Microcharacterization of heavy‐duty diesel engine piston deposits

Abstract

The composition and structure of heavy-duty diesel engine piston deposits generated in a Caterpillar 1Y540 single-cylinder bench test engine according to the Caterpillar 1N test procedure have been investigated using infrared spectroscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), XPS depth profiling and transmission electron microscopy (TEM). The test engine piston was modified to allow deposits to be examined without removal from their original surface, allowing the structure of the deposit/substrate interface to be studied for the first time. Detailed microcharacterization of specimens generated under typical conditions has shown that deposit formation is initiated by adsorption of a thin lubricant layer on the piston surface during start-up. Oil-soluble additive degradation products within this thin lubricant layer react with surface oxides to form a phosphate-rich layer. With increasing engine run time, degraded lubricant additive species react with fuel combustion acids to form inorganic sulphates and phosphates that become embedded in a gum-like matrix of non-volatile hydrocarbon residues and partial oxidation products. Extended running times result in the build-up of a concentration of crystalline species near the deposit/substrate interface as a result of agglomeration and annealing. The layer structure is completed by deposition of further lubricant additive material during over-run on completion of the engine test.

Thermal and elemental analysis of the combustion chamber deposits in a large-scale two-stroke marine diesel engine

“…However, the published data showed that carbon content is in range of 30%-70% [1,[10][11][12][13]. And the radiotracer study concluded the majority of carbon was from the diesel fuel [27].…”

“…Zn, from the Zinc dialkyldithiophosphates (ZDDP) anti-wear additives, was slightly higher on the first surface due to further oxidation at higher surface temperature on the piston top than that in the ring pack. Smith et al [12] also found the ZDDP was the first to bond to the piston top surface. It could be argued that the piston materials have influence on the initial deposit formation.…”

“…Smith et al [12] already found continuous increase of Al content in the deposit on the top of an Al alloy piston. However, Fe content on third surface caused by wearing was not clear in the SXRF test.…”

“…It should be noted that only metals on the bottom surface of PTCD were measured without any consideration of other parts of PTCD in the SXRF experiments, while the PTCD powder was used in the EA. The source of Ca on first surface is mainly from the lubricant due to the condensation of high boiling point hydrocarbon in oil on piston top at the engine warm-up [12]. The lower Ca content on bottom surface implied higher Ca content on the upper part of the PTCD, in other words, a layered structure of Ca in deposits.…”

“…Based on the results in refs. [1,[10][11][12][13], the carbon content in the CCD is in the range of 35%-70% by weight, oxygen content is in the range from 16% to 25%. Hydrogen and Nitrogen content is lower than 10%.…”