Two transient operational modes of the X-34 pressurization system were analyzed using the ROCket Engine Transition Simulation (ROCETS) program. The first operational mode considers the normal operation. For the engine burn period, the required helium mass and pressure of each propellant tank were calculated. In the second case, the possibility of failure of the pressurization system solenoid valves, its consequence on the over-pressurization, and simultaneous operation of pressurization and vent/relief systems were evaluated

Champion, R. H., Jr.

Hedayat, A.

Knight, K. C.

English

NASA Technical Reports Server

TRANSIENT ANALYSIS OF X-34 PRESSURIZATION SYSTEM
A. Hedayat and K. C. Knight
Propulsion Department
Sverdrup Technology, Inc. MSFC Group
Hunstville, AL 35806
//j--
R. H. Champion Jr.
Marshall Space Flight Center
Huntsville, AL 35812
ABSTRACT
Two transient operational modes of the X-34 pressurization system were analyzed using the ROCket
Engine Transition Simulation (ROCETS) program. The first operational mode considers the normal
operation. For the engine burn period, the required helium mass and pressure of each propellant tank were
calculated. In the second case, the possibility of failure of the pressurization system solenoid valves, its
consequence on the over-pressurization, and simultaneous operation of pressurization and vent/relief
systems were evaluated•
INTRODUCTION
The X-34 technology development program is a joint industry/government project to develop, test,
and operate a small, fully-reusable hypersonic flight vehicle demonstrating technologies and operating
concepts applicable to future Reusable Launch Vehicle (RLV) systems. The X-34 Main Propulsion
System (MPS) stores and delivers Rocket Propellant 1 (RP-I) fuel and Liquid Oxygen (LOX) oxidizer as
required by the NASA-MSFC Fastrac engine. The MPS consists of the Tank Pressurization Subsystem,
Pneumatic and Purge Subsystem, Propellant Feedline Subsystems, and Fill/Drain/Dump Subsystems. An
overview description of the X-34 MPS has been provided by Sgarlata and Winters _. The detailed
descriptions of the feed subsystem and propellant management, and pressurization subsystem are provided
by McDonald et. al 2and Brown et. at 3 , Hedayat, et. al 4, respectively.
Stored-gas pressurization systems are used to transfer propellants from the tanks to the turbopump
at the needed flow rates and pressures. In the pressurization systems, helium is commonly used because of
its lower molecular weight and thus reduced total pressurant weight Gaseous Helium (GHe) is stored in
bottles at high pressure, then it is supplied to the propellant tanks at limited flowrates using valves,
regulators, and orifices. In addition, solenoid valves control the pressurization of the LOX and RP-1 tanks
within an allowable pressure range.
In the event of a pressurization system solenoid valve failure (fail open scenario), the propellant
tank is over-pressurized. The over-pressurization can result in structural failure of the propellant tanks. A
vent/relief system on the propellant tank is intended to relieve the ullage without allowing the tank pressure
to rise above proof. In the solenoid valve failure scenario, the vent/relief valves must be capable of opening
fast enough to establish the relief flow prior to the tank pressure reaching proof. In this analysis, only the
RP-I tank is considered due to its very low initial ullage volume.
Using ROCETS s, two operational scenarios for the pressurization system were simulated. In the
first case, normal operation of the pressurization system helium usage and thermodynamic conditions were
evaluated. The second case deals with the simultaneous operation of pressurization and vent/relief systems
and maximum ullage pressure within RP-1 tank is calculated.
