NB/SH/T 0883-2014 Determination of diesel fuel ignition delay and derived cetane number — Constant volume combustion chamber method

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: NB/SH/T 0883—2014
• Chinese title: Determination of diesel fuel ignition delay and derived cetane number — Constant volume combustion chamber method
• English title: Standard test method for determination of ignition delay and derived cetane number of diesel fuel oil by combustion in a constant volume chamber
• Replacement relationship: not provided in the available source (the foreword only states "adopted by redrafting method with modification from ASTM D6890—13", and does not mention replacing any previous version)
• Adoption relationship: adopted by redrafting method with modification from ASTM D6890—13
• Publication/implementation: published on 2014-06-29, implemented on 2014-11-01
• Publishing authority: National Energy Administration
• Custodianship: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, Sinopec Yanshan Branch
• Main drafters: Wang Li, Zhang Xin, Ma Yongxu, Xu Feng

Main technical differences from ASTM D6890—13 (foreword):

• Chapter 1 does not list oils meeting foreign standard specifications;
• Chapter 2 modifies the referenced standards to the corresponding Chinese national standards and industry standards;
• Chapter 3 modifies the wording of accepted reference values; cancels the discussion of cetane number in 3.1.4.1 of ASTM D6890—13; modifies the definition of derived cetane number;
• Chapter 15 deletes and modifies the precision content, changing the expression of ignition delay deviation to the expression of derived cetane number deviation;
• Adds Annex H (summary table of main parameters) and Annex I (photographs of analyzer equipment).

2. Scope of application and non-applicability

• This standard specifies a test method for determining the ignition performance of diesel fuel by the constant volume combustion chamber method (Chapter 1).
• Applicable to: conventional diesel fuel, oil sand-based diesel fuel, blended fuels containing biodiesel, diesel fuel with cetane number improvers added, low-sulfur diesel fuel, and ordinary and automotive diesel fuels conforming to GB 252 and GB 19147; also applicable to the measurement of the ignition performance of diesel blending components.
• The method measures ignition delay by directly injecting diesel fuel into a constant-volume combustion chamber filled with heated compressed air, and calculates the derived cetane number using a formula.
• Measured ignition delay range: 3.1 ms ~ 6.5 ms, corresponding to a derived cetane number range of 64 ~ 33.
• Shorter or longer ignition delays can be measured, but precision may be affected; for calculation of longer or shorter ignition delays see clause 13.4 (i.e., Annex G).
• There is no data comparison information for derived cetane number values outside 33~64 with cetane numbers determined by GB/T 386.
• 5.3: The correlation between the determined derived cetane number and full-scale, variable-speed, variable-load diesel engines is not yet fully clear.
• 5.4: It can also be used for non-conventional fuels, but the performance of these non-conventional fuels in full-size engines is not yet fully clear.
• 5.5: Testing on equipment in normal working condition requires about 100 mL of sample and takes about 20 min.

3. Method principle

• 4.1 A small portion of oil sample is injected into a heated, temperature-controllable, constant-volume combustion chamber filled with compressed air. Each injection injects fuel only once and produces a combustion cycle by compression ignition.
• 4.2 Sensors are used to determine the time of start of fuel injection and start of combustion during each cycle, thereby determining the ignition delay. A complete automatic test process for one sample includes 15 pre-cycles and 32 formal cycles.
• 4.3 The average ignition delay of the 32 formal cycles is taken as the ignition delay result. From the measured ignition delay result, the derived cetane number of the sample is calculated according to the empirical formula for derived cetane number.
• The start of injection is indicated by the initial movement or rise of the nozzle needle valve measured by a motion sensor; the start of combustion is indicated by a point at which the pressure in the combustion chamber measured by a pressure sensor changes significantly and continuously (Note to 3.2.6).

