Four configurations of piloted flameholders were tested. The range of flame stabilization, flame propagation, pressure oscillation during ignition, and pressure drop of the configurations were determined. Some tests showed a very strong effect of inlet flow velocity profile and flameholder geometry on flame stabilization. These tests led to the following conclusions. (1) The use of a piloted flameholder in the turbofan augmentor may minimize the peak pressure rise during ignition. At the present experimental conditions, delta P/P asterisk over 2 is less than 10 percent; therefore, the use of a piloted flameholder is a good method to realize soft ignition. (2) The geometry of the piloted flameholder and the amount of fuel injected into the flameholder have a strong effect on the pressure oscillation during ignition of the fuel-air mixture in the secondary zone. (3) Compared with the V-gutter flameholder with holes in its wall, the V-gutter flameholder without holes not only has advantages such as simple structure and good rigidity but offers a wide combustion stability limit and a high capability of igniting the fuel-air mixture of the secondary zone

Guo, C. F.

Xie, Q. M.

Zhang, Y. H.

English

NASA Technical Reports Server

N87- 20278
EXPERIMENIAL INVESTIGATION OF PILOTED FLAMEHOLDERS
C.F. Guo, Y.H. Zhang, and Q.M. Xie
Gas Turbine Research Institute
Jiangyou County of Sichuan, People's Republic of China
Four configurations of piloted flameholders were tested. The range of
flame stabilization, flame propagation, pressure oscillation during ignition,
and pressure drop of the configurations were determined. Some tests showed a
very strong effect of inlet flow velocity profile and flameholder geometry on
flame stabilization.
INTRODUCTION
Pressure oscillation during the transient period from ignition to maximum
augmentation is a critical problem for the turbofan augmentor. Since this
pressure oscillation may cause fan flow to stall or surge, it is important to
know the peak pressure during augmentor ignition and to take some kind of
technical measure to reduce this peak pressure. Such a procedure is called
"soft ignition."
The combustion process in the fan flow of a turbofan augmentor is under a
severe condition. It is helpful to understand how to make use of the hot com-
bustion products in the core stream to ignite the combustible mixture in the
cold fan stream. The present research compares the capability for soft igni-
tion and the ability of different configurations of piloted flameholders to
ignite a cold fan stream.
C
F
Ga
Gf
h
M
P
p*
AP
T
SYMBOLS
pressure loss coefficient
area
alr-mass flow rate
fuel flow rate
gap height of V-gutter or peripheral length of test section
Mach number
pressure, kg/cm 2
3
stagnant pressure, kg/cm
pressure drop or pressure oscillation value, kg/cm 2
temperature, °C
Igl mLA X FLW O
https://ntrs.nasa.gov/search.jsp?R=19870010845 2020-03-20T11:08:48+00:00Z
T* stagnant temperature, °C
V velocity, m/sec
AFR alr-fuel ratio
Subscripts:
0 upstream of flow orifice
l downstream of flow orifice or upstream of air heater
2 inlet of test section
3 outlet of test section
a air or ambient
ave average
APPARATUS
The test apparatus Is shown In figure I. The airflow from the compressor
Is divided Into two streams: one stream goes to ejector 7 to create a low-
pressure exhaust condition for the test section; the other stream goes through
valve l, flow-oriflce meter 2, air heater 3, control valve 4, and plenum cham-
ber 5 into test section 6. After leaving the test section the combustion
products are cooled by water injection. The hot gas Is exhausted into the
ambient through the ejector.
