Inputs
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If available directly from a mass flow meter.
Gasoline 0.745 kg/L
Diesel 0.832 kg/L
Ethanol 0.789 kg/L
Dynamometer output if available. Or compute from torque + RPM.
kW = (Torque[Nm] × RPM) / 9550. For lb·ft use 5252 for hp.
Gasoline ~42.7 MJ/kg
Diesel ~42.5 MJ/kg
Ethanol ~26.9 MJ/kg
Results
BSFC (g/kWh)
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BSFC (lb/hp·hr)
—
Brake Thermal Efficiency (%)
—
Normalized Power & Flow
Mass flow (kg/h): —
Power (kW): —
Power (kW): —
Runs
Compare scenarios
| # | Label | Power (kW) | Flow (kg/h) | BSFC (g/kWh) | BSFC (lb/hp·hr) | BTE (%) |
|---|
Exports
Import
Graphs
Runs: Power vs BSFC
Left axis g/kWh. Right axis lb/hp·hr. Toggle overlay above.
BSFC island map (contours)
Tip: Choose range or an explicit list. Annotations snap onto iso-lines by interpolation.
Example data
Click a row to load its inputs, then calculate and add to runs.
| Case | Method | Flow | Density | Power | Torque & RPM | Notes |
|---|---|---|---|---|---|---|
| A | Volumetric | 12 L/h | 0.745 kg/L | 50 kW | — | Small gasoline engine, light load. |
| Volumetric | 18 L/h | 0.745 kg/L | 80 kW | — | Gasoline engine, mid load cruise. | |
| C | Mass | 25 lb/h | — | 120 hp | — | Imperial units demonstration. |
| D | Torque helper | 15 L/h @ 0.832 kg/L | 0.832 kg/L | — | 250 Nm, 3000 RPM | Diesel example with torque-based power. |
Formula used
Brake Specific Fuel Consumption (BSFC) quantifies fuel mass consumed per unit brake power output.
- Definition: BSFC = ṁfuel / Pbrake
- Common units: g/kWh and lb/hp·hr
- Conversions:
- g/kWh = (kg/h × 1000) / kW
- lb/hp·hr = (lb/h) / hp
- 1 hp = 0.745699872 kW
- 1 lb = 0.45359237 kg
- 1 gal (US) = 3.785411784 L
- 1 lb/hp·hr ≈ 608.277 g/kWh
- Power helper: kW = (Torque[Nm] × RPM) / 9550
- Brake thermal efficiency (optional): BTE = PkW / ((ṁkg/h × LHVMJ/kg) / 3.6)
How to use this calculator
- Select the Fuel flow input method: Mass flow or Volumetric flow + density.
- Enter the flow value and choose its unit. If volumetric, set density or pick a preset.
- Enter brake power in kW or hp. If unknown, use torque and RPM to compute kW.
- (Optional) Toggle Brake thermal efficiency, enter LHV or pick a preset.
- Press Calculate BSFC to see results in g/kWh and lb/hp·hr.
- Add the result to Runs to build a comparison table and update the plot.
- Export your runs using Export CSV or Export PDF.
- Import a runs CSV to populate the table quickly.
- Import a BSFC island grid CSV to render a contour map.
- Use custom levels or an explicit list, and add annotations.
FAQs
Smaller is better. Modern spark-ignition engines may reach 220–260 g/kWh at best efficiency points. Compression-ignition engines can be lower. Actual values vary by speed and load maps.
SI practice uses g/kWh. Legacy imperial contexts often use lb/hp·hr. This tool computes both and keeps them internally consistent through exact unit conversions.
Presets are typical values at ambient conditions. Real fuel density varies with temperature and composition. For highest accuracy, measure density or use a mass flow reading.
Yes. Provide torque and RPM and press Compute kW. The helper uses standard formulas to compute kW or hp from torque and speed.
It is output power divided by input fuel energy rate. It shows what fraction of chemical energy becomes shaft work under the given conditions.
Compute each point, click Add current result to runs, and label it. Repeat at different speeds and loads to compare consumption trends.
Yes. Use the runs import for point-wise data with power and flow. Use the island import for a torque–RPM grid containing g/kWh values.