FINAL TECHNICAL REPORT

FLAME PROPAGATION AND EXTINCTION IN

PARTICLE CLOUDS*

By

A. L. Berlad and N.D. Joshi

University of California, San Diego

La Jolla, California 92093

January, 1986 *•

(NASA-CK-177304) FLAME PBOPAG4TION AND N86-27434

EXTINCTION IN PAE1IC1E CLODDS Final

Technical Kepprt, 2 Jan 1984.- 51 Aug. ,,1985

(California Uriv.) 7 p HC A02/MF A01 Unclas

CSCL 21B G3/25 43172

* The studies reported herein were supported by NASA under

Research Grant NAG3-473. Period of grant: 01-02-84 through 08-31-85.
INTRODUCTION AND BACKGROUND

Microgravity combustion studies of particle clouds can eliminate intractable experimental and theoretical problems, thereby

permitting successful resolution of essential issues associated

with particle cloud flame propagation and extinction . It is

important to note the scientific issues at stake and UCSD approaches

to their resolution through Orbiter Middeck and related microgravity

combustion studies of premixed, quiescent particle clouds. These

previously presented observations are noted below:

The central problem in nonadiabatic theory of flames is concerned with flame propagation and extinction. For gas phase, premixed fuel and air, experimental and theoretical studies have

provided important insights into controlling mechanisms for flame

propagation and extinction. The classic studies generally conclude

the following: In the absence of natural convective processes,

flame extinction (flammability limits, pressure limits, and wall

quenching) is due to heat losses from flame to boundaries ^ ~ .

Recent studies have been aimed at a more comprehensive understanding

of flame structure and extinction through use of more complete chemical kinetic representations and general (time-dependent) constitutive equations of fluid dynamics. Modern computational systems permit numerical integration of these more comprehensive representations. Although definitive correspondence of premixed gaseous combustion theory and experiment is incomplete, a substantial level of

fundamental understanding has been achieved.

and

For the case of flame propagation/extinction in premixed clouds

of fuel particles, progress in development of both theory and experiment have been slow. ' ' The reasons are several, and complex.

Essential limitation on our understanding of premixed particle cloud

combustion derives principally from the inability of experiments

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conducted at normal gravitational conditions:

(a) to permit the establishment of uniform, quiescent

clouds of uniformly distributed (non-settling) combustible particulates;

(b) to yield data that are independent of natural convective effects.

Experiments at reduced gravitational conditions are expected to permit the resolution of both of these experimental problems. Combustion experimentation in Space Shuttle facilities can provide a unique

body of data, thereby stimulating and complementing the corresponding development of two-phase flame propagation and extinction

theory.

The current investigation has been concerned with

(a) -t-he—f-u-rt-her--development -o=f _two-phase flame propagation

and extinction theory required to support the corresponding experiments planned for space shuttle,/' ^ bti^G DfcWt-i-o?«tfc.

fM.iia 9t\)feYk) specialized collaborative, experimental and theoretical NASA-UCSD studies needed to support the ongoing definition of

needed experimental hardware, experimental procedures, data acquisition philosophy, and other ground-based support activities required

to assure the success of Space Shuttle-based experiments concerned

with Combustion of Clouds of Particulates at Reduced Gravitational

Conditions;

(-e-)' the further development of relations delineating premixed particle cloud and premixed gaseous systems as well as burnerstabilized and freely propagating flame systemsf \ &

pas P(VCf\
RECENT ADVANCES

The UCSD research team has collaborated with NASA's Lewis Research -Center in addressing technological issues required for the

Particle Cloud Combustion Experiment. These have included the successful resolution of cloud ignition, particle cloud mixing, the

suppression of wall saturation effects and the further development

of particle pyrolysis data, and two-phase flame propagation and

extinction theory.

Several papers prepared recently by UCSD researchers are reproduced in APPENDIX (A). Important aspects of our current theoretical and experimental approaches are given in these papers.

