Liquid Rocket Engine Cycles

AAE 539: Advanced Rocket Propulsion

Spring 2007

Pressure Fed Cycle

Advantages

•Simple, reliable design

•No turbo pump

Disadvantages

•Limited to small tb, low thrust

•Only limited throttling

•Tanks must withstand high pressure

•Tank bladders might be required

Used in space vehicle attitude control, apogee engines

Fuel Oxid.

He, N2

High Pressure Gas Source

Gas Generator Cycle (GG)

Open Cycle – Turbine exhaust doesn’t go thru main chamber

GG burns non-stoichiometric to eliminate turbine cooling

Advantages

•Fairly simple

•Wide thrust operating range

Disadvantages

•Turbine exhaust gives low Isp – and effective loss in performance

•Gas generator required

RS-27, MA-5, STME, Titan

Gas Generator Cycle Rocket Engine

Fuel Turbine Ox. Turbine

Production GG Cycle Engines

ENGINE HM7B Viking VC HM60 LR87 LR91MA-5A

BoosterMA-5A

SustainerRS-27A

Contractor SEP SEP SEP Aerojet Aerojet Rocketdyne Rocketdyne RocketdyneStage Ariane 4 3nd

StageAriane 4 1st

StageAriane 5 1st

StageTitan IV 1st

StageTitan IV 2nd

StageAtlas II 1st

Stage Booster

Atlas II 1st Stage

Sustainer

Delta II/III 1st Stage

Propellants LOX/LH2 N204 / UH25 LOX/LH2 N204 / Aerozine 50

N204 / Aerozine 50

LOX/RP1 LOX/RP1 LOX/RP1

ThrustSea Level, lbf -- 152,000 198,000 447,300 -- 429,500 60,500 199,945Vacuum, lbf 14,100 171,000 250,500 552,500 106,200 85,000 237,067

Throttle Fixed Fixed Fixed Fixed Fixed Fixed 45% to 100% Fixed

Specific ImpulseSea Level, sec -- 248.5 340.0 246.1 263.3 265.0 220.0 254.8Vacuum, sec 445.1 278.4 431.0 304.0 318.0 308.0 302.1Mixture Ratio 4.77 1.70 5.30 1.91 1.86 2.25 2.27 2.245

Chamber Pressure

NozzleStagnation, psia

521.8 875.7 1646.6 827.0 827.0 719.0 736.0 654.8

Area Ratio 62.5 10.48 45 15 49.2 8 25 12Dry Weight, lbs 341 1953 3571 4583 1284 3336 1035 2527.9Thrust/Weight

(Sea Level)77.8 55.4 97.6 128.7 58.5 79.1

Thrust/Weight(Vacuum)

41.3 87.5 70.1 120.6 82.7 0.0 82.1 93.8

Current Development GG Cycle Engines

ENGINE MC-1 Vulcain 2 (HM60) RS-68 XRS-2200

Contractor MSFC SEP Rocketdyne RocketdyneStage X-34 Ariane 5 1st Stage Delta IV 1st Stage X-33

Propellants LOX/Kerosene LOX/LH2 LOX/LH2 LOX/LH2Thrust

Sea Level, lbf 40,532 223,000 663,232 204,400Vacuum, lbf 63,939 303,507 745,000 266,200

Throttle Fixed Fixed 60% to 100% 50% @ 4.75 MR+/- 15 % Differential

Throttling

Specific ImpulseSea Level, sec 199.0 318.0 365.0 339.0Vacuum, sec 314.0 433.0 410.0 436.5Mixture Ratio 2.17 6.10 6.00 5.50

Chamber Pressure

NozzleStagnation, psia

633 1736.4 1410 857.0

Area Ratio 30 61.5 21.5 58Dry Weight, lbs 1870.2 4189 14460 6,558Thrust/Weight

(Sea Level)21.7 53.2 45.9 31.2

Thrust/Weight (Vacuum)

34.2 72.5 51.5 40.6

Historic GG Cycle Engines

ENGINE H-1 RS-27 F-1 F-1A J-2Contractor Rocketdyne Rocketdyne Rocketdyne Rocketdyne Rocketdyne

Stage S-1B Delta I S-1C Dev. Only S-II/S-IVBPropellants LOX/RP-1 LOX/RP1 LOX/RP-1 LOX/RP-1 LOX/LH2

ThrustSea Level, lbf 206,145 200,000 1,522,000 1,800,000 --Vacuum, lbf 230,170 237,000 1,748,000 2,020,500 230,000

Throttle none Fixed none 1350-1800K FixedSpecific ImpulseSea Level, sec 264.9 255.0 265.4 271.0 --Vacuum, sec 295.8 302.0 304.1 304.2 427.0Mixture Ratio 2.23 2.25 2.27 2.27 5.50

Chamber Pressure

NozzleStagnation, psia

652.0 700.0 982.0 1161.0 763.0

Area Ratio 8 12 16 16 27.5Dry Weight, lbs 2,003 2444 18,616 19,000 3,480Thrust/Weight

(Sea Level)102.9 81.8 81.8 94.7 --

Thrust/Weight (Vacuum)

114.9 97.0 93.9 106.3 66.1

Combustion Tap-Off Cycle

Open cycle similar to GG, but uses chamber gases instead, to drive turbine.

