Temperature Dependence of Phosphorus-Based

Flame Inhibition

M. A. MACDONALD, F. C. GOULDIN, and E. M. FISHER*

Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA

An investigation of the inhibition properties of Phosphorus-Containing Compounds (PCCs) in moderately

strained (global strain rate of 300 s21) non-premixed methane-N2/O2/Ar flames is presented. The effect of

DMMP [dimethyl methylphosphonate, O5P(OCH3)2(CH3)] on relative OH concentration profiles was

measured by using quenching-corrected Laser-Induced Fluorescence (LIF) for the first time. LIF measurements indicate a reduction in the total OH present of 23% for a non-premixed methane-air flame doped with

572 ppm of DMMP. As the stoichiometric adiabatic flame temperature is increased via substitution of Ar for

N2 in the oxidizer stream, the measurements show a strong decrease in the magnitude of the OH reduction.

Experimental results show reasonable agreement with computational predictions made using a kinetic model

that has been proposed for DMMP decomposition and phosphorus-radical chemistry. Analysis of the

computational results shows that the reactions involving phosphorus remove H and O atoms from the radical

pool, thus weakening the flame. These reactions produce OH directly, but the rest of the mechanism responds

to O and H reductions by reducing OH levels. The key reactions involved in this inhibition process are

identified. © 2001 by The Combustion Institute

INTRODUCTION

Since the advent of the Montreal Protocol in the

1990, which banned the manufacture of a variety of halogenated compounds including the fire

suppressant CF3Br, there has been a strong

interest in the development of new chemically

active fire suppressants. One of the classes of

compounds that are under consideration are

phosphorus-based agents, such as DMMP [dimethyl methylphosphonate, CAS #756-79-6,

O5P(OCH3)2(CH3)]. Extinction measurements

on non-premixed, atmospheric-pressure flames

have demonstrated DMMP to be a highly effective suppressant (2–4 times more effective than

CF3Br) [1]. Even when used in quantities that

are insufficient to cause extinction, fire suppressants are generally observed to inhibit flame

chemistry via physical and chemical effects. The

mechanism for phosphorus-based inhibition is

believed to be catalytic recombination of flame

radicals (H, OH, O) by phosphorus-containing

radicals [2, 3] formed following the decomposition of the parent compound [2, 4]. This mechanism is analogous to that of halogen-based

suppressants [5, 6]. The influence of phosphorus-containing compounds (PCCs) on radical

concentrations in flames has been demonstrated

experimentally. Chemiluminescent emission

spectroscopy was used to observe changes in

OH by Ibiricu and Gaydon [7] as well as Hastie

and Bonnell [2], who also observed changes in

H atom concentrations by using a Li/Na emission technique. Qualitative laser-induced fluorescence (LIF) measurements have shown reductions in OH fluorescence because of the

addition of DMMP [8]. In addition, quantitative

laser absorption measurements of OH in a flow

reactor have shown that the addition of PH3

(phosphine) to H2-O2 combustion product

gases increases H 1 OH recombination rates

following laser photolysis [3]. A more complete

literature review of the influence of PCCs on

flames can be found in [1, 5].

Extinction studies under a variety of flame

conditions found a significant temperature dependence for DMMP effectiveness, with higher

effectiveness being observed at lower stoichiometric adiabatic flame temperatures [9]. The

existence of a temperature dependence for

phosphorus-based flame inhibition was first suggested by Hastie and Bonnell in 1980 [2], but

since then there has been little investigation of

this behavior. There is one computational study

on premixed flame speeds [5], but aside from [9]

there is no experimental work, of which we are

aware, in which flame temperature has been

*Corresponding author. E-mail: emf4@cornell.edu. systematically varied. The influence of flame

COMBUSTION AND FLAME 125:668–683 (2001)

0010-2180/01/$–see front matter © 2001 by The Combustion Institute

PII S0010-2180(00)00236-4 Published by Elsevier Science Inc.
temperature on inhibition effectiveness is an important consideration in evaluating the feasibility

of new phosphorus-based flame suppressants, and

has direct bearing on how to maximize their

effectiveness in practical applications. The indicated trend implies that a mixture of inert and

phosphorus-based suppressants could interact

synergistically as the inert component cools the

flame, thus increasing the efficiency of the chemically active component. The use of suppressant

mixtures not only increases the overall efficiency

of the suppression system, but dramatically lowers

the quantity of the chemically active component

used, thus decreasing environmental concerns and

possible health impacts. A similar temperature

dependence has been demonstrated for CF3Br,

including the observation of synergistic interaction

with the inert suppressants N2, CO2, and H2O

[10, 11]. Increased effectiveness at lower flame

temperatures has also been observed for the

iron-based suppressant Fe(CO)5 [12, 13].

Our goals for the current study are to unambiguously identify and quantify the temperature

dependence for flame inhibition by DMMP and

to gain further insight into the inhibition mechanism. To this end, the influence of DMMP on

OH concentration profiles has been studied in

an opposed-jet burner using quenching-corrected laser-induced fluorescence (LIF). Only a

limited number of measurements of OH concentrations in the counterflow configuration

have been reported [14–17]. Several studies

have utilized LIF to observe changes in OH

concentration in flames doped with halogenated

suppressants [18–20], while work with flames

doped with phosphorus-containing agents is far

more limited [8, 16]. In the present work, the

inhibition “effectiveness” of DMMP is evaluated in terms of the reduction in OH concentration due to its presence. A series of four

non-premixed, atmospheric-pressure flames of

methane versus O2/N2/Ar mixtures were studied. Flame temperature was varied by changing

the proportions of N2 and Ar in the oxidizer

side diluent, while maintaining 21% (by vol) O2

and thus a constant stoichiometric mixture fraction of 0.055. Experimental results are also

compared to predictions from numerical calculations made using a kinetic mechanism [16]

that has been proposed for DMMP decomposition and phosphorus-containing radical chemistry. The key reactions in the mechanism that are

responsible for the observed inhibition of OH

are identified.

EXPERIMENTAL METHOD

Measurements

Our opposed-jet burner geometry and dopant

delivery system have been detailed previously

[1, 9]. The reactant nozzles are straight glass

tubes without screens (0.98 cm i.d.) with a

separation distance of 0.95 cm between opposing nozzles. Methane fuel flows from the lower

tube, and the oxidizer is introduced from the

upper tube. Reactant streams are maintained at

100°C, to prevent DMMP from condensing on

reactant tube walls. Table 1 lists the composition and stoichiometric adiabatic flame temperatures for the four flames studied; note that

these temperatures are slightly higher than typical due to the reactant preheat. All flames have

a global strain rate, a, of 300 s21 as calculated

from reactant stream flow rates and nozzle

geometry using Eq. 1 [21]:

a 5 2VO

L S1 1

VF

VO

S

rF

rO

D

1/ 2D. (1)

L refers to the separation distance between the

nozzles; V is the volume averaged stream velocTABLE 1

Flame Conditions

Flame

#

Oxidizer

Composition

Tadiabatic

[K]

Tcalculated peak

[K]

DMMP

[ppm]

VO

[cm/s]

VF

[cm/s]

1 21% O2–79% N2 2261 1967 0–572 71 96

2 21% O2–53% N2–26% Ar 2353 2080 0–715 71 101

3 21% O2–26% N2–53% Ar 2450 2189 0–715 71 106

4 21% O2–79% Ar 2547 2286 0–715 71 110

PHOSPHORUS-BASED FLAME INHIBITION 669
ity; and r is the stream density, with the subscripts O and F referring to oxidizer and fuel

respectively. Equation 1 assumes plug flow

boundary conditions at the nozzle exit planes.

