GB/T 33298-2016 Determination of cetane number of diesel fuels — Air flow adjustment method

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

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

• Standard number: GB/T 33298—2016
• Chinese title: Determination of cetane number of diesel fuels — Air flow adjustment method
• English title: Standard test method for determining cetane number of diesel fuels — Airflow regulation
• Replacement relationship: not provided in the available source (the foreword only states that it was drafted in accordance with GB/T 1.1—2009, and does not mention any replaced standard)
• Publication/implementation: published on 2016-12-13, implemented on 2017-07-01
• Custodianship: proposed by the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280); under the custodianship of SAC/TC 280/SC 1
• Drafting organizations: Fushun Research Institute of Petroleum and Petrochemicals, Sinopec Corp., etc. (see foreword for details)
• Main drafters: Zhang Huicheng, Guo Yaping, Gao Bo, Yang Xiaohui, Zhang Bo, Wu Jinlun, Jin Wu, Cao Wenlei, Wang Xiangfu, Ding Minglin

2. Scope of application and non-applicability

• Applicable to the quantitative determination of the cetane number of compression-ignition engine fuels.
• Cetane number range 0–100, typical test range 25–70.
• It may also be used for non-conventional fuels, such as synthetic fuels, biodiesel and similar products, but the precision remains to be determined.
• Not applicable: no explicit exclusion clause is provided in the available source.

3. Method principle

A dedicated cetane number testing machine is used (a dedicated diesel engine with a standard single cylinder, four strokes, variable intake air quantity, and injection advance angle adjustable at any time). Under specified operating conditions, the sample is made to obtain a defined ignition delay period by changing the air quantity, and the air meter reading is recorded; according to the sample air meter reading, two standard fuels with a difference of no more than 5 cetane number units are selected, and a defined ignition delay period is obtained by the same method, so that the sample air meter reading lies between the air meter readings of the two standard fuels, and the cetane number of the sample is calculated by interpolation. (Chapter 4)

4. Reagents and materials (purity / preparation)

• 8.1 Primary standard fuels
  • 8.1.1 n-Hexadecane: purity ≥99.0% (volume fraction), cetane number 100.
  • 8.1.2 Heptamethylnonane: purity ≥98.0% (volume fraction), cetane number 15.
  • 8.1.3 n-Hexadecane and heptamethylnonane are mixed by volume ratio, CN = 100×V n-hexadecane + 15×V heptamethylnonane (formula 1), and the result is taken to two decimal places.
  • 8.1.4 Each batch of primary standard fuel shall have a product factory certificate of conformity (meeting the requirements of GB/T 386); for physical-chemical properties, see C.1 in Annex C.
• 8.2 Secondary standard fuels
  • 8.2.1 T fuel: a diesel fuel with a typical CN_ARV of 73~75.
  • 8.2.2 U fuel: a diesel fuel with a typical CN_ARV of 20~22.
  • 8.2.3 For routine determination, secondary standard fuels calibrated with primary standard fuels and their volume-ratio mixtures may be used; each batch shall have a factory certificate of conformity (meeting GB/T 386); for properties, see C.2 in Annex C.
  • 8.2.4 T, U fuels shall be stored and used at 0 ℃ or above; low-temperature fuels shall be heated before use to at least 15 ℃ above the cloud point of the fuel in the container (cloud point tested according to GB/T 6986), and maintained for at least 30 min, then re-mixed uniformly.
• 8.3 Check fuels
  • 8.3.1 Low cetane number check fuel: typical CN_ARV is 38~42.
  • 8.3.2 High cetane number check fuel: typical CN_ARV is 50~55.
  • 8.3.3 Two typical fuels calibrated with primary standard fuels and having fixed cetane numbers, dedicated to checking the evaluation accuracy of the testing machine, and not to be mixed with other fuels.
  • 8.3.4 Each batch shall have a factory certificate of conformity (meeting GB/T 386), with physical-chemical properties and cetane number attached; for properties, see C.3 in Annex C.
• 8.4 Reagents
  • 8.4.1 Cylinder jacket coolant: water is the coolant, boiling point 100 ℃±2 ℃; when altitude has an effect, water with a commercial glycol-type antifreeze may be used, and the added amount shall meet the boiling point requirement; a commercial multifunctional water treatment agent shall be added; the water shall meet the grade-three water requirements of GB/T 6682.
  • 8.4.2 Crankcase lubricating oil: viscosity grade SAE30 of SF/CD or SG/CE, containing detergent additives, kinematic viscosity at 100 ℃ of 9.3 mm²/s~12.5 mm²/s, viscosity index not less than 85; lubricating oils with viscosity index improvers and multigrade lubricating oils shall not be used; kinematic viscosity is determined according to GB/T 265.