Advantages

•No gas generator required

Disadvantages

•Difficult to start and throttle

•Narrow thrust operating range

•Hot gas valves required

J-2, Saturn V

Tapoff Cycle Rocket Engine

Open cycle similar to combustion tap-off, but this time we use coolant bleed (vaporized) to run the turbines.

Advantages

•No gas generator needed

Disadvantages

•Limited to cryogenic fuels

•Pressure and thrust limited by fuel thermal properties

Coolant Bleed Cycle

Closed cycle; most of coolant is fed to the low pressure ratio turbines.

Advantages

•Good performance (i.e., closed cycle efficiency)

•Simple design, low weight, wide thrust operating range

Disadvantages

•Limited to low chamber pressure (< 1100 psi)

•Limited to cryogenic fluid

Used in RL-10

Expander Cycle

Expander Cycle Rocket Engine

Vaporized Fuel

Closed cycle with high flow pre-burner replacing gas generator

Advantages

•High performance

•High chamber pressure and thrust capability

Disadvantages

•Very complex, with lower reliability

•Advanced turbine, and pumps required for high Pc (boost pumps)

Used in SSME, LE-7

Staged Combustion Cycle

Dual Preburner Fuel Rich SC Cycle Rocket Engine SSME Type

Good MR and thrust level throttling characteristics

Single Preburner Fuel Rich SC Cycle Rocket Engine

Better reliability than dual PBs.

Full Flow SC Cycle Rocket Engine

Dual preburner with like on like MR eliminates key failure modes in turbomachinery and repress systems.

Single Preburner Oxidizer Rich SC Cycle Rocket Engine

Ox rich preburner eliminates sooting issue in turbopump drive turbine. Significant advantage for reusable application.

Current Production SC Cycle Engines

ENGINE KUD-7.5 LE-7 RD-0124 RD-0120 RD-0210 RD120Contractor Russian Japan Aerojet - Chemical

Automatics Design Bureau (CADB)

Aerojet - Chemical Automatics Design

Bureau (CADB)

Aerojet - Chemical Automatics Design

Bureau (CADB)

P&W - NPO Energomash

Propellants LOX/LH2 LOX/LH2 LOX/Kersoene LOX/LH2 N2O4/UDMH LOX/KeroseneThrust

Sea Level, lbf -- 187,637 347,500 141,500Vacuum, lbf 16,524 242,300 63,600 440,850 130,861 182,500

Throttle 50% to 100% 25% to 114% 100% 70% TO 100%Specific ImpulseSea Level, sec -- 349.0 358.5 264.0Vacuum, sec 461.0 446.0 359.0 455.0 327.0 341.0Mixture Ratio 5.00 6.00 2.60 6.00 2.60

Chamber PressureNozzle

Stagnation, psia853.8 1910.5 2370 3170 2175.00 2360.0

Area Ratio 54 140 85 81.3 64.4Dry Weight, lbs 642.4 3779 990 7606 1248 2609Thrust/Weight

(Sea Level)49.7 0.0 45.7 54.2

Thrust/Weight(Vacuum)

25.7 64.1 64.2 58.0 104.9 70.0

Current Production SC Cycle Engines

ENGINERD170 / RD171 /

RD172RD253 SSME Block I SSME Block II RD180

Contractor NPO Energomash (Glushko)

NPO Energomash (Glushko)

Rocketdyne Engine System: Rocketdyne, High

Pressure Turbopumps: P&W

NPO Energomash (Glushko)

Propellants LOX/Kerosene N2O4/UDMH LOX/LH2 LOX/LH2 LOX/KeroseneThrust

Sea Level, lbf 1,631,000 350,000 394,000 418,660 860,200Vacuum, lbf 1,778,000 385,000 488,800 512,950 933,400

Throttle 40% TO 100% Continous to 305,000

Continous to 343,700

Continous from 100% to 40%

Specific ImpulseSea Level, sec 309.0 285.0 365.1 368.9 311.3Vacuum, sec 337.0 316.0 452.9 452.0 337.8Mixture Ratio 2.60 2.67 6.00 6.00 2.72

