Void Orbital · Helios — Thermal, Combustion & Propulsion

01Geometry

Drop a STEP or STL

or click to browse

Units in file

STEP declares its own units and is almost always millimetres. STL declares none at all, so this is a genuine choice.

02Material

03Boundary conditions

Click a face in the viewport to select it. Shift-click adds. Every face you leave unassigned is insulated.

Apply to selection

Temperature K

04Solve

Internal generation W/m3

Mesh density 40

Geometry

No part loaded

Drop a STEP or STL on the left, or load a test part.

01Propellants

Fuel Oxidiser

Fuel inlet T K Oxidiser inlet T K

02Mixture ratio

O/F by mass Equivalence Φ

Type O/F, or Φ, which sets O/F = O/F_st / Φ. O/F = 0 runs the fuel alone, as a monopropellant.

03Chamber & nozzle

Chamber p bar

Area ratio ε

Shifting re-equilibrates at every station and is an upper bound on I_sp; frozen carries the chamber composition to the exit. Real nozzles sit between the two.

04O/F sweep

Holds this chamber pressure, nozzle area ratio, inlet state and flow model, and varies O/F alone. The range defaults to 0.4–1.1 × stoichiometric and resets when the propellant pair changes.

O/F from O/F to Points, 2–25

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specific impulse, vacuum

I_sp vacuum, c* and chamber T against O/F

Performance

Chamber

Throat

Exit

Chamber composition

The 12 largest equilibrium mole fractions above 10⁻⁴, largest first; bars are relative to the largest.

Propulsion hand-off

Writes T_c, M, k = γ_f (the chamber's frozen c_p/c_v, which is what Sutton's Table 5-5 k column matches), p_c and O/F into the Propulsion tab, and hands over this tab's c* (shifting-equilibrium or frozen-flow, as solved, and labelled that way there) to replace its ideal-gas one: for shifting flow the ideal formula on k = γ_f puts c* about 2 % low, and c* sets the mass flow and throat size. Propulsion's C_F stays the constant-k ideal nozzle, so its I_sp will not equal this tab's.

01Flame mixture

Fuel Oxidiser

Equivalence Φ Pressure atm Fuel inlet T K Oxidiser inlet T K

The Heating values panel is for this fuel.

02Laminar flame speed

Fuel, Metghalchi–Keck fits

Equivalence Φ Unburned T K Pressure atm Diluent mass fraction

03Droplet

A single droplet in a quiescent gas. Evaporation unless both Q_c and ν are above zero, when it burns.

Diameter D₀ µm Gas T∞ K Boiling T K h_fg kJ/kg Gas c_p J/kgK Gas k W/mK Liquid ρ kg/m3

Q_c MJ/kg ν O₂/fuel Y_ox,∞

For burning, Q_c is the fuel's heat of combustion (its LHV, as under Heating values) and ν the stoichiometric oxidiser-to-fuel mass ratio; Y_ox,∞ = 0.233 is air.

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adiabatic flame temperature, constant pressure

Equilibrium products at constant pressure, mole fractions

01Chamber gas

Sutton Table 5-5, shifting equilibrium at 6.9 MPa. Pick Custom to type your own, or press Send to Propulsion on the Combustion tab to bring over an equilibrium chamber gas and its c*.

Chamber T K Molar mass kg/kmol k = cp/cv Chamber p bar

02Nozzle

Area ratio ε

Cone half-angle deg Bell fraction

03Sizing

Thrust kN

L* m O/F (optional) η c* η C_F

Efficiencies stay at 1 for the ideal rocket. Real engines run ηc* 0.92–0.99 and ηC_F 0.98–0.99.

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specific impulse, vacuum

Thrust and I_sp against altitude