NAT’L INST. OF STAND & TEC!

AlllDb 41T370

NBSIR 86-3420

Combustion of Oil on Water

D. Evans

H. Baum

B. McCaffrey

G. Mulholland

M. Harkleroad

W. Manders

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

FILE COPY

00 NOT REMOVE

June 1986

Issued November 1987

Sponsored by

Minerals Management Service

Department of the Interior

QC Reston, VA 22091

100

.1156

NO. 86-3420

1987 Cm3L

NBSIR 86-3420

COMBUSTION OF OIL ON WATER

D. Evans

H. Baum

B. McCaffrey

G. Mulholland

M. Harkleroad

W. Manders

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

June 1986

Issued November 1987

Sponsored by

Minerals Management Service

Department of the Interior

Reston, VA 22091

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES v

Abstract 1

1. BACKGROUND 1

2. EXPERIMENTAL FACILITY 3

3. CRUDE OIL SAMPLES 5

4. ENERGY RELEASE RATE 6

5. SMOKE MEASUREMENT 7

5.1 Light Extinction 8

5.2 Smoke Emission 9

5.3 Size Distribution 11

5.4 Discussion 13

6. BURN RESIDUE COMPOSITION 14

7. CALCULATION OF INDUCED AIR FLOW 15

7.1 The Model for Fire Induced Flow 16

8. SAMPLE CALCULATION 23

9. ACKNOWLEDGEMENTS 24

10. REFERENCES 25

iii
LIST OF TABLES

Page

Table 1. Smoke Emission and Properties for 60 cm Diameter Prudhoe

Crude Pool Fire Test NW35 26

Table 2. Summary of Smoke Emission Data for 40 and 60 cm Diameter

Prudhoe Crude Pool Fires 27

Table 3. Distribution of Fire Energy Release Rates and Equivalent

Prudhoe Bay Crude Oil Pool Fire Diameters Used in Figure 19 . . 28

IV
LIST OF FIGURES

Page

Figure 1. Instrument hood for oil burn experiments 29

Figure 2. 3-Filter, all glass, smoke collection system 30

Figure 3. Rate of energy release for Prudhoe Bay crude oil burned

in a 0.4 meter diameter pool 31

Figure 4. Prudhoe Bay crude oil fire in 0.4 meter diameter pan 32

Figure 5 . Radiation and energy release rate from Prudhoe Bay crude

oil pool fires 33

Figure 6. Light extinction coefficient for Prudhoe Bay crude burned

in 0.6 meter diameter pool 34

Figure 7. Specific extinction coefficient relative to fuel for

Prudhoe Bay crude oil burned in a 0.4 meter diameter pool .... 35

Figure 8. C02 and CO concentrations for Prudhoe Bay crude oil

burned in 0.6 meter diameter pool 36

Figure 9. Smoke aerosol deposition on seven stages and backup

filter of cascade impactor from 0.6 meter diameter Prudhoe

Bay crude oil pool fire 37

Figure 10. Cumulative aerodynamic size distribution of smoke

aerosol produced by 0 . 6 meter diameter Prudhoe Bay crude

oil pool fire 38

Figure 11. Electron micrograph of smoke particles produced by

0.6 meter diameter Prudhoe Bay crude oil pool fire,

0.5 micrometer scale 39

Figure 12. Electron micrograph of smoke particles produced by

0.6 meter diameter Prudhoe Bay crude oil pool fire,

0.5 micrometer scale 40

Figure 13. A comparison of the aliphatic region of the 13 C NMR

spectra of (a) Prudhoe Bay North Shore crude oil, and

(b) burn residue of Prudhoe Bay North Shore crude oil 41

Figure 14. A comparison of the aromatic region of the 13 C NMR

spectra of (a) Prudhoe Bay North Shore crude oil,

(b) burn residue of Prudhoe Bay North Shore crude oil,

and (c) the difference (a-b) broad ban resonances

were normalized to equal intensity 42

v
LIST OF FIGURES (continued)

Page

Figure 15. Time averaged streamlines calculated from dimensionless

velocity field in terms of scaled radial (R) and

vertical (Z) coordinates 43

Figure 16. Ground level radial inflow showing vorticity induced

flow Ur

(tJ>) , volumetric expansion outflow Ur ( <f> )

,

and net inflow Ur 44

Figure 17. Vertical plume centerline velocities showing total

calculated velocity, data correlation, vorticity induced

flow Uz (V>) , volumetric expansion flow Uz ( <f> ) 45

Figure 18. Comparison of normalized centerline excess temperature,

velocity, and Gaussian plume width correlations with

normalized height all in arbitrary dimensional units

to show the primary scaling parameters used to

collapse the large scale pool fire data 46

Figure 19. Composite sea level induced flow generated by twenty

randomly distributed fires ranging in strength from

200 kilowatts to 3.2 megawatts. The overall area is

100 meters on a side, velocity rectors and speed contours

are shown 47

Figure 20. Detail of velocities and speed contours shown in

figure 19 centered near fire (fire #19, 3.2 MW) 2/3 to

the right and 1/5 up from bottom 48
COMBUSTION OF OIL ON WATER

D. Evans, H. Baum, B. McCaffrey, G. Mulholland, M. Harkleroad and W. Manders

Abstract

This report contains the results of measurements performed on both 0.4 m

and 0.6 m diameter pool fires produced by burning a layer of Prudhoe Bay crude

oil supported by a thermally deep layer of water. Both steady burning and

vigorous burning caused by boiling of the water sublayer were observed. The

measured energy release rate for steady burning was about 640 kW/m? . The

emission rate, the size distribution, and specific extinction coefficient were

measured for the smoke aerosol produced by the fires. Data were also obtained

on the structure of the smoke aerosol by electron microscopy and on emission

of CO and C0 2

« Analysis of the crude oil burn residue indicated selected

depletion of the short chain alkanes and cycloalkanes when compared to the

fresh oil. Mono-ring aromatics including benzene, toluene, and xylenes

present in the fresh crude were absent in the burn residue. Calculations of

the induced air flow into a simulated distribution of 20 fires over a

100 m x 100 m area showed that the maximum inflow velocity near the largest

size fire (2.5 m diameter, 3.2 MW) was 1.1 m/s.

