ASTM D613 standard test method for cetane number of diesel fuel oil
1. Scope
1.1 This test method determines 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.
1.2 The cetane number scale covers the range from zero (0) to 100 but typical testing is in the range of 30 to 65 cetane number.
1.3 The values for operating conditions are stated in SI units and are considered standard. The values in parentheses are the historical inch-pounds units. In addition, the engine measurements continue to be in inch-pounds units because of the extensive and expensive tooling that has been created for these units.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For more specific warning statements, see Annex A1.
2. Referenced Documents
2.1 ASTM Standards:
D975 Specification for Diesel Fuel Oils
D1193 Specification for Reagent Water
D2500 Test Method for Cloud Point of Petroleum Products
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
E 1 Specification for ASTM Thermometers
E 456 Terminology Relating to Quality and Statistics
E 542 Practice for Calibration of Laboratory Volumetric Apparatus
E 832 Specification for Laboratory Filter Papers
3. Terminology
3.1 Definitions:
3.1.1 accepted reference value (ARV), n - a value that serves as an agreed-upon reference for comparison, and which is derived as: (1) a theoretical or established value, based on scientific principles, or (2) an assigned or certified value, based on experimental work of some national or international organization, or (3) a consensus or certified value, based on collaborative experimental work under the auspices of a scientific or engineering group.
3.1.1.1 Discussion - In the context of this test method, accepted reference value is understood to apply to the cetane number of specific reference materials determined empirically under reproducibility conditions by the National Exchange Group or another recognized exchange testing organization.
3.1.2 cetane number, n - a measure of the ignition performance of a diesel fuel oil obtained by comparing it to reference fuels in a standardized engine test.
3.1.2.1 Discussion - In the context of this test method, ignition performance is understood to mean the ignition delay of the fuel as determined in a standard test engine under controlled conditions of fuel flow rate, injection timing and compression ratio.
3.1.3 compression ratio, n - the ratio of the volume of the combustion chamber including the precombustion chamber with the piston at bottom dead center to the comparable volume with the piston at top dead center.
3.1.4 ignition delay, n - that period of time, expressed in degrees of crank angle rotation, between the start of fuel injection and the start of combustion.
3.1.5 injection timing (injection advance), n - that time in the combustion cycle, measured in degrees of crank angle, at which fuel injection into the combustion chamber is initiated.
3.1.6 repeatability conditions, n - conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time.
3.1.6.1 Discussion - In the context of this method, a short time interval between two ratings on a sample fuel is understood to be not less than the time to obtain at least one rating on another sample fuel between them but not so long as to permit any significant change in the sample fuel, test equipment, or environment.
3.1.7 reproducibility conditions, n - conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cetane meter (ignition delay meter), n - the electronic instrument which displays injection advance and ignition delay derived from input pulses of multiple transducers (pickups).
3.2.2 Check Fuels, n - for quality control testing, a diesel fuel oil of selected characteristics having a cetane number accepted reference value determined by round-robin testing under reproducibility conditions.
3.2.3 combustion pickup, n - pressure transducer exposed to cylinder pressure to indicate the start of combustion.
3.2.4 handwheel reading, n - an arbitrary numerical value, related to compression ratio, obtained from a micrometer scale that indicates the position of the variable compression plug in the precombustion chamber of the engine.
3.2.5 injector opening pressure, n - the fuel pressure that overcomes the resistance of the spring which normally holds the nozzle pintle closed, and thus forces the pintle to lift and release an injection spray from the nozzle.
3.2.6 injector pickup, n - transducer to detect motion of the injector pintle, thereby indicating the beginning of injection.
3.2.7 primary reference fuels, n - n-cetane, heptamethyl nonane (HMN) and volumetrically proportioned mixtures of these materials which now define the cetane number scale by the relationship:
Cetane Number = % n-cetane + 0.15 (% HMN)
3.2.7.1 Discussion - In the context of this test method, the arbitrary cetane number scale was originally defined as the volume percent of n-cetane in a blend with alpha-methylnaphthalene (AMN) where n-cetane had an assigned value of 100 and AMN an assigned value of zero (0). A change from alpha-methylnaphthalene to heptamethylnonane as the low cetane ingredient was made in 1962 to utilize a material of better storage stability and availability. Heptamethylnonane was determined to have a cetane number accepted reference value (CNARV) of 15 based on engine testing by the ASTM Diesel National Exchange Group, using blends of n-cetane and AMN as primary reference fuels.
3.2.7.2 Discussion - In the context of this test method, the Diesel National Exchange Group of Subcommittee D02.018 is composed of petroleum industry, governmental, and independent laboratories. It conducts regular monthly exchange sample analyses to generate precision data for this engine test standard and determines the CNARV of reference materials used by all laboratories.
3.2.8 reference pickups, n - transducer(s) mounted over the flywheel of the engine, triggered by a flywheel indicator, used to establish a top-dead-center (tdc) reference and a time base for calibration of the ignition delay meter.
3.2.9 secondary reference fuels, n - volumetrically proportioned blends of two selected, numbered, and paired hydrocarbon mixtures designated T Fuel (high cetane) and U Fuel (low cetane) that have been rated by the ASTM Diesel National Exchange Group using primary reference fuels to determine a cetane number accepted reference value for each individually and for various combinations of the two.
