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
4. Summary of Test Method
4.1 The test is run in a 49 cm3 single-cylinder air-cooled engine operated under the conditions required by the specification against which it is being run. These are typically 4000 r/min wide open throttle (WOT) using a 20:1 ratio of gasoline to oil by volume for a minimum of 50 h. The number of incidences of preignition, as indicated by a rapid increase in combustion chamber temperature, is recorded.
NOTE 1 - Pass-Fail Criterion - The number of occurrences of preignition during the test of a candidate oil shall not exceed that permitted by the specification against which it is run.
5. Significance and Use
5.1 Two-stroke-cycle gasoline engines are generally more prone to preignition than are four-stroke-cycle engines due to the absence of the internal cooling that takes place during the induction stroke of the four-stroke-cycle engines. Preignition can lead to major piston damage, either directly due to localized overheating or as the result of preignition-induced detonation. Some lubricant additives that are widely used in four-stroke-cycle gasoline engine oils are known to increase the probability of preignition in gasoline two-stroke-cycle engines. This procedure is used to determine the tendency of an oil to induce preignition in both water-cooled and air-cooled two-stroke-cycle gasoline engines.
