentation Page ................................................................................... 

& 

. . . 

111 

vii 

vii 

1 

1 

2 

5 

11 

15 

17 

21 

23 

V 
INTENTIONALLY um BLANK. 

Vi 
List of Figures 

Figure 

1. Schematic Diagram of the Experimental Apparatus. _.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

2. Representative PLIF Images and the Corresponding OH Intensity Profiles From an 

Opposed Flow Propane/Air Flame Seeded With 0% (by Volume) CF3Br and 1.5% 

(by Volume) CF3Br . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3. Normalized OH LIF Profile Areas vs. Inhibitor Agent Delivery Concentrations.. . . 8 

4. Peak LIF Measured Temperatures (K) vs. Inhibitor Agent Delivery 

Concentrations . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*................... 11 

5. Calculated Burning Velocities vs. Delivered Inhibitor Agent Concentrations for a 

Numerical, Stoichiometric Premixed Propane/Air Flow.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

6. Normalized OH Concentrations vs. Delivered Inhibitor Agent Concentrations . .. . . . 15 

List of Tables 

Table Pae;e 

1. Inhibitor Concentrations (% Volume) and Uncertainty (&% Volume) at Flame 

Extinction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

2. Measured OH Profile Widths (FWHM, mm) for the Uninhibited Flame and 

Inhibited Flames at 50% of the Inhibitor Extinction Concentrations . . . . . . . . . . . . . . . . . . . . . . . . 9 

vii 
I 

INTENTIONALLYLEFTBLANK. 

. . . 

Vlll 
1. Introduction 

Fire protection on military platforms, including ground fighting vehicles, is being challenged 

by the impending loss of the ubiquitous fire fighting agent, Halon 1301 (CF3Br). This is due to 

environmental concerns related to the destruction of the stratospheric ozone layer. Replacement 

fire extinguishment agents are needed; they must satisfy numerous criteria, including fast fire 

suppression, minimum production of toxic gases when used, low toxicity, compatibility with 

storage materials, and environmental acceptability. 

The U.S. Army’s search for halon replacement agents has largely involved an empirical 

approach of testing and evaluation of commercially available compounds/systems. An 

alternative approach is to study the fundamental physical and chemical mechanisms responsible 

for flame inhibition, with the hope that such studies will uncover differences in the flame 

inhibition mechanisms, leading to new chemicals for further consideration and testing. To this 

end, we have initiated planar laser induced fluorescence (PLIF) and laser induced fluorescence 

(LIF) measurements of the OH radical species as flame extinction was approached in a nonpremixed, atmospheric pressure, opposed flow propane/air flame inhibited by Halon 1301 

[C&Br], N2, Fe(CO)s, FM-200 [CaF,H], FE-36 [C3F&I2], DMMP [CH3P(O)(OCH&], and PN 

[P3Nd%l- Presented here are relative OH concentrations, temperatures, and preliminary 

numerical models from this study of compounds which represent distinctly different chemical 

families in order to understand the differences between each agent’s inhibition mechanism. 

2. Background 

Chemical inhibition in a flame arises from the lowering of the radical concentrations due to 

scavenging reactions. In general, efficient inhibition mechanisms contain two types of reactions: 

(a) radical scavenging reactions and (b) reactions regenerating inhibitor species that participate in 

the inhibition cycle. As an example, for CF3Br inhibition, a free bromine from decomposed 

CF3Br forms HBr, which chemically reacts with a hydrogen atom and reduces the flame’s 

1 
hydrogen concentration. The consequence of hydrogen recombination is that the overall 

available radical concentrations (H, 0, OH) and the rate of chain-branching reactions are reduced 

[l-4], while HBr and Br2 regeneration occurs, carrying on the inhibition cycle. 

The chemicals Fe(CO)s, DMMP, and PN, investigated in our laboratory flame system, were 

chosen based on a comprehensive evaluation [ 5 ] of fire inhibitors that are more effective than 

CF3Br. The inhibition mechanisms for Fe(CO)s, DMMP, and PN are believed to. be generally 

similar to the HBr mechanism. For these postulated mechanisms, each agent decomposes during 

combustion into inhibition cycle scavenging species (e.g., FeO, FeOH, Fe(OH)z for the Fe(CO)s 

addition [6] and HOP0 and HOP02 for the DMMP and PN addition [7-g].) In the reaction zone 

of flames, these scavenging species behave much like HBr in scavenging hydrogen atoms. 

FM-200 and FE-36 were studied because of their popularity as potential halon replacement 

agents. FM-200 and FE-36 are refrigerants; it is assumed that their primary inhibition 

capabilities come from their physical properties-high heat capacities with some chemical 

reactivity due to the CF3 radical [lo]. 

To understand a chemical’s inhibition mechanism in terms of physical and/or chemical 

contributions, both N2 and CF3Br are included in this study. That is, N2 represents the upper 

boundary for an agent’s physical influence on flame inhibition since it has no chemical inhibition 

capabilities. It has been shown [l l] that at least 80% of the inhibition potential in CFjBr is 

caused by its chemical properties; therefore, CF3Br offers a good intermediate point with which 

to compare and contrast the other agents studied. 

3. Experimental 

OH PLIF imaging measurements were made using the arrangement presented in Figure 1. 

