Ostwald ripening: a decisive cause of cylinder corrosive wear

Abstract

Acids formed from fuel combustion and lubricating oil breakdown can promote corrosive engine wear. Using capillary videomicrocopy to investigate the neutralization of sulfuric acid droplets by overbased additives in lubricating oil, we have found that the Ostwald ripening of acid droplets may be a decisive factor of corrosive wear because it prolongs the lifetime of larger acid droplets. This finding provides a new understanding of how acids corrode engine parts, and in particular, why the most corrosive engine wear often occurs at piston top dead center, and may lead to new strategies for engine designs and lubricating oil additives.

Mixed Flow Reactor Experiments and Modeling of Sulfuric Acid Neutralization in Lube Oil for Large Two-Stroke Diesel Engines

“…7,56 A high load of H 2 SO 4 in the lube oil in this region could also be facilitated by the upward motion of the piston, collecting the condensed H 2 SO 4 above the top piston ring. 26 The upper part of the cylinder is also the area where the piston speed is the lowest, 1 decreasing the degree of mixing of the lube oil film, and the lube oil film thickness is at its minimum. 58 A local excess of H 2 SO 4 compared to CaCO 3 in the upper part of the cylinder liner would explain the corrosive wear that has been observed.…”

“…Duan et al show that the shrinking rate (d R SA /d t ) of acetic acid droplets in fully formulated passenger-car lube oil decreases when the acetic acid droplet concentration is decreased. Also, Fu et al report that the shrinking rate of a droplet of pure water is about 1 magnitude lower than that of an H 2 SO 4 droplet. This suggests that the shrinking rate depends on the nature, chemical interactions, and concentration of the droplets.…”

“…The reaction between (sulfuric) acid droplets and CaCO 3 reverse micelles in lube oil has been investigated in laboratory experiments over a wide range of conditions. Data in batch mode were obtained using a video-microscopy technique, − a stopped-flow method, − and by monitoring the CO 2 formed. − The video-microscopy experiments employed placing single acid droplets (70–200 μm in diameter) in a batch of lube oil, followed by measuring the subsequent shrinkage of the acid droplets. These studies indicate that the controlling step of the neutralization reaction is adsorption of a reverse micelle onto the acid droplet.…”

“…Duan et al 53 show that the shrinking rate ( / ) of acetic acid droplets in fully formulated passenger-car lube oil decreases when decreasing the acetic acid droplet concentration. Also, Fu et al 26 report that the shrinking rate of a droplet of pure water is about one magnitude lower than that of an H 2 SO 4 droplet.…”

Experimental investigation and mathematical modeling of the reaction between SO2(g) and CaCO3(s)-containing micelles in lube oil for large two-stroke marine diesel engines

“…It is therefore important to have general guidelines on how lube oil should be dosed onto the cylinder liners to limit corrosion at a minimal cost. To achieve this, an understanding of the formation of the relevant acids in the gas phase [10,[12][13][14], the transport to the lube oil film [15][16][17], the neutralization mechanism by the base additives [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35], and the corrosion of the liner material [1,4,[36][37][38][39][40][41][42][43][44] is pivotal. Information about how base additives (CaCO3 micelles) are consumed is important because this facilitates determination of the lube oil flow rate to the cylinder liners and choice of base additive concentration.…”