One of the issues with burning higher blends of biodiesel in newer diesel engines that use post-injection for controlling emissions is significant engine wear with methyl ester dilution in the engine oil crankcase.
This story from Biodiesel Magazine says Chevron Oronite Company LLC has developed a unique engine oil additive to help combat that engine wear when using B20:
Fuel dilution has always been an issue with diesels, but never more so than with post-injection. Petrol diesel dilutes engine oil too, but it volatilizes off and eventually is released through the breather system. For biodiesel, however, the story is significantly different.
Biodiesel has a higher and narrower boiling range than petroleum diesel, and its physical properties lead to larger droplet sizes exiting the fuel injectors. This means that, while the petrol portion of the blend vaporizes and follows its destination to the exhaust stream as the piston is at the bottom of the cylinder, the methyl ester fraction—with its higher, narrower boiling range and larger droplet size—remains in liquid form collecting along the exposed surface area of the cylinder wall, and as the piston rises, much of the biodiesel bypasses the rings to enter the crankcase. Once in there, the biodiesel does not volatilize off like mineral diesel does. With the heat of the crankcase, there is concern about oxidation of the oil/biodiesel mix and engine wear resulting from the organic acids.
“In the case of biodiesel, once it gets in the crankcase and as it starts to degrade, it forms organic acids and starts to polymerize,” said Gary Parsons, global OEM and industry liaison manager for Chevron Oronite. “The organic acids can aggressively attack certain metals, particularly lead in the lead bearings. And then as it polymerizes and oxidizes, it can lead to increased deposits in the engine—in particular, deposits on the pistons.”
The engine oil additive Chevron Oronite developed is designed to counter the effect of the acids, so they don’t aggressively attack the metal; and also to prevent oxidation and formation of deposits.
The product is commercially available and marketed under the Oronite Lubricating Oil Additive trademark. The article points out that greater use of biodiesel is necessitating the additive’s greater use.