The opposed flow burner apparatus is located inside a stainless steel hood to contain any toxic 

fumes that are exhausted from the burner. All flames analyzed in this work were studied at 

atmospheric pressure and consisted of 7.0 L/min synthetic air (79% N2 + 21% 02) flowing from 

2 
elay Pulse 111111111111-1-11 P Generator 

Et l”““” . . . . 

e 

I...:‘ 

zt 

Em 

3 !i 

If 

Cylindrical 

Piano-Convex Lens 

. - . . I I - l m Electrical Signal 

p Optical Signal 

- - - - - - Pulse Signal 

ATM-Pressure 

Prism 

Mobile Exhaust Hood 

Figure 1. Schematic Diagram of the Experimental Apparatus. 

the lower duct, and 5.6 L/min of propane flowing from the upper duct. The oxidizer and fuel 

ducts are separated at a distance of 1.2 cm, and the duct diameter is 2.54 cm. Based on the flow 

conditions and duct separation, the luminous flame zone is located on the oxidizer side of the 

stagnation plane; the global strain rate was calculated to be 72.5 s-’ [12]. Previous studies of 

non-premixed propane/air flames have experimentally determined global extinction strain rates 

of 489 s-l [ 131. For all studies presented here, the inhibitor agents are added to the oxidizer flow 

in gaseous form at room temperature, except for Fe(CO)s, which was cooled to 11 “C, and 

DMMP, which was heated to 70 “C. For some time, opposed flow burners have been used to 

study the capabilities of an inhibitor agent because a global parameter, the extinction strain rate 

[ 121, can be determined; this describes the flame’s strength at extinction [ 14-171. The extinction 

strain rate is useful because a decreased value demonstrates an inhibitor’s efficiency. PLIF 

measurements of radical concentrations (0, H, OH) are complimentary to the extinction strain 

rate because the measurements illustrate an inhibitor’s influence on the radical concentration 

profiles in the flame zone, which indicates whether the flame’s radical chemistry is being 

perturbed by adding agent. 

I - 

Planar laser-induced fluorescence images were measured using a Lambda Physik excimer/dye 

laser system. This system consists of a Lambda Physik Compex 102 XeCl excimer laser, a 

3 
Scanmate 2 dye laser (Coumarin 153), and a Second Harmonic Generator (SHG). The 

fundamental output of the dye laser (560~nm wavelength) was frequency doubled in the SHG 

unit with a BBO crystal to approximately 281 mn. The W laser radiation was tuned to the peak 

of the R2 (9.5) transition at 281.8 nm [(l,O) A2C’+X211] [ 18-201. The W light output of the 

SHG unit enters an optical train where the beam is turned 90”, apertured by a submillimeter iris, 

and projected through a cylindrical plano convex lens to form the W beam into a vertical sheet. 

To create a uniform sheet width, the sheet is apertured with 0.5~mm vertical slits as it is projected 

toward the center of the burner. The UV sheet is apertured just before the burner to produce a 

vertically uniform intensity that is 1.2 cm in height, allowing passage through the entire burner 

flow field. Laser-induced fluorescence fi-om OH passes through a band pass filter centered at 

3 12 nm with an 1 1-nm bandwidth; it is detected with a Princeton Instruments ICCD camera 

(Model 120) coupled with a Nikon W lens located at 90”, with respect to the W sheet. The 

ICCD camera, which has an active area of 384 x 576 pixels, has a field of view with this optical 

arrangement of approximately 33 cm2. Each image recorded was acquired with 25 total 

accumulations on the camera. With this arrangement, the entire relative OH concentration 

profile was obtained. 

Laser-induced fluorescence excitation spectra were measured in the flame using the Lambda 

Physik excimer/dye laser system. This arrangement has been utilized before for similar 

measurements and will only be summarized here [21]. The W laser radiation was scanned from 

281.5 to 282 run [ 18-201. Low laser energies were used and the laser was operated in the linear 

regime. The W light output of the SHG unit was focused to the center of the burner 30-cm 

focal length fused silica lens and had a vertical and horizontal beam waist of 0.4 and 0.5 mm, 

respectively. Fluorescence was collected at 90” <to the direction of the excitation laser beam, 

focused through a 0.5~mm iris to define the collection volume, passed through a band pass filter 

centered at 3 12 nm with an 11 -nm bandwidth, and detected by a photomultiplier tube (PMT) 

(Phillips Model XP2018B). 

4 
Before adding inhibitor, the uninhibited flame was profiled using LB? between the fuel and 

oxidizer ducts to obtain a profile of the uninhibited temperature values. To expedite 

measurements when the inhibitor was added, the burner was translated to about fl mm around 

the OH maximum, and excitation spectra were collected. Each excitation spectrum was fit using 

a nonlinear least squares algorithm to obtain the OH rotational temperature for the spectral 

measurement [20]. 

4. Results 

The effectiveness of a particular flame inhibitor is typically characterized by its influence on 

a flame’s propagation chemistry. The most common indicators of the overall reaction rates for 

premixed and diffusion flame systems are the burning velocity and extinction strain rate, 

respectively. For premixed flames, adding an inhibitor decreases the burning velocity. For 

diffusion flames, adding an inhibitor can cause chemical reactions to proceed at times near the 

characteristic flow time, which can eventually lead to flame extinction. For premixed and nonpremixed systems, measurements of radical concentrations (0, H, OH) serve as useful indicators 

of the chemistry affected by inhibitor addition and are complimentary to burning velocity and 

extinction strain rate measurements. OH is monitored in the flames studied here because it is 

relatively simple to measure, and it is a good indicator of the overall radical pool concentration, 

even though H, 0, and OH are not fully equilibrated in diffusion flames [22]. 

Figure 2 presents two representative, two-dimensional (2-D) images of OH fluorescence for 

an uninhibited propane/air flame and for a propane/air flame to which CFsBr was added 

(1.5% by volume). Both images, which are uncorrected for laser energy fluctuations and local 

quenching rates, illustrate the presence of two luminous zones as the W sheet passes through the 

flame. The lower, thicker zone is the fluorescence from the OH transition, while the upper, 

thinner zone is the broadband fluorescence due to derivative fuel species such as polycyclic 

aromatic hydrocarbons. To construct a spatially resolved OH LIF profile from a OH PLIF image, 

as shown on the right hand side of Figure 2, the pixel intensity corresponding to a given height 

5 
0 12 3 4 5 6 7 6 91011 

Distance From Fuel Duct. mm 

2500 

0 12 3 4 5 6 7 6 91011 

Distance From Fuel Duct. mm 

Figure 2. Representative PLIF Images and the Corresponding OH Intensity Profiles From 

an Opposed Flow Propane/Air Flame Seeded With 0% (by Volume) CFsBr and 

1.5% (by Volume) CFsBr. Note: The Orientation of the PLIF Images With 

Respect to the Burner System Places the Fuel and Air Ducts at the Top and 

Bottom of Each Image, Respectively. 

between the fuel and oxidizer ducts (spatial resolution of approximately 0.149~mm/pixel) was 

summed and averaged over a l-mm horizontal width. The 2-D images and LIP profiles illustrate 

that adding CFJBr to the propane flame causes a decrease in the OH fluorescence signal, while 

the broadband fluorescence appears to increase just slightly. Similar results have been observed 

previously for CFsBr added to hydrocarbon diffusion flames [23;24]. 

