prometheus-equilibrium 0.1.3

Combustion equilibrium solver for Python

Prometheus

Prometheus is an open-source Python package for chemical equilibrium and rocket-combustion analysis. It parses multiple thermo-data formats, builds a unified species database, and solves equilibrium problems such as adiabatic chamber combustion (HP) and isentropic nozzle expansion (SP).

Project Status

Pre-1.0 (v0.1), active development. Core solver infrastructure, all thermo-data parsers, and the desktop GUI are complete. The recommended solver is GordonMcBrideSolver. Expect breaking changes to the API and data formats before 1.0.

Roadmap

Core Solver

• Implement PEPSolver._tp_equilibrium (currently raises NotImplementedError).
• Add optional numerical-stability fallback modes for difficult edge cases.
• Add lightweight profiling hooks to report per-iteration timing and major matrix-solve costs.
• Investigate using species-database entries directly as propellant ingredients (e.g. methane, oxygen).

GUI

• Full report export (TXT / CSV / JSON) including sweep metadata and plots.
• Cancel support for long sweep runs in PerformanceWorker.
• Persist user session settings (units, database selection, sweep mode, recent inputs).

CLI and Tooling

• Non-interactive solve CLI for HP/TP/SP runs with machine-readable output (--json / --csv).
• Benchmark baseline mode in tests/benchmark.py with threshold-based pass/fail for CI.

Features

Thermodynamic databases

• NASA-7 and NASA-9 (including CEA-derived polynomials)
• JANAF tables
• TERRA / Shomate-equivalent (translated from binary)
• AFCESIC ionic and condensed species (translated and calibrated)

Equilibrium problem types: TP, HP, SP, TV, UV, SV

Solvers

Solver	Role	Convergence	Mean T error vs RocketCEA	Speed
GordonMcBrideSolver	Recommended	100 %	0.017 %	~14 ms/case
MajorSpeciesSolver	Alternative	95.9 %	0.023 %	~235 ms/case
PEPSolver	Not yet implemented	—	—	—

Rocket performance: frozen and shifting isentropic nozzle expansion with c*, Isp (vacuum, sea-level, and actual), and area ratio.

Shifting nozzle expansion uses full-mixture entropy as the SP isentrope constraint.

Desktop GUI (prometheus-gui): PySide6 interface for propellant composition, database selection, sweep runs (O/F or Pc), and result visualisation including solver convergence plots, nozzle expansion curves, and per-station performance charts.

Installation

Install from PyPI

pip install prometheus-equilibrium           # solver + propellant database
pip install "prometheus-equilibrium[gui]"    # + PySide6 desktop GUI

Install from source (development)

Requires uv.

git clone https://github.com/1ckendall/Prometheus
cd Prometheus
uv sync          # installs all dependencies including dev tools and GUI

Quick Start

from prometheus_equilibrium.equilibrium import (
    SpeciesDatabase,
    EquilibriumProblem,
    ProblemType,
    GordonMcBrideSolver,
)

db = SpeciesDatabase()
db.load()   # NASA-7, NASA-9, TERRA loaded by default

h2 = db.find("H2", phase="G")
o2 = db.find("O2", phase="G")
products = db.get_species({"H", "O"}, max_atoms=6)

T_react = 298.15
H0 = h2.enthalpy(T_react) * 2.0 + o2.enthalpy(T_react) * 1.0

problem = EquilibriumProblem(
    reactants={h2: 2.0, o2: 1.0},
    products=products,
    problem_type=ProblemType.HP,
    constraint1=H0,
    constraint2=30e5,   # 30 bar
    t_init=3500.0,
)

solution = GordonMcBrideSolver().solve(problem)
print(solution.summary())

Launch the desktop GUI:

uv run prometheus-gui

For a longer walkthrough, open demonstration.ipynb.

