Cetane Number — EN ISO 5165 / EN ISO 4264 / ASTM D613

What Is Cetane?

Cetane number is a measure of how easily diesel ignites in a diesel engine. The reference method is the comparison of the sample with reference fuels of known ignition quality in the CFR cetane engine (EN ISO 5165). CETANE INDEX is an estimate calculated from density and distillation data without using an engine (EN ISO 4264).

Purpose of Cetane

The aim is to evaluate the ignition delay of the fuel in the engine and hence the cold start, noise and emissions behavior.

Which Products Is Cetane Applied To?

Automotive diesel
Biodiesel blends
Marine distillate fuels
Refinery intermediate streams
Fuels with cetane improver additives

In Which Sectors Is Cetane Used?

Oil & GasPetrokimyaEnergyAutomotive

Standards Related to Cetane

TS EN ISO 5165 (cetane number — CFR engine method)
TS EN ISO 4264 (cetane index — four-variable equation)
ASTM D613 (cetane number)
ASTM D6890 / EN 16144 (derived cetane number — IQT)

Cetane Conditions

Engine method: In CFR cetane engine, under conditions defined in the standard
Index calculation: Calculated from density and distillation points; Does not reflect additive effect
Contribution: Cetane improving additive increases the number but is not reflected in the index

Equipment for Cetane

CFR cetane engine
IQT (ignition quality tester)
density meter
Automatic distillation apparatus

Sample Requirements for Cetane

Sampling determines the validity of the result in fuel analysis: ISO 3170 (manual) and ISO 3171 (automatic in-line) define the sampling rules. The sample must be taken into a clean container of a suitable material, filled with no air gap, and kept cold for volatile products.
A sufficient volume of sample is required for the engine method
Additive use must be reported
The sample must be clean and dehydrated

Duration of Cetane

Measurement by engine method takes time due to engine tuning and reference fuel comparisons. Cetane index is calculated instantly if the density and distillation results are ready.

Cetane Procedure

1The density of the sample and the distillation curve are determined.
2Cetane index is calculated according to EN ISO 4264.
3For the engine method, the CFR engine is prepared.
4Comparison is made with reference fuels.
5The cetane number is determined.
6The results are compared to the specification limit.

Cetane Acceptance Criteria

The acceptance criterion comes from the relevant product specification and varies by season, market and class. Specification versions are updated; the limit values in force for your product are confirmed from the specification text at the quotation stage.

Evaluation of Results

The difference between cetane number and cetane index carries information: the index only reflects the natural composition of the fuel, it cannot see the additive effect. If there is a big difference between the two, it means that a cetane improving additive has been made to the fuel. Specifications often define separate limits for both.

Cetane Report

Sample description and contribution declaration
Density and distillation results
Setan indeksi
Cetane number and method used
Comparison against specification limits

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

98/70/EC Fuel Quality Directive

Petroleum, Fuel and Oil Analysis — What Does This Testing Field Cover?

The section below describes the field that the Cetane test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Petroleum, fuel and oil analysis determines whether a fluid meets its specification and how it behaves in use. Standards in this field consist largely of ASTM and EN publications, with a separate method defined for each parameter.

What distinguishes this family is that product specifications are written as PARAMETER LISTS. Specifications such as EN 590 (diesel), EN 228 (petrol), EN 14214 (biodiesel) and ISO 8217 (marine fuels) state for each parameter both the limit and the method by which that limit is to be measured. If the method changes the result may change too; the specification therefore binds the method as well, and the use of an "equivalent method" is possible only where the specification allows it.

On the fuel side, parameters describe three different properties of the product. Physical properties (density, viscosity, distillation curve, pour point, cloud point) determine pumpability and cold weather behaviour. Combustion properties (cetane number, octane number, calorific value) indicate performance in the engine. Contaminant and stability parameters (sulphur, water, sediment, oxidation stability, copper strip corrosion) affect both emissions and storage life.

Oil analysis is carried out for two different purposes and the two must not be confused. Analysis of NEW oil verifies the conformity of the product to its specification: viscosity index, additive content, flash point. Analysis of USED oil, by contrast, is done to read the condition of the machine — elemental analysis shows wear metals (iron, copper, chromium, aluminium), water and fuel contamination point to leaks, and oxidation and acid number determine the remaining life of the oil.

Used oil analysis is therefore a PREDICTIVE MAINTENANCE tool. The trend of samples taken at regular intervals is followed; it is the trend rather than a single result that is meaningful. Iron levels climbing over the course of months allow intervention before a failure occurs.

Marine fuels are the most active sub-body of the field. The global tightening of sulphur limits has brought new blended fuels onto the market; for these fuels stability, compatibility (whether two fuels form deposits when mixed) and catalytic fines content have become critical parameters.

Sampling is part of the result in this family too. A sample taken from the bottom of a tank shows different water and sediment content from one taken from the upper level; in commercial deliveries the sampling point and method are set by contract.

Method groups in this field

Physical properties
Density (oscillating U-tube and hydrometer), kinematic viscosity, distillation, pour and cloud point, flash point.
Combustion properties
Cetane number and cetane index, research and motor octane number, calorific value.
Sulphur and elements
Sulphur by UV fluorescence and XRF; elemental analysis and additive content by ICP.
Stability and corrosion
Oxidation stability, copper strip corrosion, water and sediment, filter blocking tendency.
Composition analysis
Boiling range distribution by gas chromatography, hydrocarbon types (FIA), benzene and aromatics content, fatty acid methyl ester content.
Used oil
Wear metals, contamination (water, fuel, soot), oxidation, acid and base number, change in viscosity.

Commonly confused in this field

The specification binds the method as well; a result measured by a different method may not be accepted for specification conformity.
A single result on used oil is not meaningful; the decision is made on the trend.
The sampling point determines the result; the tank bottom and the upper level show different water and sediment.
The cetane index is a calculated value and is not the same thing as a measured cetane number.
Fuels blended with biodiesel behave differently in terms of storage life and microbial growth; classical diesel parameters are not sufficient.
Mixing marine fuels from different sources can cause deposits; compatibility is assessed separately.

Which decisions these results support

Conformity of a fuel lot to specification and commercial delivery
Predictive maintenance decisions based on used oil analysis
Determining parameters for customs and tax classification
Quality verification after storage, blending and transport
Compliance with sulphur limits under emissions legislation

Related Tests

Frequently Asked Questions About Cetane

Can cetane index be used instead of cetane number?

The specification limits the two separately. The index is a practical estimate but does not indicate the actual ignition quality of fuels with additives; The engine method remains the reference.