Obviously, adding an inhibitor to a flame modifies the flame structure. Specifically, an 

inhibitor can change the position and width of the flame’s reaction zone. Previous studies have 

shown [25-291 that a decrease in the flame’s reaction zone width indicates increased localized 

strain, which can cause local quenching or flame extinction [30]. To analyze reaction zone 

modifications and relative OH concentrations, each OH intensity profile is fit to a Gaussian 

function. A Gaussian function determines the area under the profile curve which provides a 

general indicator of the entire OH population for a given flame condition. The width of the 

flame’s reaction zone may be characterized by the width of a radical profile [29]. The width of 

6 
the flame’s reaction zone is defined here as the distance of one half of the maximum intensity of 

the Gaussian OH profile, which is similar to previous studies [27] that have estimated the width 

of a laminar flame reaction zone using one half of the maximum value of a temperature profile. 

Figure 3 contains the results of the analyzed OH profile areas vs. each inhibitor agent’s 

concentration as the flames were stepped towards extinction. The’reported OH profile areas are 

averaged over three or more separate inhibitor extinction experiments,.where the data for each 

experiment are normalized to the OH profile area measured in the uninhibited flame and 

acquired prior to each inhibitor extinction experiment to account for changes in burner and 

camera conditions. The data indicate that there are both physical and chemical modes of 

inhibition observed for the agents studied. That is, Nz, which is chemically inert, has the least 

impact on OH with respect to the other agents studied. For the concentration range plotted in 

Figure 3, me flame was not even extinguished by Nz. Similar results are observed for the two 

fluorinated propanes (FM-200 and FE-36), which show small initial declines in OH, but more 

rapid decreases just before extinction. For the other agents studied (PN, CFsBr, DMMP, and 

Fe[CO]S), adding these inhibitors causes precipitous decreases in the measured OH values up to 

the extinction concentrations, where the data seems to decrease more gradually. The decrease is 

highlighted for DMMP and Fe(CO)s by the graph inserted in Figure 3. Table 1 lists the observed 

inhibitor concentrations in the air stream at extinction for the agents studied, including their 

estimated uncertainties. 

For comparison purposes, the extinction concentration for CFsBr is similar to cup burner 

values (2.90) [3 1 J, but slightly less than values obtained in a coffowing propane/air flame and a 

coflowing propane/air cup burner (4.1 and 4.3) [24, 321. The fluorinated propanes have 

extinction concentrations that are approximately 50% greater than CFsBr, which is consistent 

with cup burner values of 6.3 for FM-200 and 6.6 for FE-36 [31]. For the phosphorus 

compounds, PN has an extinction concentration similar to CFsBr, while DMMP’s value is 

significantly less than CFsBr (7 to 8 times less). Previous studies by MacDonald et al. 

r33.341 show that DMMP is 2 to 4 times more effective than CFqBr. However. Fisher et al. rl31 

7 
0.0 ' I I 1 I I I 

0 1 2 3 4 5 6 

Agent Concentration, % Volume 

Figure 3. Normalized OH LIF Profile Areas vs. Inhibitor Agent Delivery Concentrations. 

The @) Are the N2 Data, the (0) Are the FM-200 Data , the (A) Are the FE 36 

Data, the (V) Are the PN Data, the (0) Are the CFsBr Data, the (m Are the 

DMMP Data, and the (0) Are the Fe(CO)s Data. Inserted in the Figure Is a 

Second Plot of the PN, CFsBr, DMMP, and Fe(CO)s Data for Agent 

Concentration up to 0.75% Volume. 

Table 1. Inhibitor Concentrations (% Volume) and Uncertainty (f% Volume) at Flame 

Extinction 

Inhibitor Agent N2 CFsBr FE-36 FM-200 PN DMMP Fe(C0)5 

Extinction Concentration 23.1 2.3 6.1 5.3 2.7 0.3 0.2 

Estimated Uncertainty 8.20 0.93 1.29 1.08 1.00 0.04 0.03 

reported that for an opposed flow propane/air flame with DMMP added to the air stream, a 

25% decrease in the normalized extinction strain rate corresponds to a DMMP concentration 

= 1200 ppm. 
Linear extrapolation of the Fisher et al. data [ 131 to the strain rate used for the opposed flow 

propane/air flame studied here finds a DMMP concentration of 4080 to 6500 ppm, or 0.4-0.65% 

volume. The DMMP concentration obtained from the extrapolated strain rate data supports the 

DMMP extinction concentration we determined. For PN, cup burner experiments found an 

extinction concentration of 1.08 [35]. The results reported here for PN and DMMP cause 

concern for several reasons. First, the obtained value for PN is larger, while DMMP is smaller 

than other cited experiments. Second, it was assumed prior to the experiments described here 

that if a given compound contained a phosphorus atom, similar extinction concentrations would 

be observed, regardless of its chemical structure. A possible explanation for the contrasting 

behavior of the two phosphorus agents is that the resonant structure of PN could be very stable 

and thus less efficient at delivering phosphorus to the flame [36]. 

One of the conveniences of monitoring relative OH concentration profiles using a PLIF 

technique is that any physical changes that occur in the OH profile are observed instantaneously 

as the inhibitor agents are added. This quality is convenient because adding an inhibitor to the 

flame modifies the flame structure by causing changes, such as a shift in the location of the OH 

maximum and/or an effect on the OH profile width. Table 2 lists the measured flame widths 

determined from the relative OH concentration profiles for each flame situation studied. For the 

inhibited flames, the widths are measured at 50% of each agent’s determined extinction 

concentration. The uncertainty in the reported widths due to measurement variance is 11%. 

