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Variable Name

Symbol

Value & Units

Description

Methodology

Chamber Pressure

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bodyP_{c}

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body2500~\textrm{kPa}

Pressure of the chamber, measured at the injector.

One of two initial values, driven by metallurgy and COTS valves/fittings.

Thrust

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bodyF_{t}

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body2500~\textrm{N}

Thrust of the engine!

Second of the two initial values, driven by competition requirements and simulations.

Mass Flow Rate

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body\dot{m}

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body1.1~\textrm{kg/s}

Mass flow rate through the engine. Mass is conserved so

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body\dot{m}
is the same at the injector, throat, and nozzle exit.

The Matlab engine sizing program interates through various

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body\dot{m}
values until the correct thrust is achieved.

Exhaust Pressure

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bodyP_{e}

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body100~\textrm{kPa}

Pressure of the exhaust. In the ideal case

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bodyP_{e}=P_{atm}
, if
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bodyP_{e} > P_{atm}
engine is “underexpanded” and vice-versa.

We design around the ideal case (

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bodyP_{e}=P_{atm}
). Some groups/teams may size for
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bodyP_{e} > P_{atm}
to avoid backflow.

Mass Ratio (also called Mass Fraction or Oxidizer Fuel Ratio (OF))

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body\mathit{MR}

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body4~4.5~\textrm{(unitless)}

Ratio, by mass, between propellants.

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