Propellant Database

Prometheus ships a TOML propellant database covering hundreds of ingredients (AP, HTPB, aluminium, MMH, UDMH, N₂O₄, kerosene, and many more) converted from PROPEP. PropellantDatabase.mix() returns a PropellantMixture with the element set, reactant moles, and total H₀ pre-computed. Pass the mixture directly to PerformanceSolver.solve_from_mixture() to get paired frozen and shifting results in one call:

from prometheus_equilibrium.equilibrium import SpeciesDatabase, PerformanceSolver
from prometheus_equilibrium.propellants import PropellantDatabase

db = SpeciesDatabase()
db.load()

prop_db = PropellantDatabase()
prop_db.load()

# AP/Al/HTPB composite solid propellant (68/18/14 by mass)
mixture = prop_db.mix([
    ("AMMONIUM_PERCHLORATE",     0.68),
    ("ALUMINUM_PURE_CRYSTALINE", 0.18),
    ("HTPB_R_45HT",              0.14),
])

result = PerformanceSolver().solve_from_mixture(
    mixture, db,
    p_chamber=70e5,    # 70 bar
    area_ratio=10.0,
)

print(f"T_chamber = {result.shifting.chamber.temperature:.0f} K")
print(f"c*        = {result.shifting.cstar:.1f} m/s")
print(f"Isp (vac, shifting) = {result.shifting.isp_vac:.1f} m/s")
print(f"Isp (vac, frozen)   = {result.frozen.isp_vac:.1f} m/s")

For liquid bipropellants:

mixture = prop_db.mix([("HYDRAZINE", 1.0), ("NITROGEN_TETROXIDE_LIQ", 1.33)])

Use prop_db.ingredient_ids and prop_db.formulation_ids to browse available ingredients. Named formulations stored in the TOML can be loaded with prop_db.expand("formulation_id").

Documentation

Online: https://prometheus-equilibrium.readthedocs.io/en/latest/

Build locally:

uv run --group docs sphinx-build -b html docs docs/_build/html

The docs include:

• API reference — every public class and function with docstrings
• Thermodynamic database guide — polynomial formats and reference-state calibration across NASA-9, TERRA, and AFCESIC
• Solver comparison — algorithm analysis and implementation notes for MajorSpeciesSolver, GordonMcBrideSolver, and PEP

Development

uv sync                              # install everything (dev tools, GUI deps, test deps)
uv run pytest                        # run the test suite
uv run pytest -m "not integration"   # fast suite (no RocketCEA required)
uv run python tests/benchmark.py     # benchmark 170 cases vs RocketCEA
uv run prometheus-build-all-thermo   # re-generate all compiled thermo databases
uv run prometheus-build-legacy all   # re-generate TERRA + AFCESIC from binaries

Package Layout

prometheus_equilibrium/
  core/constants.py              element masses, R, P° = 1×10⁵ Pa
  equilibrium/
    species.py                   Chemical, Species hierarchy, SpeciesDatabase
    mixture.py                   Mixture (mutable moles array + all properties)
    element_matrix.py            ElementMatrix, basis selection
    problem.py                   EquilibriumProblem, ProblemType
    solution.py                  EquilibriumSolution + derived properties
    solver.py                    MajorSpeciesSolver, GordonMcBrideSolver, PEPSolver
    performance.py               Frozen / shifting nozzle expansion
  propellants/loader.py          PropellantDatabase, TOML-based definitions
  thermo_data/                   Compiled JSON/CSV databases + raw source files
  tools/                         CLI build scripts (prometheus-build-*)
  gui/                           PySide6 desktop interface

Validation

Prometheus is cross-referenced against multiple existing solver implementations:

• NASA CEA
• PyProPEP / cpropep
• pep-for-zos

tests/benchmark.py runs 170 cases (H₂/O₂, CH₄/O₂, N₂H₄/N₂O₄, NH₃/O₂ across 11 O/F ratios × 5 pressures) and reports temperature, molar mass, γ, Cₚ, and speed-of-sound error against RocketCEA.

Contributing

• Open an issue first to discuss the change.
• Add or update tests for any behaviour change.
• Keep docstrings in Google style (Args:, Returns:, etc.).
• Pre-commit hooks (black + isort) run automatically on every commit after the one-time setup:

uv sync
uv run pre-commit install

License

GPL-3.0-or-later. See LICENSE.txt.

Acknowledgements

• Bonnie J. McBride and Sanford Gordon (NASA CEA)
• Boris Trusov (TERRA thermodynamic database)
• Alexander Burcat (BURCAT thermochemical database)