ASTM D613 standard test method for cetane number of diesel fuel oil
7. Apparatus
7.1 Engine Equipment - This test method uses a single cylinder engine which consists of a standard crankcase with fuel pump assembly, a cylinder with separate head assembly of the precombustion type, thermal syphon recirculating jacket coolant system, multiple fuel tank system with selector valving, injector assembly with specific injector nozzle, electrical controls, and a suitable exhaust pipe. The engine is belt connected to a special electric power-absorption motor which acts as a motor driver to start the engine and as a means to absorb power at constant speed when combustion is occurring (engine firing). See Fig. 1.

7.1.1 See Annex A2 for detail and description of all critical, non-critical and equivalent engine equipment.

7.2 Instrumentation - This test method uses an electronic instrument to measure injection and ignition delay timing as well as conventional thermometry, gages and general purpose meters.

7.2.1 A Cetane Meter, (Ignition Delay Meter) is critical and shall be used for this test method.

7.2.2 See Annex A3 for detail and description of all critical, non-critical and equivalent instrumentation.

7.3 Reference Fuel Dispensing Equipment - This test method requires repeated blending of two secondary reference fuel materials in volumetric proportions on an as-needed basis. Measurement shall be performed accurately because rating error is proportional to blending error.

7.3.1 Volumetric Blending of Reference Fuels - Volumetric blending has historically been employed to prepare the required blends of reference fuels. For volumetric blending, a set of two burets or accurate volumetric ware shall be used and the desired batch quantity shall be collected in an appropriate container and thoroughly mixed before being introduced to the engine fuel system.

7.3.1.1 Calibrated burets or volumetric ware having a capacity of 400 or 500 mL and a maximum volumetric tolerance of more or less 0.2 % shall be used. Calibration shall be verified in accordance with Practice E 542.

7.3.1.2 Calibrated burets shall be outfitted with a dispensing valve and delivery tip to accurately control dispensed volume. The delivery tip shall be of such size and design that shutoff tip discharge does not exceed 0.5 mL.

7.3.1.3 The rate of delivery from the dispensing system shall not exceed 500 mL per 60 s.

7.3.1.4 The set of burets for the reference and standardization fuels shall be installed in such a manner and be supplied with fluids such that all components of each batch or blend are dispensed at the same temperature.

7.3.1.5 See Appendix X1, Volumetric Reference Fuel Blending Apparatus and Procedures, for typical dispensing system information.

7.3.2 Gravimetric Blending of Reference Fuels - Use of blending systems that allow preparation of the volumetrically-defined blends by gravimetric (mass) measurements based on the density of the individual components is also permitted, provided the system meets the requirement for maximum 0.2 % blending tolerance limits.

7.3.2.1 Calculate the mass equivalents of the volumetrically-defined blend components from the densities of the individual components at 15.56°C (60°F).

7.4 Auxiliary Apparatus:
7.4.1 Injector Nozzle Tester - The injector nozzle assembly shall be checked whenever the injector nozzle is removed and reassembled to ensure the initial pressure at which fuel is discharged from the nozzle is properly set. It is also important to inspect the type of spray pattern. Commercial injector nozzle testers which include a lever-operated pressure cylinder, fuel reservoir and pressure gage are available from several sources as common diesel engine maintenance equipment.

7.4.2 Special Maintenance Tools - A number of specialty tools and measuring instruments should be utilized for easy, convenient and effective maintenance of the engine and testing equipment. Lists and descriptions of these tools and instruments are available from the manufacturers of the engine equipment and those organizations offering engineering and service support for this test method.

8. Reagents and Reference Materials
8.1 Cylinder Jacket Coolant - Water shall be used in the cylinder jacket for laboratory locations where the resultant boiling temperature shall be 100 more or less 2°C (212 more or less 3°F). Water with commercial glycol-based antifreeze added in sufficient quantity to meet the boiling temperature requirement shall be used when laboratory altitude dictates. A commercial multi-functional water treatment material should be used in the coolant to minimize corrosion and mineral scale that can alter heat transfer and rating results.

8.1.1 Water shall be understood to mean reagent water conforming to Type IV of Specification D1193.

8.2 Engine Crankcase Lubricating Oil - An SAE 30 viscosity grade oil meeting service classification SF/CD or SG/CE shall be used. It shall contain a detergent additive and have a kinematic viscosity of 9.3 to 12.5 cSt (mm2 per s) at 100°C (212°F) and a viscosity index of not less than 85. Oils containing viscosity index improvers shall not be used. Multigraded oils shall not be used. (Warning - Lubricating oil is combustible, and its vapor is harmful. See Annex A1.)

8.3 Primary Reference Fuels - (Warning - Primary Reference Fuel - Combustible. Vapor Harmful. See Annex A1.)

8.3.1 n-Cetane (n-hexadecane) - With a minimum purity of 99.0 % as determined by chromatographic analysis shall be used as the designated 100 cetane number component.

8.3.2 Heptamethylnonane (2,2,4,4,6,8,8-heptamethylnonane) - With a minimum purity of 98 % as determined by chromatographic analysis shall be used as the designated 15 cetane number component.

8.4 Secondary Reference Fuels - (Warning - Secondary Reference fuel - Combustible. Vapor Harmful. See Annex A1.)

8.4.1 T Fuel - Diesel fuel with a CNARV typically in the range of 73 to 75.

8.4.2 U Fuel - Diesel fuel with a CNARV typically in the range of 20 to 22.

8.4.3 Storage and use of T Fuel and U Fuel should be at temperatures above 0°C (32°F) to avoid potential solidification, particularly of T Fuel. Before a container that has been stored at low temperature is placed in service, it should be warmed to a temperature of at least 15°C (27°F) above its Cloud Point. (See Test Method D2500.) It should be held at this temperature for a period of at least 30 min and then the container should be thoroughly remixed.

8.5 Check Fuels - Diesel fuel oils typical of Specification D975 grade No. 2-D distillate fuel oil. (Warning - Check Fuel - Combustible. Vapor Harmful. See Annex A1.)

8.5.1 Low Cetane Check Fuel - With a CNARV typically in the range of 38 to 42.

8.5.2 High Cetane Check Fuel - With a CNARV typically in the range of 50 to 55.

9. Sampling
9.1 Collect samples in accordance with Practice D4057 or D4177.

9.1.1 Protection from Light - Collect and store sample fuels in an opaque container such as a dark brown glass bottle, metal can, or a minimally reactive plastic container to minimize exposure to UV emissions from sources such as sunlight or fluorescent lamps.

9.2 Fuel Temperature - Samples shall be brought to room temperature typically 18 to 32°C (65 to 90°F) before engine testing.

9.3 Filtration - Samples may be filtered through a Type I, Class A filter paper at room temperature and pressure before engine testing. See Specification E 832.