Functions of LPE Control Systems

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LIQUID PROPELLANT ROCKET ENGINE CONTROL SYSTEMS
V Gnanagandhi Programme Director CSP
/LPSC/ISRO TRIVANDRUM
WORKSHOP ON ENGINE CONTROL SYSTEM TECHNOLOGY IIT
MUMBAI 19TH NOVEMBER 2004
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LIQUID ROCKET ENGINES DEVELOPED IN ISRO
BI-PROPELLANT PUMP FED
CRYOGENIC PUMP FED
BI-PROPELLANT PRESSURE FED
MONO-PROPELLANT
6.4 KN
75KN
7.35 KN
440N
22N
50N
11N
1N
735KN
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GAS GENERATOR

• MAJOR SUB-ASSEMBLIES ARE
• GAS GENERATOR
• TURBO-PUMP
• THRUST CHAMBER
• INJECTOR HEAD
• IGNITER
• THRUST FRAME
• COMMAND BLOCK
• 16 FLUID COMPONENTS AND
• SENSORS

TURBO-PUMP
THRUST CHAMBER
CUS MAIN ENGINE
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Functions of LPE Control System

• The engine control system interconnects the
  components and logics of the engine and ensure
  proper functioning of the engine with the desired
  performance.

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Basic LPE Control Systems

• Engine start/cutoff sequence control
• Engine duration control
• Engine safety control
• Propellant Mixture ratio control
• Engine Thrust control
• Propellant tank pressurization control
• Thrust vector control by gimballing
• Engine system Checkout and test control

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Engine Start/Cut off Sequence control

• Start sequence control brings the engine systems
  safely from start signal to nominal operation.
• Cut off sequence control ensures rapid and safe
  shut down during normal operation as well as in
  an emergency with minimum and repeatable cut off
  impulse.

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Design requirements of Start Sequence Control
System

• Engine conditioning
• Safe ignition
• Safe Thrust and Mixture ratio profile
• Adequate Thrust chamber cooling
• Lead time of fuel admission with respect to
  Oxidizer admission for safe engine operation.
• Adequate pump inlet pressures to avoid Cavitation
  of pumps
• Build-up characteristics of pumps turbines
• Proper Valve response characteristics
• Purging the oxidizer circuits with inert gas to
  avoid the entry of fuel/hot gases.

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GHe purge valve
Ignitor
Thrust Chamber
Cavitating Venturi
H2 Injection Valve
Main Valve
Selector Valve
By pass Orifice
H2 Vent Valve (HVV)
LOX Tank
GH2 Source
Vent Line
Vent Line
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Start transient of a Pressure fed mode Cryogenic
engine
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Schematic diagram of a Typical LOX/LH2 Pump fed
engine
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To Engine start Tf Engine shutoff
Operating sequence of a LOX/LH2 Pump fed engine
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Chamber pressure build up in start transient of
a Cryogenic engine
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Cryogenic engine hot test Mixture ratio bulild up
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Thrust/MR control regulator movement in start
transient of a Cryogenic engine
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Engine Duration Control

• Engine shut down is either by guided cutoff or by
  propellant depletion cutoff.
• In guided cutoff, integrating accelerometer will
  give the required signal to cutoff, when the
  required vehicle velocity is achieved.
• In propellant depletion cutoff scheme, engine is
  stopped either by the signal from vehicle
  accelerometer or engine parameters like chamber
  pressure, injection pressure etc, indicating
  depletion of any one of the propellants.

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Engine Shut down transient Guidance based cutoff
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Engine Shut down transient Depletion based cutoff
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Engine System Safety Control

• Engine safety control system monitors major
  engine parameters during engine operation and
  safely aborts the operation in case of
  malfunctioning of any system.
• The upper and lower abort limits are fixed based
  on the safe operation limits of the engine.

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Typical Engine parameters to be monitored for
assessing the health

• Chamber pressure
• Coolant channel outlet temperature
• Turbo pump speed
• Pump inlet outlet pressures
• Gas generator pressure temperature

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Lower abort limit
Cryogenic engine test Engine safety control by
lower abort
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Thrust Mixture ratio Control Systems

• Thrust Mixture ratio control systems are
  necessary to achieve safe engine operation,
  required vehicle performance and minimum
  propellant outage.

Thrust Mixture Ratio Control Schemes

• Open Loop mode
• Closed Loop mode

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Thrust Control Schemes in Pressure Fed Engines

• Open loop mode Pre calibrated flow control
  devices (orifices, venturies etc) are used in the
  propellant feed circuits to maintain the thrust
  within specified limits.
• Closed loop mode Variable area flow control
  valves in the feed circuits or propellant tank
  pressure variation is used for controlling the
  thrust, based on the feed back signal.

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Thrust Control Schemes in Pump Fed Engines

• Thrust is controlled by controlling the
  throughput to the turbine.
• Open loop mode Propellant flow to Gas generator
  is controlled using fixed area orifices or
  venturies.
• Closed loop mode Propellant flow to GG or hot
  gas flow from GG to turbines is controlled by
  variable area flow control valves, based on the
  feed back signal.

