Lesson 6 principles of thermochemistry
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Lesson 6: Principles of Thermochemistry. Dr. Andrew Ketsdever. Propellants. Several Factors Must Be Addressed When Deciding on a Propellant Performance Chemical energy content, Achievable Isp Economics Availability, logistics of production and supply Physical Hazards

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Propellants l.jpg
Propellants

  • Several Factors Must Be Addressed When Deciding on a Propellant

    • Performance

      • Chemical energy content, Achievable Isp

    • Economics

      • Availability, logistics of production and supply

    • Physical Hazards

      • Stability, corrosiveness, carcinogens


Liquid propellants l.jpg
Liquid Propellants

  • Desirable Properties

    • Low Freezing Point

    • High Specific Gravity

    • Good Stability

    • High Specific Heat

    • Low Vapor Pressure (better pumping)

    • Easy Ignition (hypergolic?)


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Liquid Propellants

  • Highest Potential Specific Impulse

    • Fluorine Oxidizer

    • Hydrogen Fuel with suspended Beryllium

    • Isp=480 sec at Po = 1000 psia (sea level)

    • Oxidizer highly corrosive (not storable)

    • Beryllium suspension can not be maintained uniformly


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Liquid Propellants

  • Oxidizers

    • Liquid Oxygen

      • Boils at 90K

      • Heat of Vaporization 213 kJ/kg

      • High attainable performance

      • Does not burn spontaneously with hydrocarbons at ambient pressures and temperatures

      • Noncorrosive and nontoxic

      • Cryogenic temperature poses handling issues


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Liquid Propellants

  • Liquid Fluorine

    • Boils at 53.7K

    • Highest values of performance (typically)

    • High specific gravity

    • Extremely toxic and corrosive

    • Poisonous exhaust gases

    • Low commercial consumption

    • Expensive


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Liquid Propellants

  • Hydrogen Peroxide (H2O2)

    • Requires high concentration (70-99%)

    • Storage concerns

    • Decomposition with certain metal catalysts

  • Nitric Acid (HNO3)

    • Highly corrosive

    • Certain stainless steels and gold containers required

    • Skin burns


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Liquid Propellants

  • Nitrogen Tetroxide (N2O4)

    • Most common storable oxidizer used in the US

    • High density

    • Relatively high freezing point

    • Mildly corrosive

    • Hypergolic with many fuels

    • High vapor pressure

    • Used with hydrazine (UDMH, MMH) propellants


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Liquid Propellants

  • Fuels

    • Hydrocarbon Fuels

      • RP-1 (Kerosene-like)

        • Easy to handle

        • Cost effective

      • Methane (CH4)

        • Cryogenic (denser than liquid hydrogen)


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Liquid Propellants

  • Liquid Hydrogen

    • Boils at 20K

    • Specific Gravity 0.07

    • Bulky fuel tanks, large volumes

      • Increased drag

    • Feed system must be cryogenic compatable

    • Increased insulation

    • Nontoxic products (typically)


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Liquid Propellants

  • Hydrazine

    • Monomehtylhydrazine (MMH)

    • Unsymmetrical dimethylhydrazine (UDMH)

      • Toxic

      • High freezing point 274.3K (MMH) / 216K (UDMH)

      • Hypergolic with some oxidizers

      • Spontaneous ignition with air can occur

      • Positive heat of formation (good)

      • Good monopropellants with the right catalyst

      • Reasonable stability


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Solid Propellants

  • Classes

    • Double Base Propellant: forms a homogeneous propellant grain of a nitrocellulose and a solid ingredient dissolved in nitroglycerin plus minor additives

    • Composite Propellant: form a heterogeneous propellant grain with the oxidizer crystals and a powdered fuel held together in a matrix of synthetic rubber binders.

      • Less hazardous than double base


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Solid Propellants

  • Oxidizers

    • Ammonium Perchlorate (NH4ClO4)

      • Most widely used crystalline oxidizer

      • Good performance

      • Good availability

    • Potassium Perchlorate (KClO4)

      • Medium performance

      • Higher density than AP

      • Low burning rate


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Solid Propellants

  • Fuels

    • Powdered Aluminum

      • 5-60 micron diameter

      • 14-18% of propellant by weight (typical)

      • Small particles can burn spontaneously in air

      • Oxide particles can agglomerate and form larger particles (two phase issues)

    • Other metallic fuels

      • Boron, Beryllium


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Solid Propellants

  • Binders

    • Hydroxy Terminated Polybutadiene (HTPB)

      • Binder provides the structure or matrix in which solid ingredients are held together (composite propellant)

      • Polymer, synthetic rubber

      • Primary effect on motor reliability, storability and cost

  • Other Additives can be included

    • Improve burn rate, storability, curing


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Hybrid Propellants

  • Fuel and Oxidizer mixtures of liquid oxidizer and solid propellants (typically)

    • Combinations of propellants already discussed

    • Fuel: HTPB, PMMA, HS

    • Oxidizer: LOx, H2O2, N2O


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Nuclear Propellants

  • Fuels

    • Low molecular weights

      • Hydrogen, Water, Methane

    • No chemical reactions necessary


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