The fuel and oxidizer velocities are chosen to be

momentum balanced, which places the stagnation plane in the center of the burner in the

absence of a flame. When the flame is established, these conditions lead to a stable, laminar

flame that is well centered in the burner.

Calculations of the undoped flames were

made using the OPPDIF code version 8.5 from

the CHEMKIN III Suite [22]. The full GRIMECH 3.0 mechanism, including nitrogen

chemistry, (53 species, 325 reactions) [23] was

employed. Mixture averaged diffusion velocities

were used, and thermal diffusion was neglected.

Opposed-jet burners are typically modeled as

having either potential flow (linear axial velocity

gradient) or plug flow (zero axial velocity gradient) boundary conditions, although measurements indicate that the actual velocity field lies

somewhere between the two approximations

[24]. Calculations were performed for several

different boundary conditions, as described below. The boundary conditions of potential flow

with centerline axial velocities of twice the

measured volume averaged velocities for the

fuel and oxidizer streams were selected for use

in this study, because the resulting OH profiles

most closely agreed with our observed profiles.

The factor of two for the centerline velocities is

appropriate because the flow in the straighttube reactant nozzles (L/D . 30) is expected to

be close to Poiseuille flow, in which the centerline velocity is twice the volume average. Temperature profiles predicted by 1D calculations

have been found by other researchers to be in

good agreement with measurements made in

opposed-jet burners under a variety of conditions by using spontaneous Raman scattering in

CH4/O2/N2 [25] and H2/air [14] flames, thin SiC

filament pyrometry in CH4/O2/N2 flames [26]

and CARS in propane/air flames [27].

OH concentration measurements were made

by using point-wise LIF. Figure 1 shows a

schematic of the experimental set up. Profile

measurements were made by traversing the

laser beam and collection optics simultaneously

across the flame in 100 mm steps. The translation stages used have a resolution of 10 mm.

Excitation of the P1(9) transition of the A 4 X

(1, 0) band near 286 nm was made by using a

frequency-doubled Quanta Ray PDL 2 pulsed

dye laser, nominal linewidth of 0.2 cm21

, with

rhodamine 590 dye. This transition was selected

Fig. 1. Schematic of LIF apparatus.

670 M. A. MACDONALD ET AL.
because of the weak temperature dependence

of the rotational ground state population in the

temperature region of interest (,10% variation

for 1400 K , T , 2500 K), which helps maintain

a strong LIF signal across the entire OH profile.

The dye laser was pumped with a 6 to 7 ns pulse

at 532 nm provided by a frequency-doubled

Spectra Physics DCR 2A Nd:YAG laser operating at 10 Hz.

Detection of OH fluorescence was performed

at 90° to the laser beam axis using an RCA 8850

photomultiplier tube and color glass filters

(Schott WG305 and UG11) which transmit light

in the 305 to 371 nm range. The photomultiplier

signal was amplified by a SRS240 Fast Preamplifier (Stanford Research Systems). The filter

combination used blocks elastically scattered

laser light (and near-elastic resonant fluorescence) while passing fluorescence emission

from the (1, 1) band (312–326 nm) and emission

from the overlapping (0, 0) band (306–320 nm)

which can occur following collisionally driven

Vibrational Energy Transfer (VET) from the

n9 5 1 to the n9 5 0 states. At atmospheric pressure, VET rates can be significant [28, 29] with

more than a third of the total measured fluorescence originating from the (0, 0) band when

using excitation/detection schemes similar to

ours [30]. Fluorescence trapping of emission

from the (1, 1) band is negligible because of the

small population of the electronic ground state

with n0 5 1 over the temperature range under

consideration. Some trapping will occur for

fluorescence emission originating from the (0,

0) band, but the effect is small due to the short

path length through the flame (less than 1 cm)

and is not expected to influence the measurements [31, 32]. PAH fluorescence is a common

form of interference observed when using this

excitation/detection scheme, if significant levels

of PAH are present [31]. The moderately

strained laminar flames under investigation

here are virtually soot-free, and consequently

PAH fluorescence was expected to be low.

Measurements taken with the dye laser tuned

off resonance confirmed that interference from

PAH was negligible. The combination of the

focussed ( f 5 30 cm quartz focussing lens) UV

laser beam and slits in the detection optics give

a probe volume of less than 100 mm in diameter

and 1.5 mm in length. The opposed-jet burner

flame is locally planar near the centerline with

the long axis of the probe volume aligned in the

plane of the flame surface. Laser pulse energy

was monitored using a UV-sensitive photodiode. Both the LIF and laser energy signals

were integrated on a shot-by-shot basis using an

SRS 250 Boxcar Integrator and Averager (Stanford Research Systems), and recorded on a

personal computer using a GW Instruments

data acquisition card. Operation within the linear LIF regime was ensured by checking the

linearity of LIF signal strengths with pulse energy for all measured data points [33].

To avoid errors associated with wavelength

drift of the dye laser and the resulting changes

in the spectral overlap of the laser and molecular absorption lineshapes, the output wavelength of the dye laser was scanned across the

P1(9) transition at each measurement location

using a stepper motor to adjust the grating in

the dye laser cavity. 100 measurements of OH

fluorescence and laser pulse energy were acquired at each half-step of the motor (one

half-step corresponds to a wavelength change of

approximately 0.0012 nm), and the half-step

motor position with the maximum average ratio

of fluorescence signal to laser pulse energy was

taken to be the absorption line center for the

transition. LIF data for that half-step motor

position were used for the subsequent evaluation of OH concentration. The repeatability of

this procedure was found to be within 65% of

the mean observed ratio. The average ratio of

OH fluorescence signal to laser pulse energy

was found by fitting the 100 measurements to a

straight line by linear regression analysis. The

statistical uncertainty (one standard deviation)

in the fitted slopes was less than 63%. Additional uncertainty in these slopes arises from

statistical uncertainty in the measurement of the

zero level in the presence of electrical noise

from the Nd:YAG laser. Statistical scatter in the

zero measurement (6 one SD) corresponds to

an uncertainty of 63 to 5% of the peak slope for

all data points in the profile. In addition to shot

noise and electrical noise, the statistical uncertainty in the measurements reflects fluctuations

in flame location. For these aerodynamically

stabilized flames, perturbations in the reactant

flow can cause small, momentary flame displacements. The 100 shot LIF averaging process

PHOSPHORUS-BASED FLAME INHIBITION 671
will largely compensate for these oscillations if

they occur. Particularly for measurements made

in regions where the curvature of the OH profile

is not large, that is, away from the immediate

vicinity of the OH peak and the profile edges,

small, random fluctuations in flame position

yield symmetric fluctuations in the LIF signal

that will average to zero. The total uncertainty

for each measured data point in a given profile

due to these random errors was found by summing the contribution of the uncertainties described above (assuming statistical independence) and is estimated to be less than 610% of

the peak value in the profile. Uncertainty estimates will be illustrated for sample profiles in

the Results section.