Table 2. Measured OH Profile Widths (FWHM, mm) for the Uninhibited Flame and 

Inhibited Flames at 50% of the Inhibitor Extinction Concentrations 

Uninhibited 

N2 

FE-36 

FM-200 

CF3Br 

PN 

DMMP 

FefCOjq 

OH Profile Width, mm 

1.30 

1.24 

1.31 

1.26 

0.96 

0.96 

1.04 

0.83 

9 
The Table 2 width values indicate that the agents N2, FE-36, and FM-200 do not possess 

width changes significantly different from the uninhibited flame. On the contrary, CFsBr, PN, 

DMMP, and Fe(C0) 5 exhibit width changes that are equal to or greater than a 20% decrease from 

the uninhibited width value. The OH width trends suggest that inhibitor agents with more 

physical inhibition capabilities exhibit less effect on the flame structure than inhibitors with 

enhanced chemical inhibiting capabilities. 

From the relative OH concentration observations, similar trends might be expected for the 

peak flame temperatures. Figure 4 presents a plot of peak LIF measured flame temperatures vs. 

agent delivery concentrations for each inhibited flame. The peak flame temperature for the 

uninhibited flame is between 2125 and 2200 K. The obtained temperature values for N2 and 

FM-200 indicate that these inhibited flames do not have temperatures statistically different fkom 

those measured in the uninhibited flame, with an estimated uncertainty of +300 K. For CFsBr 

and PN, temperature differences with respect to the uninhibited flame are not observed ‘until near 

extinction concentrations are achieved. Previous studies of an atmospheric pressure, 

axisymmetric propane/air flame inhibited by adding CFjBr to the oxidizer flow, found only small 

temperature differences compared to the uninhibited flame [24, 371. On the contrary, Masri et al. 

[23] reported that for a non-premixed atmospheric pressure C&/air flame, higher temperatures 

exist in the reaction zone of a CFsBr inhibited flame than in the reaction zone of an uninhibited 

flame near extinction. With mixed results from previous investigations and the large degree of 

uncertainty in OUT measurements, the only creditable temperature values are those close to 

extinction. For Fe(CO)s and DMMP, temperature decreases with respect to the uninhibited 

flame are not observed until proximal extinction concentrations are observed as well. On a 

concentration basis, Fe(C0)5 and DMMP have decreased flame temperatures, T = 1700 K, at 

agent concentrations lower than the other agents studied. For Fe(C0)5, small decreases in flame 

temperatures have been observed by Brabson et al. [38] in studies of low-pressure premixed 

flames inhibited by Fe(C0)5. 

10 
1600 I I I I I I I 

0 1 2 3 4 5 6 

Inhibitor Agent Concentration, % Volume 

Figure 4. Peak LIF Measured Temperatures (K) vs. Inhibitor Agent Delivery 

Concentrations. The (cl) Are the Nz Data, the (0) Are the FM-200 Data, the 

(V) Are the PN Data, the (0) Are the CF3Br Data, the (F) Is the DMMP Data, 

and the (0) Are the Fe(CO)s Data. 

5. Numerical Modeling 

Numerical modeling of a stoichiometric, premixed propane/air flame inhibited by DMMP, 

Fe(C0)5, CFJBr, and N2 flame was carried out using the Chemkin suit of programs [39]. For the 

simulations, a kinetic model for propane combustion developed by Marinov et al. [40-42] was 

slightly modified and combined with a Cl-C2 hydrocarbon kinetic model [ 1 l] employed in 

earlier inhibition studies. For routine calculations, a simplified model was used to decrease 

computational time. The kinetic mechanism for phosphorus-containing species is based on the 

model suggested for analyzing the influence of PH:, products on the recombination of 

11 
hydroxyl and hydrogen atoms in a hydrogen flame [43], and kinetic models [44-46] developed to 

simulate the destruction of DMMP and TMP in a low pressure hydrogen flame. Additional 

reactions were added to the phosphorus mechanism to complete the reaction pathways for the 

consumption of some of the P-containing species. To model Fe(CO)s and CFsBr inhibition, 

previously developed mechanisms for these two species [ 1, 61 were added to the hydrocarbon 

model. 

Computations of the propane flame inhibited by DMMP demonstrate that the consumption of 

DMMP leads to the formation of CHsP02 species via a sequence of reactions. Reactions of 

CHJPO~ with H and OH create HOP0 and HOP02 species. At this stage, reactions of HOPO, 

HOP02, and PO2 with chain carriers form the following two inhibition cycles: 

(1) H+POz+M=HOPO+M 

OH + HOP0 = Hz0 + PO;? 

H+HOPO=Hz+POz 

0 + HOP0 = PO;? + OH, and 

(2) OH + PO2 +M = HOP02 +M 

H + HOP02 = Hz0 + PO2. 

These inhibition cycles represent the catalytic scavenging cycles that accelerate radical 

recombination in combustion products containing phosphorus compounds [9]. It is well known 

that adding an inhibitor decreases the burning velocity for premixed flames. Numerical results 

for burning velocity decreases by 20-30% using the original rate constants given by Twarowski 

[9], indicating that DMMP decreases the flame’s burning velocity by a factor of 1.5 to 2 relative 

to CFsBr in a methane/air flame. A sensitivity analysis reveals that the burning velocity is 

receptive to changes in the rate constants for the reactions of the PO2 radical: H + PO2 + M 

12 
= HOP0 + M, and OH + IQ + M = HOP02 + M. The reasonable adjustment of rate constants 

can lead to agreement with experimental data. 

It should be noted that phosphorus compounds have a wide range of thermal stability. 

Activation energies of decomposition reactions are in the range 15-90 kcal/mol. The influence 

of the decomposition rate was studied using global kinetics for the decomposition of PO;! to 

HOP0 species by varying overall activation energy for the decompositionreaction. Calculations 

show that for the compounds with global activation energies less than 50 kcal/mol, the burning 

velocity is not affected by the stability of the phosphorus compounds. 

Suppression calculations were carried out with increasing additive loadings until suppression 

concentration levels were achieved (burning velocity 15 cm/s [2]). The calculations were 

conducted for a gas phase model without taking into account possible condensation processes. 