NASA-LeRC scientists and engineers are currently concerned with

design and development of a Particle Cloud Combustion Experiment

(PCCE) and associated apparatuses. UCSD researchers have supported

this effort in a number of ways:

(1) Work on wall saturation effects and on optical extinction characteristics of particle clouds has furnished information required for successful design of the PCCE. Studies of particle-particle and particle-wall interactions continue.

(2) Theoretical and experimental work on particle vaporization and pyrolysis kinetics is required to support the broad

theoretical objectives of two-phase flame propagation and extinction

theory. These studies are currently in progress at UCSD.

(3) Bench top (and drop tower) studies at UCSD (and at

LeRC) have helped to resolve a number of experimental issues regarding particle cloud mixing processes, as well as particle cloud

ignition, flame propagation and extinction. These ongoing studies

support NASA's current design and development efforts, provide

quantitative bases for rational selection of the matrix of orbiter

and of ground-based experiments planned for the PCCE program.
They contribute importantly to the development of flame propagation and extinction theory. Findings reported in reference (6)

(also Appendix (A)-Part 3) illustrate the supportive importance

of drop tower and other ground-based studies.
THEORETICAL MODELLING

Methods of nonadiabatic premixed two-phase flame theory have

been extended to include a two temperature flame structure (gas

and particulates) as well as detailed information on volumetrically

distributed endothermicities (e.g., see reference 6 and part 3 of

Appendix (A), and the coupled roles of omnidirectional energy

f CZ. \

transport to boundaries . Theoretical modelling to date, taken

together with selected drop tower experimentation, has been able to

demonstrate the importance of inclusion of these considerations in

theoretical models. An extensive discussion of these theoretical

f £. \

issues is given in part (3) of Appendix (A). Based on these

approaches, the current theoretical work will be extended to include detailed homogeneous and heterogeneous pyrolysis and oxidative chemical kinetics for the particulates of interest. Under

microgravity conditions, the radiation-conduction flame propagation and extinction model will be developed further and applied to

the experimental data to be derived from the planned Space Shuttle

based experiments.
REFERENCES

1. A. L. Berlad, "Premixed Gaseous Flame Propagation and Extinction

Limits", Progress in Astronautics and Aeronautics 73, 12 (1981).

2. A. L. Berlad, "Combustion of Particle Clouds", Progress in Astronautics and Aeronautics 73, 91 (1981).

3. A. L. Berlad, "Gravitational Effects On Combustion", Progress in

Astronautics and Aeronautics 52, 89 (1977).

4. M. Lavid and A. L. Berlad, "Gravitational Effects On Chemically

Reacting Boundary Layer Flows Over A Horizontal Flat Plate",

XVI Symposium (International ) On Combustion, p. 1557. Pub.: The

Combustion Institute.

5. N. Gat, et al., "Zero Gravity Particle Cloud Combustion Experiment", TRW, Inc. Final Report on NASA Lewis Research Center Contract NAS-3-23254 (1982).

6. A. L. Berlad and N. D. Joshi, "Gravitational Effects On The Extinction Conditions For Premixed Flames". Paper presented at the

XXXV International Astronautical Federation Congress (1984).

In Press.

7. C. R. Krishna and A. L. Berlad, "A Model For Dust Cloud Autoignition", Combustion and Flame 37, 207 (1980).

8. J. 0. Hirschfelder, C. F. Curtis, and D. Campbell, Fourth Symposium (International) On Combustion, p. 190 (1953).

9. J. B. Rosen, ibid, p. 210.

10. T. Von Karman, Sixth Symposium (International) On Combustion,

P. 1 (1957).

11. D. B. Spalding,-Proc. Roy. Soc. A1957, 240, p. 83.

12. A. L. Berlad and C. H. Yang, Combustion and Flame 4, 325 (1960).

13. F. A. Williams, Combustion Theory,. Pub.: Addison-Wesley (1965)

14. L. A. Lovachev, Combustion and Flame 20, 259 (1973).

15. E. S. Oran and J. P. Boris, Progress in Energy and Combustion

Science 6, 1 (1980).