To quantify the fluorescence measurements,

corrections for collisional quenching and the fraction of the OH population that is in the pumped

rotational level must be made. However, the overall effect of these corrections on the profile shape

is small, as is expected for our excitation/detection scheme in non-premixed atmospheric-pressure flames [17, 34, 35]. Equation 2 relates the

fluorescence signal to the concentration of OH

assuming low laser energy (i.e., negligible saturation of the excited transition) [36]:

F 5 CBIfNF. (2)

Here F is the total fluorescence signal; C is a

constant that incorporates geometric factors

such as collection solid angle and probe volume

as well as detector efficiencies and gain characteristics of the integrators, amplifiers etc.; B is

the Einstein coefficient for stimulated absorption; I is the spectral overlap integral between

the laser intensity and the molecular absorption

lineshape, temporally integrated over the duration of the laser pulse; N is the total OH

population, and f is the fraction of the population that is present in the ground state rotational level excited by the laser; and F is the

fluorescence quantum yield, which depends on

the local quenching and VET rates.

Species and temperature profiles from the

undoped-flame calculations were used to estimate the required corrections to the linear LIF

data for both doped and undoped flames. The

fraction of the ground state population in the

pumped rotational level is determined using the

local gas temperature given by the calculations

and assuming rotational thermal equilibrium

(Boltzmann distribution), as implemented in

the spectral simulation software LIFBASE [37].

The total fluorescence yield can be estimated

by using [30]:

F 5

A1 1

V10

Q0

A0

Q1 1 V10

, (3)

where A1 and A0 are the spontaneous emission

rates for the n9 5 1 and n9 5 0 vibrational levels,

respectively. Equation 3 has been simplified by

assuming equal transmission and detection efficiencies of the collection optics and PMT for

both the (1, 1) and (0, 0) bands. Q1 and Q0 are

the total quenching rates for the n9 5 1 and n9 5

0 levels, and V10 is the total VET rate from n9 5

1 to n9 5 0. The influence of VET rates on the

fluorescence quantum yield is primarily because

of the higher spontaneous emission rate of the

n9 5 0 state (A1/A0 ' 0.575) [38]. The quenching

and VET rates are evaluated using Eq. 4 [30, 38]:

Q, V 5 ~P/~kbT!! O

i

xi^n&i2OHsi

Q,V

~T!, (4)

where P is pressure; T is temperature; kb is

Boltzmann’s constant; xi is the mole fraction of

OH collision partner species i; ^n&i2OH is the

mean relative collision velocity of species i and

OH given by ^n&i2OH 5 (8kbT/pmi2OH)

1/2,

where mi2OH is the reduced mass of species i

and OH; and si

Q,V(T) is the value of the

quenching or VET (superscript Q or V, respectively) cross section for collisions with species i,

averaged over all rotational levels in a given

vibrational level, assuming rotational thermal

equilibrium.

Substitution of Eq. 4 into Eq. 3 followed by

some algebraic manipulation yields [30]:

F 5 A0

Q0 3

S

A1

A0

DS^sQ&0

^sQ&1

D 1 ^sV&10

^sQ&0

1 1 ^sV&10

^sQ&1

4 , (5)

where ^sQ&1, ^sQ&0, and ^sV&10 represent the

sum over all collision partners of the thermally

averaged cross sections for quenching from n9 5

1, quenching from n9 5 0, and VET from n9 5

1 to n9 5 0, respectively. Fewer quenching

cross-section measurements have been made

672 M. A. MACDONALD ET AL.
for the n9 5 1 state than for n9 5 0 [28, 39], but

results indicate similar values to those found for

the n9 5 0 state. We have therefore approximated the quenching environment for both

states as being that for the n9 5 0 state, or

equivalently ^sQ&1/^sQ&0 ' 1. The ratio of

averaged VET cross sections to the averaged

quenching cross sections is assumed to be independent of position in the flame (e.g., ^sV&10/

^sQ&0 ' constant). As a result, the quantity in

square brackets in Eq. 5 becomes a constant,

and the fluorescence yield is simply inversely

proportional to the quenching rate for the n9 5

0 state (taken to be equal to that for n9 5 1). To

confirm the validity of the assumption ^sV&10/

^sQ&0 ' constant, we have estimated the VET

rates and resulting fluorescence yield according

to Eqs. 3 and 4, by using the limited available

VET cross-section data [28, 39, 40], some of

which are reported only as upper bounds, along

with major species and temperature profiles

from calculations. These estimates indicate that

the error in the fluorescence quantum yield

introduced by this approximation is less than

5%. Values for the quenching rate cross-sections used in this work are taken from temperature-dependent quenching cross-section data

compiled by Tamura et al. [41] from the extensive measurements that have been made for the

n9 5 0 state of OH.

The calculated quenching rate varies by 15%

across the OH containing regions in flame 1.

This variation is moderated by the presence of a

large concentration of N2 which has a relatively

small gradient in the flame zone. For flame 4,

where Ar (a highly inefficient quencher) has

been substituted for N2, the variation is substantially higher at 30%.

The same quenching environment was assumed for flames both with and without DMMP

loading. The maximum phosphorus loading was

only 715 ppm. Because the mole fractions of

phosphorus-containing species will be small in

this case, it is expected that they will not contribute significantly to quenching of OH.

Changes in major species profiles because of the

presence of DMMP are not expected to be large

enough to significantly change the overall

quenching environment. Changes in flame temperature due to the addition of these small

loadings of DMMP (see Calculations with Phosphorus Kinetics section) were also found to be

negligible (,10 K).

After correcting for the fluorescence yield

and the Boltzmann fraction of the pumped

rotational level, the corrected LIF profile is

directly proportional to OH concentration. An

estimate of the scaling constant relating the

corrected LIF measurements to absolute OH

concentrations can be made by matching the

peak of the measured profile from the undoped

flame to the peak OH concentration predicted

by the flame calculations. This matching does

not affect our observations of PCC effects on

OH, which are all presented normalized to the

undoped flame measurements. For profiles

measured in flames doped with phosphoruscontaining additives, the scaling constant is determined from undoped profiles taken on the

same day with the same instrument settings.

Because the same constant is used for both

doped and undoped flames, quantitative comparisons can be made between the two cases.

