Determination of threshold values of parameters of operating engine oils for diagnosing internal combustion engines

Technical fluids (engine oil, antifreeze) must, during the standard period of use, comply with the requirements for them to ensure the standard service life of the systems and mechanisms of the internal combustion engine. The stability of the engine oil during engine operation depends on many factors. Engine oil, in contact with all processes occurring in an internal combustion engine, can become a source of diagnostic information, which will allow maintenance and repair of engine parts as needed, and increase the reliability and durability of the internal combustion engine. Based on the results of analyzes of oil samples for each indicator, it is possible to construct curves of distribution densities for serviceable and for faulty engine states. Having received the results of the analysis, it is necessary to compare the value of the indicator with its threshold values, separating the zone of good condition from the zone of engine failure. Due to the fact that under operating conditions the number of serviceable engines is always greater than the number of faulty ones, at the first stage of monitoring oil quality indicators it is possible to determine the threshold values of indicators separating the zone of normal wear (good engine condition) from the zone of increased wear. As a result of the study, an algorithm was obtained for calculating and determining the threshold values of the indicators of engine oils for engines of tractors operated in the farms of the Omsk region. The sampling of values was carried out according to two indicators of oil: kinematic viscosity at 100ºC and flash point. As a result of the study, it was found that the distribution and the probability integral of the oil viscosity are better aligned with the normal Gaussian law. The mathematical expectation of viscosity is 11.23 ± 0.48 mm2/s. The maximum permissible viscosity of M-10-B2 oil, corresponding to the 95% boundary of the probability integral, is 13.32 mm2/s. The minimum permissible viscosity corresponding to the 5% boundary of the probability integral is 9.12 mm2/s. The mathematical expectation of the flash point is 197.6 ± 4.2ºC. The minimum allowable flash point for serviceable engines, corresponding to the 5% boundary of the probability integral, is 177.5ºC.