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Feed back signals for closed loop Thrust control
systems

• Engine parameters like chamber pressure, thrust
  chamber injection pressures etc.
• Vehicle acceleration

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Mixture Ratio Control Schemes

• Open loop mode Pre-calibrated flow control
  elements are used in the propellant feed circuits
  to attain the required mixture ratio within the
  specified limits.
• Closed loop mode Variable area flow control
  valves are used in the propellant feed circuits
  to control the mixture ratio, based on the feed
  back signal.

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Feed back signals for closed loop Mixture Ratio
control systems

• Onboard computer estimates the mixture ratio
  using the flow meter and temperature data, which
  is compared with the desired value and corrected.
• In propellant utilization control system, the
  available propellants in the tanks are estimated
  using level sensors. Modified mixture ratio based
  on the available propellant is arrived at for the
  optimum utilization of the propellants and the
  control valves are adjusted to deplete the
  propellants simultaneously.

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Schematic diagram of GG cycle engine with
open loop Thrust MR control system
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Typical Open Loop Thrust/MR Control System for a
Cryogenic Rocket Engine

• Engine Thrust and Mixture ratio is set to
  required level by properly sizing the orifices
  and venturies employed in the propellant feed
  lines of GG and main Combustion chamber.
• Control accuracy 3

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Schematic of SCC engine with closed Loop Thrust
and MR control system
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Block diagram of Typical Thrust control system
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CUS THRUST CONTROLLER
MAJOR SPECIFICATIONS
FLUID MEDIUM LOX, FLOW RATE 1.4 KG/SEC,
OPERATING PRESSURE 130 BAR
NORMAL OPERATING RANGE -125 TO 125, MAX
RANGE OF MOVEMENT -140 TO 140
MAX RESISTANCE TORQUE AT 130 BAR,(NO FLOW
CONDITION) 20 KG CM
LEAK RATE OF SHAFT PRIMARY SEL 50 SCC/MIN,GN2
AT 150 BAR, SECONDARY SEAL10SCC/MIN,1 BAR
FLOW CHARACTERISTICS
POSITION(DEGRS)
-125
-80
-50
-25
0
25
50
75
100
125
WATER FLW RATE,KG/SEC
0.46
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
PR DROP(BAR)
39.8-46.8
59.6-79.9
42.9-58.1
32.3-43.2
27.1-27.9
15.6-23
9.1-15.6
5.7-9.1
3.8-5.3
2.7-4.1
TEST RESULT, A0 (BAR) A1
35.4 38.4
59.3 77.5
24.6 26.3
5.85 6.91
43.0 45.5
33.0 35.5
17.4 18.9
10.7 12.0
3.23 3.58
2.36 1.84
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Typical Closed Loop Thrust Control System for a
Cryogenic Rocket Engine

• Thrust is regulated by controlling the LOX flow
  to Pre-combustion chamber by a variable area flow
  control valve, operated by a stepper motor.
• Using the feed back signal, the thrust control
  electronics estimates the engine thrust, its
  deviation from the requirements and command
  pulses required to nullify the deviation using
  the thrust control algorithm and actuates the
  thrust regulator.

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Thrust control algorithm For a Cryogenic engine
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Test result
Permissible limits
Engine chamber pressure with closed loop
control system in a Cryogenic engine hot test
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Block diagram of Typical MR control system
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CUS MIXTURE RATIO CONTROLLER
MAJOR SPECIFICATIONS
FLUID MEDIUM LOX, FLOW RATE 12.8 KG/SEC,
OPERATING PR 130 BAR.
NORMAL RANGE OF OPERATION -125 TO 125,MAX
RANGE -140 TO 140 LEAK RT OF PINTLE FORE END
SEAL 2000SCC/MIN AIR AT 100 BAR LEAK RT OF
PINTLE REAR END SEAL1500 SCC/MIN AIR AT 65 BAR
MAX REST TORQUE AT NO FLOW, 20 KGCM
FLOW CHARACTERISTICS
POSITION
-125
-80
-50
-25
0
25
50
75
100
125
WATER,FLOW RATE,KG/SEC
4.97
12.35
12.35
12.35
12.35
12.35
12.35
12.35
12.35
12.35
PR.DROP BAR
46.5-52.4
82-93.9
73.7-83.7
67.2-76.7
61.2-69.9
55.8-63.7
50.1-58
44.9-52.4
42.7-43.6
34.2-41.5
A0 A1
47.2 45.5
87.3 88.1
74.5 79.1
68.0 72.2
64.1 67.2
59.1 60.0
38.7 38.8
49.1 49.6
TEST RES (BAR)
52.9 54.9
44.2 44.2
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Typical Closed Loop MR Control System for a
Cryogenic Rocket Engine

• Mixture ratio is regulated by controlling the LOX
  flow to the thrust chamber by a variable area
  flow control valve (MRC regulator), operated by a
  stepper motor.
• The MR control electronics estimates the MR and
  the command pulses required to correct the
  deviation using the signals from flow meters and
  temperature sensor. MRC regulator is actuated by
  a stepper motor to achieve the required mixture
  ratio.