Determination of the magnitude of the scaling

constant is performed by minimizing the meansquare-error between calculated and measured

profiles (via a least squares technique). For this

minimization, only data points above 50% of

the measured peak value were considered. Minimization of error was performed via adjustment of the scaling constant and a position

offset (i.e., the offset between the measured

flame center, as indicated by the translation

stage micrometers, and the computational

flame center). Determination of this scaling

constant essentially calibrates the constant C

from Eq. 2, assumed to be constant for a given

set of instrument settings. This scaling procedure affects only the magnitude and position of

the observed fluorescence profile and not the

shape or width.

Calculations with Phosphorus Kinetics

To investigate the cause of the OH concentration changes observed in the LIF experiments, a

set of flame calculations was performed using a

proposed mechanism for DMMP decomposition and phosphorus-radical chemistry [16] that

has been developed in recent years. This mechanism is based on 1) the kinetic data used for

the analysis of the influence of PH3 on radical

PHOSPHORUS-BASED FLAME INHIBITION 673
recombination rates in the combustion products

of a hydrogen flame [42, 43] and 2) kinetic models

used for describing DMMP and TMP [trimethyl

phosphate, CAS#512-56-1, P(5O)(OCH3)3] destruction in a low pressure hydrogen flame [44,

45]. Reactions of phosphorus-containing species

with radicals and intermediate species of hydrocarbon combustion have been included [16]. Reactions have been added to the scheme to complete destruction pathways for some species [16].

The current version of this phosphorus mechanism includes 27 species and 166 reactions. Thermochemical data compiled by Babushok [46] for

phosphorus-containing species are mostly taken

from Refs. [3, 47–49]. Methane-O2 chemistry was

modeled using GRI Mech 3.0 [23] with nitrogen

chemistry removed (36 species, 219 reactions retained). The phosphorus mechanism predicts reductions in extinction stain rates for non-premixed methane-air flames because of the

presence of DMMP [16] that are in agreement

with experimental results from MacDonald et

al. [1]. An earlier version of the mechanism has

also been used to predict the effect of DMMP

on premixed flame speeds [5]. Figures 2a and 2b

illustrate the major species profiles from these

calculations for flames 1 and 4 without dopant

addition. Calculations were performed for all

four flames using the combined mechanisms

(phosphorus and GRI Mech), both with and

without the addition of 572 ppm of DMMP.

Calculations with the combined mechanisms

required a higher degree of mesh refinement

(both GRAD and CURV parameters for OPPDIF script 5 0.1, yielding 250–300 grid points)

than the GRI Mech calculations to produce OH

profiles for the doped flames that were independent of grid size.

RESULTS

Measurements

Figure 3 shows a comparison between measured

and calculated OH concentration profiles for

flames 1 and 4, the coolest and hottest conditions respectively. Multiple profiles, all unFig. 2. a) Calculated major species and temperature profiles for Flame 1, undoped. b) Calculated major species and

temperature profiles for Flame 4, undoped.

Fig. 3. OH concentration profiles. Flame 1 computations

are shown as the dashed line; open symbols are for four

measured profiles. Flame 4 computations are shown as the

solid line; filled symbols are for three measured profiles.

Error bars represent statistical uncertainty in the measured

values.

674 M. A. MACDONALD ET AL.
doped, are shown to illustrate the repeatability

of these measurements. The agreement between measured and calculated profiles is seen

to be quite good. The intermediate cases of

flames 2 and 3 are in similar agreement between

measured and computed profiles. Agreement in

peak OH concentration is expected since calculated profiles are used to estimate peak concentrations in our measurements for each flame.

There is also good agreement in the profile

shape, which is not affected by the matching

procedure, including the degree of asymmetry,

and width (FWHM). The peak concentration,

as determined by the calculations, is seen to

increase by 66% from 0.041 mol/m3 for flame 1

to 0.069 mol/m3 for flame 4, which has a stoichiometric adiabatic flame temperature that is

286 K hotter than flame 1. It should be noted

that the peak temperatures, from laminar flame

calculations (see Table 1), for these moderately

strained flames are approximately 300 K cooler

than the stoichiometric adiabatic flame temperatures, although the difference in calculated

peak temperatures for flames 1 and 4 (319 K) is

comparable to the change in the stoichiometric

adiabatic flame temperature (286 K).

Figure 4 illustrates the variation in computed

and measured OH profile widths (FWHM) with

adiabatic flame temperature. All flame conditions are undoped. Both the calculated and

measured OH profile widths are observed to

increase by approximately 40%, from 0.4 mm to

0.55 mm, across the range of temperatures

investigated. Good agreement between calculated and measured profile widths is observed

for all undoped flames.

The velocity boundary conditions in the calculations can also have a noticeable effect on

the calculated width of the OH profile. To

investigate the influence of these boundary conditions, two additional sets of calculations were

performed, one for plug flow boundary conditions with the measured volume averaged velocities and the other for potential flow while

matching the maximum local strain rate to 480

s

21

, or 1.60 times the global strain rate (Eq. 1)

(which required increasing the centerline velocity for the calculations to 2.8 times the volume

averaged value). The higher strain case was

motivated by measurements of axial velocity

profiles made using Laser-Doppler Velocimetry

(LDV) in a similar burner configuration [50].

These measurements indicated a substantially

higher local strain rate (axial velocity gradient

on the oxidizer side, evaluated just upstream of

the heat release region) of approximately 1.60

times the global strain rate. The original calculations, with boundary conditions of potential

flow and velocities of twice the volume average,

gave a computed velocity profile with a peak

local strain rate of approximately 1.18 times the

global strain rate or 355 s21

. The calculated OH

profile widths for the two additional sets of

boundary conditions are also shown in Fig. 4.

Both additional sets of boundary conditions

predict similar variation in profile width with

flame temperature. However, the plug flow

boundary condition overestimates the profile

widths by 10 to 15%, and the higher strain rate

case underestimates the widths by 5 to 8%.

Finite spatial resolution in the measurements

(100 mm) limits the accuracy with which the

experimental width can be determined. Heat

and radical losses to the burner as well as

radiation, which are ignored in those calculations, will also contribute to the discrepancy

between measured and calculated profiles.

However, these physical loss mechanisms are

not expected to be significant in these well

Fig. 4. OH profile widths (FWHM). Open circles are

measured values for all undoped flames. Lines with filled

symbols are computational values for three different velocity boundary conditions (B.C.). Filled circles are potential

flow B.C. with velocities of twice the volume average

(Poiseuille flow). Filled triangles are plug flow B.C. with

velocities equal to the volume average. Filled diamonds are

potential flow B.C. with local strain rate equal to 1.60 times

the global strain rate given by Eq. 1.

PHOSPHORUS-BASED FLAME INHIBITION 675
isolated, non-sooting flames. Uncertainties associated with the chemical mechanism used will

influence the computed profile width and also

affect the level of agreement between computed

and measured profile widths.