Calculation results (Figure 5) show that DMMF’ appears to be less effective in reducing the 

burning velocity compared to Fe(CO)s, but relative to CFsBr, both are more effective. For 

increases in the concentration of Fe(CO)s and DMMP, both agents exhibit increasing saturation 

effects. Typically, two types of saturation are discussed in the literature: (1) saturation of 

chemical influence [ 111, and (2) saturation due to condensation processes [6]. 

Both processes result in a decrease in inhibitor efficiency with increased inhibitor 

concentration. For example, to decrease the burning velocity to 10 cm/s requires a DMMP 

loading of approximately 0.9%, but an additional 1.2% of DMMJ? is needed to decrease the 

burning velocity to the extinction level of 5 cm/s. Such a strong saturation effect leads to a 

substantial increase in extinction concentrations and a decrease in inhibitor efficiency relative to 

CF3Br. The calculated extinction concentrations (in units of % volume) for the numerical 

propane/air flame were: DMMP = 2.1; CFsBr = 3.5; Fe(CO)s = 0.4-0.5; N2 = 40. The modeling 

results support that DMMP and Fe(CO)s exhibit superior inhibition capabilities relative to 

CF3Br. 

13 
1.0 

s-3 .E 

s 

5 0.8 

> 

P 

‘c 0.6 

m” 

u 

8 0.4 

.- 

5 

E 

8 

z 

0.2 

r 

0.25 0.50 0.75 

Agent Concentration, % Volume 

Figure 5. Calculated Burning Velocities vs. Delivered Inhibitor Agent Concentrations for a 

Numerical, Stoichiometric Premixed Propane/Air Flame. The Dashed Line Is the 

DMMP Data, the Solid Line Is the Fe(CO)s Data, the Dashed-Dot-Dashed Line Is 

the CFsBr Data, and the Near Horizontal Dashed-Dot-Dot-Dashed Line 

Represents the N2 Data Trend. 

Finally, comparing the normalized OH concentrations dependency to inhibitor concentrations 

demonstrates a correlation between experimental and calculated OH concentrations, as shown in 

Figure 6. Figure 6 illustrates that two different propane flames inhibited by the same agents have 

normalized OH concentrations that track more or less with one another. At the experimental OH 

extinction level (i.e., 0.3 to O.l), both data sets (experimentticomputational) have similar 

normalized OH reductions. 

14 
0.8 

is 

2 0.6 

.- 

5 

E 

5 0.4 

Z 

0.2 

0.0 

0.25 0.50 0.75 

Agent Concentration, % Volume 

1 .oo 

Figure 6. Normalized OH Concentrations vs. Delivered Inhibitor Agent Concentrations. 

The (0) Are the Experimental Fe(CO)s Data, and the Solid Line .Is the 

Numerical Fe(CO)s Data; the (m) Are the Experimental DMMP Data, and the 

Dashed Line Is the Numerical DMMP Data; the (0) Are the Experimental 

CF3Br Data, and the Dashed-Dot-Dashed Line Is the Numerical CF3Br Data. 

The Near Horizontal Dashed-Dot-Dot-Dashed Line Represents the Nt Data 

Trend. 

6. Conclusion 

For the first time, the experimental results presented here show changes in OH profiles as 

extinction is approached in a series of inhibited, atmospheric pressure non-premixed propane/air 

flames. The OH profiles from these flames illustrate that N2, FE-36, and FM-200, with smaller 

changes in OH areas relative to CFsBr, exhibit chemical inhibition capacities less than CF3Br. 

On the contrary, DMMP and Fe(CO)s demonstrate chemical inhibition capabilities greater than 

CF3Br with their larger changes in OH. Peak flame temperature measurements demonstrate that 

15 
inhibitor additions cause temperature values to decrease with trends similar to the relative 

OH concentrations. For the inhibitors studied, agent concentrations at extinction support these 

observations with a CFJBr concentration of 2.3% (by volume), compared to Nz with a 

concentration of 23.1%, and DMMP and Fe(CO)S each having concentrations less than 1%. An 

analysis of the OH profile widths for flames inhibited by Fe(CO)S, DMMF, CF3Br, and PN show 

that the OH profile widths are less than those experienced in the uninhibited flame. 

Contrariwise, flames inhibited by Nz, FM-200, and FE-36 do not demonstrate profile widths 

much different from those observed for the uninhibited flame. Numerical calculations for a 

stoichiometric, premixed propane/air flame demonstrate that DMMP and Fe(C0)5 exhibit 

superior inhibition characteristics relative to CF3Br. 
7. References 

1. Dixon-Lewis, G., and R. J. Simpson. “Aspects of Flame Inhibition by Halogen 

Compounds.” Sixteenth Symposium (IntemationaE) on Combustion, The Combustion 

Institute, Pittsburgh, PA, p. 1111, 1976. 

2. Westbrook, C. K. “Inhibition of Laminar Methane-Air and Methanol-Air Flames by 

Hydrogen Bromide.” Combustion Science Technology, vol. 23, p. 191, 1980. 

3. Westbrook, C. K. “Inhibition of Hydrocarbon Oxidation in Laminar Flames and 

Detonations by Halogenated Compounds.” Nineteenth Symposium (International) on 

Combustion, The Combustion Institute, Pittsburgh, PA, p. 127, 1982. 

4. Westbrook, C. K. “Numerical Modeling of Flame Inhibition by CFjBr.” Combustion 

Science Technology, vol. 34, p. 201, 1983. 

5. Babushok, V., and W. Tsang. “Chemical Limits to Flame Inhibition.” Chemical and 

Physical Processes in Combustion: Proceedings of Fall Technical Meeting of the Eastern 

States Section of the Combustion Institute, p. 79, 1997. 

6. Rumminger, M. D., D. Reinelt, V. I. Babushok, and G. T. Linteris. “Numerical Study of 

the Inhibition of Premixed and Diffusion Flames by Iron Pentacarbonyl.” Combustion 

Flame, vol. 116, p. 207, 1999. 

7. Hastie, J. W., and C. L. McBee. “Mechanistic Studies of Triphenylphosphine 

Oxide-Poly(Ethylene-terephthalate) and Related Flame Retardant Systems. Final Report.” 