4. Reagents and materials (purity / preparation)

• 8.1 Calibration reference materials
  • 8.1.1 n-Heptane: purity (volume fraction) not less than 99.5%. The established accepted reference value ID_ARV for ignition delay is 3.78 ms. Warning: flammable, vapors harmful to health, easily ignited.
  • 8.1.2 Methylcyclohexane (MCH): purity (volume fraction) not less than 99.0%. The established accepted reference value ID_ARV for ignition delay is 10.4 ms. Warning: flammable, vapors harmful to health, easily ignited. Note: Experience has found that some MCH meet the purity requirements but do not meet the ID_ARV requirements (usually shorter than ID_ARV by 1.0 to 1.5 ms); it is recommended to verify before each use of a new MCH.
• 8.2 Check standard samples
  • 8.2.1 n-Heptane: purity (volume fraction) not less than 99.5%. The established accepted reference value ID_ARV for ignition delay is 3.78 ms. Warning: flammable, vapors harmful to health, easily ignited.
• 8.3 Quality control sample: a specific diesel fuel with stable performance whose physical or chemical properties are similar to those of typical fuel samples tested daily. Warning: combustible, vapors harmful to health.
• 8.4 Charge air: compressed air with oxygen content 20.9% ± 1.0% (volume fraction), hydrocarbon content less than 0.003% (volume fraction), and water content less than 0.025% (volume fraction). Because the cylinder is filled with a nitrogen-oxygen mixture, quality control testing shall be performed after each cylinder change. Warning: compressed gas under high pressure, can support combustion.
• 8.5 Cooling system coolant: a mixture of water and commercially available glycol-type antifreeze in a volume ratio of 50:50. Warning: toxic substance, harmful or fatal if inhaled or swallowed.
  • 8.5.1 Antifreeze: concentrated liquid of commercially available glycol-type coolant used in automotive cooling systems.
  • 8.5.2 Water: distilled water or water meeting the requirements for grade three water in GB/T 6682—2008.
• 8.6 Driving compressed air: oil-free compressed air with water content less than 0.1% (volume fraction) and minimum pressure maintained above 1.5 MPa. Warning: compressed gas under high pressure, can support combustion.
• 8.7 Fuel tank compressed nitrogen: purity (volume fraction) not less than 99.9%. Warning: compressed gas under high pressure.
• Annex A Safety warnings: combustibles (diesel fuel, quality control sample); flammables (n-heptane, methylcyclohexane); toxic substances (commercial glycol-type antifreeze); compressed gases (compressed air, compressed nitrogen); hot surfaces (combustion chamber guard, exposed areas around the combustion chamber fuel injector, exposed areas around the combustion chamber inside the protective guard).