The good agreement between the measured

profiles and the calculations made with potential flow boundary conditions with centerline

velocities of twice the volume average support

our selection of this boundary condition for use

in the quenching and Boltzmann fraction corrections to the LIF data. It should be noted that

because of the relatively small impact of the

temperature and quenching correction, the

choice of the appropriate boundary conditions

does not substantially influence the conclusions

below about the influence of phosphorus additives on OH concentration. Using profiles calculated with either of the alternate boundary

conditions to correct the LIF data changes the

observed reductions in total OH by less than

1%, well within the uncertainty of the measurements.

Figure 5 illustrates the effect of 572 ppm of

DMMP on OH concentrations in flame 1. With

this loading, flame 1 is close to extinction. A

substantial reduction, approximately 20%, in

OH concentration is observed. The doped profile is seen to be smaller in magnitude, but the

width is not significantly affected. To determine

changes in the total flame OH concentration,

the profiles are numerically integrated, using a

simple trapezoidal rule approximation, across

the width of the flame, and then the integrals

from the doped and undoped flames are compared. The integration technique is particularly

useful for quantifying changes in the highertemperature flames where the OH concentration profile is less affected by the phosphoruscontaining additive. There is a 23 6 3%

reduction in total OH (by this definition) for the

data shown in Fig. 5. The uncertainty results

from the estimated statistical uncertainty of the

individual data points from the profile, and is

closely comparable to the repeatability of the

measurement.

OH concentration profiles were measured for

all four flames with DMMP loadings up to 715

ppm, with the exception of flame 1. A loading of

715 ppm of DMMP in flame 1 is sufficient to

cause extinction, at the global strain rate used in

this study. Therefore, the maximum loading

used for that flame was 572 ppm, the next

highest loading readily achieved experimentally.

Figure 6 illustrates the ratio of doped to undoped total OH for the four flames as a function

of loading. Raw data for profiles for all conditions studied in this work can be found in the

appendix of Ref. [51]. Total OH appears within

experimental uncertainty to decrease linearly

with DMMP addition over this range of loadFig. 5. Effect of 572 ppm of DMMP on OH in Flame 1.

Filled symbols are for undoped profiles; open symbols are

for doped profile. The thick line shows the computational

prediction for the undoped profile; thin line is the doped

profile. Phosphorus kinetic mechanism from Wainner et al.

[16].

Fig. 6. Effect of DMMP loading for all flames. Lines are

linear regression fits to data. Solid line and circles are Flame

1, dot-dash line and squares are Flame 2, dashed line and

diamonds are Flame 3, dotted line and triangles are Flame

4. Error bars represent uncertainty in measurements.

676 M. A. MACDONALD ET AL.
ings. Results from the calculations performed

with the phosphorus kinetic mechanism, discussed below, for a range of DMMP loadings

from 0 to 720 ppm, confirmed the linear variation in the OH reduction with loading. The

linear trends are consistent with extinction measurements on non-premixed methane-air flames

which indicated a linear variation in DMMP

effectiveness, defined in terms of reduction in

the global extinction strain rate, for loadings up

to 1500 ppm [1]. Linear variation in effectiveness with loading is observed with most flame

suppressants at low loadings. Linear regression

fits to the data for each flame are also shown in

Fig. 6. The most striking observation from Fig. 6

is the increase in inhibition effectiveness with

decreasing flame temperature. The highesttemperature case, flame 4, shows less than 5%

reduction in total OH at the maximum loading

of 715 ppm, compared to 23% reduction in

flame 1 for only 572 ppm.

We attempted extinction measurements for

the flames in this work, but were not successful

because the high extinction strain rates for

flames 2 through 4 required dramatically higher

flow velocities that were well into the turbulent

flow regime for our geometry. However, in an

earlier study we investigated the effect of

DMMP on global extinction strain rate for a

variety of different flame conditions with different stoichiometric mixture fractions and stoichiometric adiabatic flame temperatures [9]. Effectiveness in terms of extinction strain rates for

that work was defined as the fractional reduction in global extinction strain rate divided by

the mole fraction of phosphorus in the flame:

Effectivenessq ; ~aq,0 2 aq!

aq,0

1

xP

. (6)

The subscript q indicates that the measurement

is made at extinction conditions, and the subscript 0 denotes the value for the undoped

flame. Flame calculations were used to estimate

the mole fraction of phosphorus at the flame

surface, xP, taken to be the maximum temperature contour. We observed a similar trend of

decreasing effectiveness with increasing temperature. The stoichiometric adiabatic flame temperature in that study was varied in two ways.

The first was by changing the stoichiometric

mixture fraction from 0.05 to 0.7 while maintaining a fixed undoped global extinction strain

rate. The second was by decreasing the overall

dilution of the flame while maintaining a stoichiometric mixture fraction of 0.5. The range in

adiabatic flame temperatures from that work

(2130–2260 K) is substantially lower than that

investigated here. To compare the temperature

dependence from the previous investigation to

that of the current work, we define a measure of

effectiveness, analogous to the one used in the

previous study, in terms of OH reduction as the

fractional reduction in total OH concentration:

EffectivenessOH ;

(TotalOH0 2 TotalOH)

TotalOH0

1

xP

. (7)

Again, the subscript 0 denotes the measured

value for the undoped flame. The flame calculations made with the combined GRI Mech and

phosphorus mechanisms are used to determine

xP, the total mole fraction of phosphorus (sum

of mole fractions of all phosphorus-containing

species) predicted at the flame surface, taken to

be the maximum temperature contour. Because

the stoichiometric mixture fraction is fixed for

all flames, changes in xP are negligible. The use

of this parameter in the current work does not

affect the observed trends and is introduced

solely to provide a definition for effectiveness

that is analogous to that used in Ref. [9] to

facilitate a comparison to our previous extinction studies. This effectiveness definition is essentially a measure of the slope of the linear

trends indicated in Fig. 6. Figure 7 shows a

comparison of this effectiveness based on OH

with the one based on the extinction measurements from the previous study. The trends

observed in the two data sets are in good

qualitative agreement, given that different measures of effectiveness are used. When comparing the two data sets, it should also be noted

that for a given stoichiometric adiabatic flame

temperature, measurements performed at extinction conditions, such as those from [9], will

have a peak flame temperature that is cooler

than that seen in the LIF measurements, which

are performed at a fixed global strain rate of 300

s

21

, below the value required to extinguish the

flame. The effectiveness data in Fig. 7 shows a

PHOSPHORUS-BASED FLAME INHIBITION 677
substantial decrease in DMMP effectiveness

with increasing temperature. The unambiguous

trends in the LIF data confirm the hypothesis of

Hastie and Bonnell [2] of decreasing inhibition

with increasing flame temperature, with nearly a

90% decrease in effectiveness for a 300 K

increase in temperature.

