lecture11 - MECH 7221 MECH 6251/498D Solid Propellant...

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MECH 7221 Solid Propellant Rocket Engine Systems • Overview of basic component in solid rocket engine systems • solid propellant choices Reading assignment: Sutton and Biblarz Chapter 11 and 12 Objective
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Solid Rocket Engine Systems Unlike liquid rocket engines, the fuel and oxidizer are premixed in solid rocket. The result is a rubbery solid that burns when heated. Solid propellant rockets • are simpler and cost less than liquid-fueled rockets • have lower I sp than most liquid (~I sp 285 sec) • are more dense -> higher “density impulse” ρ I sp , so packaging is easier • Thrust is limited by nozzle size – not by pump capacity. Easy to get very high thrust to boosters. • Cannot be throttled or shut down during the flight (unless pre-designed to do so)
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Application for SRM • Strap-on boosters for space launch vehicles (high thrust per size) • Upper stage propulsion system for orbital transfer vehicles (OTV) • Strategic and tactical missile propulsion systems (acceleration, storage) • Jet-assisted-takeoff (JATO) units on early aircraft • Gas generators for starting liquid engines and pressurizing tanks • Attitude control propulsion systems • Apogee kick motors
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Solid Propellant Rocket Hardware
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Propellant Burn Rate St. Robert’s Law [m/s] n c b ap r = The propellant burn rate is the rate at which the exposed propellant surface is consumed. (it is measured as distance normal to surface consumed in a given time.) Solid Rocket Motor Definitions: Burn rate Coefficient:: a Burn rate exponent: n Typical values: 0.1-5 cm/s Determined experimentally! dt dx r b = (also called Veille's law)
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Propellant Burn Rate St. Robert’s Law [m/s] n c b ap r = Important: • Firing motors with different throat sizes, burn rate is obtained as a function of different chamber pressure. • Burn rate is an empirical representation and doesn’t address complex thermo- chemical and combustion processes. Regression rate proportional to pressure to some n
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• Propellant Burn rate is extremely sensitive to exponent, n • Stable operation requires 0.001 < n < 0.990 • High values of n make for a propellant whose burn rate is sensitive to chamber pressure Propellant Burn Rate
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Solid Rocket Example r = aP o n • careful with units on a Ref: Sutton and Biblarz, Chapter 11
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Solid Rocket Example Solid Propellant Saint Robert's Curve Fit (P 0 -psia, - in/sec) Propellant Name n a (in/sec-psia^n) Composite Ammonium Nitrate, -40F 0.463474 0.002965 Composite Ammonium Nitrate, 60F 0.445084 0.003909 Composite Ammonium Nitrate, 140F 0.426803 0.005243 High Energy XLDB Composite 0.720473 0.002293 Composite Ammonium Perchlorate, -30F 0.187867 0.072001 Composite Ammonium Perchlorate, 60F 0.170286 0.094044 Composite Ammonium Perchlorate, 150F 0.172255 0.107348 JPN-type Double Base, 10F
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lecture11 - MECH 7221 MECH 6251/498D Solid Propellant...

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