5. Apparatus and equipment

• 7.1 Integrated automatic analysis and measurement system, comprising:
  • a) Combustion chamber: fixed volume, compression ignition type, with external electrical heating elements, corresponding insulation, pneumatic intake valve and exhaust valve;
  • b) Injection system: heatable, fuel injected pneumatically, with pump, nozzle assembly, and connected fuel tank;
  • c) Cooling system: with liquid-air heat exchanger, filter, circulation pump, flow control valve;
  • d) Measurement and control components: including thermocouples, pressure gauges, pressure sensors, injector needle valve motion sensor, compressed gas pressure regulators, control valves, pneumatic components, solenoid valves;
  • e) Computer: used to control the test program, capable of acquiring and storing signal data collected by sensors, performing processing calculations, automatically outputting important test parameters and printing them as a report.
• 7.2 For analyzer equipment description and specifications, see Annex B.
• 7.3 Compressed gas pressure regulators:
  • 7.3.1 Charge pressure regulator: a two-stage regulating valve capable of regulating downstream pressure down to 2.2 MPa.
  • 7.3.2 Injection driving air pressure regulator: a two-stage regulating valve capable of regulating downstream pressure down to 1.3 MPa.
  • 7.3.3 Fuel tank pressure regulator: a single-stage or two-stage regulating valve capable of regulating downstream pressure down to 350 kPa.
• 7.4 Auxiliary equipment:
  • 7.4.1 Sample filter: used in conjunction with a glass syringe, with a nominal pore size of 3 μm ~ 5 μm micrometers, made of special glass fiber, polytetrafluoroethylene (PTFE), or nylon fiber.
  • 7.4.2 Syringe: glass syringe with a volume not less than 100 mL.
• Annex B Combustion analyzer description and specifications:
  • B.2 Combustion chamber assembly: cavity volume 0.213 L ± 0.002 L; 9 bullet-type resistance heaters; intake valve/exhaust valve assembly (numerically controlled solenoid valve operating pneumatic relay valve); insulation felt for thermal insulation.
  • B.3 Fuel injection system: fuel tank assembly (minimum 40 mL rust-proof metal tank, floating piston, O-type seal ring); fuel pump assembly; pneumatic air buffer tank (volume at least 5.5 L, withstand pressure not less than 4.0 MPa, prevent buffer tank pressure from exceeding 2.4 MPa); fuel nozzle and body assembly (needle valve type injector designed according to the requirements of ISO 4010); injector end cap; high-pressure fuel line.
  • B.4 Equipment sensors: combustion chamber pressure sensor (P1), charge pressure sensor (P2), injection driving air pressure sensor (P3), intake/exhaust valve driving air pressure gauge (P4), combustion chamber outer surface temperature sensor (T1, K-type thermocouple), fuel pump temperature sensor (T2, K-type thermocouple), temperature sensor beside combustion chamber pressure sensor (T3, K-type thermocouple), charge temperature sensor (T4, K-type thermocouple), nozzle coolant passage temperature sensor (T6, K-type thermocouple), coolant loop temperature sensor (T7, K-type thermocouple), nozzle needle valve motion sensor (N1).
  • B.5 Computer control, data acquisition, data analysis, and reporting system.
  • B.6 Circulating coolant system: coolant shroud, coolant storage tank, coolant pump (centrifugal pump), heat exchanger (liquid-to-air), coolant filter, manual flow control valve.
  • B.7 Optional equipment: UPS.