1 . BACKGROUND

In 1985, the Center for Fire Research (CFR) at the U.S. National Bureau

of Standards (NBS) began studies of oil spill combustion under support from

the U.S. Minerals Management Service (MMS). This work seeks to understand the

process of oil spill combustion on open waters and in water filled channels

formed in broken ice. This work is intended to be a cooperative effort

1
leading to results that may be used to generalize specific measurement of oil

spill burn efficiency performed by Smith and Diaz at the EPA-OHMSETT facility

in Leonardo, NJ [1]. The scope of the original work has been broadened by

added support from Environment Canada and the U.S. Coast Guard to include

calculations and measurements related to induced air flow velocities in the

area of the fire, burn residue chemical composition, and smoke production from

the oil spill burn.

The long range goal of the research program is to provide a means to make

quantitative predictions of the fraction of oil in a spill that can be

consumed by an in-situ combustion process, the characteristics of the residual

oil, and the characteristics of the combustion product flow from the burn. It

is hoped that this information may be cast into a form that is readily useable

by local officials and oil spill response professionals as part of their

decision making process in the event of an oil spill.

As a first step in this research program a framework for detailed study

and calculation of the open water oil spill combustion process was formulated

by Wichman [2]. It was clear from this initial work that to obtain an overall

understanding of oil spill combustion and to produce sound technical

quantification of the important effects of combustion, such as the beneficial

consumption of oil and detrimental smoke production, closely coordinated

experimental and theoretical studies must be conducted. To address many

aspects of the oil spill combustion process, both for confined and unconfined

spills, an interdisciplinary research team was assembled within the Center for

Fire Research at the U.S. National Bureau of Standards. This team brings

together expertise in combustion, fire dynamics, computational fluid flow,

2
particulate measurement, and chemical analysis. All members of the team are

contributors to this paper which contains quantitative results for confined

oil spill energy release rate, thermal radiation, smoke production, induced

air flow, and chemical composition changes between the fresh oil and burn

residue.

2. EXPERIMENTAL FACILITY

Test work in this study was conducted in the CFR large scale testing

facility in which a calorimeter hood was used. The experimental facility

accommodates oil pool fires up to 0.6 m in diameter. This facility is used

cooperatively with studies funded by U.S. Defense Nuclear Agency. A schematic

drawing of the instrumented hood is shown in Figure 1. Liquid pool fires are

situated under the 2.4 m x 2.4 m collection hood with an adjustable exhaust

rate up to about 2 m3 /s (4000 ft3 /min). A tripper plate at the stack inlet

assures uniform mixing of combustion products and dilution air before the

gases are sampled five duct diameters downstream of the inlet. The mass loss

of the burning fuel floated on a deep water layer is monitored using a water

cooled load cell with a sensitivity of about 3 grams. Thermal radiation from

the fire is measured with a Gardon-type radiometer located several pool

diameters from the pan.

Energy release rate from a fire is determined using oxygen consumption

calorimetry. This method is based on the fact that the heat of the combustion

is about 13 kJ/g of oxygen consumed for all hydrocarbon fuels [3,4]. Thus

measurements of 02 concentration and total flow rate through the stack made

downstream of the horseshoe section in the duct are used to calculate the 0

2 consumption rate and proportional energy release rate of the fire.

3
Other measurements in the exhaust duct relate directly to measurement

of smoke production and soot particulates. A cascade impactor with seven

stages and a backup filter was used for monitoring the aerodynamic size

distribution of the aerosol. Quartz fiber filters were used as the collection

substrate to minimize the smoke particle bounce that might occur on a flat

metal substrate. Particle bounce could be significant for the solid, agglomerate type particles making up the smoke aerosol. Each collection substrate including metal disk and filter were weighed to the nearest 0.01 mg.

The sampling flow was about 22 1/min and a conical probe with 0.64 cm orifice

was used to assure isokinetic sampling at a velocity of about 10 m/s. The

impactor was preheated in a convection oven for thirty minutes and then was

rapidly positioned in the stack just before igniting the crude oil pool. This

was done to minimize moisture condensation on the impactor stages.

The filter collection system, illustrated in Figure 2, allowed for the

sequential collection of three filter samples over the course of a pool fire

test. The transfer line, manifold, and filter holders were all heated to match

the stack temperature during the burn. This was done to minimize the evaporation/condensation of the smoke aerosol during transport or on the filter and to

minimize the thermophoretic driven deposition of particles on the walls. Th<

sample flow, about 10 1/min, and nozzle inlet, 0.48 (3/16 inch), were selected

to insure isokinetic sampling. The all glass construction of the filter

collection system allowed ready inspection of deposition and ease in cleaning.

The transmittance of a He-Ne laser, X = 633 nm, through the smoke in the stark,

0.48 m pathlength, was monitored with a photometer and ratioed to the incident

laser intensity to compensate for variations in the source intensity,

design of the photometer is reported by Babrauskas [5],

4
The laser beam in located about 1 m above the sampling probes. The

optics are purged with room air to avoid smoke deposition on the lenses during

a test. The uncorrected optical densities (OD's derived from the transmittance

measurements agree to within 5% with the values of neutral density filters.

The OD's of the smoke aerosols were in the range 0.3-1. 5. The transmittance

measurement is essentially instantaneous and thus provides an indication of the

fluctuation in the smoke concentration in the stack.

The gas sampling probe, pitot tube, and thermocouples are located downstream of the horseshoe section of duct. The gas velocity in the stack was

determined from the pitot tube measurement together with the thermocouple

reading. The sampled gas was cooled with a dry ice trap to remove water vapor,

filtered, and then drawn into the gas analyzers. Non-dispersive infrared

detectors are used for monitoring the concentrations of CO and C02

. This

information is used in determining the smoke emission based on the carbon

balance method.

Samples for study using a transmission electron microscope (TEM) were

obtained by rapidly inserting a carbon coated TEM grid into the stack for a few

seconds . The primary collection mechanism under these conditions is thought to

be via thermophoresis.

3. CRUDE OIL SAMPLES

Three different crude oils were obtained for study from supplies at EPAOHMSETT. These were Murban, Larosa, and Prudhoe Bay North Shore crude oils.

Testing performed in this study has been limited to evaluations of the Prudhoe

Bay North Shore crude oil.

