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Chemical Rockets Performance and propellants. Niklas Wingborg FOI, Energetic materials. Principle of rocket engines. Combustion chamber Nozzle. Throat Exit. Principle of rocket engines. De Laval nozzle.
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Chemical Rockets Performance and propellants Niklas Wingborg FOI, Energetic materials
Principle of rocket engines Combustion chamber Nozzle Throat Exit
Principle of rocket engines De Laval nozzle M<1 M=1 M>1 Tc Tt<Tc Te<Tt
Gustav de Laval, 1845-1913 1883 AB Separator → Alfa Laval 1893 AB de Lavals Ångturbin → Stal-Laval AB →ALSTOM Sverige AB
Rocket propellant classification Fuel + oxidizer gas + energy • Propellant = fuel + oxidizer • Liquid propellants • Bipropellant (storable, non-storable, hypergol) • Monopropellant • Solid propellants
Propulsion systems in the Ariane 5 Upper stage with storable propellants and Aestus engine Solid propellant booster Cryogenic main core stage Vulcain engine
Propellant performnace • Propellant content: up to 90% • Not unusual with 50% • The performance of the propellant very important • Propellant figure of merit: Specific impulse, Isp • Isp unit: Ns/kg, m/s or s
Specific impulse, Isp • Optimum mixture oxidizer/fuel high Tc • High heat of formation, ΔHf high Tc • High hydrogen content low M CO2 44 g/mol CO 28 g/mol N2 28 g/mol H2O 18 g/mol H2 2 g/mol
Calculation of specific impulse • Nozzle/chamber • Pressure in combustion chamber, pc • Nozzle expansion • Pressure ratio: pc/pe • Area ratio: Ae/At • Chemical equilibrium or frozen equilibrium • Propellant • Chemical composition of fuel and oxidizer • Heat of formation of fuel and oxidizer • Mixing ratio fuel/oxidizer
Thermochemical computation • Computer programs for calculation of thermochemical equilibrium and Isp • NASA CEA (chemical equilibrium with applications) • NASA Reference Publication 1311 (June 1996) • Equation of state: ideal • Chemical equilibrium minimizing ΔG = ΔH-TΔS • CEA can be obtained for free • http://www.grc.nasa.gov/WWW/CEAWeb/ • http://www.openchannelsoftware.com/projects/CEA
Common liquid rocket propellants • Oxidizers • Liquid oxygen, O2 • Dinitrogen tetroxide, N2O4 • Nitric acid, HNO3 • Hydrogen Peroxide, H2O2 • Fuels • Liquid hydrogen, H2 • Hydrazine, N2H4 • Monomethylhydrazine • Methane • Unsymetrical dimethylhydrazine • Kerosene • Ethanol
Liquid oxygen (LOX), O2 • Non storable oxidizer • Nontoxic • Mp= -219oC, Bp = -183oC • Used in combination with H2, kerosene, ethanol • Density = 1.14 g/cm3
Dinitrogen tetroxide (NTO), N2O4 • Widely used storable oxidizer • Different percentages (1-3%) of nitric oxide, NO, added as stress corrosion inhibitor (MON-1 and MON-3) • MON-1 and MON-3 are used more often than pure NTO • Bp= 21°C, Mp=-11°C, dens=1.43 g/cm3
Dinitrogen tetroxide (NTO), N2O4 • Safety concerns • Concern about reactivity of MON with titanium alloys, ignition by friction on freshly formed surfaces (e.g., pyrovalves). • History of accidents • Toxicity of vapor clouds in case of launch mishaps • State governments impose restrictions on transportation of NTO/MON • Space agencies have considered manufacturing NTO (and other toxic fuels) at the launch site to alleviate transportation restrictions
Liquid hydrogen, H2 • Non storable cryogenic fuel, Mp= -259oC, Bp = -253oC • Used in combination with LOX • Density = 0.07 g/cm3 bulky fuel tank • Material problems brittle at low temperature • Air / H2 explosive
Hydrazine, N2H4 • Can be used as a bipropellant fuel and as a monopropellant • Thermally unstable and cannot be used as a regenerative coolant in bipropellant engines • As a fuel, it is hypergolic with many oxidizers • Positive enthalpy of formation (+50.434 kJ/mol =+12.05 kcal/mol, liquid at 298 K) • Bp= 114°C, Mp=+2°C, dens= 1.00 g/cm3