The test rlg assembly Is shown In figure 2. It Is a rectangular duct
300 mm by 175 mm. The piloted flameholder Is mounted inside the test section
by bolts. Flame extinction Is recorded through a quartz window by a flame-
detection device. Flame extinction can also be observed visually. The igni-
tion in the primary zone is provided by a hlgh-energy ignitor of 12 J. The
combustible mixture in the secondary zone Is ignited by flame propagation from
the primary zone. The inlet flow Is measured by the static pressure tap, the
stagnant pressure tube, and the chromel-alumel thermocouple. The outlet tem-
perature Is monitored by a platlnum/platlnum-rhodlum thermocouple. Outlet
stagnant pressure Is measured by three water-cooled stagnant pressure probes;
each has three measuring points. The transient pressure is measured by an
Inductlon-type pressure transducer (CyG-l, 0 to l.O kg/cm 2) wlth an LR-I
carrier wave amplifier and an Sc-60 ultraviolet oscilloscope. The fuel flow
rate is measured by a turblne-type flowmeter wlth a digital frequency
indicator.
The fuel Is injected through a spray bar. There Is one spray bar In the
primary zone. The total length of the bar Is 280 mm. There are slx pairs of
holes (0.4 mm In dlam) on the bar at an intersection angle of 60 °. In the
secondary zone there are slx spray bars. The two bars In the center have four
pairs of holes (0.35 mm In dlam) at an intersection angle of 30°; the other
four spray bars have four holes (0.35 mm In dlam) each. Fuel injection In the
secondary zone is In the counterflow direction. The test configurations of
piloted flameholders are shown In figure 3.
192
TESTMETHOD
The test conditions were as follows:
l_ 60 to 70 °C or 500 °C
M2 0.23
P_ 0.25 to 1.2 kg/cm 2
The test procedures were as follows: First, the air supply was adjusted to
maintain the inlet conditions of P_, M2, and T_ as specified. After the
primary zone had been ignited the ejector air supply was adjusted to maintain
P_, M2, and T_ constant. Then the fuel flow in the primary zone Gfp was
increased until fuel-rlch flameout occurred. After that, the _rlmary zone was
reignited at the specified inlet condition and P_, M2, and T2 were kept
constant. Finally, the fuel flow was reduced until there was fuel-lean flame
extinction. Before ignition, the pressure drop between the inlet and outlet
was measured. During ignition the peak pressure, the fuel-alr mixture in the
secondary zone, and the pressure oscillation were also recorded.
RESULTS AND DISCUSSION
Peak Pressure Measurements
As shown in figure 4, the peak pressure rise during ignition is usually
lower than lO percent of the inlet pressure (AP2/P _ < TO percent). The
peak pressure rise in the augmentor is normally related to the amount of fuel
injected (as in these tests). Since the ignition is realized in a small vol-
ume, the amount of fuel necessary for ignition is small. Thus, the peak pres-
sure is lower than that for normal augmentor ignition. This proves that using
a piloted flameholder makes it easier to obtain a soft ignition in a turbofan
augmentor.
Pressure Oscillation Measurements
Pressure oscillation measurements were performed under the same conditions
as the peak pressure measurements. The amount of fuel injected in the primary
zone has a very strong effect on the pressure oscillation in the augmentor
during ignition in the secondary zone (figs. 5(a) and (b)). It has been shown
that, with the same amount of fuel injected in the secondary zone, the pressure
oscillation during the onset of secondary combustion varies with the amount of
fuel injected in the primary zone. It is clear that there is an optimum fuel
injection in the primary zone which minimizes the pressure oscillation during