5
Samples of Prudhoe Bay North Shore crude oil were burned in both 0.4 m

and 0.6 m diameter pans. In both cases, the oil was floated on a thermally

deep layer of water. Emphasis is given in this report to analysis of the

combustion process measured in tests with the larger 0.6 m diameter pool

fires. Partial results from each of two 0.4 m and two 0.6 m diameter pool

fires are given.

4. ENERGY RELEASE RATE

Figure 3 shows the history of the energy release rate from one of the

0.6 m diameter pool fires. The energy release rate of the burning oil rises

rapidly after ignition and flame spread across the surface to a plateau value

of about 180 kw (640 kW/m2 ). As seen in Figure 3, the energy release rate

remains steady through most of the test, but increases dramatically during the

last 30 seconds of the burn when the amount of oil left on the water surface

is small. The burning rate during this vigorous combustion increases by more

than a factor of two. Radiation levels increase to such an extent that the

positions where once it was tolerable to stand and observe the experiment now

become too close for human comfort. The sublayer of water under the oil can

be seen to be boiling vigorously. This boiling persists even after the flames

extinguish. The two burning regimes can be seen in Figure 4, photographs of a

0.4 m diameter pool fire experiment. Energy release rates and thermal radiation from both the 0.4 m and 0.6 m diameter pool fires are quantified in

Figure 5 for both the steady burning period (open symbols) and the vigorous

but short burning period before flame extinction (filled symbols). The

largest energy release rate measured for the 0.6 m diameter pan was 0.^ MW

(1800 kW/m2

) during the vigorous burning period. This vigorous burning period

6
appears as the oil layer becomes thin and sufficient energy from the hot

surface and flame causes the supporting water layer to boil. The erupting

surface lifts droplets of oil into the flame accelerating the burning process

and increasing the energy feedback to the water sublayer which enhances the

boiling. Quantification of this process will be part of studies underway

involving temperature measurements with rakes of thermocouples immersed in the

oil and water layer during burning. The partitioning of energy and its

relation to film thickness are important characteristics of the oil combustion

process that need to be understood.

5 . SMOKE MEASUREMENT

The smoke aerosol sampling techniques used in this study are suitable to

quantify smoke production only during the nominally steady state burning of

the oil and not during the relatively short transient period at the end of the

burn when vigorous boiling of the water sublayer increases the combustion

rate.

Qualitatively there are indications that the smoke aerosol produced

during this intense burning contained a tarry component soluble in toluene, in

addition to the low density, sooty particles produced during the steady state

combustion. A tarry residue was observed on both the impactor and filter

nozzles which extend into the exhaust duct. Apparently this resulted from

tarry droplets generated during the intense burning impacting on the nozzles.

In one experiment, a tarry residue was observed within the impactor, and this

was the one experiment in which smoke from the intense burning at the end of

the fire was collected. Further discussion of smoke production will be

limited to analysis of the steady burning period.

7
5.1 Light Extinction

The light extinction coefficient K is related to the light transmittance,

I/I

Q

, via Bouguer's law,

I/I

o = e"

KL

, (1)

where L is the path length in meters. As seen in Figure 6, the value of K has

a large variability around a fairly constant mean value of about 2 m

_1

. This

large variability is a result of the pulsating characteristic of buoyant

plumes in which puffs of smoke can be seen arising from the flame at a

frequency of a few Hz. The other instruments, including the gas analyzers and

thermocouples, have response times of several seconds and thus do not pick up

this pulsation.

In addition to the extinction coefficient, there are two reduced

extinction coefficients of interest. The first is Kg, the extinction coefficient per mass concentration of smoke, mg:

K = K/m (2)

s s

The quantity Ks is an intrinsic property of the smoke depending on the wavelength of light, the optical properties of the smoke, and the size distribution of smoke. As indicated in Table 1, Kg is relatively constant during the

burn and has a mean value of 8.8 m^/g. This is to be compared to Seader and

Einhorn's [6] value of 7.6 n^/g obtained from smoke produced during the

flaming combustion for a variety of fuels including wood and plastics. Some

8
difference in the results is expected since Seader uses a white light source

while a monochromatic source with X = 633 nm is used in this study.

The second reduced extinction coefficient, Kf , is the extinction coefficient per unit mass loss concentration,

= K/(dm/dt/dv/dt) (3)

where dm/dt is the sample mass loss and dv/dt is the volumetric flow rate of

gas up the stack. One advantage of this quantity is that a measurement of the

smoke concentration is not required. The plot of Kf in Figure 7 suggests that

there is a gradual increase in Kf with respect to time. This trend may result

from the higher vapor pressure paraffin component of the fuel burning preferentially early in the test with a lower soot yield while the higher sooting

aromatic and asphaltene components burn at the later stage.

5.2 Smoke Emission

Two methods were used for determining the smoke conversion factor, e

,

which is defined by

e = mass of smoke aerosol produced/mass of fuel burned

The first method, termed the flux method, is based on the measurement of the

smoke collected on the filter, mg, and on the mass loss of the sample, m^

,

over the same time period. The factor <j> , which equals the ratio of the mass

flow of air up the stack to the mass flow to the filter, accounts for the

small fraction of the total smoke yield sampled.

9
e

l ' ( m

s /ml> (4)

The second method is the carbon balance method, which is based on the

measurement of C02 , CO, and smoke aerosol. These represent the major carbon

containing products of combustion for free burning. The concentrations of C02 and CO are relatively constant throughout the tests as shown in Figure 8. The

C0 2 concentration in the stack minus the background concentration equals 0.55%

by volume which is a factor of 15 greater than the CO concentration. The mass

concentration of carbon in the form of C02 , Mc (C02 ), is obtained from the

The factor (12/44) accounts for the carbon mass fraction of C02

, and pC02

refers to the density of C02 within the instrument. A similar expression is

obtained for Mc (CO). The mass fraction of carbon in the smoke aerosol is

given by the formula:

Finally, we obtain e 2 by multiplying f

s by the carbon mass fraction of the

Lacking data on F c for Prudhoe Bay crude oil, we have taken F c to be 0.8b,

which is at the upper range for elemental carbon in crude oils. A slight

(5)

f = M /(M + M fCOj + M (C0)1

s s

v s c

v 2' c

' ( 6 )

fuel, F

C

:

(7)

10
over estimate is obtained in this analysis since the smoke is assumed to be

100% carbon. One might also expect a slight contribution from the hydrocarbon

gases. Overall, we expect that these approximations will affect the final

result by less than 5%.