6. Recommended operating conditions

• 10.4 Operating conditions:
  • 10.4.1 Charge pressure (P2): 2.137 MPa ± 0.007 MPa (310 psi ± 1 psi).
  • 10.4.2 Charge temperature (T4): 545 °C ± 30 °C; in 32 combustion cycles, the temperature difference (T4max − T4min) shall be less than 2.5 °C.
  • 10.4.3 Combustion chamber surface temperature (T1): initial value given at factory, monitored by computer, set and adjusted by operator, required to be consistent with the calibration procedure.
  • 10.4.4 Combustion chamber pressure sensor temperature (T3): 130 °C ± 20 °C; in 32 combustion cycles, the temperature difference (T3max − T3min) shall be less than 8.0% (unclear in the source text, suspected to be 8.0 °C, requires confirmation against the source standard (source-text extraction)).
  • 10.4.5 Coolant return temperature (T7): 40 °C ± 10 °C.
  • 10.4.6 Fuel tank pressure (P5): 345 kPa ± 35 kPa (50 psi ± 5 psi); not recorded by the data acquisition system, requires visual verification of the reading.
  • 10.4.7 Fuel pump temperature (T2): 35 °C ± 3 °C.
  • 10.4.8 Injector coolant passage temperature (T6): in 32 combustion cycles, both T6max and T6min shall be within the range of 50 °C ± 4.0 °C.
  • 10.4.9 Injection drive air pressure (P3): 1.21 MPa ± 0.03 MPa (175 psi ± 4 psi).
  • 10.4.10 Intake/exhaust valve drive air pressure (P4): 480 kPa ± 35 kPa (70 psi ± 5 psi); not recorded by the data acquisition system, requires visual verification of the reading.
• 10.3 Settings based on component specifications:
  • 10.3.1 Injector opening pressure: each time the nozzle assembly is reinstalled or replaced, adjust the pressure-adjusting nut according to the nozzle tester so that the fuel injection quantity is consistent with the equipment manual requirements.
  • 10.3.2 Injector motion sensor position: place the sensor when the nozzle needle valve movement signal can be observed on the computer screen (see Appendix D, Figure D.1).
  • 10.3.3 Injector coolant passage thermocouple position: use a dedicated depth gauge tool to establish the insertion depth.
  • 10.3.4 Charge air temperature sensor position: use a dedicated depth gauge tool to establish the insertion depth.
  • 10.3.5 Combustion chamber pressure (P1) decay rate: lower than 3.5 kPa/s (0.50 psi/s), measured during the combustion chamber seal integrity check (see C.5).
• Appendix H Summary table of main parameters (value ranges/adjustment factors/measured value examples):
  • Combustion chamber pressure decay rate: lower than 3.5 kPa/s (0.50 psi/s); measured example 0.07 psi/s.
  • Charge pressure: 2.137 MPa ± 0.007 MPa (310 psi ± 1 psi); measured example 309.9 psi.
  • Charge temperature: 545 °C ± 30 °C, in 32 cycles the temperature difference shall be less than 2.5 °C; measured example 559.8 °C.
  • Combustion chamber surface temperature: cannot be set independently, adjusted by the set temperature; measured example 584.4 °C.
  • Combustion chamber pressure sensor temperature: 130 °C ± 20 °C; measured example 133.2%.
  • Coolant return temperature: 40 °C ± 10 °C; measured example 42.5 °C.
  • Fuel tank pressure: 345 kPa ± 35 kPa (50 psi ± 5 psi); measured example 50 psi.
  • Fuel pump temperature: 35 °C ± 3 °C; measured example 35.3 °C.
  • Injector coolant passage temperature: within 50 °C ± 4.0 °C; measured example 51.4 °C.
  • Injection drive air pressure: 1.21 MPa ± 0.03 MPa (175 psi ± 4 psi); measured example 175.2 psi.
  • Intake/exhaust valve drive air pressure: 480 kPa ± 35 kPa (70 psi ± 5 psi); measured example 69 psi.
  • Combustion chamber front gas temperature: cannot be set independently, adjusted by the set temperature; measured example 560.1 °C.
  • Combustion chamber rear gas temperature: feedback from the set temperature and ignition combustion conditions; measured example 588.0 °C.
  • n-Heptane: ID_ARV = 3.78 ms; the average of 3 calibration runs is within 3.78 ms ± 0.01 ms; the measured value is within the range of 3.78 ms ± 0.06 ms; measured examples 3.776 ms, 3.783 ms, 3.781 ms.
  • Methylcyclohexane: ID_ARV = 10.4 ms; the average of 2 calibration runs is within 10.4 ms ± 0.6 ms; the measured value is within the range of 10.4 ms ± 0.5 ms; measured examples 10.420 ms, 10.393 ms.

7. Sampling and test specimen preparation

• 9.1 Sampling
  • 9.1.1 Sample in accordance with the provisions of GB/T 4756 or SY/T 5317. Warning: opaque containers such as dark brown glass bottles, metal cans, or less reactive plastic containers shall be used for both sampling and storing samples to minimize exposure to sunlight or ultraviolet light.
  • 9.1.2 Mix and handle the sample in accordance with the relevant content in ASTM D 5854.
• 9.2 Preparing the sample
  • 9.2.1 Fuel temperature: before opening the sample, bring it to room temperature. Typical room temperature is 18 °C ~ 32 °C (original text "184~32°", requires confirmation against the source standard (source-text extraction)).
  • 9.2.2 Filtration: use a glass syringe to draw at least 100 mL of sample, inject it into a filter with a pore size of 3 μm ~ 5 μm for filtration, and use the filtered sample as the test specimen. Warning: samples are collected in dark brown glass bottles, metal cans, or less reactive plastic containers.
• 12.2.1 At room temperature, use a glass syringe and a disposable filter element to filter the sample to be tested for at least 100 mL.

