The Effect of Biodiesel on Engine Lubricants

[DF Sales&Marketing]

many of you own or operate diesel trucks……
for those of you who do, this article will open your eyes for using biodiesel or not.​

The availability of biodiesel as a diesel fuel extender or alternative fuel for both heavy-duty and passenger car diesel engines is becoming more widespread and mainstream. This is occurring as concerns over energy security and climate change drive a growing demand for viable renewable energy resources.
Simultaneously, as biodiesel usage increases, questions are being asked as to whether biodiesel-containing fuels have any effect on the performance of engine oil.
Biodiesel as a fuel has similar combustion properties to normal petroleum diesel, but its physical and chemical properties are significantly different. This raises some legitimate concerns over the performance of biodiesel in automotive engines.
While much attention has been given to fuel issues, such as cold flow properties and the sensitivity of the fuel injection system to the presence of biodiesel, there are also potential consequences for the crankcase lubricant. Biodiesel is less volatile than petroleum diesel; any non-combusted biodiesel that gets past the engine piston rings has a tendency to accumulate in the crankcase oil sump and dilute the engine oil. The risks associated with excessive fuel dilution of the oil by biodiesel are known. Yet, work is ongoing in the industry to fully establish the actual impact of biodiesel-containing fuels in modern diesel engines that are running on modern lubricating oils and May be equipped with exhaust aftertreatment devises such as diesel particulate filters.

out in the field​

Diesel engines May be run on biodiesel blends without any modification of the engine. In general, the problems that could arise would be expected to increase with the proportion of biodiesel present in the fuel.
Fuel injection equipment manufacturers are extremely wary of biodiesel blends above b5 (5%). The attitudes of diesel engine manufacturers vary more, but many are still cautious pending full specifications for b20 or higher blends. For engines where the use of biodiesel blends above b5 (such as b20 or b30) is sanctioned, most oems recommend close monitoring of the oil condition or suggest a substantial reduction - perhaps halving of the oil change interval.
The main fuel performance concerns arising from biodiesel use relate to the impact on the fuel injection system and the cold flow characteristics. Biodiesel has poor oxidative stability, restricting the shelf life of biodiesel fuel to six months, and there are material compatibility issues with certain metals and elastomers.
Biodiesel oxidation products and contaminants from biodiesel production process, such as methanol, glycerol, glycerides, free fatty acids, metallic soaps and water, are known to contribute to fuel system problems. These include fuel filter plugging, fuel pump failure, injector coking and corrosion, while inadequate flow properties at low temperatures remain a critical issue.

in the sump​

For the engine lubricant, the main concerns have been the effect of biodiesel on engine cleanliness and the consequences of fuel dilution. Any non-combusted fuel striking the cylinder wall is scraped down past the piston rings and enters the engine oil sump. The rate of fuel dilution is expected to be somewhat higher with biodiesel fuel as it has a higher viscosity, density and surface tension than petroleum diesel, factors that increase fuel droplet size. Biodiesel tends to accumulate in the oil sump due to its lower volatility and narrower boiling range than petroleum diesel, and this concentrates the biodiesel contribution to fuel dilution. In addition, any severe fuel injector deposits caused by biodiesel that disrupt the fuel spray pattern will further exacerbate the rate of fuel dilution.
The risk areas associated with biodiesel fuel dilution in the lubricant are the impact on wear, corrosion, engine deposits and oil degradation. The initial effect of fuel dilution will be reduction in the viscosity of the lubricant. Loss of viscosity can reduce the oil film thickness, which could increase abrasive wear. This does not appear to be a major issue currently as the biodiesel itself has some inherent lubricity properties. Biodiesel May actually be used to improve the lubricity of ultra low sulfur diesel fuels, though the treat rate required is substantially higher than for conventional lubricity additives.
Increased corrosion of engine bearings is a significant concern. Biodiesel oxidation products and any free fatty acids present in biodiesel are known to be aggressive towards the soft metals such as lead and copper used in bearings. Although evidence for increased bearing corrosion with biodiesel is mixed, corrosion is a known issue in the fuel system.
There does seem to be a tendency towards increased engine fouling from piston deposits or sludge precipitation from biodiesel use. These issues again relate to the poor oxidative stability of biodiesel. The unsaturated and polyunsaturated esters present in biodiesel can undergo oxidative polymerization, resulting in oil thickening and deposit formation. Fuel quality May also be a factor in contributing to sludge formation. Excessive upper piston deposits can have further consequences when they cause the piston rings to stick. Stuck rings will increase the quantity of soot and blow-by gases entering the lubricant, thereby promoting further viscosity increase and degradation of the lubricant. The crankcase lubricant has to provide sufficient antioxidancy and dispersancy to help combat these effects.

dpf woes​

A pressing issue that dramatically increases fuel dilution rates is the use of fuel post-injection to regenerate diesel particulate filters, dpfs. While dpfs reduce particulate matter emissions, the carbonaceous soot that accumulates in the filter has to be periodically burnt off. One favored method of doing this is to post-inject a small amount of fuel into the exhaust stroke, where it burns and raises the temperature of the exhaust gas such that dpf regeneration can occur. Such post-injection tends to cause significant fuel dilution. The resultant volume of fuel that builds up can be such that the sump overflows, suggesting that engineering changes as well as lubricant solutions May be required to solve this problem.
Biodiesel itself May assist dpf regeneration due to its producing less soot or a more combustible type of soot, but metallic contaminants in biodiesel can also contribute significantly to the build-up of metallic ash in the dpf.

why go there?​

The rather unfavorable nature of some biodiesel properties and concerns over energy supply and the effect of fossil fuels on climate change has created an unstoppable momentum towards the use of more renewable energy resources. The use of biodiesel is thought to contribute to an overall reduction of greenhouse gas emissions compared with petroleum diesel, over the entire life cycle of the fuels.

Dick floryanowich