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Rocket Specific Impulse vs Jet Engine Specific Impulse

  1. Jul 24, 2015 #1
    I really can't seem to wrap my head around why the specific impulse on a rocket is so much lower than that on a jet. I know a jet engine has a larger supply of oxygen, but I don't see why that has such a huge effect.
    I also know exhaust velocity plays a large part, but I would have thought that a rocket has higher-velocity exhaust.
     
  2. jcsd
  3. Jul 24, 2015 #2
    https://en.wikipedia.org/wiki/Specific_impulse

    The bigger part is that jets have much larger exhaust velocities. A small part is that rockets carry their own oxidizers, so the mass includes the oxidizer in rocket specific impulse calculations, but not jet engine specific engine calculations.
     
  4. Jul 24, 2015 #3

    PeterDonis

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    2016 Award

    Staff: Mentor

    I think you mean effective exhaust velocity, not actual exhaust velocity, correct? As the Wikipedia article you linked to notes, the two can differ for jet engines by orders of magnitude.
     
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