Rocket Specific Impulse vs Jet Engine Specific Impulse

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SUMMARY

The discussion clarifies that jet engines exhibit a higher specific impulse compared to rockets primarily due to their larger effective exhaust velocities. While rockets carry their own oxidizers, which affects their specific impulse calculations, jet engines utilize atmospheric oxygen, allowing for a more efficient combustion process. The distinction between actual and effective exhaust velocity is crucial, as it can vary significantly for jet engines, impacting their performance metrics.

PREREQUISITES
  • Understanding of specific impulse in propulsion systems
  • Knowledge of exhaust velocity and its impact on engine performance
  • Familiarity with rocket and jet engine operation principles
  • Basic grasp of oxidizers and their role in combustion
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  • Research the differences between effective and actual exhaust velocity in propulsion systems
  • Explore the role of oxidizers in rocket propulsion and their impact on specific impulse
  • Study the thermodynamics of jet engines and their efficiency compared to rockets
  • Investigate the implications of specific impulse on mission design for space travel
USEFUL FOR

Aerospace engineers, propulsion system designers, students of aerospace technology, and anyone interested in the comparative performance of rocket and jet engines.

Juhannuskokko
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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.
 
Science news on Phys.org
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.
 
Dr. Courtney said:
jets have much larger exhaust velocities

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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