Calculations with Phosphorus Kinetics

The combined mechanism of phosphorus kinetics by Wainner et al. [16] and CH4-O2 kinetics

from GRI Mech [23] was used to calculate

species and temperature profiles for all four

flames with and without the addition of 572 ppm

of DMMP. The predicted temperature profiles

showed no significant effect from the addition

of DMMP (,10 K change in peak temperature). However, significant changes were observed in OH, H, and O profiles. Figure 8

illustrates the doped and undoped profiles of

OH, H, and O for flame 1. Relative to the

undoped profile, the OH profile for the doped

flame is lower in magnitude. The change is

similar to that observed in the measured data,

but not as large. A comparison of computational predictions to measured data is shown in

Fig. 5. It is interesting that the reduction in H

and O atom concentrations seen in Fig. 8 is

significantly greater than the reduction for OH,

indicating a larger effect of phosphorus chemistry on the concentrations of those species.

After performing the spatial integration of

the computed profile across the flame, as described above, the change in total OH between

the doped and undoped cases is evaluated.

Figure 9 shows a plot of effectiveness, as defined

in terms OH reduction (Eq. 7), as a function of

the stoichiometric adiabatic flame temperature

for both the experiments and the computations.

The computational and experimental results in

Fig. 9 display the same trend of decreasing

effectiveness with increasing temperature, alFig. 7. Temperature dependence of effectiveness. Open

circles are effectiveness data from Ref. [9] defined in terms

of reduction of global extinction strain (Eq. 6). Filled

squares are effectiveness data from the current work defined in terms of reduction in OH concentration (Eq. 7).

Error bars represent uncertainty in the measurements.

Fig. 8. Effect of 572 ppm of DMMP on calculated OH, H,

and O concentration profiles in Flame 1 (CH4/O2/N2). Dark

lines are undoped profiles and thin lines are with DMMP

addition.

Fig. 9. Temperature dependence of effectiveness defined as

in terms of reduction in total OH (Eq. 7). Filled circles with

the dashed line are computational predictions, filled squares

are measured data. Error bars represent uncertainty in the

measurements.

678 M. A. MACDONALD ET AL.
though the temperature dependence of the

computational results is weaker. The magnitude

of effectiveness from the flame calculations

agrees well with LIF data from the highest

temperature case, flame 4, but the calculations

under-predict effectiveness for flames 1 through

3. In these calculations the magnitude of the

reduction in OH (i.e., total OHundoped 2 total

OHdoped) is nearly constant for all flames. For

these flame calculations, changes in the effectiveness (which is a fractional measure of the

reduction of total OH) with temperature are

due mainly to the increases in the total OHundoped, which is larger by a factor of 2.25 for flame

4 (CH4/O2/Ar) compared to flame 1 (CH4/O2/

N2) in the calculations. This estimate of the

increase of total OH for the undoped flames is

not sufficient to explain the variation in effectiveness observed in the LIF measurements

(reduced by a factor of 10 in flame 4 compared

to flame 1).

The processes responsible for the observed

reductions in [OH] were determined by analysis

of individual reaction rates from the phosphorus mechanism. Since the experimental and

computational results both show a reduction in

OH concentration with the addition of DMMP,

it would be expected that the reactions involving

phosphorus remove OH from the flame. In fact,

for all four flames the sum of the chemical

production rates for OH over all reactions

involving phosphorus in the mechanism is positive across most of the OH profile, indicating

that these reactions directly produce OH rather

than destroy it. Thus the drop in OH upon

introduction of phosphorus kinetic sub-mechanism must occur indirectly, through an effect on

rates of reactions not involving phosphoruscontaining species. Poor efficiency for direct

recombination of OH by reactions involving

suppressant species has been observed previously for iron-based [52] and halogen-based [53,

54] suppressants. The net production rates for

flame radicals OH, H, and O by all reactions

involving phosphorus in flames 1 and 4 are

shown in Figs. 10a and 10b, respectively. It is

clear from these figures that the action of the

phosphorus-containing species is similar in both

flames. The regions of radical production/destruction in flame 4 are somewhat wider, in

keeping with the wider flame (see Fig. 4), but

the peak magnitudes of the production rates for

H, O, and OH are 5 to 10% lower.

The cause of the observed reduction in OH is

the fast removal of H and O atoms by the

reactions involving phosphorus. Smyth et al.

[55] have studied the interrelationships of H, O,

and OH concentrations in non-premixed methane-air flames and found that while these species are generally not in equilibrium, their reFig. 10. a) OH, H, and O production rates in Flame 1: sum over all reactions involving phosphorus. Solid line is OH

production rate, dotted line is H production rate, dot-dash line is O production rate. b) OH, H, and O production rates in

Flame 4: sum over all reactions involving phosphorus. Solid line is OH production rate, dotted line is H production rate,

dot-dash line is O production rate.

PHOSPHORUS-BASED FLAME INHIBITION 679
spective populations are still interdependent on

one another through a variety of fast radical

shuffle reactions. Because of this interdependence, the reductions in H and O atom levels

created by the reactions involving phosphorus,

observed in Fig. 8 for flame 1, cause the radical

shuffle reactions not involving phosphorus to

respond by reducing OH.

Figure 11 illustrates the shift in OH production rates by the GRI sub-mechanism (sum of

OH production rates over reactions not involving phosphorus) because of the addition of 572

ppm of DMMP to flame 1. The OH production

in the doped flame is generally lower than that

in the undoped case, particularly on the oxidizer

side of the flame. The individual reactions that

are primarily responsible for the shift seen in

Fig. 11 were identified by comparing the shift in

doped and undoped reaction rates for all reactions not involving phosphorus. Three reactions

show significant shifts in OH production rates

due to the presence of phosphorus. Two of

these reactions, R1 and R2, undergo a substantial decrease in OH production for the doped

flame. R1 is one of the important chain branching reactions:

O 1 H2 7 OH 1 H. (R1)

H 1 HO2 7 OH 1 OH (R2)

The third reaction that undergoes significant

changes because of addition of phosphorus is

R3:

OH 1 H2 7 H2O 1 H. (R3)

This reaction has been identified by Twarowski

[3, 42, 43] as playing an important role in

increased recombination rates OH 1 H 3 H2O

due to the presence of phosphorus containing

compounds. In our non-premixed flames the

overall effect of R3 in the presence of phosphorus addition is not clear, as the reaction has

regions of increased OH production as well as

regions of decreased OH production across the

flame width.

Figure 12 shows the contribution of individual reactions involving phosphorus to OH production rates and compares them to the changes

in the reaction rates of R1 and R2 (doped

rate 2 undoped rate) that occur when DMMP

is added to the flame 1. OH production by

reactions involving phosphorus is dominated by

P1:

O 1 HOPO 7 OH 1 PO2. (P1)

Fig. 11. Total OH production rates in flame 1 by reactions

not involving phosphorus. The dark line is the undoped rate.

The thin line is the rate with the addition of 572 ppm of

DMMP.