8. Analysis procedure

• 12.1 Calibration period operating procedure
  • 12.1.1 If necessary, preheat the combustion analyzer (see C.1).
  • 12.1.2 Check whether the combustion chamber is completely sealed (see C.5).
  • 12.1.3 Perform quality control tests to check whether the combustion analyzer is suitable for use (see 11.4).
• 12.2 Measurement procedure
  • 12.2.1 At room temperature, use a glass syringe and a disposable filter element to filter the sample to be tested for at least 100 mL.
  • 12.2.2 Rinse the fuel injection system with the sample to be tested, fill the fuel tank, and remove air bubbles (see C.2.2).
  • 12.2.3 Fill the fuel tank with the sample to be tested.
  • 12.2.4 Apply the corresponding computer command to start the automatic determination of the ignition delay period (see Appendix D).
  • 12.2.5 Check whether all standard operating conditions meet the requirements.
  • 12.2.6 If the operating conditions do not meet the requirements, it is necessary to return to step 12.2.2 and readjust.
  • 12.2.7 To facilitate the calculation of the derived cetane number, record the average ignition delay period rounded to the 3th decimal place.
• 12.3 Shutdown
  • 12.3.1 Discharge the unused sample and clean the injection system (see C.2.3 or C.2.4).
  • 12.3.2 Turn off the combustion analyzer (see C.6).
• 11 Calibration and quality control tests
  • 11.1 Calibration: calibration is required once per week. Calibration must be performed promptly under the following conditions: a) after the combustion analyzer is installed and awaiting use; b) after replacement of key components of the combustion chamber assembly (see B.2), the fuel injection system (see B.3), or the instrument sensor (see B.4); c) after calibration of the data acquisition board, the injection drive air pressure sensor, or the charge pressure sensor; d) when the verification results of the check standard or quality control sample are unreasonable.
  • 11.2 Pre-calibration steps: 11.2.1 Clean the combustion chamber pressure sensor assembly (see C.3 and C.4); 11.2.2 Start and warm up the analyzer (see C.1).
  • 11.3 Calibration steps: Calibrate with two filtered calibration reference materials: (1) n-heptane establishes the combustion chamber temperature set point so that the ignition delay period is within the specified limits; (2) methylcyclohexane establishes the measurement sensitivity of the combustion analyzer so that the ignition delay period is within the specified limits.
    • 11.3.1 n-Heptane calibration reference material: after filtration, continuously measure the ignition delay period 3 times.
      • 11.3.1.1 The average value of 3 measurements is reasonable if it is within the range 3.78 ms ± 0.01 ms.
      • 11.3.1.2 If the average value exceeds the limits, the combustion chamber set temperature must be adjusted to change the charge temperature. Note: When the combustion chamber set temperature is lowered, the ignition delay period value is lengthened; and vice versa.
      • 11.3.1.3 If the adjustment range of the temperature control set point exceeds the previous set value 4 °C, suspect a system fault and activate the diagnostic program. Note: After replacing the nitrogen-oxygen blended charge gas cylinder, under the conditions of oxygen limit value 20.9% (volume fraction) ± 1.0% (volume fraction), the temperature control set point adjustment must not exceed the previous set value 4 °C to meet the requirements.
      • 11.3.1.4 After completing the adjustment of the combustion chamber set temperature, wait at least 10 min before starting a new calibration to ensure thermal equilibrium is reached.
      • 11.3.1.5 Each ignition delay period measurement result is reasonable if it is within the range 3.78 ms ± 0.06 ms.
      • 11.3.1.6 If any one of the three results exceeds the error range, suspect a system fault and activate the diagnostic program.
    • 11.3.2 Methylcyclohexane calibration reference material: after filtration, continuously measure the ignition delay period 2 times.
      • 11.3.2.1 Each ignition delay period measurement value is within the range 10.4 ms ± 0.6 ms, and the average of the two results is reasonable if it is within the range 10.4 ms ± 0.5 ms.
      • 11.3.2.2 If either of the two test values, or the average of the two measurement values, exceeds its respective range, it is not appropriate to continue system operation and the diagnostic program must be activated.
    • 11.3.3 Calibration of the combustion analyzer is considered complete only when both the n-heptane and methylcyclohexane calibration data are acceptable.
  • 11.4 Quality control: Carry out a periodic statistical quality assurance (quality control) program in accordance with the technical requirements of NB/SH/T 0843 or equivalent standards.
    • 11.4.1 At the beginning of each verification period, first perform a quality control test, separately measuring the ignition delay period of the check standard and the quality control sample.
    • 11.4.2 When using local nitrogen-oxygen mixed gas as charge air, a quality control test must be performed whenever a cylinder is replaced. Note: The oxygen content of the nitrogen-oxygen mixed gas in a new cylinder may differ from that of the previous cylinder, which can have a significant effect on the ignition delay period test value.
    • 11.4.3 Check standard test: after filtering n-heptane, perform a single measurement of the ignition delay period.
