Oxidizerfuel

An oxidizer-fuel propulsion system, often referred to as a bipropellant system, is a chemical rocket configuration in which the oxidizer and the fuel are stored separately and combined in a combustion chamber to produce thrust. The oxidizer supplies the oxygen needed for combustion, enabling propulsion in environments with little or no atmospheric oxygen, including space.

In bipropellant engines, the oxidizer and fuel are injected and combusted in the chamber. Common oxidizers include liquid oxygen (LOX), nitrogen tetroxide (N2O4), and hydrogen peroxide, while common fuels include kerosene (RP-1), liquid hydrogen, and methane. Some propellants are hypergolic, igniting on contact to simplify engine start and reliability of ignition systems.

Monopropellants use a single chemical that decomposes to hot gas, usually with a catalytic bed, without an external oxidizer. Concentrated hydrogen peroxide is a typical monopropellant. In contrast, hypergolic bipropellants—such as hydrazine derivatives combined with certain oxidizers—ignite spontaneously upon mixing, enabling reliable restart and simple ignition sequences.

Performance is described by specific impulse (Isp) and thrust, with hydrogen-oxygen (LH2/LOX) systems offering high Isp but requiring cryogenic storage; kerosene-oxygen (RP-1/LOX) provides simpler handling but lower Isp. The mixture ratio—proportion of oxidizer to fuel—affects efficiency, pressure, and thrust, and it is tuned for a given engine design.

Oxidizer–fuel propellants are used in rocket stages, maneuvering thrusters, and missiles, with ongoing research addressing safer handling, higher performance, and reduced cost, including methane-based and LOX/methane systems for reusable launch vehicles.