Fig. 12. Influence of the addition of 572 ppm of DMMP on

OH production rates in flame 1 (CH4/O2/N2). Rates of OH

production by reactions involving phosphorus P1–P3 and

changes (DR1 and DR2) in OH production (doped rate 2

undoped rate) for non-phosphorus containing reactions R1

and R2. The net effect (DNET) of these reactions is shown

in bold.

680 M. A. MACDONALD ET AL.
There are two phosphorus containing reactions

that consume OH, but the rates are small

(15–30%) relative to P1:

OH 1 PO2 1 M 7 HOPO2 1 M (P2)

OH 1 HOPO 7 H2O 1 PO2. (P3)

Figure 12 also shows the net change in OH

production for all reactions in that figure (P1,

P2, P3, R1, and R2). The net rate curve shows

overall destruction of OH, indicating that the

shift towards decreased production by R1 and

R2 is more than sufficient to balance the direct

production of OH by P1.

Removal of H and O atoms by reactions

involving phosphorus clearly plays an important

role in the observed inhibition. Calculation results show that removal of H atoms by reactions

involving phosphorus is done primarily by:

H 1 PO2 1 M 7 HOPO 1 M (P4)

and to a lesser extent by:

H 1 HOPO2 7 H2O 1 PO2 (P5)

H 1 HOPO 7 H2 1 PO2 (P6)

Figure 13 shows the contribution of P4 to the

total H destruction rate by all reactions involving phosphorus. Removal of O atoms by reactions involving phosphorus is done primarily by

the OH-producing reaction P1. The contribution of P1 to O removal is also shown in Fig. 12.

Significant uncertainties remain for the rate

coefficients of several of the key reactions involving phosphorus species that have been identified here (P1, P2, and P4) [46]. Suggestions

that the rate coefficients for the recombination

reactions P2 and P4 might need to be increased

by a factor of 2 or more [46] could help reconcile the observed differences in magnitude of

effectiveness between the measurements and

the computational predictions.

SUMMARY AND CONCLUSIONS

For the first time, quenching-corrected LIF

measurements of the influence of DMMP, a

phosphorus-based flame suppressant, on relative OH radical concentration profiles in moderately strained (global strain rate of 300 s21

)

non-premixed flames have been made. Measurement results in an atmospheric-pressure

methane-air flame indicated that a loading of

only 572 ppm reduces the total OH population

(integrated across the flame width) by 23%. OH

profiles in doped flames are smaller in magnitude than the undoped cases. As the flame

temperature is increased via substitution of Ar

for N2 in the oxidizer stream, the effectiveness

of DMMP is dramatically reduced. For an increase in stoichiometric adiabatic flame temperature of 300 K (all N2 in the oxidizer stream

replaced with Ar), the effectiveness of DMMP

decreases by nearly 90%. The trend of increasing effectiveness at lower temperatures implies

that a mixture of inert and phosphorus-based

suppressants could interact synergistically as the

physical agent cools the flame, thus increasing

the efficiency of the chemically active component.

Calculations performed with a proposed

mechanism for DMMP decomposition and

phosphorus radical chemistry show reasonable

agreement with the measured DMMP effectiveness and the observed temperature dependence.

Measurements show a generally higher effectiveness, and a larger variation in effectiveness

with temperature than that predicted by the

computations with this kinetic mechanism. Significant uncertainties remain for several of the

reaction rate coefficients in the phosphorus

Fig. 13. H and O production rates by all reactions involving

phosphorus (solid lines) and by individual reactions (dashed

lines, see legend), in Flame 1.

PHOSPHORUS-BASED FLAME INHIBITION 681
mechanism. Further refinement of these values

is still needed to improve the agreement of the

computational predictions with the experimentally observed magnitude and temperature dependence of OH reductions. Analysis of the

mechanism shows that the direct role of the

phosphorus-containing species in the flame is

the production of OH and the fast removal of H

and O atoms. This removal of H and O atoms

leads indirectly to the net observed decrease in

OH. Calculation results show that inhibition is

due to the phosphorus-containing radicals, PO2,

HOPO, and HOPO2, formed after the decomposition of the parent compound. This result

implies that flame inhibition does not depend

on the form of the parent compound, provided

that the parent breaks down in the flame. Thus,

a broad class of potential PCC fire suppressants

should exist, from which an alternative to halons

with minimal health and environmental impact

may be selected.

The authors gratefully acknowledge the pre-publication use of the kinetic mechanism developed

by V. Babushok of NIST, and thank J. Fleming and

B. Williams of the Naval Research Laboratory for

their assistance and many helpful discussions.

This research is part of the Dept. of Defense’s Next

Generation Fire Suppression Technology Program, funded by Dept. of Defense Strategic Environmental Research and Development Program

under DARPA contract #MDA972-97-M-0013.

Support was also provided by the Natural Sciences

and Engineering Research Council of Canada.

REFERENCES

1. MacDonald, M. A., Jayaweera, T. M., Fisher, E. M.,

and Gouldin, F. C., Combust. Flame 116:166–176

(1999).

2. Hastie, J. W., and Bonnell, D. W., Molecular Chemistry

of Inhibited Combustion Systems, National Bureau of

Standards, Final NBSIR 80-2169; PB81–170375, 1980.

3. Twarowski, A., Combust. Flame 94:91–107 (1993).

4. Korobeinichev, O. P., Il’in, S. B., and Mokrushin,

V. V., Combust. Sci. Technol. 116–117:51–67 (1996).

5. Babushok, V., and Tsang, W., Influence of PhosphorusContaining Fire Suppressants on Flame Propagation,

Proc. Third Int. Conf. on Fire Res. and Eng., Chicago,

IL, p. 257–267 (1999).

6. Babushok, V., Tsang, W., Linteris, G. T., and Reinelt,

D., Combust. Flame 115:551–560 (1998).

7. Ibiricu, M. M., and Gaydon, A. G., Combust. Flame

8:51–62 (1964).

8. Skaggs, R. R., Daniel, R. G., Miziolek, A. W., and

McNesby, K., Spectroscopic Studies of Inhibited Opposed Flow Propane/Air Flames, Presented at First

Joint States Meeting of the U.S. Sections of the

Combustion Institute, Washington, DC, 1999.

9. MacDonald, M. A., Jayaweera, T. M., Fisher, E. M.,

and Gouldin, F. C., Proc. Combust. Inst. 27:2749–2756

(1998).

10. Saso, Y., Ogawa, Y., Saito, N., and Wang, H., Combust. Flame 118:489–499 (1999).

11. Lott, J. L., Christian, S. D., Sliepcevich, C. M., and

Tucker, E. E., Fire Technol. 32:260–271 (1996).

12. Reinelt, D., and Linteris, G. T., Proc. Combust. Inst.

26:1421–1428 (1996).

13. Rumminger, M. D., and Linteris, G. T., Combust.

Flame 120:451–464 (2000).

14. Brown, T. M., Tanoff, M. A., Osborne, R. J., Pitz,

R. W., and Smooke, M. D., Combust. Sci. Technol.

129:71–88 (1997).

