These works on the sounding rocket module and on the sounding rocket experiments ..... exist in the environment conditions in a sounding rocket module, the following parameters ...... heat of vaporization. R - Universal constant for perfect gas.
DEPARTAMENTO DE MOTOPROPULSION Y TERMOFLUIDODINAMICA ESCUELA TECNICA SUPERIOR DE U*$ENIEROS~AERONAUTlCOS
UNIVERStDAD POLITECNICA DE "MADRID SPAIN
STUDY ON COMBUSTION PROCESSES IN REDUCED GRAVITY VOLUME I by C. Sanchez Tarifa A. Lifian Martinez J.J.Salva Monfort G.L. Juste J.M. Tizon Pulido J.M. Cura Velayos It is a c k n o w l e d g e the valuable c o l l a b o r a t i o n given to t h i s work by Professor A . C . F e r n a n d e z - P e l l o U n i v e r s i t y of C a l i f o r n i a , Berkeley
LABORATQflrO DE PROPULSION, E,T.S.I. AERONAUTICOS Ciu-dad Universitaria* £ 8 0 4 0 Madrid^SPAIN
March, 1990
I
CONTENTS
1. ABSTRACT OF THE WORK
page 1
1.1. GENERAL CONSIDERATION ON THE WORKING PACKAGES
2
1.2. MULTIPLE EXPERIMENTS
3
1.3. FORCED CONVECTION EFFECTS AT LOW REYNOLDS NUMBER
4
1.4. THEORETICAL STUDIES
5
2. WP1. PARABOLIC AIRCRAFT FLIGHT
6,
2.1. INTRODUCTION
7
2.2. THEORETICAL ANALYSIS AND ESTIMATIONS
8
2.3. EXPERIMENTAL WORK
10
2.3.1. Preliminary ground test
10
2.3.2. Experiments performed at microgravity conditions
13
2.4. EXPERIMENTAL RESULTS AND ANALYSIS
15
2.4.1. Flame spreading process
15
2.4.2. Quiescent combustion on cylindrical rods
16
2.4.3. Disk pool fire
17
2.5. CONCLUSIONS
3. WP2 AND WP3. SOUNDING ROCKET MODULE AND SOUNDING ROCKET EXPERIMENT
3.1. REVIEW OF POSSIBLE EXPERIMENTS
18
39
40
3.1.1. Introduction
40
3.1.2. Conclusions
48
3.2. REFILLING OF THE MODULE
49
3.2.1. Introduction
49
3.2.2. Methods for velocity measuring
49
II
3.2.3. Experimental work
51
3.2.4. Experimental results
53
3.3. FORCED CONVECTION EFFECTS
60
3.3.1. Introduction
60
3.3.2. Motion of the sample
60
3.3.3. Forced convection flow generation
61
3.3.4. Analysis of the system
62
4. WP4 THEORETICAL ASPECTS OF FLAME SPREAD ALONG SOLID FUEL RODS OR SOLID
75
4.1. INTRODUCTION
76
4.2. GRAVITY EFFECTS ON FLAME SPREAD ALONG FUEL SLABS
78
4.3. GRAVITY EFFECTS ON FLAME SPREAD ALONG FUEL RODS
83
4.4. FLAME SPREAD ALONG FUEL SLABS AGAINST CONVECTION
85
4.5. FLAME SPREAD ALONG FUEL RODS AGAINST CONVECTION
88
4.6. EFFECTS OF FINITE REACTION RATES AND RADIATION LOSSES
91
5. WP4. NUMERICAL STUDY ON QUIESCENT COMBUSTION
99
5.1. INTRODUCTION
102
5.2. MODEL ADOPTED
103
5.2.1. Assumptions
103
5.2.2. Governing equations
104
5.2.3. Initial and boundary conditions
105
5.3. COMPUTATIONAL SOLUTION METHOD
105
5.3.1. Preliminnary comments
105
5.3.2. Grid Characteristics
106
5.3.3. Discretization
107
5.3.4. Source term linealization
108
5.3.5. Solution procedure
109
Ill
5.4. APPLICATIONS, RESULTS AND ANAL SIS no 5.4.1. Results and analysis of the process. Chemical kinetics influence
111
5.4.2. Perfomances analysis of the ignitor
111
5.4.3. Effect of radiation and oxygen mass fraction
112
6. PROPOSED EXPERIMENT
136
1
1. ABSTRACT OF THE WORK
1. ABSTRACT OF THE WORK 1.1. GENERAL CONSIDERATION ON THE WORKING PACKAGES
The following tasks have been carried out under the present Contract:
WP1. Continuation of the experiments on flame spreading in parabolic aircraft flights, conducted in one flight campaign. These
experiments
have
been,
in
part,
a
continuation
of
the
preceeding research programmes and they were directed to the study of the influence of fuel thickness at reduced gravity on the flame spread velocity.
In addition, a few experiments were carried out in order to obtain some preliminary information on possible combustion experiments to be performed in a sounding rocket module.
WP2 and WP3. These works on the sounding rocket module and on the sounding rocket experiments were preceeded by a common study, which consisted in a review of the combustion experiments that could be carried out in a sounding rocket module. The requirements of the experiments were analised, with special emphasis on the essential factors of the time and space needed for each possible experiment.
It was definitively concluded that there is no practical way to keep constant the gaseous atmospheric composition in the module chamber throughout a stationary combustion process in a still atmosphere. This is due to the fact that there is not any practical feasible way to extract the combustion products and to feed into the module the oxygen or the reactant gases consumed without strongly disturbing the flow field.
This
velocities
occurs in
because
combustion
under
processes
microgravity at
constant
conditions
gas
pressure
are
essentially controlled by diffusion and they are usually very small.
