ISO 5165 Petroleum products - Determination of the ignition quality of diesel fuels - Cetane engine method
7 Sampling and sample preparation
Samples shall be collected in accordance with ISO 3170, ISO 3171 or an equivalent national standard.

To minimize exposure to UV emissions, collect and store samples in opaque containers such as dark brown glass bottles, metal cans or minimally-reactive plastic containers.

Samples shall be brought to room temperature, typically 18 °C to 32 °C, before engine testing. If necessary, samples shall be filtered through a Type 1, Class A filter paper, conforming to ASTM E832-81, at room temperature and pressure before engine testing.

Inspect the sample for wax precipitation: if precipitates are present, bring the test sample to a temperature of at least 14 °C above the expected cloud point of the material being tested, taking care not to lose any lower boiling range components. The fuel sample should be homogeneous before engine testing or filtration.

8 Basic engine and instrument settings and standard operating conditions
8.1 Installation of engine equipment and instrumentation
Locate the cetane test engine in an area where it will not be affected by certain gases and fumes that can have a measurable effect on the CN test result.

Installation of the engine and instrumentation requires placement of the engine on a suitable foundation and hook-up of all utilities. Engineering and technical support for this function is required, and the user shall be responsible for conformity with all applicable codes and installation requirements. Proper operation of the test engine requires assembly of a number of engine components and adjustment of a series of engine variables to prescribed specifications. Some of these settings are established by component specifications, others are established at the time of engine assembly or after overhaul and still others are engine-running conditions that shall be observed and/or determined by operator adjustment during the testing process.

8.2 Engine speed
The engine speed shall be 900 r/min +/- 9 r/min when the engine is operating with combustion with a maximum variation of 9 r/min occurring during a rating. Engine speed when combustion is occurring shall not be more than 3 r/min greater than for motoring without combustion.

8.3 Valve timing
The engine shall use a four-stroke cycle with two crankshaft revolutions for each complete combustion cycle. The two critical valve events are those that occur near top-dead-center (t.d.c.); intake valve opening and exhaust valve closing. Intake valve opening shall occur 10.0° +/- 2.5° after-top-dead-center (a.t.d.c.) with closing at 34° after-bottom-dead-center (a.b.d.c.) on one revolution of the crankshaft and flywheel. Exhaust valve opening shall occur 40° before-bottom-dead-center (b.b.d.c.) on the second revolution of the crankshaft or flywheel with closing at 15.0° +/- 2.5° a.t.d.c. on the next revolution of the crankshaft or flywheel. ASTM D 613, Annex A4 (Apparatus Assembly and Setting Instructions) defines the procedures for camshaft timing which shall apply for this International Standard.

8.4 Valve lift
Intake- and exhaust- cam lobe contours, while different in shape, shall have a contour rise of 6.223 mm to 6.350 mm (0.245 in to 0.250 in) from the base circle to the top of the lobe so that the resulting valve lift shall be 6.045 mm +/- 0.05 mm (0.238 in +/- 0.002 in). ASTM D613, Annex A4 (Apparatus Assembly and Setting Instructions) defines the procedures for measuring valve lift which shall apply for this International Standard.

8.5 Fuel pump timing
Closure of the pump plunger inlet port shall occur at a flywheel crank angle between 300° and 306° on the engine compression stroke when the fuel flow-rate-micrometer is set to a typical operating position and the variable timing device lever is at full advance (nearest to operator). See ASTM D613, Annex A4 (Apparatus Assembly and Setting Instructions) for detailed instructions on setting and checking the fuel pump timing which shall apply for this International Standard.

8.6 Fuel pump inlet pressure
A minimum fuel head established by assembly of the fuel tanks (storage reservoirs) and flow-rate-measuring burette so that the discharge from them is 635 mm +/- 25 mm above the centerline of the fuel injection pump inlet.

8.7 Direction of engine rotation
Clockwise rotation of the crankshaft shall occur when observed from the front of the engine.

