Fatty acid methyl ester causing diesel filter plugging, Peugeot Citroën says

Higher biodiesel blends are seeing significant use in Europe due to the Renewable Energy Directive (RED) and the Fuel Quality Directive (FQD), but employing higher blends does not come without its cost to post-treatment systems. Gerald Crepeau, fuels and post-treatment systems expert at PSA Peugeot Citroën, illustrated this at a talk at the UNITI Mineral Oil Technology Conference in Stuttgart, Germany, this week. Specifically, the fatty acid methyl ester (FAME) used to make biodiesel is causing diesel filter plugging, he said.

Some member-states of the European Union use high biodiesel blends, such as Poland (B20), the Czech Republic (B30) and Latvia (B30). France permits the sale of B30, but only for captive fleets. The CEN working group on diesel, Crepeau shared, is preparing a draft standard for blends between B11 and B30, including two grades, B20 and B30, for captive fleets. This would enable more harmonised usage. RED, which aims for a 10% share of renewable energy sources in the transport fuel sector within the European Union by 2020, prompted countries to come up with their own biodiesel blending requirements.

“The current specifications are not sufficient, and are not in line with vehicles,” Crepeau said, in reference to high levels of saturated FAME in biodiesels. Used cooking oil methyl ester and animal fat methyl ester have high levels of saturated FAME, and some countries such as France have an upper limit on how much of it can be used in a biofuel. The United Kingdom has no such restriction. High levels of saturated FAME, Crepeau said, can push the fuel past its cloud point (CP), which is the point at which a fuel becomes cloudy with waxes that are beginning to solidify. This can then clog diesel filters, which are designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. DPFs have been standard in Peugeot passenger cars since 2000, in anticipation of at that time, future Euro 5 regulations.

Crepeau referenced a rig test that found no correlation between saturated and unsaturated monoglycerides and filter plugging. There is, however, a correlation between the CP and the saturated FAME content. When the filters were analysed after the rig test, mostly saturated FAME was found inside.

According to Crepeau, the Cold Filter Plugging Point or CFPP should include a provision restricting the levels of FAME to be used in the winter. U.K. consumers have encountered problems during the colder months, he said. He also suggested a filter-blocking test (FBT), to evaluate the cleanliness of middle distillate fuels, biodiesel and biodiesel blends, or a centrifugation test after a cold soak.

CFPP is the lowest temperature, expressed in degrees Celsius (°C), at which a given volume of diesel type of fuel still passes through a standardized filtration device in a specified time when cooled under certain conditions. This test gives an estimate for the lowest temperature that a fuel will give trouble free flow in certain fuel systems.

“Appropriate market fuel standards are essential,” Crepeau said, to ensure that vehicles function properly in all applications and in all seasons. Changing the standard to include different FAME allowances for winter and summer may be a step toward meeting RED, he said.