Pumping Soy

It may be hard to imagine pulling up to the pumps at your local gas station and asking the attendant to "fill it up with soy." But a family of fuels called biodiesels is making it possible for internal combustion engines to run on mixtures containing compounds made from renewable biomass.

Biodiesels are diesel fuels that have been blended with fatty acids or alkyl esters, which are formed by mixing vegetable oils or animal fats with an alcohol such as methanol or ethanol. Although biodiesels made from canola and rapeseed oil are fairly common, recent attention has focused on another hardy, high-yield species: the soybean.

The use of soybean-based biodiesels is already fairly widespread in areas of the United States where plant production is sufficient to meet commercial needs. As part of the effort to determine its potential here in Canada, Environment Canada, Health Canada and the Ontario Soybean Growers Marketing Board have been working together to determine how tailpipe emissions from this plant-based fuel compare to those of other more conventional types, such as gasoline and diesel fuel.

Testing was carried out at Environment Canada's Environmental Technology Centre in Ottawa, on a light-duty truck equipped with a 5.9-litre, 24-valve turbo diesel engine and an oxidation catalyst. Baseline tests were conducted using a commercially available low-sulphur diesel fuel, then the biodiesel tests were done with various percentage blends of methyl soyate and conventional diesel. The tests were run at two standard temperatures–one at room temperature and the other in a cold cell that simulated the effects of a typical Canadian winter.

The tests determined that, at these temperatures, emissions from biodiesel blends and low-sulphur diesel fuel differed very little—likely because the oxidation catalysts found on modern cars are so effective at reducing pollutant emissions. However, it was found that hydrocarbon emissions were lower in all biodiesel tests, and seem to be related to the amount of methyl ester in the blend. These results could indicate that the catalytic converter is more efficient at converting the hydrocarbons in biodiesel exhaust than in diesel exhaust. Since hydrocarbons include a family of pollutants that can affect the environment and human health, this finding could be important.

The most interesting result, however, came from the tests done for particulates—tiny, microscopic particles found in the emissions of burned fossil fuels, the smaller of which can be inhaled deeply into the lungs and are implicated in a variety of respiratory problems. They revealed that, in a typical low-sulphur diesel fuel, 100 per cent of the particulate matter is of inhalable size—that is, 2.5 microns or less in diameter. With methyl soyate, on the other hand, the figure is closer to 60 per cent—meaning that widespread use of biodiesels could result in a 40-per-cent reduction in the fine particulate emissions that are a significant health concern.

Averaged emission rates compared between low-sulphur diesel and the mid-range methyl soyate during testing of engine started cold, and testing of warmed-up engine. Measurements are at 0ºC, and in grams per mile.

While it isn't likely that biodiesels will ever completely replace fossil fuels, efforts will continue to make them more efficient and clean-burning. Now available in small quantities in Canada, and in larger quantities in the United States, further advancements in biodiesels will help reduce dependency on fossil fuels. The result could be fewer emissions from transportation sources that affect both climate change and clean air.

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