8.8 Injection timing
This shall occur 13.0° b.t.d.c. for the sample and reference fuels.

8.9 Injector nozzle opening pressure
This shall be 10.3 MPa +/- 0.34 MPa.

8.10 Injection flow rate
This shall be (13.0 +/- 0.2) ml/min [(60 +/- 1)s/13.0 ml].

8.11 Injector coolant passage temperature
This shall be 38 °C +/- 3 °C.

8.12 Valve clearances
Setting the clearance between each valve stem and valve rocker half-ball to the following approximate measurements, upon assembly with the engine cold prior to being operated, will typically provide the controlling engine-running and hot clearance:
- intake valve 0.075 mm (0.004 in);
- exhaust valve 0.330 mm (0.014 in).
These clearances should ensure that both valves have sufficient clearance to cause valve seating during engine warm-up. The adjustable-length valve push rods shall be set so that the valve rocker adjusting screws have adequate travel to permit the final clearance setting. Engine running and hot clearance for both intake and exhaust valves shall be set to 0.20 mm +/- 0.025 mm (0.008 in +/- 0.001 in) measured under standard operating conditions with the engine running at equilibrium conditions on a typical diesel fuel oil.

8.13 Oil pressure
This shall be 172 kPa to 207 kPa.

NOTE 11 The CFR engine unit is equipped with a pressure gauge in psi and the oil pressure shall be 25 psi to 30 psi. ASTM D613, Annex A4 (Apparatus Assembly and Setting Instructions) defines the adjustment procedure which shall apply for this International Standard.

8.14 Oil temperature
This shall be 57 °C +/- 8 °C.

NOTE 12 The CFR engine unit is equipped with a temperature gauge in degrees Fahrenheit and the oil temperature shall be 135 °F +/- 15 °F.

8.15 Cylinder jacket coolant temperature
This shall be 100 °C +/- 2 °C.

8.16 Intake air temperature
This shall be 66 °C +/- 0.5 °C.

8.17 Basic ignition delay
This shall be 13.0° for the sample and the reference fuels.

8.18 Cylinder jacket coolant level
Treated coolant added to the cooling condenser/cylinder jacket to a level just observable in the bottom of the condenser sight-glass, with the engine cold prior to being operated, will typically provide the controlling engine, running and hot operating level.

8.19 Engine-crankcase lubricating oil level
The controlling engine-running and hot operating level of the oil in the crankcase shall be approximately mid-position in the crankcase sight-glass.

NOTE 13 Oil added to the crankcase so that the level is near the top of the sight-glass, with the engine cold prior to being operated, will typically provide this condition.

8.20 Crankcase internal pressure
As measured by a gauge or manometer connected to an opening to the inside of the crankcase through a snubber orifice to minimize pulsations, the pressure shall be less than zero (a vacuum) and typically from 25 mm to 150 mm of water less than atmospheric pressure. Vacuum shall not exceed 254 mm of water.

8.21 Exhaust back-pressure
As measured by a gauge or manometer connected to an opening in the exhaust surge tank or main exhaust stack through a snubber orifice to minimize pulsations, the static pressure should be as low as possible, but shall not create a vacuum nor exceed 254 mm of water differential in excess of atmospheric pressure.

8.22 Exhaust and crankcase breather system resonance
The exhaust and crankcase breather piping systems shall have internal volumes and be of such length that gas resonance does not result.

NOTE 14 ASTM D613, Appendix X2 (Operating Techniques) provides a suitable procedure to determine if resonance exists in the application of this International Standard.

8.23 Piston over-travel
Assembly of the cylinder to the crankcase shall result in the piston protruding above the top of the cylinder surface 0.381 mm +/- 0.025 mm (0.015 in +/- 0.001 in) when the piston is at t.d.c. Proper positioning is accomplished through the use of plastic or paper gaskets, available in several thicknesses and selected by trial and error for assembly between the cylinder and crankcase deck.