National Bureau of Standards, Final Report No. NBSIR, pp. 75-741, 1975. 

8. Twarowski, A. “The Influence of Phosphorus Oxides and Acids on the Rate of H + OH 

Recombination.” Combustion Flame, vol. 94, p. 91, 1993. 

9. Twarowski, A. “The Effect of Phosphorus Chemistry on Recombination Losses in a 

Supersonic Nozzle.” Combustion Flame, vol. 102, p. 55, 1995. 

10. Williams, B.A., J. W. Fleming, and R. S. Sheinson. “Extinction Studies of Hydrocarbons 

in Methane/Air and Propane/Air Counter-flow Diffusion Flames: The Role of the CF3 

Radical.” Halon Options Technical Working Conference, Albuquerque, NM, p. 3 1, 1997. 

11. Noto, T., V. Babushok, D. R. Burgess, A. Hamins, W. Tsang, and A. Miziolek. “Effect of 

Halogenated Flame Inhibitors on Cl -C2 Organic Flames.” Twenty-Sixth Symposium 

flntemational) on Combustion, Pittsburgh, PA p. 1377, 1996. 

17 
12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

Seshadri, K., and F. Williams. “Laminar Flow Between Parallel Plates With Injection of a 

Reactant at High Reynolds Numbers. ” International Journal of Heat and Mass Transfer, 

vol. 21, p. 251, 1978. 

Fisher, E. M., F. C. Gouldin, T. M. Jayaweera, and M. A. MacDonald. “Flame Inhibition 

by Phosphorus-Containing Compounds.” Final Technical Report, Distributed by Defense 

Advanced Research Projects Agency, Arlington, VA 1998. 

Potter, A. E., S. Heimel, and J. N. Butler. “A Measure of Maximum Reaction Rate in 

Diffusion Flames.” Eighth Symposium (International) on Combustion, The Combustion 

Institute, Pittsburgh, PA, p. 1027, 1962. 

Carrier, G. F., F. E. Fendell, and F. E Marble. “The Effect of Strain Rate on Diffusion 

Flames.” SIAM Journal of Applied Mathematics, vol. 28, pp. 463-500, 1975. 

Linan, A. “The Asymptotic Structure of Counterflow Diffusion Flames for Large 

Activation Energies.” ActaAstronaut, vol. 1, p. 1007, 1974. 

Williams, F. A. “Review of Flame Extinction.” Fire Safety Journal, vol. 3, p. 163, 1981. 

Chidsey, I. L., and D. R. Crosley. “Calculated Rotational Transition Probabilities for the 

A-X System of OH.” Journal of Quantitative Spectroscopy and Radiative Transfer, 

vol. 23, p. 187, 1980. 

Dieke, G. H., and H. M. Croswhite. “The Ultraviolet Bands of OH Fundamental Data.” 

Journal of Quantitative Spectroscopy and Radiative Transfer, vol. 2, p,. 97, 1962. 

Kotlar, A. Personal communication. U.S. Army Research Laboratory, Aberdeen Proving 

Ground, MD, 1998. 

Skaggs, R. R., K. L. McNesby, R. G. Daniel, B. Homan, and A. W. Miziolek. 

“Spectroscopic Studies of Low Pressure Opposed Flow Methane/Air Flames Inhibited by 

Fe(CO)s, CFsBr, or Nz.” Accepted for publication to Combustion Science Technology, 

Sept. 1999. 

Smyth, K. C., P. J. H. Tjossem, A. Hamins, and J. H. Miller. “Concentration 

Measurements of OH and Equilibrium Analysis in a Laminar Methane-Air Difision 

Flame.” Combustion Flame, vol. 79, p. 366, 1990. 

Masri, A. R., B. B. Dally, R. S. Barlow, and C. D. Carter. “The Structure of Laminar 

Difision Flames Inhibited With CFsBr.” Combustion Science Technology, vol. 17, 

p. 113-114, 1996. 

18 
24. Smyth, K. C., and D. Everest. “The Effect of CF31 Compared to CF3Br on OH and Soot 

Concentrations in CO-Flowing Propane/Air Diffusion Flames.” Twenty-Sixth Symposium 

(International) on Combustion, The Combustion Institute, Pittsburgh, PA, p. 1385, 1996. 

25. Peters, N. “Local Quenching Due to Flame Stretch and Non-Premixed Turbulent 

Combustion.” Combustion Science Technology, vol. 30, p. 1, 1983. 

26. Liew, S. K., K. N. C. Bray, and J. B. Moss. “A Stretched Laminar Flamelet Model of 

Turbulent Nonpremixed Combustion.” Combustion Flame, vol. 56, p. 199, 1984. 

27. Haworth, D. C., M. C. Drake, and R. J. Blint. “Stretched Laminar Flamelet Modeling of a 

Turbulent Jet Diffusion Flame.” Combustion Science Technology, vol. 60, p. 287, 1988. 

28. Roberts, W. L., J. F. Driscoll, M. C. Drake, and J. W. Ratcliffe. “OH Fluorescence Images 

of the Quenching of a Premixed Flame During an Interaction With a Vortex.” 

Twenty-Fourth Symposium (International) on Combustion, The Combustion Institute, 

Pittsburgh, PA, p. 169,1992. 

29. Miller, J. H. “Applications of Conserved Scalars to Combustion Chemistry.” Chemical 

and Physical Processes in Combustion: Proceedings of Fall Technical Meeting of the 

Eastern States Section of the Combustion Institute, The Combustion Institute, Pittsburgh, 

PA, p. 1, 1996. 

30. Bilger, R. W. “The Structure of Turbulent Nonpremixed Flames.” Twenty-Second 

Symposium (International) on Combustion. The Combustion Institute, Pittsburgh, PA, 

p. 1377, 1988. 

3 1. NMERI. “Cup-Burner Flame Extinguishment Concentrations.” http://www.nmeri.unmcget, 1998. 