      • 11.4.3.1 If the test result meets the limits specified in NB/SH/T 0843 or equivalent standards, the result is considered reasonable.
      • 11.4.3.2 In accordance with the requirements of NB/SH/T 0843 or equivalent standards, before establishing the n-heptane ignition delay period deviation, based on the average of three reasonable n-heptane ignition delay period measurement results, ±0.07 ms may be used as the warning limit for the n-heptane ignition delay period deviation, and ±0.106 ms as the action limit (as described in 11.3.1). Note: The n-heptane warning limit and action limit are determined from round-robin test data.
    • 11.4.4 Quality control sample test: after filtering the quality control sample, measure the ignition delay period and calculate its derived cetane number.
      • 11.4.4.1 The quality control sample is a typical diesel fuel with a representative ignition delay period that can cover the main operating range of the combustion analyzer.
      • 11.4.4.2 If the ignition delay period of the sample measured by the combustion analyzer exceeds the usual range (too high or too low), another quality control sample with a different ignition delay period must be used to calibrate the system.
      • 11.4.4.3 If the test result meets the limits specified in NB/SH/T 0843 or equivalent standards, the result is reasonable.
    • 11.4.5 When the ignition delay period measurement values of both the check standard (n-heptane) and the quality control sample are reasonable, it indicates that the combustion analyzer can be used for sample determination. If either ignition delay period is unreasonable, first recalibrate the instrument, and then perform the ignition delay period test.
• Appendix C Combustion analyzer operating procedure:
  • C.1 Startup and warm-up: Turn the switch to "ON"; start the instrument warm-up program; typical heating time 1300 s ~ 1800 s, typical total warm-up time 1500 s ~ 2300 s (original text "1500g~2300s", requires confirmation against the source standard (source-text extraction)); if the heating time significantly exceeds the average (exceeds 5%), or the total warm-up time significantly increases (increases by 10%), it indicates that the combustion chamber heating element may have failed; open each compressed gas source valve and adjust the pressure; perform at least one ignition delay period pre-measurement on a typical diesel sample or n-heptane according to 11.2.
  • C.2 Operating steps for the fuel injection system: C.2.2 Flush the fuel injection system, fill the sample, and remove air bubbles; C.2.3 Drain the unused sample and clean the fuel system; C.2.4 After measuring an oil sample containing an unknown concentration (or a concentration greater than 2000 mg/kg) of a 2EHN cetane number improver, immediately drain the remaining sample and clean the fuel system (no adjustment of equipment hardware is required); if the 2EHN concentration exceeds 2000 mg/kg, flushing may be insufficient; after draining the remaining sample, clean the fuel tank and injection system with toluene or n-heptane.
  • C.3 Cleaning procedure for the pressure sensor assembly: periodically (twice daily) performing an ignition delay period test with n-heptane has the same cleaning effect as manually cleaning the pressure sensor; if the nozzle needle valve fails, fuel is sprayed directly onto the sensing surface of the pressure sensor, and only manual cleaning is possible.
  • C.4 Alternative procedure for cleaning the pressure sensor assembly.
  • C.5 Combustion chamber seal integrity check procedure: automatically checked by computer command, pressurize the combustion chamber with charge air, and monitor the pressure change within 20 s; the pressure drop rate should be less than 3.5 kPa/s (0.50 psi/s); if it exceeds this limit, poor sealing is determined, and it is recommended to activate the diagnostic program.
  • C.6 Combustion analyzer shutdown procedure: Check that all samples have been drained from the fuel injection system and fuel tank and cleaned; close the compressed gas cylinder valves; open the vent valve to release pipeline pressure and then close the vent valve; set the power switch to "OFF"; Note: After the combustion analyzer is shut down, the circulating cooling system must continue to run for 3 h.
• Appendix D Auxiliary program information:
  • D.1.1 An automatic sample test process includes 15 preliminary (pre-test injection) combustion cycles and 32 subsequent (test injection) combustion cycles. One combustion cycle includes: (1) charging the combustion chamber to the test pressure, (2) injecting a small portion of the oil sample into the combustion chamber, (3) releasing the combustion gases.
  • D.1.3 The average of 32 ignition delay period results is taken as the analytical result for the ignition delay period of the oil sample.
  • D.1.4 For every 1 cycles out of 32 combustion cycles, record: ignition delay period, derived cetane number, charge pressure, injection drive air pressure, charge temperature, combustion chamber pressure sensor temperature, injector nozzle cooling tube temperature, coolant return temperature, fuel injection pump temperature.
  • D.1.5 At the end of the test, the individual measured values, average values, minimum values, and maximum values of the above parameters from the 32 combustion cycles are automatically printed on the test report (see Appendix F).