8.24 Belt tension
The belts connecting the flywheel to the absorption motor shall be tightened, after the initial break-in so that, with the engine stopped, a 2.25 kg weight suspended from one belt halfway between the flywheel and motor pulley depresses the belt approximately 12.5 mm.

8.25 Injector opening or release pressure
The pressure adjusting screw is adjustable and shall be set to release fuel at a pressure of 10.3 MPa +/- 0.34 MPa. This setting shall be checked each time the nozzle is reassembled and after cleaning.

NOTE 15 Use of a commercial injector nozzle bench tester is recommended. ASTM D613, Annex A4 (Apparatus Assembly and Setting Instructions) provides details which should apply for this International Standard.

CAUTION - Personnel shall avoid contact with the spray pattern from injector nozzles because of the high pressure which can penetrate the skin. Spray pattern performance checks shall be made in a hood or where adequate ventilation ensures that inhalation of the vapours is avoided.

8.26 Injector spray pattern
The injector nozzle spray pattern shall be checked for symmetry and characteristics by inspection of the impression of a single injection made on a piece of filter paper or other slightly absorbent material placed at a distance of approximately 76 mm from the nozzle.

8.27 Indexing handwheel reading
8.27.1 General
Handwheel readings are a simple and convenient indication of engine compression ratio which is a critical variable in the cetane method of test.

NOTE 16 The actual compression ratio is not important but an indication of compression ratio which relates to CN is a useful guide for selecting reference fuels to bracket the sample of diesel fuel oil. Indexing the handwheel when the engine is new, or any time the matched handwheel assembly/cylinder head combination is interchanged or mechanically reassembled, involves setting the variable compression plug, setting the micrometer drum and scale and setting the handwheel reading. ASTM D613, Appendix A3, (Maintenance Techniques), provides handwheel assembly reworking instructions for application of this International Standard.

8.27.2 Basic setting of variable compression plug
Position the variable compression plug so that the flat surface is just visible and exactly in line with the edge of the threads of the combustion pickup hole, as verified with a straightedge.

8.27.3 Setting handwheel micrometer drum and scale
With the variable compression plug at the basic setting, set the handwheel drum and scale so that the handwheel reads 1000.

NOTE 17 For cylinders which have been rebored to oversize diameters, the handwheel micrometer drum and scale setting may be offset an appropriate amount to achieve unit operation with comparable handwheel readings. See ASTM D613 for recommended settings.

8.27.4 Setting handwheel reading
Tighten the small locking handwheel snugly by hand to ensure that the variable compression plug is held in place in the bore. Loosen the lock nut of the large handwheel and remove the locking "L" shaped key. Turn the large handwheel so that the edge of the drum is in alignment with the 1000 or other selected graduation on the horizontal scale. Reinstall the L-shaped key in the nearest keyway slot of the large handwheel with the shorter leg in the handwheel. Any slight shifting of the handwheel to achieve slot line-up will not affect the indexing. Tighten the lock nut hand-tight to hold the key in place. Remove the locating screw from the drum and rotate the drum so that the zero graduation mark is in line with the selected reading. Locate the screw hole in the drum which lines up with the handwheel hub hole and reinstall the locating screw. Wrench tighten the large handwheel lock nut and recheck that the variable compression plug is properly positioned and the handwheel reading is in accordance with the selected value.

8.28 Basic compression pressure
At a handwheel reading of 1000, the compression pressure for an engine operated at a standard barometric pressure of 101.3 kPa shall be 3275 kPa +/- 138 kPa when read as quickly as possible after shutdown of the engine which has been at standard operating conditions. If the condition is not within limits, recheck the basic handwheel setting and, if necessary, perform mechanical maintenance.

