1295243821-31

LIQUID PROPELLANT ROCKET ENGINE

CONTROL SYSTEMS

V GnanagandhiProgramme Director

CSP /LPSC/ISROTRIVANDRUM

WORKSHOP ON ENGINE CONTROL SYSTEM TECHNOLOGY

IIT – MUMBAI

19TH NOVEMBER 2004

735KN7.35 KN440N22N 6.4 KN50N

LIQUID ROCKET ENGINES DEVELOPED IN ISROLIQUID ROCKET ENGINES DEVELOPED IN ISRO

75KN11N1N

MONO-PROPELLANT

BI-PROPELLANT

PUMP FED

CRYOGENIC

PUMP FED

BI-PROPELLANT

PRESSURE FED

GAS GENERATOR

TURBO-PUMP

THRUST CHAMBER

MAJOR SUB-ASSEMBLIES ARE:

GAS GENERATOR

TURBO-PUMP

THRUST CHAMBER

INJECTOR HEAD

IGNITER

THRUST FRAME

COMMAND BLOCK

16 FLUID COMPONENTS AND

SENSORS

CUS MAIN ENGINE

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.

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

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.

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.

LOX Tank

Cavitating Venturi

By pass Orifice

Vent Line

GHe purge valve Ignitor

Thrust Chamber

H2 Injection Valve

H2 Vent Valve (HVV)

GH2 Source

Vent Line

Selector Valve

Main Valve

Start transient of a Pressure fed mode Cryogenic engine

0

10

20

30

40

50

0 0.5 1.0 1.5

Chamber pressureLOX injection pressure

H2 valve open

Main valve open

Main valve Command

IGNITIONBypass valve Open

Time(s)

Pre

ssu

re (

bar

)

Schematic diagram of a Typical LOX/LH2 Pump fed engine

LOX & LH2 FEED SYSTEM CHILLING

- LOW FLOW RATE

- HIGH FLOW RATE

LH2 & LOX TANK PRESSURE

GHe SUPPLY FOR FBU

BRING THRUST & MRC REGULATORS T0 - 1250

PURGE ME & GG USING GHe

PURGE SE USING GHe

LH2 SUPPLY FOR ENGINE UNIT (GG, ME & SE)

OPERATE IGNITER OF SE

OPERATE IGNITOR OF ME

LOX SUPPLY TO SE

LOX SUPPLY TO ME

OPERATE IGNITOR OF GG

LOX SUPPLY FOR GG

MOVE THRUST & MRC ACTUATORS TO NOM POSITION

To – 150

3.7 0.2 bar

To - 150

To + 2.3

To + 1 Tf + 2.3

Tf+10

To + 1 To + 3

To + 1.5

Tf + 2 To + 1.5

To + 2

To + 2

To+0.5

To + 3.5 Tf + 1

To – 150

To-900

To - 155

To + 1

Tf +1

Tf

To-900

To - 155 To + 1 Tf+2.3 +2.3

To + 3 To + 1

To + 1 Tf + 2.3

Tf+10

Operating sequence of a LOX/LH2 Pump fed engine

To – Engine startTf – Engine shutoff

Chamber pressure build up in start transient of a Cryogenic engine

0

2

4

6

0 2 4 6 8

Gas Generator Ignition

Main Engine Ignition

Time (s)

Pre

ss

ure

(MP

a)

3

4

5

6

2.5 5.0 7.5 10.0

Safe Upper Limit

Time(s)

MR

Cryogenic engine hot testMixture ratio bulild up

-150

-100

-50

0

50

0 2 4 6 8 10

Thrust regulator angleMRC Regulator angle

Time(s)

An

gle

(de

gre

es

)

Thrust/MR control regulator movement in start transient of a Cryogenic engine

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.

Engine Shut down transientGuidance based cutoff

0

5

10

15

20

999 1000 1001 10020

3

6

9

LOX Injection PressureVehicle Acceleration

H2 Cutoff

ME LOX Cutoff

GG-LOX Cutoff

Engine cutoff command(Guidance based cutoff)

Time(s)

Acc

eler

atio

n(m

/s2 )

Pre

ssu

re(M

Pa)

Engine Shut down transientDepletion based cutoff

0

2

4

6

8

262 264 266 268 270

Command pressureChamber pressure

Command cutoff at 50% Chamber Pressure

Propellant Depletion

Time (s)

Pre

ssu

re(M

Pa)

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.