5. Instruments and equipment

• 7.1 Air flow adjustment method cetane number testing machine: a dedicated single-cylinder diesel engine capable of continuously changing the cylinder intake air quantity, including a fuel delivery system, an adjustable compression pressure system, a starting motor, an auxiliary stabilization system and instruments; fixed compression ratio 21, air meter readings expressed as relative values; the overall structure is shown in Figure 1, and the component arrangement is shown in Figure 2.
• 7.2 Main technical parameters of the dedicated diesel engine (Table 1):
  • Engine type: single cylinder, horizontal, four-stroke
  • Cylinder diameter: 90 mm
  • Cylinder stroke: 90 mm
  • Cylinder working capacity: 573 mL
  • Compression pressure: measurement
  • Compression ratio adjustment method: air flow adjustment
  • Rated speed: 1 000 r/min
  • Cooling method: closed water cooling
  • Starting method: electric starting
  • Injection advance angle: 20° before top dead center
  • Ignition delay angle: 20°
  • Injection pressure: 12.75 MPa
  • Compression pressure range: 0 kPa–20 kPa, satisfying compression ignition of fuels with cetane numbers 15–100
• 7.3 Ignition delay period meter: measures the injection and ignition delay time, expressed in crankshaft rotation angle degrees, with a resolution display accuracy of 0.1°.
• 7.4 Air meter: a reading display meter for the compression pressure adjustment system, display range 0–9999, display accuracy ±1, corresponding to an adjusted compression pressure of 0 kPa–20 kPa.
• 7.5 Compression pressure adjustment system: satisfies linear adjustment, range 0 kPa~20 kPa, adjustment accuracy ±2.5%.
• 7.6 Combustion sensor: outputs a positive pulse with a peak voltage of 1.5 V.

6. Recommended operating conditions

• 10.3 Standard operating conditions:
  • 10.3.1 Engine speed: 1000 r/min±10 r/min
  • 10.3.2 Injection advance angle: 20.0° before top dead center
  • 10.3.3 Injector injection pressure: 12.75 MPa±0.5 MPa
  • 10.3.4 Injection quantity: (180 s±3 s) is 20 mL, (90 s±1.5 s) is 10 mL
  • 10.3.5 Valve clearance: intake valve 0.20 mm±0.025 mm, exhaust valve 0.25 mm±0.025 mm
  • 10.3.6 Cylinder coolant temperature: 100 ℃±2 ℃
  • 10.3.7 Intake air manifold temperature: 66 ℃±0.5 ℃
  • 10.3.8 Crankcase lubricating oil temperature: 57 ℃±8 ℃
  • 10.3.9 Clearance between the reference sensor magnetic needle and the flywheel magnetic needle: 2.0 mm~2.5 mm
  • 10.3.10 Clearance between the injector needle valve extension rod and the injection sensor magnetic needle: 0.5 mm~0.8 mm
  • 10.3.11 Ignition delay period: 20.0°
• 10.2 Startup and warm-up: switch the selector valve to connect the warm-up fuel sample tube; press the start button, appropriately increase the fuel supply to facilitate initial ignition; rotate the intake air quantity control knob counterclockwise to increase the intake air quantity; after continuous ignition, warm up for about 30 min until the standard operating conditions are reached.
• 11.1 The heating-up time of the testing machine generally requires 30 min.

7. Sampling and sample preparation

• 9.1 Sampling shall be carried out according to GB/T 4756 or GB/T 27867.
• 9.2 Opaque containers (dark brown glass bottles, metal cans or less reactive plastic containers) shall be used for both sampling and storing samples, and exposure to sunlight or ultraviolet light shall be minimized.
• 9.3 Before determination, the sample shall be placed indoors until it is close to room temperature.
• 12.1 Add the sample to the middle sample tube, and thoroughly flush the fuel system lines by pressing the drain valve button to avoid air entering.

