Transcript Rocket Engines - Troy University
• Liquid Propellant – Mono propellant • Catalysts – Bi-propellant • Solid Propellant – Grain Patterns • Hybrid • Nuclear • Electric
Performance Energy Safety Simplicity Expanding Gases Thrust Termination Restart
Liquid Rocket Engine
Oxidizer Fuel Propellants Combustion Chamber Throat Nozzle
The force required to accelerate a body is proportional to the product of the mass of the body and the acceleration desired.
F = ma m =
F a F
• Thrust is produced by the expanding propellants.
• There is thrust from the difference between the ambient pressure and that of the exhaust gases at the nozzle exit ( Pressure Thrust ) and from the momentum of the propellants ( Momentum Thrust ).
Total Thrust = Momentum Thrust + Pressure Thrust Propellant Mass Flow times Velocity Nozzle Area times pressure differential .
W F = + A g V e e ( P e - P a )
Exhaust Plumes and Nozzles
P exhaust < P ambient Under Expanded P exhaust = P ambient Ideal Expansion P exhaust > P ambient Over Expanded
• Ratio of the nozzle exit area divided by the area at the nozzle throat.
= A e A t Throat Exit
• A measure of the energy in the propellants and of the efficiency of the rocket engine design • Specific Impulse is the ratio of the Thrust (Force) produced divided by the weight rate flow of propellants
I sp = W F .
Mass Ratio of a Vehicle Mass Ratio is the ratio between the booster mass before the rocket engine burn divided by the booster mass after rocket engine burn.
MR = m i m f The Mass Ratio for a multistage rocket is the product of the Mass Ratios of all the stages, i.e.
MR Over All = MR 1 x MR 2 x MR 3 x …x MR n
• Measure of booster or stage design and manufacturing technology.
= Thrust Vehicle Weight = F W
• The higher the thrust-to-weight ratio the faster the vehicle will accelerate • The initial acceleration of a vehicle in “g’s” equals
= ( Y - 1 )
Ideal Rocket Equation
• The ideal velocity change ( D
) for each stage of a rocket is a function of the mass ratio (
) of the stage and the specific impulse (
) of the rocket D
V i = I sp
• Ideal means you do not consider gravity changes, drag, or rotating Earth