Calculator Inputs
The page is arranged in one clean column, while the form fields use a responsive three, two, and one column grid.
Example Data Table
| Sample | Density (g/mL) | T10 (°C) | T50 (°C) | T90 (°C) | D4737 A | D4737 B | D976 |
|---|---|---|---|---|---|---|---|
| Sample A | 0.8320 | 210.0 | 260.0 | 320.0 | 52.2 | 51.6 | 51.7 |
| Sample B | 0.8450 | 220.0 | 270.0 | 335.0 | 49.9 | 49.6 | 49.5 |
| Sample C | 0.8200 | 205.0 | 250.0 | 305.0 | 54.6 | 53.7 | 53.6 |
These rows demonstrate how the same fuel profile can return slightly different cetane index estimates across ASTM screening methods.
Formula Used
The calculator supports three screening equations so you can compare older and newer cetane index approaches with the same input dataset.
ASTM D4737 Procedure A
CCI = 45.2 + 0.0892×T10N + [0.131 + 0.901×B]×T50N + [0.0523 − 0.420×B]×T90N + 0.00049×(T10N² − T90N²) + 107×B + 60×B²
Where DN = D − 0.85, B = e^(−3.5×DN) − 1, T10N = T10 − 215, T50N = T50 − 260, and T90N = T90 − 310.
ASTM D4737 Procedure B
CCI = −399.90×D + 0.1113×T10 + 0.1212×T50 + 0.0627×T90 + 309.33
This version is a direct four-variable linear screening equation for specified low sulfur diesel use cases.
ASTM D976 Two-Variable Equation
CCI = 454.74 − 1641.416×D + 774.74×D² − 0.554×T50 + 97.803×[log10(T50)]²
This older method needs only density and the 50% recovery temperature, making it convenient when full distillation points are unavailable.
How to Use This Calculator
- Enter a sample name to identify the fuel in exports and printed reports.
- Choose the ASTM method that best matches your test scope or data availability.
- Input density at 15°C in g/mL, then enter T10, T50, and T90 in °C when required.
- Press Calculate Cetane Index to show the result above the form.
- Review the displayed method note, screening band, and intermediate details.
- Use the export buttons to create a CSV line item or a concise PDF summary.
Engineering Notes
Important: Cetane index is a calculated screening value, not a direct engine-measured cetane number.
Results can be misleading when cetane improver additives are present, because the equations estimate base fuel ignition behavior from physical properties.
For formal certification, regulatory work, or disputes, confirm with the applicable laboratory method and the exact fuel specification.
Frequently Asked Questions
1. What does cetane index represent?
It is a calculated estimate of diesel ignition quality based on density and distillation behavior. It helps screen fuels when full cetane engine testing is unavailable or impractical.
2. Why are there three methods here?
Different ASTM methods use different property sets and intended fuel ranges. This calculator lets you compare a modern four-variable approach with a simpler legacy equation.
3. Which method should I prefer?
Use ASTM D4737 when you have density and full recovery temperatures. Use ASTM D976 mainly when only density and T50 are available or when legacy comparisons are needed.
4. Can I use this for biodiesel blends?
Use caution. These screening equations were developed for distillate fuels, and blend chemistry or additives may reduce how well the estimate matches measured cetane number.
5. Why must T10, T50, and T90 increase?
They are sequential recovery temperatures from the distillation curve. If they are not in ascending order, the data are physically inconsistent and the estimate becomes unreliable.
6. Does a higher value always mean better fuel?
Higher ignition quality can improve cold starting and combustion smoothness, but overall fuel suitability also depends on sulfur, lubricity, stability, viscosity, and application requirements.
7. Why does the calculator show a screening band?
The band offers a practical engineering interpretation for quick review. It is not an ASTM classification and should not replace formal specification limits.
8. What is exported in CSV and PDF?
The export includes sample name, chosen method, inputs, calculated cetane index, interpretation note, and timestamp so you can archive the run or share it internally.