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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. European car manufacturers have reached a consensus to allow B7 as the maximum blend level. Adoption of the ASTM D7467 standard opened the door for increased use of blends up to B20 in North America.