Compatibility of Biodiesel with Petroleum Diesel Engines

Hannu Jääskeläinen, W. Addy Majewski

This is a preview of the paper, limited to some initial content. Full access requires DieselNet subscription.
Please log in to view the complete version of this paper.

Abstract: The use of biodiesel in existing engines may cause a number of issues related to materials compatibility, lubricating oil dilution, fuel injection equipment, and exhaust aftertreatment devices. To minimize these potential impacts and ensure engine longevity, engine manufacturers often limit the use of biodiesel to low level blends.


A number of factors related to fuel compatibility need to be considered when using biodiesel in any particular engine. Logically, the effect of biodiesel on engines and aftertreatment systems depends on the blend level used. While in many cases the most significant effect would be expected with neat B100 or high level blends, intermediate level blends can be most prone to the precipitation of fuel insolubles and filter plugging. Some cumulative effects can be also caused by prolonged operation with low biodiesel blends.

Biodiesel advocates, including biodiesel manufacturing groups and those environmental organizations that support the use of biodiesel, often claim that biodiesel can be used in existing diesel engines without modifications. While it may be true that most diesel engines can be started and operated for a number of hours with biodiesel fuel (at least under mild weather conditions), engine manufacturers limit the use of biodiesel in many engine models to ensure no adverse effects over the entire life of the engine. The restrictions on the use of biodiesel fuels are typically imposed through new engine warranties that become void if the engine is operated with a fuel that does not meet the manufacturer’s specifications, such as B100 or high level biodiesel blends. Another common issue is the lack of standard specifications for neat biodiesel and/or higher biodiesel blend fuels. Even if the engine is designed for an average B100 fuel, problems may arise due to the variability of a non-standard fuel without a widely accepted and enforced quality specification.

The potential issues with biodiesel fuels may be grouped as follows:

In the initial period of biodiesel commercialization, from the 1990s to the early 2000s, neat biodiesel was available at the pump in some geographical areas, for example in Germany. Due to the fuel compatibility issues, the trend is to limit the usage of biodiesel to low level blends. B5 blends have been generally accepted by fuel injection and engine manufacturers worldwide. Most European car manufacturers allow B7 as the maximum blend level.

Material Compatibility

Whenever the fuel composition is changed in the fuel system, material compatibility is a major concern. Fuel system designers incorporate materials based on laboratory testing and the available historical data. Thus, changes in fuel composition and the introduction of alternative fuels often create unforeseen problems in seals, gaskets, o-rings, and metallic components in the fuel system. The consequences of changing the fuel composition without prior compatibility studies are best illustrated by the reduction of aromatics in low sulfur diesel fuel in California. This “minor” change resulted in numerous problems due to o-ring shrinkage, including leakage in pumps and other fuel system components [152].

Material compatibility of biodiesel and its blends with elastomers and metals was investigated in an experimental laboratory study [149]. Samples of tested elastomers were stored in biodiesel blends at 51.7°C for up to 694 hours. The tensile strength, elongation, hardness, and swell were determined for each sample after the storage period. It was concluded that the physical properties of nitrile rubber, nylon 6/6, and high density polypropylene were affected by biodiesel and its blends while Teflon, Viton 401-C and Viton GFLT appeared to have good resistance to biodiesel, Table 1.

Table 1
Biodiesel compatibility with elastomer materials
Material Effect of Biodiesel Relative to Diesel Fuel
FluorosiliconHardness little change, swell +7%
Nitrile rubberHardness -20%, swell +18%, reduced tensile strength
Nylon 6/6Decreased elongation, reduced tensile strength
High density polypropyleneHardness -10%, swell +8 to 15%
TeflonLittle change
Viton 401-CLittle Change
Viton GFLTLittle change
PolyurethaneHardness little change, swell +6%
PolyvinylMuch worse

Metals evaluated in the study included copper, steel, brass, aluminum, and bronze. Samples of metals were stored in the biodiesel and its blends for 6 months at 51.6°C. The samples were rated visually and the total acid number (TAN) of the fuels was determined. Copper containing metals (this included brass and bronze) exhibited severe corrosion when exposed to biodiesel and its blends. They also formed large amounts of gum when stored at elevated temperatures. The steel and aluminum samples did not exhibit gum formation, but did exhibit exceptionally high total acid numbers which could corrode various parts of the fuel system. Zinc is also incompatible with biodiesel.