MAE 112 PROPULSION FINAL EXAM March 25, 2004 Do all three problems in 120 minutes. Books, notes and calculators can be used freely. 1. Consider a combination of rocket propellants with a specific impulse (I sp ) of 300 seconds for expansion from a pressure of 20 atmospheres in the combustion chamber to a Mach number of 3.5 at the nozzle-exit, with the value of γ = 1.2 and the ambient-pressure value of zero. Assume 100% polytropic efficiency for the nozzle expansion. The combustion product has an average molecular weight of 30. Calculate (a) the thrust coefficient, C F (C T in Hill and Peterson), and the characteristic velocity, c*; (b) the combustion chamber temperature; and (c) the mass-flow rate of propellants necessary to produce 100,000 pounds of thrust. (d) Consider now that the convergent-divergent nozzle is replaced by a nozzle that only has the convergent section with choked flow at the exit. Calculate the new value of I sp . 2.
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