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Mixture ratio control algorithm For a Cryogenic
engine
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Mixture ratio control algorithm For a Cryogenic
engine-contd
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Test result
Permissible limits
Engine mixture ratio with closed loop
control system in a Cryogenic engine hot test
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Factors affecting Mixture ratio in a typical
cryogenic engine
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Design Criteria of Thrust/MR Control Regulators

• The regulator flow area profile is designed based
  on the following conditions
• Rate of change of thrust/MR w.r.t pintle movement
  should be constant
• dF/db Constant dk/da Constant
• Cross coupling between thrust and MRC systems
  should be minimum
• dk/db 0 dF/da 0
• K MR F Thrust
• a MRC regulator angle b Thrust regulator
  angle

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Thrust/MR control regulator area For a typical
cryogenic engine
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CUS ENGINE HOT TEST
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PS2 Engine Hot test
PS2 Engine 735 KN Thrust
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Typical Thrust control system for earth
storable engine
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Typical Closed Loop Thrust Control System for an
Earth Storable Rocket Engine

• Earth storable engines generally employ pneumo
  hydraulic/hydraulic systems for Thrust and MR
  control.
• The thrust control regulator uses a piston,
  balanced by the chamber pressure feedback on one
  side and the required chamber pressure fed as
  command pressure on the other side. Any unbalance
  will move the piston thereby varying the
  propellant flow rate to the gas generator
  resulting in an increase or decrease of chamber
  pressure as required.

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Typical Mixture ratio control system
for earth storable engine
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Typical Closed Loop MR Control System for an
Earth Storable Rocket Engine

• Since the effect of propellant temperature on MR
  is negligible, MR is controlled by controlling
  the thrust chamber inlet pressures.
• MR control regulator equalizes the oxidizer and
  fuel pressures at thrust chamber inlet by means
  of a balancing piston. The required MR is ensured
  by suitably sizing the calibrated orifice mounted
  in the propellant line.

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LH2 TANK
GAS BOTTLE
LH2 PAS
UMBILICAL CONNECTOR
RCS THRUSTERS
ITT
AMBIENT HEL. GAS BOTTLE
LOX TANK
LOX PAS
GIMBAL ACTUATOR
ENGINE
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Propellant Tank Pressurization Control

• Control of propellant tank pressure is essential
  for the safe operation of the engine (non
  cavitating operation of the pumps), and safety of
  the tanks (avoiding over pressurisation).
• Tank pressure is controlled either by a Pressure
  regulator based system or algorithm based
  bang-bang mode ON-OFF system.

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Propellant Tank Pressurization Control(Contd)

• In pressure regulator based pressurization
  system, tank pressure is regulated by controlling
  the pressurant flow into the tank by a pressure
  regulator.
• In bang-bang mode pressure regulation system, the
  tank pressure is monitored by pressure
  switches/pressure transducers and pressurant is
  admitted/vented by means of ON-OFF valves, based
  on the command generated using a
  pressurization/vent logic.

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Pressure regulator based Tank pressurization
system
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Tank pressure Regulator based control
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ON/OFF mode Tank pressurization system
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Tank pressure ON/OFF mode control
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Thrust Vector Control by Engine Gimballing

• Thrust vector control is used for steering the
  vehicle over a desired trajectory.
• TVC can be done by gimballing main engine by
  small angle (lt5o) or by gimballing small
  auxillary engine by large angles (30-50o)
• Based on the vehicle trajectory, the onboard
  computer generates the necessary error signal and
  gimbal the engine using actuators.

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VIKAS ENGINE INTEGRATED WITH GIMBAL CONTROL
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L40 STAGE - VIKAS ENGINE TEST
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FUTURE ENDEAVORS

• GSLV MKIII
• PAYLOAD 4.5 T
• CONFIGURATION 2xS200 L110 C25
• LIFT-OFF WEIGHT 629 T
• OVERALL LENGTH 40.5 m

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LPSC
GS L V MK III
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C-25 STAGE
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TSTO
GSAT
INSAT
IRS
GSLV MkIII 2007
GSLV MkII 2003
GSLV MkI 2001
PSLV 1994
C25 STAGE
HIGH THRUST ENGINE
GS2 STAGE
PS2 STAGE
PS4 STAGE
CUS ENGINE
L110
LIQUID PROPULSION TECHNOLOGY GROWTH PROFILE
Ion THRUSTER
SAT. PROP. MODULE
HIGH PERFORMANCE LAM
L40 STAGE
Beyond 10th Plan
8th Plan
9th Plan
10th Plan
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