As an example, for Sample 1 from Test NW35 (Table 1), we calculate the

mass fraction of carbon in the form of C02

, CO, and smoke aerosol. First

eq. (5) is used to calculate the mass concentration of carbon corresponding to

the volume fractions FC0 2 and Fco in Table 1. The density of C02 and CO under

test conditions is computer from the ideal gas law as:

_

44P . =

28P

Pc o 2 RT ’ P co Rq1 ( 8 )

For Test NW35 (Table 1) P = 0.976 atmospheres, and T = 295 K. The appropriate

gas constant R is 0.082 liter-atm/gmole/K. The mass fraction of carbon in the

smoke aerosol is obtained from eq. (6). The mass fractions of C02 and CO are

also obtained from eq . (6) with Ms in the numerator replaced by Mc (C02

) and Mc

(CO), respectively. The results are 0.867 of carbon in the form of C02

, 0.049

as CO and 0.084 as smoke aerosol.

5.3 Size Distribution

Samples collected from the seven stages and backup filter of the cascade

impactor are shown in Figure 9. The first impaction stage is a single relatively low velocity nozzle, which impacts out particles with aerodynamic

diameters greater than 13 nm. With each successive stage, smaller and smaller

particles are impacted out as indicated by the particle size cutoffs in

11
Figure 9. The fact that the size distribution is very wide is indicated by the

smoke aerosol deposition on each stage.

The quantitative results regarding the size distribution function are

shown in Figure 10. The cumulative aerodynamic size distributions are plotted

for data obtained from two 60 cm Prudhoe Bay crude oil burns. In both cases,

about 20 mg of smoke aerosol were collected on the impaction stages plus backup

filter. Since the plot in Figure 10 is on log-probability paper, the straightline fit to the data indicates that the mass distribution is log-normal. The

mass median diameter, the 50% point in terms of mass, is found to be 0.5 fim for

both experiments. The geometric standard deviation, a , for the size distribution is obtained from the relation:

a

g = D (84 . 1%)/D (50%) (9)

We find cr g equal 7.1 and 6.4 for the 60 cm pool burns on test number NW35 and

test number NW36, respectively. For a log-normal distribution [7] 67% of the

aerosol mass is in the particle diameter range log D50 by a

g

; for D 50 - 0.50 jim

and cr g = 7.1, this corresponds to the size range 0.07-3.55 nm. This represents

a very broad size distribution.

The complexity of the particle structure is indicated by the transmission

electron micrographs in Figures 11 and 12. It is seen that the particles have

a low density agglomerate structure made up of many small spherules in the si:-.<-

range 0.02-0.16 /an. As is apparent from Figure 11, there is a wide range in

cluster size.

12
5.4 Discussion

A summary of the results from four pool burns is given in Table 2.

Increasing the pool size from 40 to 60 cm more than doubles the heat release

rate and the mass loss rate of fuel, but it has a relatively minor effect on

the smoke conversion factor and in the smoke properties. The emission of

smoke is high with e about 0.10 (10% conversion to smoke) and the specific

extinction coefficient, Ks = 9.1, is similar to what has been observed for

other soot producing fuels. Over 50% of the smoke aerosol is in the submicrometer aerodynamic size range, which is indicative of a long atmospheric

residence time and potentially high deposition in the lower respiratory tract.

One of the most striking features of the burning oil is the very rapid

combustion over the final thirty seconds. There are qualitative indications

that the smoke aerosol produced under these conditions has a significant tarry

component not seen in the smoke collected during the steady combustion phase.

This is potentially an important effect since the thickness of the oil layer

resulting from a spill may be relatively small compared to the initial thickness in the test fires of 0.27 m. A significant fraction of the total smoke

emitted from combustion of an oil spill originates from the intense burning

phase.

The fact that we do not see any significant scale effect in regard to

smoke emission may simply be a result of the relatively narrow range of scales

studied. An increase by a factor of 10 to 100 in burning rate may have a

significant effect on the smoke aerosol emission and smoke properties.

13
The smoke aerosol collection and characterization has been carried out at

elevated temperatures around 100 C. Without further study, one can not be

certain whether the results are directly applicable to diluted, aged smoke

aerosol that would be characteristic of smoke far downwind of actual fires.

6. BURN RESIDUE COMPOSITION

The burning effects on the composition of Prudhoe Bay crude oil was

examined by comparative 13 C NMR spectroscopy [8] between fresh oil and the

burn residue. Of specific interest was the fate of the lighter fractions,

which include the short-chain alkanes, cycloalkanes, and substituted benzenes.

The 13C NMR spectra were collected at 100 MHz with proton decoupling and

nuclear Overhauser enhancement. Solutions of crude oil and burned crude oil

were 50% by volume in deuterochloroform.

The principal peaks in the aliphatic region of the crude oil spectrum are

assigned in Figure 13 to either chain-ending carbons (C

1 through (^ ) or chaininterior carbons (C^) in alkanes. Their relative intensities reflect the

distribution of alkane chain lengths. Upon burning, the C 1 through

intensities are uniformly attenuated in relationship to the intensity of .

This result is interpreted as a selective depletion of short chain alkanes in

the burned crude. A similar fate is indicated for the cycloalkanes. Their

resonances, which are marked with asterisks (Fig. 13), are either absent from

or attenuated in the spectrum of the burned crude. Evidence of burning

effects is much more dramatic in the aromatic region (Fig. 14) of the crudr

oil spectra. The sharp signals in Figure 14, which are due mainly to raono14
ring aromatics including benzene, toluene, and xylenes, are for the most part

absent in the burned crude spectrum (Fig. 14).

A more quantitative examination of the depletion of specific alkanes and

cycloalkanes would require a combination of gravimetric and NMR analyses

of distillation fractions. This type of analysis is being planned.

7. CALCULATION OF INDUCED AIR FLOW

In recent years there has been an interest in determining if it is

possible for fire induced air flows into large fires to cause a migration of

the oil spill towards the burning area. Large oil burns on water have been

conducted to measure this induced surface air flow [9]. These experiments,

although carefully conducted, are hard to interrupt because of non-ideal

conditions encountered in field testing such as uncontrolled ambient winds.

It is also known, particularly in the case of oil spills, that clean-up will

require the ignition of many relatively small patches of oil that are

separated by either open water or layers of oil too thin to ignite.

