Liquid Propellant Rocket Engines

INTRODUCTION

  • Liquid propellant rocket propulsion systems include:

    • Rocket engine

    • Tanks for storage and supply of propellants

  • Components required for operation to produce thrust:

    • Thrust chambers

    • Feed mechanism

    • Power source

    • Plumbing/piping

    • Control devices (e.g., valves)

  • Propellants can be delivered via high-pressure gas or pumps to thrust chambers.

CATEGORIES OF LIQUID PROPELLANT ROCKET ENGINES

  1. Boosting engines - Impart significant velocity increase to payloads

  2. Auxiliary propulsion - For trajectory adjustments and attitude control:

    • Cold gas jets

    • Warm gas jets

    • Chemical combustion gases

CLASSIFICATIONS OF LIQUID PROPELLANT ROCKET ENGINES

  1. Reusable engines (e.g., Space Shuttle main engine)

  2. Single flight engines (e.g., expendable launch vehicles)

  3. Restartable engines (e.g., reaction control engines)

  4. Single firing engines

MAJOR COMPONENTS OF CHEMICAL ROCKET ASSEMBLY

  • Body frame/structural system

  • Propulsion system:

    • Rocket motor/engine

    • Propellant

  • Control and guidance systems

  • Payload system

PROPELLANTS

  • Working substance of rocket engines, can be categorized as:

    1. Oxidizers (e.g., liquid oxygen, nitrogen tetroxide)

    2. Fuels (e.g., kerosene, liquid hydrogen)

    3. Monopropellants (e.g., hydrazine)

TYPES OF LIQUID PROPELLANTS

  1. Anergolic - Requires outside ignition source

  2. Hypergolic - Ignites spontaneously upon contact

  3. Cold gas - High-pressure ambient gases, low performance

  4. Cryogenic - Stored at low temperatures (e.g., liquid oxygen, hydrogen)

  5. Petroleum-based - Derived from crude oil

  6. Storable - Remain liquid in ambient conditions

  7. Gelled - Thixotropic liquids that don’t spill easily

COMMON PHYSICAL HAZARDS

  1. Corrosion - From certain propellants, requiring specific coatings

  2. Explosion - Risks with certain unstable compounds

  3. Health hazards - Many propellants are toxic (e.g. Hydrazine)

  4. Accidental Spills - Unforeseen mishaps

  5. Health Hazard-

  6. Material Compatibility -

DESIRABLE PHYSICAL PROPERTIES OF PROPELLANTS

  1. Low freezing point

    - The addition of small amounts of special chemicals has been found to help depress the freezing point

  2. High specific gravity

    - a dense propellant is required

  3. Stability over long-term storage

    - No deterioration and no decomposition with long-term (over 15 years)

  4. High heat transfer properties

  5. Minimal temperature variation impact

  6. Good pumping properties (low vapor pressure)

,.S OF LIQUID PROPELLANT ROCKET ENGINES

  1. Thrust Chamber:

    • Combustion device for burning propellants

    • Cooling mechanisms necessary due to high temperatures

    • The thrust chamber has three major parts:

      • Injector/s

        • To introduce and meter liquid propellant flows into the combustion chamber.

        • To break up liquid jets into small droplets (a process called atomization)

        • To distribute and mix the propellants

      • Combustion Chamber

        • portion of the thrust chamber where nearly all propellant burning takes place

      • Propellant Tanks

        • vehicle’s center of gravity

        • with an impervious thin inner liner of metal to prevent leakage

        • Ullage - A necessary space that allows for thermal expansion of the propellant liquids (3 and 10% of tank volumes)

      • Supersonic Nozzle

      • Various Mounting Provisions

INJECTOR TYPES

  • COAXIAL

    • simplest type is rather like a shower head, except the adjacent holes inject fuel and oxidant so that the propellants can mix

  • PARALLEL

    • each orifice has the fuel injected through an annular aperture which surrounds the circular oxidant aperture, and this is repeated many times to cover the area of the injector

  • IMPINGING JET UNLIKE-PROPELLANT INJECTOR

    • designed to make sure that propellants mix as early as possible, while still in liquid phase, and is useful for hypergolic propellant combinations.

  • IMPINGING JET LIKE-PROPELLANT INJECTOR

    • jets of the same propellant impinge on one another and is useful where fine holes are not suitable. T

COOLING OF THRUST CHAMBERS

  • Methods:

  1. Regenerative cooling

  2. Radiative cooling

  3. Film cooling

  4. Heat sink cooling

    • a simple all-metal chamber (steel, copper, stainless steel, etc.) made with walls sufficiently thick to absorb the required heat energy, often used for the short duration

  5. Ablative cooling

    • series of strong, oriented fibers (such as glass, Kevlar, or carbon fibers) engulfed by a matrix of organic binder materials

  6. Sweat cooling

    • coolant through pores

  7. Dump cooling

    • dumped overboard at the aft end of the nozzle.

SEVERAL CATEGORIES OF TANKS IN LIQUID PROPELLANT PROPULSION SYSTEMS

  1. Pressurized Feed Systems

    • 1.3 and 9 MPa or about 200 to 1800 psi.

    • Such tanks have thick walls and are heavy.

  2. High-pressure Stored Gases

    • 6.9 and 69 MPa or 1000 to 10,000 psi.

    • Usually spherical for minimum inert mass.

PROPELLANT TANKS-PIPING

  • the amount of propellant that can be expelled or available for propulsion divided by the total amount of propellant initially present.

  • 97 to 99.7%.

LIQUID PROPELLANT FEED SYSTEMS

  1. to raise the pressure of the propellants

  2. to supply them at design mass flow rates to one or more thrust chamber

    • Gas Pressure Feed System – one of the simplest, most common, and very reliable means by displacing propellants with high-pressure gas.

    • Turbo Pump Feed System – the propellant is pressurized by pumps driven by gas turbine and finally displaced into the combustion chamber. • Turbo Pump – combination of pump and turbine

2E1NGINE CYCLES

  • Open Cycle:

    • Working fluid from turbine discharged into nozzle

  • Closed Cycle:

    • All working fluid injected into combustion chamber for efficiency

    • Types include Expander Cycle and Staged Combustion Cycle