Diagnosis of the condition of diesel engines in city buses on the basis of used oil analyses

Abstract

-- in 10% of the oil samples, the content of water was higher than that characteristic for an engine with a tight cooling system when the engine is in good condition, i.e., more than 0.03% water; -- the viscosity of 4% of the samples was below the viscosity of the fresh oil, indicating dilution of the oil with fuel and malfunctions in the engine fuel system; -- in 30% of the samples, the oil had no dispersancy or stabilizing properties as determined by paper chromatogaphy; in three cases, the used oil had an unduly high water content; in two cases, the oil change period had been exceeded (samples at the time of oil change were taken every 7-13 thousand kilometers of bus travel); and in practically all of the oil samples, high concentrations were noted for the elements indicating wear of engine parts; -- in 60% of the samples, the silicon content was high (this element characterizes not only wear of parts made of silicon-containing alloys, but also access of unfiltered air to the engine; In 4% of the samples, the contents of iron, copper, and lead were high, with relatively low silicon concentrations, possibly because of breakdown of the working surfaces of rubbing parts made of bearing alloys (grooving, increased wear). With high concentrations of silicon in the used oil, we also noted significantly increased contents of iron, aluminum, and chromium, and to a lesser degree lead and copper. In particular, with an increase of the silicon concentration in the oil from 3-70 ppm to 500-1000 ppm, the contents of iron and aluminum increased by two orders of magnitude, and the contents of lead, copper and chromium by one order of magnitude. Such large increases of metal contents are characteristic for diesel operation when the air cleaning system is not functioning properly, as this leads to wear rates that are several tens of times higher, particularly for the cylinder-piston group. The end results are higher oil consumption in burning, increased exhaust smoke, and poorer power characteristic of the transport vehicles. In a number of cases, with high concentrations of silicon and wear-indicating elements, the following were noted: Increased content of insoluble sludge up to 5-6% and incombustible products up to 0.7-0.8%; increased viscosity up to 19 mm2/sec at 100~ absence of dispersant and stabilizing properties. All this is typical of wear damage in the piston/cylinder group of diesel engines [6]. The large volume of work that has been performed has made it possible to apply a method set forth in [6] to calculate the limiting values of wear-indicator element concentrations corresponding to good and poor working condition for the diesels RABA-MAN D 2356 HM6 in Icarus 260.50 and Icarus 280.64 buses.