This part of the study details a calculation of induced wind into an area

containing randomly distributed fire sources having various steady energy

release rates. Present calculations do not include any interaction between

the induced flow and the surface. A sample calculation of the induced air

flow velocity field 0.8 m above the surface over an area 100 m x 100 m

containing 20 fires ranging in energy release rate from 200 kW to 3.2 MW was

performed. Based on the measured energy release rate for Prudhoe Bay crude

oil in a 0.6 m diameter pool of 640 kW/m2 these fires would represent crude

oil pools ranging in diameter from 0.63 m to 2.5 ra.

15
7.1 The Model for Fire Induced Flow

The flow induced by an oil spill fire is primarily determined by three

factors: the geometrical arrangement of the burning parcels of fuel, the rate

of energy released by each individual fuel element, and the atmospheric

environment in the neighborhood of the spill. In any given spill scenario,

there is a considerable amount of randomness in each of these factors. The

mathematical model described below attempts to deal with this situation by

combining random distributions of location and burning rate of the individual

patches of fuel with a deterministic description of the composite flow

generated by a given realization of the spill scenario. Each patch of burning

oil is assumed to be sufficiently removed from the others so that the buoyant

plume of hot gas and smoke rising above the patch evolves independently.

Under these circumstances, the composite flow field can be decomposed into a

collection of individual flows associated with each plume. The flow pattern

associated with a single plume is then analyzed in detail and the results

compared with experimental data. The process by which the composite flow is

calculated is then outlined; and the induced surface wind for a sample distribution of plumes is displayed.

The starting point is the inviscid equations of fluid mechanics which

control the large scale fluid motion of interest. These laws, expressing

conservation of mass, momentum, energy, and an equation of state, respectively

are:

16
+ pv • U = 0

Du . ~ ( \ n

P Dt VP “ " O S

= °

( 10 )

pCp ^jr = Q (r,t)

P = pRT

o

Here P, p, u, and T are, respectively, the local pressure, density, velocity,

and temperature in the gas at position r and time t induced by a rate of

energy release Q (r,t). The gas has a specific heat Cp and gas constant R,

while g is the gravitational acceleration. The quantities P0 and p 0 are sea

level ambient pressure and density, while p represents the small perturbation

from hydrostatic pressure that drives the motion. All plumes are assumed to

evolve in uniform atmosphere at rest far from the plumes. The convective

operator D/Dt includes local time dependence:

D_

Dt

V

It is certainly not feasible to contemplate solving eq. (10) directly.

Instead, we make use of two equivalent results. If the first of eq. (10) is

multiplied by Cp and added to the third and the equation of state is used, the

divergence of the velocity field can be expressed as:

V 5 - Q (r,t)/p

o C

p

T

o (ID

17
Physically, eq. (11) states that the volumetric expansion rate of any fluid

element is proportional to the net rate of heat addition. It is important to

note that although the heat is added to the atmosphere only in the vicinity of

each patch of burning fuel, eq. (11) is valid everywhere above the surface.

The second result needed is Bjerknes theorem [10]. The fluid vorticity,

— —

u>, is defined in terms of the fluid velocity, u, as:

Vxu = w (12)

Now consider a closed loop of Lagrangian marked particles moving with the local

fluid velocity. The circulation T around that closed loop is defined as:

r = <£u*dr = ^a)* ndA (13)

a

Here n is a unit vector normal to any surface A bounded by the closed loop £ of

marked particles. The momentum conservation equation, the second of eq . (10),

can then be manipulated into the form:

dr

dt = i> { [ (p - £

P0 )/P0 ) g

- Vp/p) • dr ( 14 )

Equation (14) is Bjerknes theorem. Physically, it states that vorticity can bo

created in a fluid away from a boundary only through the mechanism of donsitv

gradients. In the absence of such gradients the circulation around the closed

loop, and hence the vorticity contained within the loop, cannot change.

18
Now consider the history of a fluid element originating from rest far from

any of the plumes generated by the oil spill fire. Initially the fluid

contained no vorticity, and in its approach to the fire it remains irrotational. As it enters one of the smoke plumes it encounters large density

gradients, and an intense vortex field is created. Thus, eq . (12) can be

rewritten as:

Vxu = w

p (r , t) (15)

Here w

p denotes the vorticity in the plumes. Just as in the case of eq. (11),

— eq. (15) holds everywhere even though w

p only involves the velocity gradients

inside the plumes.

Two further points should be noted. First, since the right hand sides of

eqs . (11) and (15) involve only information inside the plumes, if the plumes

remain distinct we can write:

Q (r , t) = 2. Q. (r , t)

w

p (r , t) = 2. wp

. (^,t) (16)

— Here the sum is taken over each individual plume. Thus, a velocity field ui can be associated with each plume, where the velocity field is the solution to

V * ui = Qi/P0 C_T0

y x Ui = Wpi

(17)

19
Second, these formulae are valid both instantaneously and in a time averaged

sense. If time dependent information about the structure of an individual

fire plume is available, then it can be used in eq. (17). At present, only

time averaged information is available. In either case, the kinematics of a

general vector field insures that a knowledge of the divergence and curl of

the vector is sufficient to determine it everywhere uniquely.

The physical information available on the time averaged structure of fire

plumes has been analyzed by McCaffrey [11]. He notes that there is ample

experimental support for a Gaussian radial distribution of the mean vertical

velocity in the plume. This can be expressed analytically in the form:

u = U (Z) exp {- [r/R(Z)} 2

} (18)

Here u is the vertical velocity component, U(Z) its value on the center-line

of the axially symmetric plume, and R(Z) the mean plume width. The variable Z

is the height above the sea surface and r is the radial distance from the

plume centerline. McCaffrey furnishes an analytical correlation of the experimental data for U(Z) and the centerline temperature. By enforcing the

requirement for energy and momentum conservation on average across the plume

at each height Z, he is able to infer the mean radius R(Z). Using eq . (18)

and the fact that the time average plume is axially symmetric, the vorticity

to can be inferred as:

(19)

w = [2U(Z)/R(Z)]{r/R exp [-(r/R)

2 ]}

20
The quantity | is a unit vector in the azimuthal direction.

The detailed form of the centerline velocity correlation will be shown

below. For the moment, the most important aspect of the correlation is the

scaling law implied by the overall conservation of energy in each plume.

