PROPULSION DESIGN TOOL · REV 12

Rocket Injector Calculator

01
DESIGN TARGET

Injector design mode

Calculate the required orifice diameter from the target mass flow.

02
OXIDIZER CIRCUIT

Oxidizer setup

GOxProperty preset · Ideal-gas O₂ · user-defined stagnation stateCompressible ideal gasReady
Flow regimeP₂/P₀Automatic choking checkUses absolute pressures.
03
FUEL CIRCUIT

Fuel setup

EthanolProperty preset · Approx. 20 °CIncompressible liquidReady
Flow assumptionρConstant densitySingle-phase incompressible model.
COMPETITION CONTEXT

R2S PDR Support

Keep the engineering result, model limits, and competition context separate.

04
ELEMENT CONFIGURATION

Injector type

IMPINGING · UNLIKE DOUBLET

Jet angles

TMR DEFINITIONOxidizer momentum ÷ Fuel momentumTMRO/F = (ṁV)oxidizer / (ṁV)fuel

Angles are measured from the injector-face normal. The momentum balance predicts the resultant sheet direction, not the full spray-fan spread.

CALCULATION OUTPUT

Inputs are ready

Results remain separate from the input workspace and open in a focused report window.

05
CALCULATION MODEL

Mass flow equations

COMPRESSIBLE · GOx · r = P₂/P₀
Unchoked: ṁ = NCdAP₀/√T₀ × √{2γ/[R(γ−1)] · [r2/γ−r(γ+1)/γ]}Choked: ṁ = NCdAP₀/√T₀ × √(γ/R) · [2/(γ+1)](γ+1)/[2(γ−1)]Choked when r ≤ [2/(γ+1)]γ/(γ−1)
INCOMPRESSIBLE · LIQUIDS
qm = Cd / √(1 − β⁴) × π/4 × d² × √(2ρΔp)
Equation & ReferenceModel: ideal-gas choked / unchoked GOx flow; single-phase incompressible liquid flowReference: NASA Glenn Research Center — Mass Flow ChokingAssumptions: steady flow · constant Cd · ideal-gas GOx · selected fluid properties

The GOx model uses absolute pressures and automatically applies the critical pressure-ratio limit. The liquid model retains the β = d/D correction.

Engineering note: The N2O calculation assumes single-phase liquid. Flashing or two-phase N2O requires an appropriate two-phase flow model.

INJECTOR ANALYSIS · SIZING

Design results

GOx / Ethanol · Target O/F 1.000 · 0.10000 kg/s total

PROPELLANT SPLITGOx / Ethanol
GOx0.05000kg/s
+
Ethanol0.05000kg/s
Target total 0.10000 kg/sTarget O/F 1.000
OXIDIZERGOx
Required orifice diameter—mm / hole
Total open area
— mm²
Flow regime
—
Pressure ratio
—
Effective throat velocity
— m/s
Use in PDR
Quantity
Value
Calculated using
Inputs
Assumptions
FUELEthanol
Required orifice diameter—mm / hole
Total open area
— mm²
Diameter ratio
—
Injection velocity
— m/s
Use in PDR
Quantity
Value
Calculated using
Inputs
Assumptions
Reference
Pending verification
IMPINGING ELEMENT · UNLIKE DOUBLET

Momentum balance

NUMERATOROXIDIZER÷DENOMINATORFUEL
TMRO/F
—
(ṁV)oxidizer / (ṁV)fuel
Geometric included angle
—
αox + αfuel
Resultant sheet angle
—
—

Preliminary momentum-vector estimate. Atomization and actual spray-fan width require test data or a validated correlation for the selected element geometry.

Use in PDR
Quantity
Impinging-element momentum ratio
Value
—
Calculated using
Unlike-doublet momentum-vector estimate
Inputs
Assumptions
steady jets · momentum-vector balance · spray fan width not calculated
Reference
Pending verification
OXFUELRESULTANTINJECTOR FACE NORMAL
OXIDIZERGOx
D = 20.00 mmd = — mmP₁P₂1 × orifice
FUELEthanol
D = 20.00 mmd = — mmP₁P₂1 × orifice
R2S PDR SUPPORT · PRELIMINARY

R2S Injector Design Basis

Summary of current calculator inputs and model context. Missing information is not inferred.

Engine configuration
Injector architecture
Fuel
Oxidizer
Calculation mode
O/F ratio
Total mass flow
Pressure drop
Model
Engineering status

Important assumptions

    Model limitations

      Competition context

      Race 2 Space Korea · 2026 Rapid Season

      Source: R2SK 2026 Rapid Season Application Guide v1.1 · 2026-09-03

      AEL Interface Check: Not configured · AEL ICD required

      Race2Space guidance shown by this calculator is provided to assist preliminary design work. Current official R2S Korea rules, PDR guidelines, announcements, and applicable AEL documentation take precedence.