NOTE 18 For engines operated at other than standard barometric pressure, the compression pressure will typically be in proportion to the ratio of the local barometric pressure divided by standard barometric pressure. As an example, an engine located where the barometric pressure is 94.6 kPa would be expected to have a compression pressure of approximately 3060 kPa +/- 138 kPa.
CPL = 3275 x pL/pSTD
where
CP L is the compression pressure at the local barometer, in kilopascals;
pL is the barometric pressure at the engine location, in kilopascals;
pSTD is the standard barometric pressure, in kilopascals.

NOTE 19 The ratio pL/pSTD is independent of measuring units, provided both elements are in the same units. ASTM D613, Annex A4 (Apparatus Assembly and Setting Instructions) provides instructions for checking compression pressure which shall apply for this International Standard. Compression pressure testing using a compression pressure gauge shall be completed in as short a period of time as possible, to avoid the possibility of combustion occurrence due to the presence of any small amount of oil in the gauge or combustion chamber.

8.29 Fuel-pump lubricating oil level
With the engine stopped, sufficient engine-crankcase lubricating oil shall be added to the pump sump so that the level is at the mark on the dip stick.

NOTE 20 As a result of engine operation, especially when the pump barrel/plunger assembly begins to wear, the level in the sump will increase due to fuel dilution as observed through a clear plastic side-plate on the pump housing. When the level rises appreciably, the sump should be drained and a fresh charge of oil added.

8.30 Fuel-pump timing gear-box oil level
With the engine stopped, unplug the openings on the top and at the mid-height of either side of the gear box. Add sufficient engine-crankcase lubricating oil through the top hole to cause the level to rise to the height of the side opening. Replace both openings.

NOTE 21 The pump and timing gear box oil sumps are not connected to each other and the lubrication for the two is independent.

8.31 Setting instrumentation reference pickups
Positioning of the reference pickups is important to ensure that timing of the injection and ignition delay functions is uniform and correct. The two reference pickups, which are identical and interchangeable, are installed in a bracket positioned over the flywheel so that they clear the flywheel indicator which triggers them. Position each pickup in the bracket so that it is properly referenced to the flywheel indicator in accordance with the instructions supplied with the specific pickup. Measurement of pickup to flywheel indicator clearance, if required, shall be made using a non-magnetic feeler gauge.

8.32 Setting injector pickup gap
Set the air gap to typically 1 mm (0.040 in) with the engine stopped.

NOTE 22 Individual pickups may require more or less air gap to obtain steady meter operation when the engine is ultimately running. However, too little gap can cause the ignition delay angle display to drive off scale.

9 Calibration and engine qualification
9.1 Engine compliance
The engine shall be commissioned in a manner that all settings and operating conditions are at equilibrium and in compliance with basic engine and instrument settings and standard operating conditions.

NOTE 23 Engine warm-up requires typically 1 h to ensure that all critical variables are stable.

9.2 Checking performance on check fuels
This engine test does not have any satisfactory standardization fuel blend or blends to qualify the engine. Test one or more of the check fuels as a guide to engine performance.

Engine performance may be judged to be satisfactory if the CN rating obtained on a check fuel is within the following tolerance range:
Tolerance limits = CNCF +/- 1.5 x sCF
where
CNCF is the average CN of the check fuel calibration data;
1.5 is a selected tolerance limit factor (K) for normal distributions;
sCF is the standard deviation of the check fuel calibration data.

NOTE 24 This statistical tolerance limit factor (K), based on a sample size (n), permits an estimation of the percentage of engines that would be able to rate the check fuel within the calculated tolerance limits. Based on a calibration data set of 17 to 20 ratings, and a value of K = 1.5, it is estimated that, in the long run, in 19 cases out of 20, at least 70 % of the engines would rate the check fuel within the calculated tolerance limits.

9.3 Check in the case of non-conformity
If the results are outside this tolerance range, check all operating conditions, followed by mechanical maintenance which may require critical parts replacement.

NOTE 25 The injector nozzle can be a very critical factor and this should be the first item checked or replaced.