A If is the total rate of energy release into an individual fire plume, then

the velocity field induced by that fire depends on a single length scale, D^,

defined as:

D. = (Q./p C T /g)

2/5

(20)

1

v 1 o p oJ

Moreover, the velocity field, u^, must be of the form:

*

u.l

-»

( 21 )

Thus, a single dimensionless velocity, uA , can be calculated from eqs. (17)

and (19) which is valid for a fire of any strength. Given the dimensionless

result, u*, the physical velocity field for a given fire strength can be

determined from eqs. (20) and (21).

The details of the calculation of the universal dimensionless velocity,

u*, will be omitted here. However, the resulting mean streamline pattern is

shown in Figure 15. The flow enters nearly horizontally from the right, then

turns abruptly upwards as it enters the plume. The approximate plume boundary

is moving slowly to the right, growing nearly linearly with increasing height.

21
The relatively close spacing of the streamlines after they enter the plume

indicates the high velocities present in the plume. Figure 16 shows the

ground level radial inflow velocity induced by the plume. The inflow velocity

has two components. The dotted line denoted Ur (\J>) represents the very strong

inflow induced by the vorticity in the plume. The dashed line denoted U r

(ij>)

represents a weak outflow due to the volumetric expansion associated with the

heat released in the flames at the base of the plume. The solid line is the

net radial inflow. The peak value corresponds to a location near the outer

edge of the flame zone at the base of the plume.

These results can be checked against experimental data in two stages.

Figure 17 shows the calculated centerline vertical velocity, the upper solid

line, plotted as a function of height. The lower solid line is the dimensionless centerline correlation developed by McCaffrey, based on measurements of

laboratory scale fires. The agreement is quite good; the maximum discrepancy

between the two curves is about four percent. The calculated velocity is

further broken down into the vorticity and expansion induced components,

denoted as before by dotted and dashed lines, respectively. Figure 18 shows

the correlation compared with experimental data taken from a variety of large

scale pool fires. The velocity correlation used is replotted but in different

units to agree with experimental data in the middle curve. Also shown for

completeness are comparisons for plume width and excess temperature. In each

case, the data, though relatively sparse, tracks the correlation quite well.

Given the non-dimensional solution for the flow induced by a single fire,

we now turn to the calculation of the composite flow. The individual plumf

flow pattern is symmetric about a vertical axis centered above the patch of

22
burning fuel. However, an assemblage of such flows, each with an axis of

symmetry in a different location, is inherently three dimensional. Moreover,

allowance must be made for the fact that the fires can vary widely in

strength. In order to proceed, it is necessary to make some assumptions about

location and fire strength. In practice very little information is likely to

be available about an oil spill event other than the approximate area covered

and the amount of fuel released and burning. Accordingly, a computational

scheme was set up which randomly distributes a prescribed number of fires into

a series of five discrete energy release rate groups, each rate of energy

release a factor of two larger than the next smaller in the series. In the

absence of any better information, the probability distribution is taken to be

uniform with respect to fire strength. Each of the fires is then distributed

randomly into an overall rectangular area which is prescribed. The composite

velocity near water level is then calculated on a uniform 100 x 100 grid

within the spill area.

8. SAMPLE CALCULATION

A sample calculation is shown in Figure 19. Twenty plumes from the

series of five energy release rate groups; 200 kW, 400 kW, 800 kW, 1600 kW and

3200 kW (see Table 3), are randomly introduced into a square 100 meters on a

side. Velocity vector arrows of length proportional to the magnitude of the

local velocity field are introduced at 5 meter intervals. Contours of

constant dimensionless speed are also shown as an aid to locating the burning

areas. The areas where the speed contours cluster tightly together indicate

the location of the individual fires. The velocities are actually calculated

at a height about 0.8 m above the surface. Distances and velocities are

23
normalized with respect to the scaling laws introduced in eqs. (20) and

(21). The largest individual fire of strength 3.2 MW is used in the nondimensionalization. The maximum dimensionless velocity visible at this

resolution scale (Figure 19) corresponds to a dimensional velocity of approximately 0.8 m/sec. The dimensionless distance tick marks on the boundaries

correspond to a dimensional spacing at 1 meter intervals.

Figure 20 shows a local detail magnified ten times in each direction

centered near the large fire 3.2 MW (fire #19) about 2/3 of the way to the

right and 1/5 up from the bottom of Figure 19. At this resolution, the inflow

into the fire plume is clearly visible. Since it is possible to resolve the

flow nearer to the plume, the maximum velocity in the fine grid approaches the

dimensionless peak inflow velocity for an individual plume U r in Figure 16.

The peak velocity shown in Fig. 20 corresponds to a dimensional velocity of

about 1.1 m/sec.

Calculations of this type may be extended using idealized wind conditions

and measured soot properties to predict convection of the soot produced by the

oil spill fires. Basic studies related to the formulation of this more

advanced model are presently underway.

9. ACKNOWLEDGEMENTS

This work was supported under the joint sponsorship of the Minerals

Management Service, U.S. Department of Interior, Office of Research and

Development, U.S. Coast Guard and Environmental Protection Service,

Environment Canada.

24
Special thanks is extended to the scientific officers, Mr. Edward

Tennyson, LCDR Peter Tebeau and Mr. Kenneth Meikle, for their continued

interest in the progress of these studies.

10. REFERENCES

[1J Smith, N.K., Diaz, A., "In-Place Burning of Crude Oil in Broken Ice,

1985 Testing at OHMSETT", Proceedings of the Eighth Annual Arctic Marine

Oilspill Program Technical Seminar, June 18-20, 1985, Edmonton, Alberta,

Technical Services Branch, Environmental Protection Services, Ottawa,

Canada K1A 1C8, 176-191 (1985).

[2] Wichman, I.S., A Preliminary Analysis of Oil-Slick Combustion,

NBSIR 85-3266, U.S. Department of Commerce, National Bureau of

Standards, Gaithersburg, MD 20899, November 1985.

[3] Huggett, C., Fire and Materials _4_, 61 (1980).

[4] Thornton, W.M., Philos. Mag. 33, 196 (1917).

[5] Babrauskas, V., Smoke Measurement Results from the Cone Calorimeter,

Paper presented at United States-Japan Natural Resources (UJNR) meeting,

May 1985.

[6] Seader, J.D. and Einhorn, I.N., Sixteenth Symp. (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 1423 (1976).