https://ntrs.nasa.gov/search.jsp?R=19990009082 2020-06-18T00:41:20+00:00Z
SystemDescription
ANALYSIS
A schematic of pressurization and vent/relief systems is shown in Figure 1. Helium is supplied to the
propellant tanks through two regulators. During the pressurization process, the second regulator is
considered to be completely open while the passage of the fast regulator is adjusted such that the pressure
at the exit is maintained at 350 psi. The helium pressurant is stored initially at 5000 psia and 530 °R.
The allowable pressure range for the LOX and RP-1 tanks are 55-61 psia and 47-53 psia, respectively. A
closed loop control circuit uses tank pressure sensor output to control opening/closing of the flow control
solenoid valves, thus maintaining tank pressure within the above control band as propellant is expelled
from the tanks.
In the event of a pressurization system failure, the vent valve must respond fast enough to prevent tank
pressures from rising above their proof ratings. If the solenoid valves fail open, the continuous flow of
helium and its accumulation in the tank leads to the pressure build-up and eventually over-pressurization of
the RP-I tank. As the pressure reaches a specified value, the relief/vent valve is opened to allow ullage to
leave, therefore relieving the pressure. The over-pressurization magnitude depends on the vent/relief valve
response time. In this analysis, for the vent/relief valve, a response time range of 0.5 to 1.0 second is
considered. In addition, the following assumptions are made:
1. Helium initial temperature and pressure are 530 °R and 5000 psia.
2. LOX temperature is 163 °R.
3. RP-I line has an ID of 0.65" (OD = 0.75"), and the rest of the system has an ID of 0.83" (OD
=1'3.
4. Densities of LOX and RP-I at described conditions are 71.5 lbm/fl 3 and 50.5 lbm/ft 3,
respectively.
3 3
5. Volume of LOX and RP-I tanks are 300 ft and 188.51 ft, respectively.
6. Start transient flowrates data for the fast 2.5 seconds from reference 6.
7. LOX tank initial ullage volume is 19.6 f13.
8. The 2.5" Vent/Relief valve has a relief capacity that of a 1.5" equivalent sharp-edged orifice
diameter with a discharge coefficient of 0.60. In addition, the vent have a capacity of 2.5"
equivalent sharp-edged orifice diameter with a discharge coefficient of 0.60.
9. Considering V'= volume flowrate, m "= mass flow rate, p = density, and V" = mTp, engine
requirements during the steady state engine operating period are as followsT:
.Fluid m'(lbm/sec) V" (tl3/sec)
LOX 144.0 2.014
RP-I 66.0 1.307
In the analyses, the ROCETS models were run for 3 different initial RP-1 tank ullage volumes of
0.5% (0.94 t_3), 1.0% (1.88 if3), and 1.5% (2.82 if3) of the RP-1 tank volume. Also, the ROCETS model
contained the pressurization model as described in Hedayat, et. al. 4. When the RP-1 tank reaches a 85 psia
a delay equivalent to the vent/relief valve response time (0.5-1.0 second) is imposed, then the vent/relief
valve is set to full open allowing the ullage to exit. As the helium discharges from the tank, the pressure
within RP-1 tank drops. When the ullage pressure drops below 75 psia, the vent/relief valve is closed.
Aft LOX
Tank RP-1
Tank
All Components are 0,75"
350 psia
Check Valve
[] Solenoid Valve
Pressure Regulator
[] Latching Solenoid Valve
[1] Orifice
[] Relief/Vent Valve
Helium Bottles
5000 psia
Figure 1. Pressurization and Vent Systems Schematics.
Results
In the ROCETS model, the delay from the instant tank ullage pressure reaches the specified set-point
until a signal reaches the solenoid valve is considered to be 0.04 seconds. The additional delay due to the
valve response to a signal is assumed to be 0.05 seconds. The valve closing/opening area variation is
modeled linearly.
Figure 2 shows the pressure history of the ullage within the RP-1 tank. Initially, the ullage
