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Lesson 6: Principles of Thermochemistry

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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Lesson 6: Principles of Thermochemistry

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  1. Lesson 6: Principles of Thermochemistry Dr. Andrew Ketsdever

  2. 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

  3. Liquid Propellants • Desirable Properties • Low Freezing Point • High Specific Gravity • Good Stability • High Specific Heat • Low Vapor Pressure (better pumping) • Easy Ignition (hypergolic?)

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. Liquid Propellants • Fuels • Hydrocarbon Fuels • RP-1 (Kerosene-like) • Easy to handle • Cost effective • Methane (CH4) • Cryogenic (denser than liquid hydrogen)

  10. 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)

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. Nuclear Propellants • Fuels • Low molecular weights • Hydrogen, Water, Methane • No chemical reactions necessary

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