Overview

Selecting the fuel and oxidizer combination is one of the most important parameters in bi-propellant liquid rocket engine development. This combination is oftentimes referred to as the propellant combination. This selection will be the most important parameter for engine sizing, engine performance, and a multitude of other design, engineering, and operations considerations.

Caveats

This document will focus exclusively on bi-propellant systems. Many groups, including amateurs, will use some of the propellants discussed here for other propulsion systems such as hybrids, tri-brids, tri-propellant liquids, etc. The technical considerations for these engines differ from those discussed here. Moreover, the decision to use a bi-propellant architecture is a complex one that will not be discussed here, it will be assumed that a bi-propellant system is being used when discussing engineering or other considerations. Lastly, some engines will use fuel additives, such as PDMS, for thermal insulation. This is not a propellant and will not be discussed here.

Derived Requirements for Propellant Combination

This engine is subject to numerous requirements. Some of these come from our “governing bodies” i.e. the CPLC rules and Rose-Hulman rules. Both of these groups allow for leniency but they must allow us to use the propellant combination we select.

Requirements:

Oxidizer

Oxidizers make up the most exciting (and dangerous) of the three sides of the fire triangle. Table 1 lists most of the oxidizers used by both amateurs and industry. Note that many of these were not seriously considered but are listed for the sake of completeness.