Chapter 1: Parts Of A Rocket Engine

Before getting into equations or other concepts, we must first define some parts of the rocket engine and the notation that we will use.

In the image above you can see a typical rocket engine with its different parts and with some notation that we will explain below.


Credit: @destebafabrega (DailySpace)

We can see mainly two parts:

  • Chamber: The chamber is the place where the combustion of the propellant (fuel & oxidizer) takes place. The result of this combustion are very hot gases (from 2,500 K to 3,500 K) at high pressures (10 to 300 bar).
  • Nozzle: The nozzle is the place where the really hot gases at high pressures from the combustion chamber are expanded to very high velocities (supersonic). As you can see in the image, the nozzle is made up of 3 parts:

    • Converging section: Area becomes smaller as we go forward.
    • Throat: Minimum area.
    • Diverging section: Area becomes bigger as we go forward.

    In the next chapters we will see why the nozzle is made up of these 3 parts.
    WHAT IS AN EXPANSION?
    Here expansion refers to the process where the pressure and temperature of the gases will decrease as their speed is increased.
    WHAT DOES SUBSONIC, SONIC AND SUPERSONIC MEAN?
    When the speed of an object is smaller than the speed of sound, we say the object is subsonic, when the speed is the same as the speed of sound is called sonic and when the speed of the object is greater than the speed of sound is supersonic.

Here the notation used is at follows:

  • Subindex 1: All the magnitudes with subindex 1 refer to magnitudes from the chamber.
    E.g. P1, T1 or A1
  • Subindex t: All the magnitudes with subindex t refer to magnitudes from the nozzle throat.
    E.g. Pt, Tt or At
  • Subindex 2: All the magnitudes with subindex 2 refer to magnitudes from the nozzle exit.
    E.g. P2, T2 or A2
  • Subindex 3: All the magnitudes with subindex 3 refer to magnitudes from the medium that surrounds the engine, usually the atmosphere or vacuum.
    E.g. P3 or T3

That's all for the first post of this series!


Written by David Esteba Fàbrega on 2020-06-18.

TEST YOURSELF WITH THIS SURVEY!

What is the narrowest part of a rocket engine?

  • Chamber
  • Nozzle entry
  • Throat
  • Nozzle exit

EXPLANATION

The narrowest part of a rocket engine is the throat.

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What is the notation used for the throat pressure?

  • P1
  • P2
  • P3
  • Pt

EXPLANATION

As we have seen, we will use Pt for the pressure at the throat.

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What is the notation used for the chamber temperature?

  • T1
  • T2
  • T3
  • Tt

EXPLANATION

As we have seen, we will use T1 for the temperature at the chamber.

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What is the notation used for the exit area?

  • A1
  • A2
  • AExit
  • A3

EXPLANATION

As we have seen, we will use A2 for the exit area.

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