🔢 Cetane Index of Diesel Fuel
In short
Calculation of cetane index of middle distillate fuels based on density at 15°C and distillation temperatures at 10%, 50% and 90% recovery. The test is performed according to PN-EN ISO 4264:2018; Applicability range: Cetane index 32.5–56.5. The procedure comprises 8 steps; it is used for: Rapid assessment of diesel fuel ignition quality without test engine, Fuel quality control in distribution and terminal laboratories, Specification requirement PN-EN 590: cetane index ≥46.0.
At a glance
- Standard: PN-EN ISO 4264:2018
- Category: Petrochemistry
- Procedure steps: 8
- Applicability range: Cetane index 32.5–56.5
- Density (input): 805.0–895.0 kg/m³ at 15°C
- T₁₀ distillation (input): 171–259°C
Overview
Cetane index is a calculated measure of diesel fuel's ability to auto-ignite in the combustion chamber of a compression-ignition engine. It is an estimate of cetane number (determined on test engine per ISO 5165) and allows assessment of fuel ignition quality without need for test engine or large sample quantity.
Cetane index calculation is based on four measurable physicochemical parameters: fuel density at 15°C and distillation temperatures corresponding to evaporation of 10%, 50% and 90% of sample volume. These four variables are substituted into a polynomial correlation equation (four variable equation) which was determined empirically based on data from several hundred fuel samples with known cetane numbers.
The method is applied to middle distillate fuels with cetane index in range 32.5–56.5, density 805–895 kg/m³ and distillation temperatures in appropriate ranges. It is not suitable for fuels with cetane improvers (2-ethylhexyl nitrate etc.) because additives increase cetane number without changing physical parameters. It is also not applied to biodiesel (FAME) and blends with high FAME content.
Standard PN-EN 590 requirements for diesel fuel specify minimum cetane index of 46.0. This is a parameter routinely reported in fuel quality certificates.
Method principle
Cetane index is calculated from four-variable equation: CI = 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: B = [exp(-3.5 × DN)] - 1, DN = D - 850 (D is density at 15°C in kg/m³), T₁₀N = T₁₀ - 215, T₅₀N = T₅₀ - 260, T₉₀N = T₉₀ - 310 (distillation temperatures in °C). Input data (density and distillation temperatures) are obtained from determinations per ISO 12185 (density) and ISO 3405 (distillation). Expected prediction error is less than ±2 cetane units for 65% of samples.
Applications
- Rapid assessment of diesel fuel ignition quality without test engine
- Fuel quality control in distribution and terminal laboratories
- Specification requirement PN-EN 590: cetane index ≥46.0
- Fuel quality monitoring in distribution chain
- Evaluation of crude oil batches and middle distillates in refineries
- Fuel control for vehicle and construction equipment fleets
Key parameters
| Parameter | Value |
|---|---|
| Applicability range | Cetane index 32.5–56.5 |
| Density (input) | 805.0–895.0 kg/m³ at 15°C |
| T₁₀ distillation (input) | 171–259°C |
| T₅₀ distillation (input) | 212–308°C |
| T₉₀ distillation (input) | 251–363°C |
| Prediction accuracy | ±2 cetane units (for 65% of samples) |
Standard
- Standard number
- PN-EN ISO 4264:2018
- Title (PL)
- Przetwory naftowe — Obliczanie indeksu cetanowego paliw ze średnich destylatów za pomocą równania czteroczynnikowego
- Title (EN)
- Petroleum products — Calculation of cetane index of middle-distillate fuels by the four variable equation
Step-by-step procedure
-
Density determination per ISO 12185
Measure fuel sample density at 15°C using oscillating density meter. Result to 0.1 kg/m³ accuracy. (Full procedure — see ISO 12185 density method).
-
Distillation determination per ISO 3405
Perform atmospheric distillation of 100 mL sample. Record temperatures at 10%, 50% and 90% recovery (T₁₀, T₅₀, T₉₀). (Full procedure — see ISO 3405 distillation method).
-
Barometric correction of temperatures
Correct distillation temperatures to normal pressure 101.3 kPa using correction formula given in ISO 3405.
-
Check applicability range
Ensure density and distillation temperatures are within equation applicability range: D 805–895, T₁₀ 171–259, T₅₀ 212–308, T₉₀ 251–363°C.
-
Calculate auxiliary variables
DN = D - 850; B = [exp(-3.5 × DN)] - 1; T₁₀N = T₁₀ - 215; T₅₀N = T₅₀ - 260; T₉₀N = T₉₀ - 310.
-
Calculate cetane index
CI = 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.
-
Result rounding
Round result to one decimal place (e.g., 51.3). Compare with PN-EN 590 requirement: CI ≥ 46.0.
-
Reporting
In report state: cetane index, density at 15°C, temperatures T₁₀, T₅₀, T₉₀, reference methods (ISO 4264, ISO 12185, ISO 3405), date and sample number.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Oscillating density meter | Anton Paar DMA 4500 M (per ISO 12185) | 50 000–120 000 PLN |
| Atmospheric distillation apparatus | Normalab NDI 450 (automatic, per ISO 3405) | 50 000–120 000 PLN |
| Distillation apparatus (manual) | Koehler K45000 Front View (per ISO 3405) | 15 000–35 000 PLN |
| Distillation thermometer | ASTM thermometer range 0–400°C, Pt100 sensor in automatic apparatus | 500–2 000 PLN |
| Calculation software | Built into density meter or LIMS, alternatively Excel sheet with ISO 4264 formula | 0–5 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Distillation reference materials | — | CRM with certified distillation temperatures, e.g., Paragon Scientific distillation standards |
| Density standard | — | SI-traceable density CRM for density meter verification |
| Acetone (for cleaning) | 67-64-1 | Purity ≥99.5%, for rinsing distillation flask and condenser |
Health and safety (OHS)
- Calculated determination — no direct chemical hazards
- Hazards arise from input determinations (density, distillation) — see respective methods
- Diesel fuel — flammable (Class II), store away from ignition sources
- Safety glasses and gloves when handling fuel samples
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 4264:2018 — “Petroleum products — Calculation of cetane index of middle-distillate fuels by the four variable equation”.
How does this method work?
Cetane index is calculated from four-variable equation: CI = 45.2 + 0.
What is the measuring range and accuracy?
Applicability range: Cetane index 32.5–56.5; Density (input): 805.0–895.0 kg/m³ at 15°C; T₁₀ distillation (input): 171–259°C; T₅₀ distillation (input): 212–308°C.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Oscillating density meter, Atmospheric distillation apparatus, Distillation apparatus (manual), Distillation thermometer, Calculation software. Indicative cost of the core instrument (Oscillating density meter): 50 000–120 000 PLN.
Where is this test used?
Rapid assessment of diesel fuel ignition quality without test engine; Fuel quality control in distribution and terminal laboratories; Specification requirement PN-EN 590: cetane index ≥46.0; Fuel quality monitoring in distribution chain; Evaluation of crude oil batches and middle distillates in refineries; Fuel control for vehicle and construction equipment fleets.
What safety precautions apply?
Calculated determination — no direct chemical hazards; Hazards arise from input determinations (density, distillation) — see respective methods; Diesel fuel — flammable (Class II), store away from ignition sources; Safety glasses and gloves when handling fuel samples.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 4264.