9. Qualitative and Quantitative Calculation Formulas

• 13.1 Based on the average ignition delay period recorded in accordance with the requirements of 12.2.7, calculate the derived cetane number of the sample according to formula (1):
  • DCN = 4.460 + 186.6 / ID ………………(1)
  • Where: DCN — derived cetane number of the sample; ID — average ignition delay period of the sample, in milliseconds (ms).
• 13.2 Round the calculated derived cetane number of the sample to one decimal place.
• 13.3 The derivation and maintenance of formula (1) are given in Appendix E.
• 13.4 For samples with an ignition delay period lower than 3.1 ms or higher than 6.5 ms, the calculation of the derived cetane number is given in Appendix G.
• Appendix G Related equations:
  • G.1 For samples with an ignition delay period lower than 3.1 ms or higher than 6.5 ms, based on the average ignition delay period recorded in accordance with the requirements of 12.2.7, calculate the derived cetane number of the sample according to formula (G.1):
    • DCN = 83.99(ID − 1.512)^−0.088 + 3.547 ………………(G.1)
    • Where: DCN — derived cetane number of the sample; ID — average ignition delay period of the sample, in milliseconds (ms).
  • G.2 Round the calculated derived cetane number of the sample to one decimal place.
  • G.3 The equation (G.1) is derived from a related test program and includes the ASTM National Exchange Group (NEG) check fuels, heptamethylnonane, hexadecane, and an internal check fuel. Note: For samples with ignition delay less than 3.1 ms or greater than 6.5 ms, the derived cetane number calculated by this equation has no precision.
• Appendix E Derivation and maintenance of the DCN formula: The formula was derived using interlaboratory collaborative test data organized in 2004, and was initially validated using interlaboratory collaborative test data organized in 2002 and test data from the 2004 IP and NEG fuel exchange programs; the derivation of the formula is described in detail in report RR:D02-1602; it is continuously validated through the monthly NEG and IP fuel exchange programs, and is reviewed at least once every three years by ASTM D02.01 through the application of ASTM D6708.

