Rockets#
This section introduces the CT-ROCKET module for computing the performance of chemical rocket propulsion systems using a one-dimensional flow approximation. The schematic in Fig. 17 depicts the physical components considered in this analysis:
Injector (inj), where propellants are introduced at negligible velocity.
Combustion chamber (c), a region of constant cross-sectional area \(A_c\), bounded by an adiabatic wall.
Converging nozzle section (c-t), with decreasing area \(A(x)\), which accelerates the subsonic flow toward the throat.
Throat (t), the location of minimum area \(A_t\) where the flow becomes sonic.
Diverging nozzle section (t-e), with increasing area \(A(x)\), which enables supersonic expansion and thrust generation.
Fig. 17 Schematic of a chemically reacting rocket flow including chamber, throat, and expanding nozzle.#
The solver is implemented in the RocketSolver class and provides tools to evaluate the idealized performance of a propellant system under a set of simplifying assumptions:
One-dimensional flow.
Uniform cross-sectional area in the chamber.
Negligible inlet velocity at the injector.
Infinitely fast chemistry at injection.
Adiabatic combustion.
Isentropic expansion through the nozzle.
Homogeneous mixture (no slip or temperature difference between phases).
Ideal gas equation of state.
Continuity of temperature and velocity between gaseous and condensed species.
Thermochemical states are handled through the CT-EQUIL module. The formulation follows the methodology originally developed in NASA’s CEA code [Gordon and McBride, 1994], while the implementation and validation of CT-ROCKET within Combustion Toolbox are discussed in [Cuadra et al., 2026].
Two limiting cases are supported through RocketSolver:
ROCKET_IAC- Infinite-area-chamber approximation (IAC): Isentropic combustion process.ROCKET_FAC- Finite-area-chamber approximation (FAC): Entropic combustion process.
These models allow for rapid estimation of propulsion performance, including the characteristic velocity (\(c^*\)), thrust coefficient (\(C_F\)), and specific impulse (\(I_{\text{sp}}\)), while accounting for chemical equilibrium, composition-dependent thermodynamics, and finite expansion effects.
The two formulations differ in how the combustion chamber is modeled:
In the IAC model, the chamber is treated as infinitely large. The combustion process is therefore modeled as an isobaric equilibrium transformation, followed by an isentropic acceleration toward the throat and nozzle exit.
In the FAC model, the chamber has a finite cross-sectional area. The flow accelerates inside the chamber, so the injector, chamber outlet, and throat states must be determined consistently.