ASTM D4858 Method for Determination of the Tendency of Lubricants
ASTM D4858 Standard Test Method for Determination of the Tendency of Lubricants to Promote Preignition in Two-Stroke-Cycle Gasoline Engines
6. Apparatus
6.1 Test Engine and Stand:
6.1.1 Test Engine Configuration - A Yamaha CE-50 49 cm3 loop-scavenged air-cooled two-stroke-cycle engine is used. This has 40 mm (1.57 in.) bore, 39.2 mm (1.54 in.) stroke, with an aluminum piston operating in a cast iron cylinder bore. The cylinder head is removable, with a hemispherical combustion chamber. For the purposes of this test the head shall be modified as specified in Further details are given in Annex A1.

NOTE 2 - The engine designation normally includes a final letter indicating the model, such as CE-50S, the model on which this test was developed. If this model is not available check the suitability for this test of available models with the manufacturer.

6.1.2 Test Stand - The dynamometer shall be able to absorb 2.5 kW (3.4 hp) at 4000 to 6000 r/min with an inherent torque measurement accuracy of +/-0.5 % or better, and be capable of maintaining 4000 +/- 30 r/min with varying power input. A direct shaft drive or a belt drive from the engine crankshaft may be used. A complete test stand assembly, as shown in Fig. 1, is available.

6.1.3 Cooling Blower - The original internal engine fan shall be removed or have its blades machined off. A variable delivery blower with a free flow capacity of about 34 m3/min (1200 ft3/min) of air is recommended. The flow from the blower shall be directed toward the intake side of the engine. A suitable arrangement is shown in Fig. 1.

6.1.4 Fuel System - Fuel delivery pressure shall be maintained at 19 to 21 kPa (2.7 to 3.0 lb/in.2). The temperature of the fuel entering the carburetor shall not exceed 25°C (77°F), and this may require cooling in hot climates.

6.2 Instrumentation:
6.2.1 Tachometer - An electronic tachometer accurate to +/-25 r/min.

6.2.2 Measurement of Ambient Conditions - 6.2.2 is written on the assumption that the engine draws ambient air from the test room. If it is supplied with air from a controlled source, references to ambient temperature, pressure and humidity apply to the air from the controlled source. Temperature - A thermocouple or thermometer shall be provided to read air temperature in the range 10 to 50°C (50 to 120°F). Barometric Pressure - A barometer recording the pressure in the test room is required. Humidity - A hygrometer or a wet and dry bulb thermometer is also required. Recorder - Continuous recording of the ambient conditions is recommended.

6.2.3 Calibration - Calibrate the tachometer, ambient temperature, and pressure measurement devices every 90 days. The calibration standard shall be traceable to NIST.

6.3 Engine and System Temperatures:
6.3.1 Combustion Chamber Temperature: Modification of Cylinder Head - The cylinder head shall be fitted with a shielded thermocouple. A thermocouple of the iron-constantan type meeting the requirements of ANSI 91.6 Type J (summarized very briefly in Specification E 230) is recommended, but any thermocouple capable of performing satisfactorily under the conditions of the test can be used. The general dimensions and machining requirements are shown in Fig. 2. The through hole, in which the thermocouple is required to fit closely, is about 3-mm (0.12-in.) diameter, and the counterbore shall not extend closer than 4 mm (0.16 in.) to the combustion chamber surface. The dimensions of the counterbore and thread are not critical, being suitable to available thermocouples, but the thread diameter shall be less than 14 mm (0.55 in.). A 1/8 27-NPTF thread is recommended. The thermocouple shall be made so that the last 3 to 4 mm (0.12 to 0.16 in.) of its tip is a snug fit into the 3-mm diameter portion of the hole, and be mounted in the head so that its tip protrudes sufficiently to allow it to be ground flush with the internal surface of the head without penetrating the shield. When a head has been newly fitted with a thermocouple, run a break-in in accordance with 10.2 and Table 1. The thermocouple reading normally requires about 90 min to stabilize. Shutdown Provision - Provision shall be made for shutdown of the engine in the case of a rapid (1 min or less) combustion chamber temperature increase of 10°C (18°F) or more. This normally indicates an incidence of major preignition, and is required to minimize the risk of damage to the engine. An automatic shut down when such an increase is experienced is recommended. At the least an alarm shall be provided to operate after a temperature increase of 6 to 7°C (11 to 13°F) to allow manual shut down by the operator if the 10°C limit is exceeded.

