Combustión of a solid at microgravity conditions at zero or at very small forced flow velocities is in the first place discussed, pointing out that this is the basic process of a fire in a manned spacecraft, in which might exist small air currents originated by the air conditioning equipment or by the motion of the people. Results of an experimental programme carried out in the 23rd ESA Flight campaign 96/12 and utilising a NASA aircraft laboratory, are shown and discussed. Six combustión chambers were utilised provided with video and infrared cameras. Non visible flames in the visual range were originated at two oxygen concentrations, and photographs were taken by means of an infrared camera. Several ignition tests at different oxygen concentrations were performed and flammability limits were obtained. Fíame spread velocities were measured and compared at three different gravity levéis (1 g, ~10"2 g and 10"4 g). A combustión research programme to be carried out in a Texus rocket, already in progress is briefly discussed. Finally, the scope of a complete research programme, which is in the process of being carried out in the NASA combustión module of the International Space Station is briefly resumed

López Juste, Gregorio

Sánchez Tarifa, Carlos

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A study of the combustion problems of solid materials at conditions existing in space stations

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

A STUDY OF THE COMBUSTIÓN PROBLEMS OF SOLID MATERIALS AT CONDITIONS EXISTING IN 
SPACE STATIONS 
C. Sánchez Tarifa Prof. (Emeritus). 
Universidad Politécnica de Madrid, E.T.S.I.Aeronáuticos. 
Consultant to SENER 
G. López Juste. Assistant. Professor 
Universidad Politécnica de Madrid, E.T.S.I. Aeronáuticos. 
Plaza Cardenal Cisneros 3, 28040 Madrid, Spain 
phone: 34.91.336 6352, fax: 34.91.336 6371 
email: starifa@aero.upm.es 
email: juste@prop.dmt.upm.es 
ABSTRACT 1.- INTRODUCTION 
Combustión of a solid at microgravity conditions at 
zero or at very small forced flow velocities is in the first 
place discussed, pointing out that this is the basic 
process of a fire in a manned spacecraft, in which 
might exist small air currents originated by the air 
conditioning equipment or by the motion of the people. 
Results of an experimental programme carried out 
in the 23rd ESA Flight campaign 96/12 and utilising a 
NASA aircraft laboratory, are shown and discussed. 
Six combustión chambers were utilised provided 
with video and infrared cameras. Non visible flames in 
the visual range were originated at two oxygen 
concentrations, and photographs were taken by means 
of an infrared camera. 
Several ignition tests at different oxygen concentra-
tions were performed and flammability limits were 
obtained. 
Fíame spread velocities were measured and 
compared at three different gravity levéis (1 g, ~10"2 g 
and 10"4 g). 
A combustión research programme to be carried out 
in a Texus rocket, already in progress is briefly 
discussed. 
Finally, the scope of a complete research 
programme, which is in the process of being carried out 
in the NASA combustión module of the International 
Space Station is briefly resumed. 
The School of Aeronautics of the Polytechnic 
University of Madrid, with the collaboration of the 
engineering company SENER, have been conducting 
research programmes on the combustión of solids in 
02-N2 atmospheres. 
The experimental programme has been carried out 
by means of parabolic flights, three in the NASA KC-
135 aircraft laboratory, and one in the ESA Caravelle 
(refs. 1, 3 and 4). A very relevant part of this 
experimental programme has been performed in a 
MiniTexus sounding rocket; launched in the 
ESRANGE in Kiruna, in 1995, in which twelve 
experiments were carried out on the influence of forced 
flow velocities on the combustión of cylinders of 
polymethylmethacrylate (PMMA). One of the most 
important findings was the verification of the existence 
for a 30 seconds period of a non-visible fíame in the 
visual range at zero flow velocity; the fíame becoming 
very rapidly visible when a flow of very low velocity in 
a direction parallel to the cylinder axis impinges on the 
fíame. These results were published in the First 
Symposium on the Utilisation of the International 
Space Stations (ref. 6). 
The existence of these non-visible flames had been 
already observed for short times in drop towers 
experiments (ref. 2, for example); but not their 
existence and stability for such a long time as 30 
seconds. 
In that work it was commented that tires were, and 
still are, a high risk área in manned spacecraft, and it 
will become more acute in space travel in which 
maintenance work will be severely limited. 
The basic process of a fire in a spacecraft is the 
combustión of a solid at microgravity conditions and at 
zero or very low convective flow velocities, such as 
those originated by the air conditioning equipment or 
by the motion of the people. 
When free convection is absent and forced convec-
tion is nil or very small, the combustión process is 
diffusion controlled and become very involved. Since 
characteristic diffusion velocities are very small (a few 
mm/s), the combustión process becomes very sensitive 
to very small valúes of forced convective velocities, as 
well as to oxygen concentration valúes. The combustión 
rates are very small, and the flames become in some 
cases non-visible in the visual range. 