32. Grosshandler, W. L., R. G. Gann, and W. M. Pitts. “Evaluation of Alternative in Flight 

Fire Suppressants for Full Scale Testing in Simulated Aircraft Engine Nacelles and Dry 

Bays.” NIST SP 861, Gaithersburg, MD, 1994. 

33. MacDonald, M. A., T. M. Jayaweera., E. M. Fisher, and F. C. Gouldin. “Inhibition of 

Non-Premixed Flames by Phosphorus-Containing Compounds.” Combustion Flame, 

vol. 116, p. 166,1999. 

34. MacDonald, M. A., T. M. Jayaweera, E. M. Fisher, and F. C. Gouldin. “Variation of 

Chemically Active and Inert Flame Suppression Effectiveness With Stoichiometric Mixture 

Fraction.” Twenty-Seventh Symposium (International) on Combustion, The Combustion 

Institute, Pittsburgh, PA, 1998, in press. 

19 
35. 

36. 

37. 

38. 

39. 

40. 

41. 

42. 

43. 

44. 

45. 

46. 

Kaizerman, J. A., and R. E. Tapscott. “Advanced Streaming Agent Development, 

Volume III: Phosphorus Compounds.” Report No. NMERI 96/5/32540, New Mexico 

Engineering’Research Institute, NM, 1996. 

Gann, R. Personal communication. U.S. Army Research Laboratory, Aberdeen Proving 

Ground, MD, 1999. 

Niioka, T., T. Mitani, and M. Takahashi. “Experimental Study on Inhibited Difision and 

Premixed Flames in a Counterflow System.” Combustion Flame, vol. 50, pp. 89-97, 1983. 

Brabson, G. D., E. A. Walters, A. R. Gennuso, J. P. Owen, and R. E. Tapscott:‘” “Molecular 

Beam Mass Spectrometry of Low-Pressure Flames Seeded With Iron Pentcarbonyl.” 

Submitted to Journal of Physical Chemistry, 1998. 

Kee, R. J., F. M. Rupley, and J. A. Miller. “Chemkin-11: A Fortran Chemical Kinetics 

Package for Analysis of Gas Phase Chemical Kinetics.” Sandia National Laboratories 

Report No. SAND-8009B, UC-706, 1989. 

Marinov, N. M., W. J. Pitz, C. K. Westbrook, M. J. Castaldi, and S. M. Senkan. “Modeling 

of Aromatic and Polyaromatic Hydrocarbon Formation in Premixed Laminar Flames.” 

Combustion Science Technology, vol. 211, pp. 116-l 17, 1996. 

Marinov, N. M., M. J. Castaldi, C. F. Melius, and W. Tsang. Combustion Science 

Technology. Vol. 128, p. 295, 1997. 

Marinov, N. M., W. J. Pitz, C. K. Westbrook, A. M. Vincitore, M. J. Castaldi, and 

S. M. Senkan. “Aromatic and Polycyclic Aromatic Hydrocarbon Formation in a Laminar 

Premixed n-Butane Flame.” Combustion Flame, vol. 114, p. 192, 1998. 

Ewing, C. T., J. T. Hughes, and H. W. Carhart. “Extinction of Hydrocarbon Flames Based 

on the Heat-Absorption Processes Which Occur in Them.” Fire andMaterials, vol. 8, 

p. 148, 1984. 

Werner, J. H., and T. A. Cool. “A Kinetic Model for the Decomposition of DMM? in a 

Hydrogen/Oxygen Flame.” Combustion Flame, vol. 117, p. 78, 1998. 

Korobeinichev, 0. P., S. B. Il’in, V. V. Mokrushin, and A. G. Shmakov. Combustion 

Science Technology. Vol. 51, pp. 116-l 17, 1996. 

Mokrushin, V. V., T. A. Bol’shova, and 0. P. Korobeinichev. Personal communication. 

Gaithersburg, MD, 1999. 

20 
NO. OF 

COPIES 

2 

1 

1 

1 

1 

ORGANIZATION 

NO. OF 

COPIES 

DEFENSE TECHNICAL 1 

INFORMATION CENTER 

DTIC DDA 

8725 JOHN J RINGMAN RD 

STE 0944 

FT BELVOIR VA 22060-62 18 

1 

HQDA 

DAM0 FDT 

400 ARMY PENTAGON 

WASHINGTON DC 203 lo-0460 

OSD 3 DIRECTOR 

OUSD(A&T)lODDDR&E(R) US ARMY RESEARCH LAB 

RJTREW AMSRL CI LL 

THE PENTAGON 2800 POWDER MILL RD 

WASHINGTON DC 20301-7100 ADELPHI MD 20783-l 145 

DPTY CG FOR RDA 

US ARMY MATERIEL CMD 

AMCRDA 

5001 EISENHOWER AVE 

ALEXANDRIA VA 22333-0001 

1 

INST FOR ADVNCD TCHNLGY 

THE UNIV OF TEXAS AT AUSTIN 

PO BOX 202797 

AUSTIN TX 78720-2797 4 

DARPA 

B KASPAR 

3701 N FAIRFAX DR 

ARLINGTON VA 22203-1714 

US MILITARY ACADEMY 

MATH SC1 CTR OF EXCELLENCE 

MADN MATH 

MAJ HUBER 

THAYER HALL 

WEST POINT NY 10996-1786 

DIRECTOR 

US ARMY RESEARCH LAB 

AMSRL D 

D R SMITH 

2800 POWDER MILL RD 

ADELPHI MD 20783-l 197 

ORGANIZATION 

DIRECTOR 

US ARMY RESEARCH LAB 

AMSRL DD 

2800 POWDER MILL RD 

ADELPHI MD 20783-l 197 

DIRECTOR 

US ARMY RESEARCH LAB 

AMSRL CI AI R (RECORDS MGMT) 

2800 POWDER MILL RD 

ADELPHI MD 20783-l 145 

DIRECTOR 

US ARMY RESEARCH LAB 

AMSRL CI AP 

2800 POWDER MILL RD 

ADELPHI MD 20783-l 197 

ABERDEEN PROVING GROUND 

DIR USARL 

AMSRL CI LP (BLDG 305) 