Chamber PressureNozzle

Stagnation, psia3456.0 2160 3100.0 3008.0 3722.0

Area Ratio 36.4 26 77.5 69.0 36.9Dry Weight, lbs 26575 1248 7004 7480 11889Thrust/Weight

(Sea Level)61.4 56.3 56.0 72.4

Thrust/Weight(Vacuum)

66.9 308.5 69.8 68.6 78.5

SSME With Identified Components

OxidizerPreburner

High-PressureOxidizer Turbopump

Low-PressureFuel Turbopump

Controller

PropellantValves

HydraulicActuators

Nozzle

Main CombustionChamber

Hot GasManifold

Fuel Preburner

Low-PressureOxidizer Turbopump

High-PressureFuel Turbopump

SSME Main InjectorAssembly

Liquid Main Engine Cycle Options

Staged Combustion, Bell Annular /

Dual Expander

Staged Combustion,

Single Chamber

Tripropellant

Staged Combustion,

Dual Preburner

Staged Combustion,

Single Preburner

Gas Generator

Expander Tap-off

Number of Main Turbopumps 3-4 3-4 2 2 2 2 2

Number of Boost Pumps 3-4 3-4 0-2 0-2 0-2 0-2 0-2

Number of major valves (typical) 11-16 7-9 5-7 5 4 4 3

Number of GG/PB's 2 2-3 2 1 1 0 0

Number of Thrust Chambers 2+ 1 1 1 1 1 1

Number of Main Injectors 2+ 1 1 1 1 1 1

Number of Nozzles 2+ 1 1 1 1 1 1

Increasing Complexity Decreasing Complexity

• A number of thermodynamic cycle options exist

• Which one used depends on application

• One cycle is not RIGHT for every application

• Table below shows comparison of cycle complexities

Liquid Rocket Engine Cycle Uses

Staged Combustion, Bell

Annular / Dual Expander

Staged Combustion,

Single Chamber Tripropellant

Staged Combustion, Dual

Preburner

Staged Combustion,

Single Preburner

Gas Generator Expander Tap-off

Advantages

High performance from altitude

compensation and /or propellant bulk density benefits.

Can use combination of

open and closed cycles

Highest integrated performance

available (closed cycle). Maximizes

propellant bulk density and Isp.

High performance (closed cycle).

Very attractive for reusable

applications. Easlier MR and

thrust level throttling

characteristics.

High performance (closed cycle). Simplier than

multi preburner options to left.

Very attractive for reusable

applications

Simple cycle, low production costs, easlier to develop

High reliability, benign failure

modes (containted), simple cycle

Simple cycle with fewer parts, lower production costs,

easier maintainability

Disadvantages

Essentially 2 engines in one.

Very complex and difficult to

develop. Very costly to produce. Production cost makes reusable

applications manditory.

Vehicle must be very performance

driven such as SSTO.

Most difficult to develop. Will be very expensive. Production cost makes reusable

applications manditory.

Vehicle must be very performance

driven such as SSTO.

More difficult to develop than

single PB. Tends to be very expensive.

Failure modes tend to be more

involved. Production cost makes reusable

applications almost manditory.

More difficult to develop. Tends to

be more expensive.

Failure modes tend to be more

involved.

Lower performance

because of open cycle.

Performance level makes this

unattactive for most reusable applications.

Limited to LOX/LH2

propellants only. Limited

performance because of heat

transfer limitations.

Hot gas duct that taps off from the MCC and mixes dilluent fuel to regulate gas temperature.

Lower performance (Open cycle).

Potential Applications

Reusable SSTO. Reusable SSTO.Booster or

upperstage, reusable rockets

Booster or upperstage, reusable or expendible

rockets (May depend on propellant choices)

Booster or upper stage, expendible

rockets

Booster or upperstage, reusable or expendible

rockets

Booster or upper stage, expendible

rockets

Example Exercise

• Application: Expendable launch vehicle using LOX/ RP-1 for the booster engine. Vehicle needs relatively high performance (Isp > 310 sec vacuum). Using the trade tree below, select the appropriate engine cycle and provide your rationale. Use the data provided earlier in this presentation to justify your rationale.

Engine Cycle Trade

GG cycle Expander Tapoff Staged Combustion

Fuel Rich GG

Ox Rich GG

RP-1 Cooling

Lox Cooling

Fuel Rich Single PB

Ox Rich Single PB

Full Flow Dual PB

Fuel Rich Dual PB