ISO 5165 Petroleum products - Determination of the ignition quality of diesel fuels - Cetane engine method
WARNING - The use of this International Standard may involve hazardous materials, operations and equipment. This International Standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1 Scope
This International Standard establishes the rating of diesel fuel oil in terms of an arbitrary scale of cetane numbers using a standard single cylinder, four-stroke cycle, variable compression ratio, indirect injected diesel engine. The cetane number provides a measure of the ignition characteristics of diesel fuel oil in compression ignition engines. The cetane number is determined at constant speed in a pre-combustion chamber-type compression ignition test engine. However, the relationship of test engine performance to full scale, variable speed, variable load engines is not completely understood.

This International Standard is applicable for the entire scale range from zero cetane number (CN) to 100 CN but typical testing is in the range of 30 CN to 65 CN.

This test may be used for unconventional fuels such as synthetics, vegetable oils, etc. However, the relationship to the performance of such materials in full scale engines is not completely understood.

Samples with fluid properties that interfere with the gravity flow of fuel to the fuel pump or delivery through the injector nozzle are not suitable for rating by this method.

NOTE 1 This International Standard specifies operating conditions in SI units but engine measurements are specified in inch-pound units because these are the units used in the manufacture of the equipment, and thus some references in this International Standard include these units in parenthesis.

NOTE 2 For the purposes of this International Standard, the expression "% (V/V)" is used to represent the volume fraction of a material.

2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 3015:1992, Petroleum products - Determination of cloud point.
ISO 3170:1988, Petroleum liquids - Manual sampling.
ISO 3171:1988, Petroleum liquids - Automatic pipeline sampling.
ISO 3696:1987, Water for analytical laboratory use - Specification and test methods.
ISO 4787:1984, Laboratory glassware - Volumetric glassware - Methods for use and testing of capacity.
ASTM D613-95, Standard test method for cetane number of diesel fuel oils.
ASTM E 832-81, Specification for laboratory filter papers.

3 Principle
The cetane number of a diesel fuel oil is determined by comparing its combustion characteristics in a test engine with those for blends of reference fuels of known cetane number under standard operating conditions. This is accomplished using the bracketing handwheel procedure which varies the compression ratio (handwheel reading) for the sample and each of two bracketing reference fuels to obtain a specific ignition delay permitting interpolation of CN in terms of handwheel reading.

4 Definitions
For the purposes of this International Standard, the following definitions apply.
4.1 cetane number
Measure of the ignition performance of a diesel fuel oil obtained by comparing it to reference fuels in a standardized engine test. Ignition performance is understood to mean the ignition delay of the fuel as determined when the standard test engine is operated under controlled conditions of fuel flow rate, injection timing and compression ratio.

4.2 compression ratio
The ratio of the volume of the combustion chamber including the pre-combustion chamber with the piston at bottom dead center (b.d.c.) to the comparable volume with the piston at top dead center (t.d.c.).

4.3 ignition delay
Period of time between the start of fuel injection and the start of combustion. It is expressed in degrees of crank angle rotation.

4.4 injection timing; injection advance
Time in the combustion cycle at which fuel injection into the combustion chamber is initiated. It is expressed in degrees of crank angle.

4.5 handwheel reading
Arbitrary numerical value, related to compression ratio, obtained from a micrometer scale that indicates the position of the variable compression plug in the pre-combustion chamber of the engine.

4.6 cetane meter; ignition delay meter
An electronic instrument which displays injection advance and ignition delay derived from input pulses of multiple transducers (pickups).

4.7 injector opening pressure
Fuel pressure that overcomes the resistance of the spring which normally holds the injector nozzle pintle closed, and thus forces the pintle to lift and release an injection spray from the nozzle.

4.8 reference pickup
Transducer(s) mounted over the flywheel of the engine, triggered by a flywheel pointer, used to establish a t.d.c. reference and a time base for calibration of the ignition delay meter.

4.9 injector pickup
Transducer to detect motion of the injector pintle, thereby indicating the beginning of injection.

4.10 combustion pickup
Pressure transducer exposed to cylinder pressure to indicate the start of combustion.

4.11 primary reference fuels
Hexadecane (cetane), heptamethylnonane (HMN) and volumetrically proportioned mixtures of these materials which now define the CN scale by the relationship given in the following equation:
CN = % cetane + 0.15 (% HMN)

NOTE 3 The arbitrary CN scale was originally defined as the volume percent of cetane in a blend with 1 -methylnaphthalene (AMN) where cetane had an assigned value of 100 and AMN an assigned value of zero. A change from 1 -methylnaphthalene to heptamethylnonane as the low CN ingredient was made in 1962 to utilize a material of better stability and availability. Heptamethylnonane was determined to have a CN of 15 based on engine calibration by the ASTM Diesel National Exchange Group, using blends of cetane and AMN as primary reference fuels. The use of 1 -methylnaphthalene as a primary reference fuel is allowed.

4.12 secondary reference fuels
Volumetrically proportioned blends of two selected hydrocarbon mixtures designated "T fuel" (high CN) and "U fuel" (low CN) where each numbered paired set of "T fuel" and "U fuel" is calibrated by the ASTM Diesel National Exchange Group in various combinations by comparison to primary reference fuel blends.

4.13 check fuels
Diesel fuel oils calibrated by the ASTM Diesel National Exchange Group which provide a guide for an individual laboratory to check the cetane rating performance of a specific engine unit.