[7] Reist, P.C., Introduction to Aerosol Science, New York: Macmillan

Publishing Company, Inc., p. 21 (1984).

[8] Rualkeim, O.M., Aksnes, D.W., Brekke, T., Eide, M.D., Sletten, E., and

Telnaes, N., Anal. Chem. 57, 2858 (1985).

[ 9 j Buist, I. A. and Twardus, E.M., "Burning Uncontained Oil Slicks: Large

Scale Tests and Modeling", Proceedings of the Eighth Annual Artie Marine

Oilspill Program Technical Seminar, June 18-20, 1985, Edmonton, Alberta,

Technical Services Branch, Environmental Protection Service, Ottawa,

Canada K1A 1C8, 103-130 (1985).

[10] Turner, J.S., Buoyancy Effects in Fluids, Cambridge University Press,

Cambridge, 8, 1973.

[11] McCaffrey, B.J., Momentum Implications for Buoyant Diffusion Flames,

Comb, and Flame 52, 149 (1983).

25
Table 1. Smoke Emission and Properties for 60 cm Diameter

Prudhoe Crude Pool Fire Test NW35

Sample 1, 30 sec.

a Sample 2, 230 sec. Sample 3, 335 sec. Property after ignition after ignition after ignition

dQ/dt, kW 153 186 181

e 2

0.72 x 10" 1 0.80 x

10" 1 0.87 x

10" 1

Fco^» Vol. fraction^ 0.46 x 10"2 0.55 x 10"2 0.54 x 10" 2

Fco , Vol. fraction 0.26 x

10" 3 0.34 x 10"3 0.36 x

10" 3

K

s> m2/ § 9.30 8.84 8.25

M

s

, g/l 3 c 0.217 x 10" 3 0.293 x

10" 3 0.312 x 10" 3

aThe filter samples are collected for 1 minute and the properties listed in

column 1 are averaged over this time interval.

^The background CO2 concentration has been subtracted.

cSmoke concentration corrected to ambient conditions.

26
Table 2. Summary of Smoke Emission Data for 40 and 60 cm Diameter

Prudhoe Crude Pool Fires

Property

Test NW33

40 cm pool

Test NW34

40 cm pool

dQ/dt, kW 63 61

dm/dt, g/s 1.81 1.75

£

1 0.107 0.096

e

2 0.098 0.079

Fco , , Vol. fraction 0.15 x

10"2 0.18 x 10';

Fco , Vol. fraction - -

K

s

, m

2 /g 8.95 10.00

K

f , m

2 /g 0.96 0.96

Dm> 0.74 0.62

a 5.8 6.4

Test NW35 Test NW36

60 cm pool 60 cm pool Average

173 178

0.080 0.090 0.087 0.009

0.52 x 10~2 0.53 x 10~2

0.32 x 10" 3 0.32 x 10

-3

8.80 8.64 9.10 0.61

0.50 0.50

7.1 6.4

27
Table 3. Distribution of Fire Energy Release Rates and Equivalent Prudhoe

Bay Crude Oil Pool Fire Diameters Used in Figure 19

ire

No.

Location X

Unit from Left

Border (Fig. 19)

Location Y

Units from Bottom

Border (Fig. 19)

Energy

Release

Rate

kW

Equivalent

Pool

Diameter

m

1 96.613 14.762 200 0.63

2 40.852 61.420 1600 1.78

3 5.483 92.562 200 0.63

4 8.217 29.148 1600 1.78

5 94.120 49.268 800 1.26

6 52.152 89.503 1600 1.78

7 86.683 46.312 3200 2.52

8 39.632 55.463 1600 1.78

9 13.900 2.955 400 0.89

10 33.547 44.622 200 0.63

11 71.857 90.247 200 0.63

12 41.348 22.350 3200 2.52

13 1.095 26.527 800 1.26

14 2.737 40.275 1600 1.78

15 48.530 86.992 800 1.26

16 28.918 32.567 400 0.89

17 74.675 39.835 1600 1.78

18 5.935 32.542 1600 1.78

19 68.680 21.433 3200 2.52

20 74.535 72.075 3200 2.52

28
\l /

POOL

RADIOMETER

i LOAD CELL

(WATER COOLED)

Figure 1. Instrument Hood for Oil Burn Experiments

29
AC >

lU -I JUJ Z

30

Figure

2.

3-Filter,

All

Glass,

Smoke

Collection

System
0 90 180 270 360 450 540 630

TIME, s

Figure 3. Rate of Energy Release for Prudhoe Bay Crude Oil Burned in a 0.6 Meter Diameter Pool

31
oT3C

CD

QJ rCu

flj ooC

•He3

CQ

CO -l-J 3 CO O CD U H O

00 <D •H X

p» 4-J

32

Figure

4.

Prudhoe

Bay

Crude

Oil

Fire

in

0.4

Meter

Diameter

Pan
INCIDENT

FLUX

TO

NEARBY

TARGET

(kW/m

2)

Figure

12 1

11 1 1 1

10 -

8 •

•

6

- •

4

o

»

0.4m diameter

o O 0.6m diameter

c.

0

&

i 1

• 0.6m diameter, measured

during vigorous boiling of

water sublayer

i i i i 0 0.1 0.2 0.3 0.4 0.6 0.6 0.7

ENERGY RELEASE RATE (MW)

5. Radiation and Energy Release Rate From Prudhoe Bay Crude

Oil Pool Fires

33
K, m

Figure 6.

0 90 180 270 360 450 540 630

TIME, s

Light Extinction Coefficient For Prudhoe Bay Crude Burned in

0.6 Meter Diameter Pool

34
2.5 I

1

' ' '

1 f

2.0 -

0 180 360

i i i i 640 720 900 1080

TIME, s

l —•> 1260 1440

I Figure 7. Specific Extinction Coefficient Relative to Fuel for Prudhoe

Bay Crude Oil Burned in a 0.4 Meter Diameter Pool

II

}

35

•

••
TIME, s

Figure 8. C0

2 and CO Concentrations for Prudhoe Bay Crude Oil Burned in

0.6 Meter Diameter Pool

36
37

Figure

9.