Hydrazine, N2H4 • Hydrazine toxicity concerns • Acute toxicity: short-term exposure • Chronic toxicity: long-term exposure • Volatile • Carcinogen
Monomethylhydrazine (MMH), H3C-NH-NH2 • Frequently used storable, hypergolic bipropellant fuel for satellites and upper stages • Can be used as a regenerative coolant in bipropellant engines • Low freezing point (-52°C) • Density = 0.87 • Concern about toxicity of vapors (more volatile than hydrazine itself), Bp= +88°C
AMSAT P3-D Launch Campaign Kourou MMH filling operation N2O4 filling operation http://www.amsat-dl.org/launch
Aestus: Ariane 5 upper stage engine • Fuel: MMH • Oxidizer: N2O4 • MMH regenerative cooling • Multiple re-ignition capability • Thrust: 3 tons • Engine mass: 120 kg • Length: 2183 mm
Rocket engine design Injector Chamber At Lc Ae
Injector face Mass flow and mixing diameter of chamber
Characteristic velocity, c* • Depends on the properties of the propellant • Unit: m/s (but it is not a velocity) • Independent of pressure (as long the reactions don't change) • CEA c* • c*-efficency; ratio between calc. and measured c*
Characteristic velocity, c* UDMH / HNO3
Rocket engine design: summary • Propellant • Thrust, pressure and Ae/At • CEA Isp, c* • Massflow • c* and massflow At Ae • Injector and massflow Ac • Propellant Lc
Solid rocket motors Igniter Nozzle Case with propellant
Solid propellants • Solid mixture of oxidizer and fuel • Oxidizer: Ammonium perchlorate (AP), NH4ClO4 • Rubber binder matrix: HTPB • Fuel: Aluminium powder • Burns on the surface • Burn time determined by the smallest dimension
Solid propellant geometry • The case is protected by the propellant • Shape of combustion channel pre-programmed pressure and thrust profile
Combustion of solid propellants Piece of solid propellant: 10x20x50 mm
Combustion of solid propellants Small pices of propellants
Combustion of solid propellants • Small pieces burn fast • The combustion proceeds perpendicular to the surface • Gas generation proportional to burning surface and burning rate, r
Combustion of solid propellants • r measured at different pressures • a and n calculated In this case at atmospheric pressure
Combustion of solid propellants n must be < 1, preferably 0.5 or lower
Combustion of solid propellants • r is altered by the initial temperature. A warm propellant burn faster T2 > T1 T2 T1 pressure time
Solid propellant mechanical properties • Cracks in the propellant > Ab > pc • Might lead to failure • Good mechanical properties is important • Must be elastic • Tg < minimum service temperature • Good bonding to case important • Debonding > Ab > pc
Manufacturing composite solid propellants • Liquid rubber (HTPB), AP and Al are mixed under vacuum • When properly mixed a curing agent is added • Continued mixing • Cast in mould to obtain desired shape • Cured at elevated temperatures • Mould = rocket motor • Machining • Final charge X-rayed to detect cracks, voids etc
~80% Isp (Ns/kg) % AP Manufacturing composite solid propellants • Not possible to obtain maximum theoretical Isp • Isp limited by viscosity • AP particle size: bimodal or trimodal
Composite solid propellants • Large amount of smoke is formed • AP HCL hydrochloric acid • Shuttle ~600 tons conc. hydrochloric acid • Ariane-5 ~300 tons conc. hydrochloric acid
Current trends • Green solid propellants to replace AP (ADN, AN, HNF) • Green cryogenic solid propellants • Green oxidizers (N2O, H2O2) • Hypergolic rocket fuels to replace hydrazine and MMH • Green monopropellants to replace hydrazine • Exotic molecules, HEDM (N4, N8)
Why is smoke a concern? NC-baserat AP/Al/HTPB
Ammonium dinitramide, ADN • Solid white salt • Intended for solid propellants • No chlorine content • Minimum smoke • High performance • Very soluble in water (80% at RT) • Synthesis developed at FOI • Produced on license by EURENCO Bofors in Sweden NH4·N(NO2)2
Solid propellant testing at FOI Testing of missiles for the Swedish defense