3
As a consequence, the module has to contain a sufficient amount of oxidizer such that its variation during the combustion process should be permissible. This requirement imposes limitations in the volume and combustion time, which are interdependent and in the size of the experiment.
In addition, the volume available has to be sufficiently large in order to avoid significant interference of the walls of the module on the combustion field. If the experiment is of a non-stationary nature and
the
flame
combustion
size
increases
processes,
this
with
time,
imposes
as
it
another
occurs
in many
limitation
in
the
combustion time and in the size of the experiment.
The aforementioned review of the combustion processes is shown in this Final Report and from its conclusions the basic data for the study and specifications of the combustion module were obtained.
1.2. MULTIPLE EXPERIMENTS
From
the
aforementioned
combustion experiments
review
times of
it was
the order
concluded of
one
than
minute
in most would be
sufficient.
Since
there are
problem of utilizing
six minutes at
reduced
the module for several
gravity
available,
experiments has
the
to be
considered, specially taking into account the high cost of the launching of a sounding rockets. Except for the experiments in which a little amount of oxidizer is consumed, such as in droplet combustion, reutilization of the module for multiple experiments require emptying the module and refilling it with the specified gaseous mixture. This process is mechanically simple but it presents the difficult problem of knowing the time required for the
4
oxygen or gaseous mixture introduced into the chamber to become at rest. The process is asymptotic, therefore it has to be specified the minimum value admitted for the gas fluctuation velocities (for example o3 cc
CO •—t
o a.
a. oo
cc
CO LU CC
CO
LU
o
o
CD
to
cc o
cc o
on LU Of
*d-
I
LU CC
o
LU
«=*- cc i O
co s
g CO
CO
LU CJ
CO LU
CO LU
3 : CC
>-
>-
CO
a. h-t
»21 LU
3E KH CC LU
K_J =3 X LU
s:
< cc
LU CC
o CJ
LU CC
O CJ
3; 1—
Q LU CJ CC
3; 1—
o
I—I
3 •>-^
o Ll-
CO LU CC >- O
CJ
i—i •^—»
o Ll-
CO LU CC >-
o
in
C/l
to
(/)
o 1 o CO
o 1 1 o en
o CVJ
o co •
o
1
CO > •
IZ> >- GO
LU
a.
CO
Cr •—( i
CC LU
O
^ >- S c_>
ce: ^—** o CO LU CO
X UJ
zc Q.
CO LU
>-
CO
>-
00
CO
Lf)
un • o
C\J •
•
a:
o H3;
has been left out, because it is of
80
order unity. When Eqs.(l)
and (2) are used, we obtain the relations 11/3
/
,T
g
We
anticipate
here
possible if the size 8
, 8 =a
g
that
2 / 3
S
U =(ga )
g
the
"
1 / 3
/O
g
\
(3)
g
flame
spread
process will
not be
of this region is smaller than the thickness of g
the premixed flame of a stoichiometric mixture of the fuel and air. In order to calculate the flame spread velocity we need to describe the heating
of
the solid
from
its
initial
temperature
T
to the
00
vaporization temperature T .
Let k
V
solid and 5
be the heat conductivity of the
s
the transverse thickness of the heated layer in the solid;
s
by requiring the continuity of the heat fluxes at the solid-air interface^just upstream of the vaporization front, we obtain, in order of magnitude, k (T -T )/S = k (T -T )/S g f o o
g
s v o o
(4) s
or
5 / S = N = k (T -T )/k g s
(T -T )
(5)
g f o o s v o o
The parameter N measures the relative importance, for thick fuel slabs, of the upstream heat conduction along the solid and along the gas.
If N »
1,
upstream
heat
conduction
along
the
solid
can be
neglected; then, the thickness 5 of the heated layer in the solid under s
the flame front region is S « 8 , small compared with its longitudinal s
q
extent. In this case, the balance of convection, with the velocity U , and p
transverse heat conduction in the solid leads
to the relation
81
8 = / a S /U ' s
From E q s .
(1),
(5)
and (6)
V
s g
we o b t a i n
U 8
p q
5
_
a
fir
Ut^^^^L
•££n,£i
If 8 »a, then in the gas phase we encounteTVAn outer region where g
convection^ and radial and axial heat conduction and diffusion are balanced, so that U
and 5
g
g
are related by (1),
and an interior region
close to the rod r ~ a, where only radial heat conduction and diffusion
84
are important, including perhaps the effects of the radial convection due to vaporization. The analysis of this inner region can be carried out using the approach of Ref.10, and leads to the introduction of a large Nusselt number N = (S /a)/ln(l
+5 /a)
q
u
(11)
q
in the right hand side of Eq (12) when writing the energy balance for the fuel rod upstream
of the vaporization region.
In this case we
obtain p c (T -T )na2U = 2na k (T -T ) N s s v o o
p
g
f
o
o
(18)
u
Then the front velocity U is given by p
U = 2a. N(S /a2)/ln p 2/3
where 5 = a g
g
-1/3
1/3
g
— tyfor g>g ^ that/ior
(19)
q
, as long as U = (ga )
g
Notice
(1+8 /a)
q
s
._ t. the
is larger than U .
g
p
o resulting
value of pU
decreases with
decreasing values of g, with g given by the condition 2/3 -1/3...
a g
U
g
/
/N = a,
„ .
(20)
i
goes through a minimum,when g~g ,and then begins to grow, according
p
i
to Eq (19), as g"1/3. When at a second critical value g
of g, U has grown to a value U 2
p
a
such that U = 2oc N(S /a2)/ln(l+8 a
s
2
/a)
= (g ct )
1 / 3
(21)
2 q
2
2/3 -1/3
where
5= = a 2
g
g
=