Smoke

Aerosol

Deposition

on

Seven

Stages

and

Backup

Filter

of

Cascade

Impactor

from

0.6

Meter

Diameter

Prudhoe

Bay

Crude

Oil

Pool

Fire
DIAMETER,

pm

Figure 10. Cummulat ive Aerodynamic Size Distribution of Smoke Aerosol l’rodin .•<! 1 0.6 Meter Diameter Prudhoe Bay Crude Oil Pool Fire

38
39

Figure

11.

Electron

Micrograph

of

Smoke

Particles

Produced

by

0.6

Meter

Diameter

Prudhoe

Bay

Crude

Oil

Pool

Fire,

3

Micrometer

Scale
40

Figure

12.

Electron

Micrograph

of

Smoke

Particles

Produced

by

0.6

Meter

Diameter

Prudhoe

Bay

Crude

Oil

Pool

Fire,

0.5

Micrometer

Scale
41
r— ! 1 1 1 1 1 1 1 1 r

~ 155 150 145 140 135 130 125 120 115 110 105

PPM

13

Figure 14. A Comparison of the Aromatic Region of the C NMR Spectra of (a) I’rudhoe

Bay North Shore Crude Oil, (b) Burn Residue of Prudhoe Bay North Shore

Crude Oil, and (c) The Difference (a-b) , Broad Ban Resonances were Normalized to Equal Intensity.

42
R

Figure 15. Time Averaged Streamlines Calculated from Dimensionless Velocity

Field in Terms of Scaled Radial (R) and Vertical (Z) Coordinates

i

i

I A3
0.2

Figure 16. Ground Level Radial Inflow Showing Vorticity Induced Flow U

r Volumetric Expansion Outflow ($)> and Net Inflow

44
z

Figure 17. Vertical Plume Centerline Velocities Showing Total Calculated

Velocity (Upper Solid Line) , Data Correlation (Lower Solid Line)

,

Vorticity Induced Flow U (ij;) and Volumetric Expansion Flow U ( <f>

)

Lj L»

45
0.06

0.04

0.02

0

2.0

1.0

0

1200

1000

800

600

400

200

0

<

. Con

Continuous Intermittent

Flame

A A

Plume

D(m)

0 Haptana 2

JP-4 2x2

D Mathanol 2.4

JP-4 3. 7x7.

3

Gaaollna 3. 7x7.

3

o Haptana • JP-4 10x10

• JP-4 15

A K • o • • c • 30

Yumoto A Kotakl

Hagglund A Ptnion

Kung A Stavrlanldla

Gordon A McMillan

Gordon A McMillan

Yumoto A Koaakl

Hagglund A Paraaon

Japan Soc. for

Aafaty Engr.

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

HEIGHT

>arison of Centerline Temperature, Velocity, and Gaussian Plume

:h Correlations with Large Scale Pool Fire Data
Figure 19. Composite Sea Level Induced Flow Generated by Twenty Randomly

Distributed Fires Ranging in Strength from 200 Kilowatts to

3.2 Megawatts. The Overall Area is 100 Meters on a Side.

Velocity Rectors and Speed Contours are Shown.

47
ffnTf

rtf

rrrf

rrrf

mTrr

fi n ft 1 1 f'l rrhrifl'i i h

\ \ \ V

TfrrJTtTnilt?Yinnnfrrrfn nil V / V N N N N V

V V V// V V V N

N N /n N N N

' V V V V V V

V V V N N N

V /

' V V / S. V. V V

V V V N V

•y s V N V

V N N V N

N V N N N \

V V N V N V

V\ V V \ V \

\ \"\N \ \

l\\ \ \s \ O \

\ ’l\ A. \ \ \

\

\ \ x

\\ \ \ \

\\ \ \ \

\

'v\ \ \

AnA. 1 1 l\ 1 1 A

Y

\ \ \

\

\ \ \ \ \

\ \ \ \ \ \ \\\\\\\\\\\\\\

i iN 1 1 1\ i : A 1 1 1\ ii A 1 1 1\ 1 1 iN 1 1 1\ 1 1 1\ 1 1 \ 1 1 1\ 1

1\ i 1 1\ 1 1 N i i i\i i , N 1 1 N 1 1 Ki 1 1 Ki 1 1 Ki 1

K 1 1 i ; T j 1 1 xj ,

Figure 20. Detain of Velocities and Speed Contours Shown in Figure 19

Centered Near Fire (Fire #19, 3.2 MW) 2/3 to the Right and

1/5 Up from Bottom. Scale Magnified 10 Times.

48

bn

i

inim

i

uri

ini

im

im

iin i

lti i

itn

i^i i

uf1

i/i i

i/i i

ufAi

i^i i

uf1

uf

1

i^iin

1

n

1n

LLHUJiLiiLLrl/
FORM NBS-1 14A (REV. 1 1-84}

I

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date REPORT NO.

BIBLIOGRAPHIC DATA

SHEET (See instructions) NBSIR-86/3420 November 1987

4. TITLE AND SUBTITLE

Combustion of Oil on Water

5. AUTHOR(S)

D. Evans, H. Baum, B. McCaffrey, G. Mulholland, M. Harkleroad and W. Manders

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

7. Contract/Grant No.

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Minerals Management Service

Department of the Interior

Reston, VA 22091

10. SUPPLEMENTARY NOTES

2 Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report contains the results of measurements performed on both 0.4 m and 0.6 m

diameter pool fires produced by burning a layer of Prudhoe Bay crude oil supported by

a thermally deep layer of water 0 Both steady and vigorous burning caused by boiling of

the water sublayer .were observed. The measured energy release rate for steady burning

was about 640 kW/m . The emission rate, the size distribution, and specific extinction

coefficient were measured for the smoke aerosol produced by the fires. Data were also

obtained on the structure of the smoke aerosol by electron microscopy and on emission

of CO and C0„. Analysis of the crude oil burn residue indicated selected depletion

of the short chain alkanes and cycloalkanes when compared to the fresh oil. Mono-ring

aromatics including benzene, toluene, and xylenes present in the fresh crude were

absent in the burn residue. Calculations of the induced air flow into a simulated

distribution of 20 fires over a 100 m x 100 m area showed that the maximum inflow

velocity near the largest size fire (2.5 m diameter, 3.2 MW) was 1.1 m/s.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) burning rate; fire plumes; liquid fuels; offshore platforms; oilspill; pool fires;

smoke generation

13. AVAILABILITY

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20402.

14. NO. OF

PRINTED PAGES

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15. Price

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