The theoretical modelling is very complicated, with 
the result that theoretical solution do not exist except 
for a very few simple cases (combustión of spherical 
particles, for example). 
A review of the experimental date available and on 
the state of the problem may be consulted in refs. 7 to 
11. 
An experimental programme is developed to study 
this type of combustión processes and to obtain 
flammability and fíame spread rates. 
In the first place the programme has been carried 
out in parabolic flights, and the results of this 
programme are presented in this work. It will be 
followed by a Texus programme already approved by 
ESA. The launching will be performed in the 
ESRANGE, Kiruna in 1999. 
2.- PARABOLIC FLIGHTS EXPERIMENTAL 
PROGRAMME 
2.1.- Experiments and Test Equipment 
The European Space Agency (ESA) launched its 
23rd Parabolic Flight Campaign 96/12, which was 
carried out in the NASA KC-135 aircraft laboratory 
utilising the Bourdeaux-Mérignac International 
Airport, France, with the ground help of the Sogerma-
Socea installations at the airport. 
Two flights were made available by ESA to perform 
the experiments. The main objective of the programme 
was to carry out infrared photographs of non-visible 
flames in the visual range. Another important objective 
was to perform flammability limits test by burning 
hollow cylinders at different oxygen concentrations. 
Six chambers already utilised in previous parabolic 
campaigns were used, refurbishing two of them with 
infrared transparent windows (CaF2), as well as with an 
arrangement to permit simultaneous photograph of a 
video camera and an infrared camera. 
The six chambers were placed in a semicircular 
platform. The video camera was located in the centre 
and rotated after each flight. The infrared camera was 
arranged to take photographs of the cameras, provided 
with infrared windows (Fig. 1). 
Attachment to rails 
To: Power 
Aircraft supply 
28DCV 
Fig. 1 Test chambers 
Twelve experiments were performed, with some 
additional ignition tests in flammability experiments 
PMMA hollow cylinders of 6 mm in diameter and wall 
thickness from 2 to 0.2 mm were utilised. Oxygen mass 
fraction ranged from 19 to 40%. Pressure was always of 
100 kPa and there were no forced convective flow. All 
the experiments performed are shown in Table I and II. 
2.2.- Infrared Visualisation Experiments 
Two series of non-visible flames were observed 
simultaneously with video and infrared camera and are 
shown in Figs. 2 and 3. Oxygen concentration mass 
fraction was of 21% and 23%, and cylinder wall 
thickness of 2 mm. 
In these experiments, ignition took place before the 
flight entering at reduced gravity región, and in about 
6-7 seconds after ignition or else in 3-4 seconds after 
low gravity is initiated, the fíame becomes non visible. 
The fíame remains in this non visible condition 
throughout the parabolic flight, becoming again visible 
once the low gravity concludes. The low gravity period, 
as usual, was of the order of twenty seconds. 
It may be pointed out that for the first time these 
flames have been observed with infrared cameras. 
Visible Ranee 
In f rared Range 
2.25 2.75 5.75 9.50 
Visible Range 
Infrared Range 
18.75 20.25 20.50 24.25 
Fig. 2.-Simultaneous video colour and infrared photographs of a PMMA Cylinder burning at reduced 
gravity. [(Times from ignition (sec)] (Y02 = 23%); (small differences in time of the order of 0.2 s 
between IR and visible photographs might exist). 
Visible Range 
2.25 
Infrared Range 
ü.25 3.25 4.25 5.75 
I n f r a r e d Range 
15.OO 20.25 22.OO 22.50 
Fig. 3.- Simultaneous video colour and infrared photographs of a PMMA Cylinder buming at reduced 
gravity. [(Times from ignition (sec)](Y02 = 21%); (small differences in time of the order of 0.2 s 
between IR and visible photographs might exist). 
t = t i. t + 0 . 0 4 s o 
t^-t + 0 .2 s 
o 
t - t + 10.2 s 
o 
Fig. 4 Ignition and combustión processes. Yo2= 40 % , thickness = 2 mm 
Combust. 
Chamber 
1 
2 
3 
4 
5 
6 
Experiment 
40% 0 2 , 2 mm thick. 
Reproduction 
MiniTexus 
experiment (IR 
camera) 
23% 0 2 , 2 mm thick. 
Flame visualisation 
(IR camera) 
40% 0 2 , 1 mm thick. 