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

AUTO ABORT CONDITIONS FOR HOT TEST OF TYPICAL CRYOGENIC ENGINE

PARAMETER ABORT VALUE NOMINAL

VALUE

INTERVAL

1. a. CHAMBER PRESSURE

b. CHAMBER PRESSURE

c. LOX INJECTION PRESSURE

‘PC1’ > 69 bar

‘PC2’ > 69 bar

‘POCI-1’ > 104 bar

64.7 bar

64.7bar

81.7 bar

To to Tf

(2 out of 3) 2. a. TEMPERATURE OF GAS AT GG OUTLET

b. TEMPERATURE OF GAS AT TURBINE

EXIT

‘TGGE-1A’ > 950 K

‘TGGE-1B’ > 950K

‘TGTE-A’ > 900 K

‘TGTE-B’ > 900 K

670K

630K

To to Tf

(4 out of 4) 3. a. CHAMBER PRESSURE

b. CHAMBER PRESSURE

c. LOX INJECTION PRESSURE

‘PC1’ < 8 bar

‘PC2’ < 8 bar

‘POCI-1' < 8.5 bar

58.3 bar

58.3 bar

81.7 bar

To+3 sec to Tf

(2 out of 3)

0

20

40

60

0 2 4 6 8 10

Successful test

Test aborted due to non-ignition(Lower limit abort group)

Time(sec)

Pre

ssu

re(b

ar)

Cryogenic engine testEngine safety control by lower abort

Lower abortlimit

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

• 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.

Thrust Control Schemes in Pressure 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.

Thrust Control Schemes in Pump Fed Engines

Feed back signals for closed loop Thrust control systems

– Engine parameters like chamber pressure, thrust chamber injection pressures etc.

– Vehicle acceleration

• 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.

Mixture Ratio Control Schemes

• 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.

Feed back signals for closed loop Mixture Ratio control systems

Schematic diagram of GG cycle engine with open loop Thrust & MR control system

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 %

Schematic of SCC engine with closedLoop Thrust and MR control system

Required Chamber Pressure

Thrust Control

Electric Drive

Thrust Control

Regulator

Engine

Control Electronics

Chamber Pressure

Feed back

Block diagram of Typical Thrust control system

CUS THRUST CONTROLLER

POSITION(DEGRS)

WATER FLW RATE,KG/SEC

PR : DROP(BAR)

TEST RESULT, A0

(BAR) A1

-125 -80 -50 -25 0 25 50 75 100 125

0.46 1.26 1.26 1.26 1.26 1.26 1.26 1.26 1.26 1.26

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

35.4

38.4

59.3

77.543.0

45.5

33.0

35.5

24.6

26.317.4

18.9

10.7

12.0

5.85

6.913.23

3.58

2.36

1.84

FLOW CHARACTERISTICS

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 SEAL=10SCC/MIN,1 BAR

• 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.

Typical Closed Loop Thrust Control System for a Cryogenic Rocket Engine

START

INPUT SIGNALSCHAMBER PRESSUREMEASURED [PIO(M)]

CHAMBER PRESSURE REQUIRED [PIO(R)]

ISPIO(L)<PIO(M)<PIO(H)

NO

YES

PIO(M)PIO(R)

ISF >D

NOU=0

YESIS

F <D1 YES

U=A x1

U <99

U=Ax

NO

NO U=99xSIGN[U]

YES

0.06025[U]

>0+ U YES U)-0.06025U=

<0-LYES )-

U= 0.06025

L

+0.06025*U

OUT PUT

U=16.6x[

NO

NO

Thrust control algorithmFor a Cryogenic engine

Engine chamber pressure with closed loop control system in a Cryogenic engine hot test

Permissible limits

Test result

5.0

5.5

6.0

6.5

7.0

0 400 800

Chamber pressure control accuracy : +0.025 MPa

TIME (s)

Pre

ssu

re (

MP

a)

Block diagram of Typical MR control system

CUS MIXTURE RATIO CONTROLLER

POSITION

WATER,FLOW RATE,KG/SEC

PR.DROP

BAR

TEST RES

(BAR)

A0

A1

-125 -80 -50 -25 0 25 50 75 100 125

4.97 12.35 12.35 12.35 12.35 12.35 12.35 12.35 12.35 12.35

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

47.2

45.5

87.3

88.1

74.5

79.1

68.0

72.2

64.1

67.2

59.1

60.052.9

54.9

49.1

49.6

44.2

44.2

38.7

38.8

FLOW CHARACTERISTICS

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 SEAL=1500 SCC/MIN AIR AT 65 BARMAX REST TORQUE AT NO FLOW, = 20 KGCM

• 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.