8. Analysis procedure

• 10.1 Testing machine startup check: the coolant addition amount is at the 1/3 height of the display tube; the crankcase lubricating oil level is between the upper and lower scale lines when the machine is cold; the flywheel rotates counterclockwise when facing it; open the cooling coil tap water valve until water is seen at the drain outlet; add warm-up fuel to one sample tube to expel air from the oil circuit.
• 12.2 Fuel flow rate measurement and adjustment: usually use the 10 mL metering bulb; rotate the fuel supply adjustment knob counterclockwise to increase the fuel supply, and vice versa to decrease it; the final flow rate is (180 s±3 s)/20 mL or (90 s±1.5 s)/10 mL; record the fuel supply adjustment knob reading for reference.
• 12.3 Ignition delay period meter reference point adjustment: press the switch to “CAL”, observe the upper and lower display windows, and adjust the upper and lower displays to 25.0°±0.2° through the adjustment knob on the right side.
• 12.4 Injection advance angle adjustment: press the switch to "RUN", the upper row window displays the actual injection advance angle, adjust the knob to make it reach 20.0°±0.2°.
• 12.5 Ignition delay period measurement: press the switch to "RUN", rotate the intake air quantity adjustment knob (the gas meter indicated value is proportional to the cylinder pressure and temperature), finally adjust the ignition delay period meter (lower row window) to be fixed within the range of 20°±0.2°, record the gas meter reading.
• 12.6 Select two standard fuels differing by no more than 5 cetane number units, when their ignition delay period is 20°, the sample gas meter reading is between the gas meter readings of the two standard fuels, the test procedure is the same as the sample determination; the standard fuels have similar properties, when changing them it is not necessary to measure the fuel injection quantity per unit time.
• 12.7 After changing the fuel, run the engine for about 2 min to ensure the fuel system is flushed clean and stable before testing.
• 12.8 Ignition delay period reading: the test time is generally stable within 5 min~10 min, record the reading after stabilization; the reading time for the sample and each standard fuel should be consistent, with a difference not greater than 3 min.
• 12.9 The sample and standard fuels are each tested at least three times, in the cyclic order of sample, standard fuel 1, standard fuel 2, and all test conditions are rechecked during repeated tests.
• 13 Shutdown: when the sample CN is lower than 45, before shutdown first add preheated fuel to one sample inlet tube (CN should be higher than 45), wait until it is obviously injected into the engine combustion chamber (as can be seen from the ignition delay period meter indication), then press the stop button; cut off the power to the ignition delay period meter, drain the fuel from the sample cup and pipeline; turn off the main power; close the cooling water valve.
• 11 Calibration and verification: the testing machine can be adjusted to a good state using check fuel; if the check fuel test result is within the allowable limit calculated according to formula (2)), the performance is good; allowable limit = CN_ARV ± 1.5×S_ARV (formula 2); if it exceeds the allowable limit, sample determination cannot be carried out, and all operating conditions should be checked.

9. Qualitative and Quantitative and Calculation Formulas

• 14.1 Calculate the arithmetic mean of the gas meter readings for the sample and each standard fuel separately, retaining to one decimal place.
• 14.2 Interpolation calculation (formula 3): CN = CN₁ + (CN₂ − CN₁) × (a − a₁)/(a₁ − a₂) Where: CN— sample cetane number; CN₁—low ignition quality standard fuel cetane number; CN₂—high ignition quality standard fuel cetane number; a— arithmetic mean of sample gas meter readings; a₁—arithmetic mean of low cetane number secondary standard fuel gas meter readings; a₂—arithmetic mean of high cetane number secondary standard fuel gas meter readings. (Note: In formula 3, the original text source-text extraction is displayed as "CN=CN, + (CN.-CN,)91_Q / a1[unreadable separator]a2", suspected to have source-text extraction noise, requires confirmation against the source standard (source-text extraction).)
• 14.3 The calculated cetane number is rounded to one decimal place.
• Calculation of primary standard fuel CN is given in formula (1): CN = 100×Vn-hexadecane + 15×Vheptamethylnonane.

10. Precision

• The precision is based on cooperative tests of 7 laboratories, 10 petroleum-based diesel samples in the cetane number range 25~70, statistically analyzed according to GB/T 6683 (95% confidence level).
• 16.1 Repeatability r: The difference between two consecutive test results obtained by the same laboratory, same operator, same instrument, same sample shall not exceed formula (4): r = 0.138 m^2.4689 (m is the arithmetic mean of the two test results).
• 16.2 Reproducibility R: The difference between two single independent test results obtained by different laboratories, different operators, different instruments, same sample shall not exceed formula (5): R = 0.722 m^0.4342 (m is the arithmetic mean of the two test results).
• Table 2 Typical values of repeatability and reproducibility:

  Average cetane number level	Repeatability r	Reproducibility R
  26	0.6	3.0
  30	0.7	3.2
  35	0.7	3.4
  40	0.8	3.6
  45	0.8	3.8
  50	0.9	3.9
  55	0.9	4.1
  60	0.9	4.3
  65	1.0	4.4
  68	1.0	4.5

11. Report

• 15.1 Report the calculated result as the cetane number of the sample.
• 15.2 If the sample was filtered before testing, it should be stated in the report.

12. Normative References

• GB/T 265 Petroleum products—Determination of kinematic viscosity and calculation of dynamic viscosity
• GB/T 386 Determination of cetane number of diesel fuels
• GB/T 4756 Petroleum liquids—Manual sampling
• GB/T 6682 Water for analytical laboratory use—Specification and test methods
• GB/T 6683 Petroleum products—Determination of precision data in relation to methods of test
• GB/T 6986 Petroleum products—Determination of cloud point (the extracted method-title wording is garbled, requires confirmation against the source standard (source-text extraction))
• GB/T 27867 Petroleum liquids—Automatic pipeline sampling
• References: GB/T 511, GB/T 1884, GB/T 1885, GB/T 2430, GB/T 6536, GB/T 6540, SH/T 0234, SH/T 0236, SH/T 0604, SH/T 0724

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference Q&A