Flame spreading 
velocity 
23% 0 2 , 0.5 mm 
thick. Flammability 
limit 
23% 0 2 , 0.5 mm 
thick. Flammability 
limit 
23% 0 2 , 0.2 mm 
thick Flammability 
limit 
Remarks 
Visible 
flame 
Non-
visible 
flame 
Visible 
flame 
Flaming 
follows 
ignition 
Flaming 
follows 
ignition 
Flaming 
follows 
ignition 
TABLE I (Flight No 2) 
Combust. 
chamber 
1 
2 
1 
2 
2 
3 
4 
5 
6 
3 
Experiment 
19 % 0 2 , 2 mm 
thick (IR camera) 
Flame visualisation 
2 1 % 0 2 , 2 m m 
thick (IR camera) 
Flame visualisation 
Reigntion tests 
Reignition tests 
Reignition tests 
19 % 0 2 , 1 mm 
thick. Ignition tests 
21 % 0 2 , 1 mm 
thick. 
23 % O, 2 mm 
thick. 
23 % 0 2 , 1 mm 
thick. 
19 % 0 2 , 1 mm 
thick. Reignition 
tests 
Remarks 
Flame 
extinguish. 
Non-visible 
fíame 
Flame 
extinguish. 
Flame 
extinguish. 
Flame 
extinguish. 
Flame 
extinguish 
Flame 
spread. vel. 
measur. 
Flame 
spread. vel. 
measur. 
Flame 
spread. vel. 
measur. 
Flame 
extinguish. 
TABLE II (Flight 3) 
It may be observed that the flame shape become 
almost spherical, reaching what appears to be a quasi 
stationary state. Burning rates are very low and 
difficulties to measure. 
An approximate theoretical model is being 
developed with the aim of explaining the thermal and 
stability conditions of these flames. Radiation from the 
flame and from the PMMA surface will be taken into 
account. 
It is important to investígate if these type of non-
visible flames, which might present special detection 
characteristics, might exist in an Space Statíon at 23% 
or a somewhat higher oxygen concentrations (up to the 
máximum valúes allowed) and at zero or very low 
convective flow velocities. 
2.3.- Flammability Limits and Spread Rates Velocities 
No sufficient experiments were available in order to 
obtain precise valué of the flammability limits, and 
burning rates. The influence of thickness was very 
limited. 
The flames originated by the ignition process and 
the subsequent onset of the flame spreading process are, 
in general, very different than those observed in the 
MiniTexus experiments as shown in ref. 6. This is not 
only due to the difference in gravity levéis (~10~2 and 
~10"4), but also to the oscillation of the gravity level in 
the parabolic flight, quite often of the order of 0.1 g. 
However, the following results were obtained: 
Flammability limits at 100 kPa for rod wall 
thickness of 2 mm was of the order of 20% in the 
parabolic flight (~10~2 g) at the ground at 1 g of 18%. 
At the same conditions that in the MiniTexus 
experiment (40% 02, 2 mm wall thickness) the flame 
was of the normal visible type, as shown in Fig. 4. This 
shows the important difference of the two gravity 
levéis. 
Results of flame spread velocities are shown in Fig. 
5, including some results with forced flow velocities. It 
may be observed the very low valúes of the spread rate 
at zero flow velocity and 23% 02, mass fraction when 
the flame is of the non-visible type. 
In Fig. 6 flame spread rates are compared for three 
gravity levéis, showing the very large influence of this 
parameters. 
1.2 
1.01 
_ 0.8 
I °-«cb 
0.4 
o1 
X 
X 
X-iE^tg 40%O2 ;2 
• 1 g , 40% 0 2 ; 2 mm 
OlE-2g 
A1E-2g-
40%O2 
23% 02 ; 
;2 
1 
mm 
mm 
Tim 
1.2 
1.0 
_ °8 
£ 0.6 
3
 0.4 
0.2 
0.0 
2 4 6 8 10 
Ux (cm/s) 
Fig. 5.- Experimental results 
40%O2 
PMMA Dia meter :6 mm 
wall thickness : 2 mm 
12 14 
10 10 10 10 
Gravity Level (g) 
10 10 
Fig. 6- Influence of gravity level on flame spread 
velocities. YQ2= 40%, diameter=6 mm, thicknes=2 mm 
3.- TEXUS PROGRAMME 
An experimental programme sponsored by the 
European Space Agency to be carried out in a Texus 
sounding rocket is already in progress. 
The experiments are already specified and a 
preliminary design carried out by the company SENER 
is already available. 
The experiments will be performed with three 
PMMA hollow cylindrical rods. A video camera and IR 
camera supplied by ESA will be utilised. 
The following experiments will be performed 
during the 330 seconds micrograviry period: 
-Measurements of temperature profiles in non-visible 
flames by means of radially moving thermocouples. 
-Flammability limits obtained by reducing continuously 
the oxygen concentrations at two constant small flow 
velocities until the fíame extinguishes. 
-Ignition tests at different oxygen concentrations, at 
zero and at very small flow velocities at different 
locations in the rods. 