15. Arnold, A., Becker, H., Hemberger, R., Hentschel, W.,

Ketterle, W., Kollner, M., Meienburg, W.,

Monkhouse, P., Neckel, H., Schafer, M., Schindler,

K. P., Sick, V., Suntz, R., and Wolfrum, J., Appl. Optics

29:4860–4872 (1990).

16. Wainner, R. T., McNesby, K. L., Daniel, R. G.,

Miziolek, A. W., and Babushok, V. I., Experimental

and Mechanistic Investigation of Opposed-Flow Propane/Air Flames by Phosphorus-Containing Compounds, Proc. of the 10th Halon Options Technical

Working Conf., Albuquerque, NM, 2000.

17. Barlow, R. S., and Collignon, A., Linear LIF Measurements of OH in Nonpremixed Methane-Air Flames:

When are Quenching Corrections Unnecessary, AIAA

91-0179, 29th Aerospace Sciences Meeting, Reno,

1991.

18. Masri, A. R., Dally, B. B., Barlow, R. S., and Carter,

C. D., Combust. Sci. Technol. 113–114:17–34 (1996).

19. Smyth, K. C., and Everest, D. A., Proc. Combust. Inst.

26:1385–1394 (1996).

20. L’Espe ́rance, D., Williams, B. A., and Fleming, J. W.

Combust. Flame 117:709–731 (1999).

21. Seshadri, K., and Williams, F., Int. J. Heat Mass

Transfer 21:251–253 (1978).

22. Kee, R. J., Rupley, F. M., Miller, J. A., Coltrin, M. E.,

Grcar, J. F., Meeks, E., Moffat, H. K., Lutz, A. E.,

Dixon–Lewis, G., Smooke, M. D., Warnatz, J., Evans,

G. H., Larson, R. S., Mitchell, R. E., Petzold, L. R.,

Reynolds, W. C., Caracotsios, M., Stewart, W. E., and

Glarborg, P., Chemkin Collection, Release 3.5, Reaction Design, Inc., San Diego, CA (1999).

23. Smith, G. P., Golden, D. M., Frenklach, M., Moriarty,

N. W., Eiteneer, B., Goldenberg, M., Bowman, C. T.,

Hanson, R. K., Song, S., Gardiner, W. C. Jr., Lissianski, V. V., and Qin, Z., GRI Mech 3.0 (1999) http://

www.me.berkeley.edu/gri_mech/.

24. Chelliah, H. K., Law, C. K., Ueda, T., Smooke, M. D.,

and Williams, F. A., Proc. Combust. Inst. 23:503–510

(1990).

682 M. A. MACDONALD ET AL.
25. Sung, C. J., Liu, J. B., and Law, C. K., Combust. Flame

102:481–492 (1995).

26. Ravikrishna, R. V., and Laurendeau, N. M., Combust.

Flame 120:372–382 (2000).

27. Magre, P., Aguerre, F., Collin, G., Versaevel, P.,

Lacas, F., and Rolon, J. C., Exp. Fluids 18:376–382

(1995).

28. Beaud, P., Radi, P. P., Franzke, D., Frey, H-M.,

Mischler, B., Tzannis, A.-P., and Gerber, T., Appl. Opt.

37:3354–3367 (1998).

29. Smith, G. P., and Crosley, D. R., Appl. Opt. 22:1428–

1430 (1983).

30. Allen, M. G., McManus, K. R., Sonnenfroh, D. M.,

and Paul, P., Appl. Opt. 34:6287–6300 (1995).

31. Puri, R., Moser, M., Santoro, R. J., and Smyth, K. C.,

Proc. Combust. Inst. 24:1015–1022 (1992).

32. Arnold, A., Bombach, R., Ka ̈ppeli, B., and Schlegel,

A., Appl. Phys. B—Lasers Opt. 64:579–583 (1997).

33. Kelman, J. B., and Masri, A. R., Appl. Optics 33:3992–

3999 (1994).

34. Ko ̈llner, M., and Monkhouse, P., Appl. Phys. B 61:499–

503 (1995).

35. Norton, T. S., Smyth, K. C., Miller, J. H., and Smooke,

M. D., Combust. Sci. Technol. 90:1–34 (1993).

36. Crosley, D. R., High Temp. Material Proc. 7:41–54

(1986).

37. Luque, J., and Crosley, D. R., LIFBASE: Database and

Simulation Program (v 1.6), SRI International Report

MP 99-009 (1999).

38. Paul, P. H., J. Quant. Spectrosc. Radiat. Transfer 51:

511–524 (1994).

39. Paul, P., J. Phys. Chem. 99:8472–8476 (1995).

40. Hartlieb, A. T., Markus, D., Kreutner, W., and Kohse–

Ho ̈inghaus, K., Appl. Phys. B 65:81–91 (1997).

41. Tamura, M., Berg, P. A., Harrington, J. E., Luque, J.,

Jefferies, J., Smith, G. P., and Crosley, D. R., Combust.

Flame 114:504–514 (1998).

42. Twarowski, A., Combust. Flame 102:55–63 (1995).

43. Twarowski, A., Combust. Flame 102:41–54 (1995).

44. Werner, J. H., and Cool, T. A., Combust. Flame

117:78–98 (1999).

45. Mokrushin, V. V., Bol’shova, T. A., and Korobeinichev, O. P., A Kinetic Model for the Destruction of TMP

in a Hydrogen/Oxygen Flame, unpublished.

46. Babushok, V. I., personal communication, 2000.

47. Mallard, W. G., and Linstrom, P. J., Eds., NIST

Chemistry Webbook, NIST Standard Ref. Database 69,

1998.

48. Gurvich, L. V., and Glushkov, V. P., Thermodynamic

Properties of Individual Substances, NIST Special Database 5, IVANTHERMO-PC, 1998.

49. Melius, C., http://hertzberg.ca.sandia.gov/carl_melius.html, 1998.

50. Fisher, E. M., Williams, B. A., and Fleming, J. W.,

Determination of the Strain in Counterflow Diffusion

Flames from Flow Conditions, Presented at Fall Technical Meeting of the Combustion Institute, Eastern

States Section, Hartford, CT, 1997.

51. MacDonald, M. A., Ph.D. Dissertation, Cornell University, (2000).

52. Rumminger, M. D., Reinelt, D., Babushok, V. I., and

Linteris, G. T., Combust. Flame 116:207–219 (1999).

53. Linteris, G. T., and Truett, L., Combust. Flame 105:

15–27 (1996).

54. Hynes, R. G., Mackie, J. C., and Masri, A. R., Combust. Flame 113:554–565 (1998).

55. Smyth, K. C., Tjossem, P. J. H., Hamins, A., and

Miller, J. H., Combust. Flame 79:366–380 (1990).

Received 5 June 2000; revised 2 October 2000; accepted 30

October 2000

PHOSPHORUS-BASED FLAME INHIBITION 683