10. Precision

• 15.1 Overview: The precision description is based on the results of an interlaboratory collaborative test study (conducted in 2002, with continuous supplementation from 2004 1 to 2009 7); multiple laboratories exchange samples monthly; results are reported to the ASTM National Exchange Group (NEG) and the British Energy Association (IP); test results are statistically analyzed according to ASTM D6300 or ISO 4259 standards. This includes 2002 years of round-robin test data (10 samples from 15 laboratories) and sample exchange data (145 samples exchanged among 34 laboratories). All samples cover the ID range 3.24 ms ~ 6.24 ms (corresponding to the DCN range 62.0 ~ 34.4).
• 15.2 Precision (95% confidence level):
  • 15.2.1 Repeatability r: The difference between two consecutive test results obtained by the same laboratory, using the same method, the same operator, the same instrument, and the same test sample shall not exceed the value specified in Table 1.
  • 15.2.2 Reproducibility R: The difference between two single, independent test results obtained by different laboratories, using the same method, different operators, and different instruments, on the same test sample shall not exceed the value specified in Table 1.
• Table 1 Repeatability and reproducibility of ignition delay and derived cetane number:

• Table 2 Typical values of repeatability and reproducibility of ignition delay:

• Table 3 Typical values of repeatability and reproducibility of derived cetane number:

• 15.3 Bias: The ignition delay determined by this standard has no bias, because ignition delay is only defined in this standard.
• 15.4 Relative bias between ASTM D613 (corresponding to GB/T 386): In accordance with ASTM D6708, using the 2002 interlaboratory collaborative test study and the 2004 to 2009 IP and NEG exchange programs, a statistical evaluation of the expected degree of agreement between the results of DCN and CN was conducted (95% confidence level).
  • 15.4.1 In ASTM D6708, there is no bias that can further improve the consistency between the test results of ASTM D6890 (corresponding to this standard) and ASTM D613 (corresponding to GB/T 386). Biases for specific samples as defined in ASTM D6708 may be observed in some samples.
  • 15.4.2 Using ASTM D6890 (corresponding to this standard) and ASTM D613 (corresponding to GB/T 386), samples of the same type and same properties within the studied range were tested separately, and the difference between the two sets of results does not exceed the reproducibility Rxy between the two methods as defined in ASTM D6708.
  • 15.4.3 Reproducibility limit between a single DCN result and a single CN result:
    • 15.4.3.1 Due to bias for specific samples, the difference between a single DCN and CN result may be greater than the reproducibility of their respective methods.
    • 15.4.3.2 Based on the results of the interlaboratory collaborative study, in long-term, correctly operated tests, for samples meeting the applicable range of this method, the difference between single results of DCN and CN does not exceed the Rxy in Table 4.
• Table 4 Reproducibility between the two methods:

• Note: Rxy = 0.1094 × [(DCN + CN)/2 − 11.02].
• Note 1: For any average value between the listed values, the corresponding reproducibility Rxy is calculated using the formula given in Table 4.
• Note 2: For certain specific samples, due to the bias between the measured values of this standard and GB/T 386, Rxy may exceed the reproducibility specified in this standard, or exceed the reproducibility specified in GB/T 386, or vice versa. It is recommended that users of this standard evaluate the expected value of predictions made according to Rxy to determine the applicability of using derived cetane number results to predict cetane number.

11. Report

• 14 Report the following information:
  • a) The standard number of this standard;
  • b) Sample information;
  • c) Date of determination;
  • d) Ignition delay, rounded to two decimal places;
  • e) Derived cetane number, rounded to one decimal place;
  • f) Average temperature of the charge air (°C), rounded to one decimal place;
  • g) Differences between the actual test procedure used and the test procedure specified in this standard, as agreed or otherwise arranged.
• Appendix F Example of test output (informative appendix): IQT Results—test cycle details, including sample sequence number, sample number, version, test method, date and time, operator, set point, authorization number, etc.; test output includes injection drive air pressure, charge pressure, derived cetane number, ignition delay, charge temperature (T4), minimum/maximum charge temperature, combustion chamber pressure sensor temperature (T3), minimum/maximum combustion chamber pressure sensor temperature, injector coolant return temperature (T7), fuel pump temperature (T2), maximum/minimum injector coolant temperature (T6max/T6min), and other parameters.

12. Normative references

• GB 252 Automotive diesel fuel
• GB/T 386 Determination of cetane number of diesel fuel
• GB/T 4756 Manual sampling of petroleum liquids (GB/T