6.3.2 Exhaust Temperature - A thermocouple is required in the exhaust elbow within about 65 mm (2.5 in.) of the cylinder exhaust port to monitor exhaust temperature. The thermocouple junction shall be located within +/-3 mm (0.12 in.) of the center of the pipe.

6.3.3 Spark Plug Gasket Temperature - The spark plug gasket may be fitted with one or two thermocouples, the number depending on the instrumentation used. A design that has been found satisfactory is described in Appendix X1.

6.3.4 Combustion Chamber and Spark Plug Gasket Temperature Recorders - These temperatures shall be recorded using a system capable of storing the data for later retrieval. Maximum interval between successive recordings of the combustion chamber temperature is 2 s. A system with a range from 40 to 750°C (100 to 1400°F) and an overall accuracy of +/-2°C (4°F) is suitable.

6.3.5 Calibration - Calibrate the combustion chamber, exhaust and spark plug gasket temperature measurement devices every 90 days. The calibration standard shall be traceable to NIST.

6.4 Fuel System:
6.4.1 Flow Meter - Any type accurate to +/-0.01 kg/h (+/-0.02 lb/h) at about 1 kg/h (2 lb/h) flow rate may be used. Instruments measuring mass directly are preferred. If a volumetric measurement meter is used the temperature-density relationship shall be determined over the operating range for the actual fuel-non-reference oil mixture used for use in volume-mass conversion.

6.4.2 A temperature measuring device reading to at least 40°C (100°F) to an accuracy of +/-1°C (2°F) and a pressure gage or transducer reading up to about 35 kPa (5 lbf/in.2) to an accuracy of +/-2% are required to monitor the temperature and pressure of the fuel entering the carburetor.

7. Materials and Reagents
7.1 Test Fuel - The test fuel shall be a leaded gasoline consisting essentially of hydrocarbons, except for conventional lead antiknock, anticorrosion, anti-icing, etc. additives in normal concentration, and containing no non-lead metallic antiknock compounds or oxygenated blending compounds such as alcohols or ethers. It shall contain 0.4 to 0.6 g/L (1.5 to 2.2 g/gal) of lead as lead alkyls with conventional motor mix or aviation mix scavengers, and shall have a minimum motor octane number of 83, a maximum sensitivity (research octane number minus motor number) of 12 as determined by Test Methods D2699, D2700, or D2885, as applicable, and shall otherwise meet the requirements of Specification D439 volatility grade A or B. Aviation gasoline meeting these requirements and otherwise conforming to Specification D 910 Grade 100 or 100LL may be used. Fuel from the same batch shall be used for calibration running and for any other tests referenced to that calibration. About 40 L (10 gal) of fuel are required for a test, plus 12 L (3 gal) for the break-in.

7.2 Reference Oils - ASTM 601 and 605 reference oils are used for calibration purposes.12 ASTM 600 reference oil is used for break-in and as an assembly lubricant.12 About 4 L (1 gal) of reference oil is required to run a calibration test, and 0.4 L (0.1 gal) of 600 for a break-in. The properties of these oils are summarized in Annex A2.

7.3 Non-Reference Oil - About 4 L (1 gal) are required for a 50 h test, varying according to the number of test hours specified. It is recommended that at least twice this amount be provided in case the test is rerun.

7.4 Grease - OMC needle bearing grease or petroleum jelly.

8. Calibration
8.1 After 30 tests or 180 days, whichever occurs first, or at any time a new or completely rebuilt engine or test bed is put in service, conduct calibration tests. Run a test for 50 h using reference oil 605. There shall be a minimum of four and a maximum of ten major preignitions during this test. If reference oil 605 fails to provide a minimum of four and a maximum of ten preignitions, investigate the cause and repeat the test. Run a test for 50 h using reference oil 601 as if it were a non-reference oil. When not more than one major preignition is obtained, no further action is required. If more than one preignition is obtained, investigate the cause and repeat the test.

8.2 In order for a test stand to be accepted for non-reference oil qualification, it shall be calibrated by the procedure of 8.1.