-Measurements of fíame spreading velocities. 
Launching of the Texus is programmed to take 
place in the ESRANGE, Kiruna, Sweden, in November 
1999. 
4.- INTERNATIONAL SPACE STATION 
PROGRAMME 
As it has been previously commented a very large 
matrix of tests is required in order to acquire a 
sufficient knowledge of the problem of the combustión 
of solids at conditions existing in a spacecraft, specially 
if actual materials and configurations are going to be 
investigated. 
A programme of this kind is not practically feasible 
by utilising only drop towers, parabolic flights and 
sounding rockets. 
The most suitable facility to carry out an extensive 
research programme of this kind it is an orbital 
laboratory. At this respect a proposed was presented to 
NASA, as a response to NR17-97-11EDS-01. 
The main scope of the proposed programme is as 
follows: 
-Completion of the research programme on PMMA 
samples (flammability limits, ignition and fíame spread 
velocities as function of oxygen concentration, forced 
flow velocities, pressure, configuration and thickness of 
the samples. 
-Research combustión programme (applied) with actual 
materials in actual configurations. 
-Attainment of basic knowledge for possible 
improvement of fire safety standards. 
ACKNOWLEDGEMENT 
The European Space Agency supplied free of charge 
the Aircraft Laboratory, and ground support equipment. 
In Spain, the programme was supported by the 
Comisión de Investigación Científica y Técnica 
(CICYT) (Proyecto ESP96-1997-E). This support is 
fully acknowledged and appreciated. 
The collaborations of Miss María Teresa Gómez 
(SENER) and Mr. Antonio Romero (ETSIA) are fully 
appreciated. 
REFERENCES 
1. Sánchez Tarifa, C; Corchero, G. and López Juste, 
G.: An Experimental Research Programme on 
Heterogeneous Combustión Processes under 
Microgravity Conditions. Preliminary Results. XVII 
IAF Congress, Innsbruck. IAF-86-288 (1986). 
2. Olson, L. Sandra: Near Limit Fíame Spread over a 
Thin. Solid Fuel in Microgravity. 22nd Symposium 
(International) on Combustión, 1988. 
3. Sánchez Tarifa, C; Corchero, G. and López Juste, 
G.: An Experimental Programme on Fíame 
Spreading at Reduced Gravity Conditions. Appe. 
Microgravity Tech. Vol. 1. 1988. 
4. Sánchez Tarifa, C; Liñan, A.; Salva, J.J.; Corchero, 
G. and López Juste, G.: Heterogeneous Combustión 
Experiments during KC-135 Parabolic Flights. ESA 
SP-1113, 1989. 
5. Ramachandra, P.A.; Altenkirch, R.A.; Battacharjee, 
S.; Tang, L.; Sacksteder, K. and Wolverton, M. 
Katherine: The Behaviour of Flames Spreading over 
Thin Solids in Microgravity Combustión and 
Fíame. Numbers 1/2, 1995. 
6. Sánchez Tarifa, C; Salva, J.J. and López Juste, G.: 
Fíame Spreading over Solid Fuels at Microgravity 
Conditions Results Obtained in the MiniTexus 
Rocket and Future Programmes. The First 
Symposium on the Utilisation of the International 
Space Station. 30 September - 2 October 1996, 
ESOC, Darmstadt, Germany. 
7. Altenkirch, R.A.; Bhattacharjee, S.; West, J.; Tang., 
L.; Sacksteder, K. and Delichatsios, M.A.: Solid 
Surface Combustión Workshop, pp. 381-386, 
Cleveland, Ohio, 1997. 
8. Bhattacharjee, S.; Altenkirch, R.A.; Worley, R.; 
Tang, L.; Bundy, M.; Sacksteder, K. and 
Delichatsios, M.A.: Reflight of the Solid Surface 
Combustión Experiment: Opposed-Flow Fíame 
Spread Over Cylindrical Fuels. Fourth International 
Microgravity Combustión Workshop, pp. 387-392, 
Cleveland, Ohio, 1997. 
9. Olson, Sandra L.; Altenkirch, R.A.; Bhattacharjee, 
S.; Tang, L. and Hedge, U.: Diffusive and Radiative 
Transpon in Fires Experiment: DARTFire. Fourth 
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pp. 393-398, Cleveland, Ohio, 1997. 
lO.Tien, J.S.; Sacksteder, K.R.; Ferkul, F.V.; Bedir, H. 
and Hsin-Yi Shih: Solid Inflammability Boundary 
at Low Speed (SIBAL). Fourth International 
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Cleveland, Ohio, 1997. 
ll.Merril, K.K. and Howard, D.R.: Overview of the 
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A study of the combustion problems of solid materials at conditions existing in space stations

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