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Fuel Spray
Calculator

Characterize fuel injection sprays without a wind tunnel. Compute droplet size, penetration, evaporation timescales, and cone angles using correlations validated against high-speed Mie scattering experiments.

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agnicycle · spray_calculator · hiroyasu · iso-octane
SMD
Sauter Mean Diameter
D²
Evaporation law
CSV
Exportable results
6+
Fuel blends supported
2
Validated correlations
What it does

Spray physics without
the lab equipment

Based on correlations used daily in injection system design and validated in peer-reviewed combustion research.

💧
Sauter Mean Diameter (SMD)
Hiroyasu–Arai and Reitz–Diwakar correlations. Computes volume-weighted average droplet diameter from injection pressure, orifice size, and fuel properties.
📏
Spray Penetration Curves
Intact liquid jet length and spray tip penetration vs. time. Covers both the momentum-controlled and drag-controlled regimes.
📐
Cone Angle Prediction
Spray cone half-angle as a function of injection pressure differential, orifice length-to-diameter ratio, and ambient density.
🌡️
Droplet Evaporation
D² law with fuel vapor pressure correction. Tracks droplet lifetime from injection to complete evaporation across temperature and pressure conditions.
⛽
Multi-Component Fuels
Diesel, biodiesel, DME, ethanol blends E10–E85. Fuel-specific density, viscosity, and surface tension at injection conditions.
📤
Exportable Histograms
Droplet size distribution histograms exportable as CSV for post-processing or SVG for direct inclusion in publications and reports.
Validated correlations

The physics behind the numbers

Every correlation is from peer-reviewed literature. No black-box outputs.

Hiroyasu–Arai (1990)
SMD from injection pressure drop, orifice diameter, and fuel-air density ratio. Primary correlation for diesel injection systems.
Reitz–Diwakar (1987)
Alternative SMD correlation accounting for atomization regime — bag breakup vs. stripping breakup — for GDI and port injection.
Hiroyasu Penetration (1980)
Spray tip penetration in two phases: intact jet controlled by injection velocity, then atomized spray controlled by aerodynamic drag.
D² Evaporation Law
Classical droplet evaporation model with Spalding mass transfer number correction for high-temperature and high-pressure conditions.
// The dimensionless groups that govern breakup
Weber number — ratio of disruptive aerodynamic force to stabilizing surface tension. High We means the droplet breaks apart.
Ohnesorge number — relates viscous force to surface tension/inertia. Together, We and Oh set the breakup regime every correlation above predicts.
Who actually uses this

Same atomization physics, different reasons to open it

🎓
Students
See how injection pressure and orifice geometry actually change droplet size and penetration — not just read about it in a textbook.
🔬
Researchers
Cross-check which SMD correlation best fits your regime before writing it into a paper or a CFD boundary condition.
⚙️
Industry Engineers
Get a fast, defensible spray estimate for an injector spec change without waiting on a full CFD atomization study.

Start characterizing your spray

No wind tunnel needed. Results in seconds, ready to include in your next paper.

Launch Spray Calculator
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