21 
NO. OF 

COPIES ORGANIZATION 

ABERDEEN PROVING GROUND 

1 DIR USARL 

AMSRL-WM-TB 

14 AMSRL-WM-BD 

K MCNESBY (3 CPS) 

W MIZIOLEK (5 CPS) 

R DANIEL (3 CPS) 

W AIMEN (3 CPS) 

22 
REPORT DOCUMENTATION PAGE Form Approved 

0848 No. 07060188 

‘ublic reporting burden for thir cchction of infommion 15 mimated to average 1 hour per rmponss. tidmg the tima fw mviawing msuuctionf. searching onsting dam *aces. 

pharing end maintaining the data medad. and compking and nviwing the colection of infomdim Send conunanls mgarbmg this burden estimate or any othsr aspact of this 

:dlenion of information, including suggmtions for miucing this burdsn, 10 Washington Headquatton Servises, Dir*ctomte for lnfmation Operations and Reports, 1215 Jsfferson 

lwi* Highway, Suite 1204, Mington, VA 222024302, and to the 0th~~ of Hanagomsnt and Buda*, Paperwork Reduction Proisct(S7M0~88), Washington, DC 20503. 

I. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED 

February 200 1 Final, Jul98 - Mar 99 

I. TITLE AND SUBTITLE 5. FUNDING NUMBERS 

Spectroscopic Studies of Inhibited Opposed Flow Propane/Air Flames 622618.H43 

i. AUTHOR(S) 

R. R. Skaggs, R. G. Daniel, W. W. Miziolek, K. L. McNesby, 

V. I. Babushok,. W. Tsang,’ and M. D. Smooke+ 

‘. PERFORMING ORGANIZATION NAME(S) AND ADDRESS 8. PERFORMING ORGANIZATION 

;J.S. Army Research Laboratory REPORT NUMBER 

4TTN: AMSRL-WM-BD ARL-TR-2388 

4berdeen Proving Ground, MD 210055066 

#. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS lO.SPONSORING/MONITORlNG 

AGENCY REPORT NUMBER 

II. SUPPLEMENTARY NOTES 

’ National Institute of Standards and Technology, Gaithersburg, MD 20899 

+ Yale University, Department of Mechanical Engineering, New Haven, CT 06250 

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 

4pproved for public release; distribution is unlimited. 

13. ABSTRACT (?hximum 200 words) 

Planar laser induced fluorescence (PLIF) and laser induced fluorescence are used to measure relative OH 

concentration profiles and maximum flame temperatures in an atmospheric pressure, opposed flow, propane 

(C&)/air flame. Flame inhibiting agents CF,Br, N2, Fe(CO)s, FM-200, FE-36, DMMP, and PN were added to the 

flame, and relative OH concentration profiles and peak flame temperatures were measured as each flame approached 

extinction. The measured OH profiles illustrate that adding Nr, FM-200, and FE-36 to the flame produced smaller 

changes in OH concentrations relative to CF3Br, implying these agents have chemical inhibition capacities less than 

CF3Br. However, adding DMMP and Fe(C0)5 to the flame demonstrated chemical inhibition capabilities greater than 

CF3Br, with larger changes in OH concentrations; similar trends are observed for peak flame temperatures. CF3Br, 

PN, DMMP, and Fe(CO)S have temperature values (1600-1800 K) that are lower than the uninhibited flame peak 

temperature (2200 K). OH profile widths were measured in the uninhibited flame and in each inhibited flame with 

inhibitor addition at 50% of determined extinction concentrations. Profile widths for CFar, PN, DMMP, and 

Fe(CO)S were at least 20% less than the uninhibited flame. Numerical modeling of a stoichiometric, premixed, 

&H&r flame inhibited by DMMP, Fe(CO)5, CFsBr, and NZ indicated DMMP and Fe(CO)5 have greater decreases in 

burning velocities and OH relative to CF3Br. 

14. SUBJECT TERMS 15. NUMBER OF PAGES 

OH PLIF, halon replacement, opposed flow burner 28 

16. PRICE CODE 

7. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT 

OF REPORT OF THIS PAGE OF ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL 

8Cb.l 7~.4n~n,~c)lln~4T;nll 

23 

Standard Form 298 (Rev. 2-89) 

Prescribed by ANSI Std. 239-18 298-l 02 
I 

INTENTIONALLY LEFT BLANK. 

24 

. 

. 
USER EVALUATION SHEET/CHANGE OF ADDRESS 

This Laboratory undertakes a continuing effort to improve the quality of the reports it publishes. Your comments/answers to 

the items/questions below will aid us in our efforts. 

1. ARL Report Number/Author ARL-TR-2388 (Skanns) Date of Report February 2001 

, 

2. Date Report Received 

a 3. Does this report satisfy a need? (Comment on purpose, related project, or other area of interest for which the report will be 

used.) 

. 

4. Specifically, how is the report being used? (Information source, design data, procedure, source of ideas, etc.) 

5. Has the information in this report led to any quantitative savings as far as man-hours or doIlars saved, operating costs 

avoided, or efficiencies achieved, etc? If so, please elaborate. 

6. General Comments. What do you think should be changed to improve future reports? (Indicate changes to organization, 

technical content, format, etc.) 

Organization 

CURRENT 

ADDRESS 

Street or P.O. Box No. 

E-mail Name 

City, State, Zip Code 

7. If indicating a Change of Address or Address Correction, please provide the Current or Correct address above and the Old or 

Incorrect address below. 

, OLD 

ADDRESS 

Organization 

Name 

Street or P.O. Box No. 

City, State, Zip Code 

(Remove this sheet, fold as indicated, tape closed, and mail.) 

(DO NOT STAPLE) 
DEPARTMENT OF THE ARMY 

OFFICIAL BUSINESS 

BUSINESS REPLY MAIL 

FIRST CLASS PERMIT NO OOOl,APG,MD 

I IN THE 

UNITED STATES I 

POSTAGE WILL BE PAID BY ADDRESSEE 

- 

DIRECTOR 

US ARMY RESEARCH LABORATORY - 

ATTN AMSRL WM BD 

ABERDEEN PROVING GROUND MD 210055066