pressure is 53 psia. The ullage reaches a maximum of approximately 54.2 psia after 2.5 seconds. Figure 3
illustrates the RP-1 tank helium usage history. After 110 seconds, the RP-1 tank contains 7.58 ibm ff
helium. At this point, the solenoid valve is closed and the ullage mass is kept constant until the end of
the engine burn. At the end of the pressurization process, the RP-1 tank ullage pressure is 39 psia.
The LOX ullage pressure history is shown in Figure 4. The LOX tank was maintained at 65 psia
with a +3 psi control range. The LOX ullage pressure reaches a maximum of 68.5 psia after 1.5 seconds.
The LOX tank ullage mass history is depicted in Figure 5. This figure indicates that at the end of
pressurization process, the LOX tank contains 44 Ibm of helium.
Figures 5 and 6 show the RP-1 tank ullage pressure history for the pressurization system solenoid
valve failure scenario. Figure 6 illustrates the RP-1 tank ullage pressure history for a vent/relief valve
response time of 1 second. For 0.5%, 1.0%, and 1.5% initial ullage volumes, the maximum ullage
pressures are 190 psia, 118 psia, and 89 psia, respectively. For a response time of 0.5 second, Figure 7
indicates that the maximum ullage pressure for the 0.5%, 1.0%, and 1.5%, initial ullage volumes are 142
psia, 110 psia, and 80 psia, respectively.
60
50
40
3O
2O
Presell
0
Figure 2.
_sia)
I I
50 100 150
Time (sec)
RP- 1 Tank Ullage Pressure History.
45
40
35
3O
25
15
Mas_o(
S,
o
Figure 5.
I I
50 100 150
Time (sec)
LOX Tank Ullage Mass History.
8,
7,
6'
5,
4,
3'
Mas?,
1
0 i !
50 lOO
Time (see)
150
Figure 3. RP-I Tank Ullage Mass History.
70
60
50
40
30
2O
PressuI
lO
o
o
)sia)
I !
50 100 150
Time (see)
Figure 4. LOX Tank Ullage Pressure History.
210.
180'
150.
120.
90'
60
Pressure
30
0
0
." [ 0.5% ullage
." : -- --1.0% ullage
: _1.5% ullage
,' ,---" -7.?,........ .
• ..,-' : o.
I I
1 2 3
Time (see)
Figure 6. RP-1 Tank Ullage Pressure History
for a Vent/Relief Response Time of 1.0 second.
210
180
150
120
90
60
Pressure
30
0
0
..... 0.5% ullage
-- -- 1.0% ullage
.': _1.5% ullage
- , ,,-"
.. .. ,,->'_
.'"
! I
1 2
Time (sec)
Figure 7. RP-1 Tank Ullage Pressure History
for a Vent/Relief Response Time of 0.5 second.
ACKNOWLEDGMENTS
The authors would like to acknowledge the Propulsion Department of Orbital for providing technical
information in support of the X-34 Main Propulsion System design. In addition, the authors acknowledge
Mr. David Wood of Sverdrup Technology Inc., for providing the specific component performance
information. Finally, the authors would like to acknowledge Mr. Mike Martin and Mr. Charles White d"
Propulsion Laboratory at Marshall Space Flight Center for their assistance with ROCETS.
REFERENCES
l°
.
.
.
.
6.
7.
Sgarlata, P. And Winters, B., (1997) "X-34 Propulsion System Design," AIAA paper, AIAA-97-
3304.
McDonald, J. P., Minor, R. B., Knight, K. C., Champion, R. H., Jr., (1998)"Propellant Feed
Subsystem for the X-34 Main Propulsion System," AIAA paper, AIAA-98-3517.
Brown, T. M., McDonald, J. P., Hedayat, A., Knight, K. C., and Champion, R. H., Jr., (1998)
"Propellant Management And Conditioning Within the X-34 Main Propulsion System," AIAA paper,
AIAA-98-3518.
Hedayat, A., Steadman, T. E., Brown, T. M., Knight, K.C., White, C.E., Champion, R. H., (1998)
"Pressurization, Pneumatic, and Vent Subsystems of X-34 Main Propulsion System," AIAA paper,
AIAA-98-3519.
"ROCETS User's Manual ," Pratt & Whitney, West Palm Beach, Florida, January 1995.
"Updated Pump Flowrates," E-mail provided by Mike Martin, EP13, MSFC, April 8, 1998.
Russell, J., and Champion, R., "MSFC X-34 Main Propulsion System Propellant Inventory Report,"
X-34-MPS-RPT-004A, Propulsion Systems Team, EP72, MSFC, NASA, January 1998.


Transient Analysis of X-34 Pressurization System

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