secondary zone ignition.
Flow Resistance
Figure 6 shows the variation of the pressure loss coefficient with the
Reynolds number Re for different configurations. When Re increases, the
pressure loss coefficient C decreases slightly. The pressure loss coeffi-
cient C also decreases with the increase of gap height h. The pressure loss
coefficient C for a V-gutter is slightly lower than that for a semlspherical
shape.
193
Effect of Inlet Flow Distortion
lhe inlet flow distortion is shown in figure 7. Figure 8 shows the effect
of inlet flow d_stortlon on flame stabilization. When the inlet flow is dis-
totted, the range of flame stabilization is narrowed, and the peak value of the
stabilization parameter is also reduced. For instance, at P_ = 0.25 kg/cm 2
when there is no inlet distortion, it is possible to ignite the secondary zone
in 3 sec; but, when there is inlet distortion (even at P_ = 0.3 kg/cm2), the
range of flame stabilization is very narrow and the ignltablllty in the sec-
ondary zone is very weak. (It is impossible to ignite the fuel-alr mixture in
the secondary zone.)
Effect of Secondary Air Entry Holes on Stabilization
of the SJ410-4A Flameholder
When 54 secondary holes (8 mm in diam) are opened, the range of flame
stabi]izatlon is very narrow (fig. 9). When these holes are blocked, the
stabilization range is broader. The secondary air entry holes also reduce the
capability of igniting the fuel-air mixture in the secondary zone. It seems
that the secondary air dilutes the primary combustion products and reduces the
temperature.
Effect of Gap Height
Figure lO(a) and (b) show the effect of gap height h on flame stabili-
zation for the SJ410-4B and SJ410-3A configurations. The range of flame
stabilization decreases with the increase of the gap height h, and the Ignlt-
ability also decreases. From this test we found that, for a specified con-
figuration, there is an optimum gap height. For instance, when the width of
the V gutter is ?0 mm (SJ410-3A), the optimum gap height is 3 to 5 mm, the
width of V-gutter is 40 mm (SJ410-4B), and the optimum gap height is 2 to 3 mm.
Under these conditions, the range of ignition and flame stabilization and the
ignition capability in the secondary zone are nearly the same for the two
configurations.
Effect of Bluff Body Shape on Flame Stabilization
Figure ll(a) shows the flame stabilization range for the SJ410-3A con-
figuratlon under ambient air temperature with a different bluff body shape.
lhe range of flame stabilization of the V-gutter bluff body is wider than that
of the semlspherIcal bluff body. But as shown in figure ll(b), at T_ = 500 °C
the ranges of flame stabilization for both bluff bodies are nearly the same.
Ibis can be explained as follows. At high inlet temperature, the vaporlzatlon
rate of the fuel spray (before entering the primary zone) is hlgh for both
flameholders; therefore, the gaseous fuel-air ratios of the mixtures in the
primary zone are nearly the same. But at low temperature, the fuel vaporl-
7_flnn r_f_ nn fh_ V_nllff:r ¢llrf_ro ic hinh_r fh_n fhmf nn fha :ami_(nharlr}l
body, and the fuel-alr ratio in the primary zone of the V-gutter is higher than
that of the seml-spherlcal body. lhus, the V-gutter has a wider range of flame
stabilization.
Effect of Air Entry Holes in V-Gutter Wall on Flame Stabilization
Figure 12 shows the range of flame stabilization for the SJ410-3B con-
figuratlon with different air entry holes in the V-gutter wall. For a given
194
opening area, fewer holes with larger diameters offer better flame stabili-
zation than smaller holes. A comparison of figure lO(b) with figure 12 shows
that the reclrculatlon zone created by the gap provides better flame stabili-