Typical Closed Loop MR Control System for a Cryogenic Rocket Engine

START

RECEIVEDCOMMAND 47

COMMAND 47-A

SIGNAL PROCESSING UNIT

SIGNAL FROM LOX temp. SENSORD D R2 R3R1

SIGNAL FROM LOX FLOW METERN , N , N01 02 03

SIGNAL FROM LH FLOW METERN , N , Nf1 f3f2

2

N <N <NLIM LIM0HL

D <D LIMRR

r = D DR = r

Da=a-a1/a2U = -16.6 Da

K =A(a +B N )(1-B R)D

0 0 0md

Ka(a +b N )(1-C T)f f f

D-1

K =d DDbb

K = K + Kd d db

S

YES

NO

NO

NO

NO

NO

YES

YES

YES

YES

YESRECEIVED

SIGNAL FROM AVR D b

D

fN <N <NLIML H

LIM

R

Mixture ratio control algorithmFor a Cryogenic engine

U = -S

U = 0

U=99 *sign(U)

ANALISIS OF

U =

OUT PUT

U = 0SIGNAL PLUS STOP

U > Um

U < 99

NO YES

YES

NO

NO

NO

NO

YES

YES

YES

YES

(a +a )-a0.060250 reg

Hi-1

U = 0.06025

reg(a -a )-a0 i-1

a =ai-1i +0.06025*U

L

a < (a +a )reg0H

a > (a -a )0 regL

a=a +0.06025*Ui-1

S=F* KdSm1

d K > Km md

S=F* K +F* Kd2 dm 1b

NO

Mixture ratio control algorithmFor a Cryogenic engine-contd

5.4

5.5

5.6

5.7

5.8

400 800

Mixture ratio control accuracy : + 0.35%

Time (s)

MR

Permissible limits Test result

Engine mixture ratio with closed loop control system in a Cryogenic engine hot test

Factors affecting Mixture ratio in a typical cryogenic engine

Parameters Variation during flight

Change in MR (%)

1. LH2 temperature change in flight,K

2. LOX temperature change in flight,K

3. LH2 temperature variation during loading, K

4. LOX temperature variation during loading, K

5. LH2 pump inlet pressure variation,bar

6. LOX pump inlet pressure variation,bar

7. Engine tuning error

+1.5

+3.0

+0.4

+0.5

+0.5

+0.5

+2

+6.0

-3.0

+1.6

+0.5

+1.0

+0.8

+2.0

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/d : Constant dk/d : Constant

– Cross coupling between thrust and MRC systems should be minimum

dk/d ~ 0 dF/d ~ 0

K : MR F : Thrust : MRC regulator angle : Thrust regulator angle

Thrust/MR control regulator areaFor a typical cryogenic engine

0.5

1.0

1.5

2.0

-150 -50 50 1500

0.2

0.4

0.6

0.8

1.0

Safe transientRegime

dThrust/d - constant

dMR/d - Constant

Mixture ratio regulator

Thrust Regulator

Regulator pintle position(Degrees)

MR

Reg

ult

or

Are

a (c

m2)

Th

rust

Reg

ula

tor

Are

a(cm

2)

CUS ENGINE HOT TEST

PS2 Engine 735 KN Thrust PS2 Engine Hot test

Typical Thrust control system for earth storable engine

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.

Typical Mixture ratio control system for earth storable engine

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.

Ø4000

13

63

0

LH2 TANK

LH2 PAS

AMBIENT HEL. GAS BOTTLE

LOX TANK

LOX PAS

ENGINE

GAS BOTTLE

UMBILICAL CONNECTOR

GIMBAL ACTUATOR

RCS THRUSTERS

ITT

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.

• 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.

Propellant Tank Pressurization Control(Contd)

Pressure regulator based Tank pressurization system

0.600

0.625

0.650

0.675

0.700

0 100 200 300

Control band : 0.62 + 0.01 MPa

sec

Pre

ssu

re(M

Pa)

Tank pressureRegulator based control

ON/OFF mode Tank pressurization system

0.10

0.12

0.14

0.16

0.18

0.20

0 200 400 600

Minimum Pressure - 0.13 MPa

Time(s)

Pre

ssu

re(M

Pa)

Tank pressureON/OFF mode control

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 (<5o) 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.

VIKAS ENGINE INTEGRATED WITH GIMBAL CONTROL

L40 STAGE - VIKAS ENGINE TEST

FUTURE ENDEAVORS

GSLV MKIII

• PAYLOAD 4.5 T

• CONFIGURATION 2xS200 + L110 + C25

• LIFT-OFF WEIGHT 629 T

• OVERALL LENGTH 40.5 m

LLPPSSCC

GGSSLLV V MMKKIIIIII

C-25 STAGE

Ø4000

13

63

0

PS

LV

199

4

GS

LV

MkI

200

1

GS

LV

MkI

II 2

007

L110

C25STAGE

HIGH THRUSTENGINE

IonTHRUSTER

L40 STAGE

GS2 STAGE

SAT. PROP.MODULE

PS2 STAGE

PS4 STAGE

LAMAOCS

HIGH PERFORMANCE

LAM

LIQUID PROPULSIONTECHNOLOGY

GROWTHPROFILE

GS

LV

MkI

I 20

03

CUS

CUS ENGINE

8th Plan 9th Plan 10th Plan Beyond 10th Plan

TS

TO

INSATIRS

GSAT