zation than that created by circular holes.
- CONCLUSIONS
These tests led to the following conclusions.
(1) The use of a piloted flameholder in the turbofan augmentor may
minimize the peak pressure rise during ignition. At the present experimental
conditions, AP/P_ is less than lO percent; therefore, the use of a piloted
flameholder is a good method to realize soft ignition.
(2) The geometry of the piloted flameholder and the amount of fuel
injected into the flameholder have a strong effect on the pressure oscillation
during ignition of the fuel-alr mixture in the secondary zone.
(3) Compared with the V-gutter flameholder wlth holes in its wall, the
V-gutter flameholder without holes not only has the advantages such as simple
structure and good rigidity but offers a wide combustion stability limit and a
hlgh capability of igniting the fuel-alr mixture of the secondary zone.
BIBLIOGRAPHY
Branstetter, J.R.; and Juhasz, A.J.: Experimental Performance and Combustion
Stability of a Full Scale Duct Burner for a Supersonic Turbofan Engine. NASA
TN D-6163, 1971.
Cullom, R.R.; and 3ohnsen, R.L.: Operating Condition and Geometry Effects on
Low-Frequency Afterburner Combustion Instability in a Turbofan at Altitude.
NASA TP-1475, 1979.
Kurkov, A.P.: Turbofan Compressor Dynamics During Afterburner Transients.
NASA TM X-?IT41, 1975.
Marshall, R.L.; and Canuel, G.E.: Augmentation Systems for Turbofan Engines.
Presented at Crafleld International Symposium, 1976.
195
7Exhaus_
I
Air supply
W " -- 2_.,x,,,_
C _
6 5 4 3
D
Figure 1. - Test apparatus. Valve, 1; orifice flowmeter,
2; air heater, 3; contro] valve, 4; plenum chamber,
5; test section, 6; ejector, 7; valve, 8.
I Secondary zone 2 _ 4
Air
"IL,o _a_ ___5__l_J_ _ ___
Figure 2. - Test rig assembly. High energy ignitor, I; quartz
window, 2; thermocouple, 3; pressure probe, 4; pressure
transducer, 5; test configuration, 6; fuel spray, 7; fuel
spray bar, 8; thermocouple, 9; pressure probe, 10; pressure
tap, 11.
196
I I I I { I l * ' • 1 l !i
• ' i / ' ! 1 _ 1 / / r ;
I
I
J
I
o i
q
-i
J
1
/ •
(a) Configuration $3410-4A; h = 4 mm.
I / / I / ,' [ I / /. ,' t t _ / ,' {
f J I • I / I
i
I
t '- i I f_ / 7 • " ! ," . 1
(b). Configuration $3410-4B; h = 2, 3, 4, and 6 mm.
Figure 3. - Test configurations of piloted flameholders.
(All dimensions in mm.)
197
(c) Configuration SJ410-3A; h = 3, 5, and ? mm.
\
(d) Configuration SE410-3B.
T_pe Spacing Number Diameter
A 30 34 12mm
B I_ 76 Bmm
C 7 3OZ_ 4mm
(e) Air-entry holes on the V-gutter.
Figure 3. Concluded.
198
_pe A B
p_ kg/cm2 I.2 O.B
_P2 Kg/c=2 0.057 0.047
n P2/F_ % 4.8 5.
C D E
0.6 O.4 O.3
0.051 0.0085 0.0085
2.5 2.1 Z.8
Figure 4. - Pressure oscillation during ignition.
199
c-
o
N
0
¢_}
t-
O
-r-
-4-'
t---
0
I
200
.... o' ....o- .'o 0 0 0 o 0
cO _D _ _U _ GD
_y_Tey _On(I
o_
0
c-
O
0
o
U,--
I--4
I
r"
Q)
"m
O_
(J
I
C_
aJ _
I
0 0
_UaTOTJ3OOO c_oI eun_s_ud
o
o
,?
o
0
r'-
0
r"
r-
CL_--
Ln ¢.J
,4*-*
u,--_--
O_-
_P
-_ 0
"' 0
i
_P _n
-_ L
201
oo _ _
t-
O
4-J
>_ _-
4_ E_
t-.r-
.,- C_) ou
0
•¢" U
_ e,-- o
4._ m
e'-,_
i
0 0 0 0
0 0 0 0
o
o
I
o _
o o o o
o o o
8
o
Q
Q;
EO
_Q
q..
I!
c-
O_
cu
_-F-
0
0 J
4_0
Q; e-
,-- 0
_-.,-
0
4_.,-
_- 0
t_J
i_ II
N
Iii-
202
e--
o
n:l
N
0r'-
-I--.
n_
V)
(1)
E
p...-
t-
O
c-
e,-
o
_1 .! [ _
v
i
C_
r"-
S-
C)1
203
I I _ _1 . _[
0 0
_a/_A
:11;
f
0
g
0
I!
I-
o
II
-Ic
F--
I
Q
el)
0
N
0 r--
.i _ e-_
•r- O_
4- E
v
II
X
o
o
F--
I
t-
O
s,-
0
e_
J_
0
0
r-
204
300 I t
@
I I
300 600
AFR
Figure 12. - Effect of alr-entry holes in
V-gutter wall on flame stabilzatlon.
Configuration SJ410-3B; T2* = 500 °C,
M2 = 0.23.
205


Experimental investigation of piloted flameholders

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server