Biodiesel use in spark-ignited engines

Biodiesel has a very high cetane number and low volatility. These two properties make it unsatisfactory for use in conventional spark-ignited engines. Its use as a fuel is almost certainly to be restricted to compression ignited engines with one possible exception. Biodiesel has been considered as a potential ingredient in two-cycle engine oils. It blends well with gasoline and has excellent lubricity. However, there are currently no data showing that biodiesel can provide the properties needed for two-cycle oil.

The attraction of using biodiesel as a blending agent in the oil portion of a two-stroke engine gas-oil mix is that a large portion of the gas-oil mix passes through to the exhaust of these engines without burning. In marine engines, this unburned hydrocarbon material produces an unsightly oil slick that can damage plant and animal life. While the volatile gasoline portion of the slick may evaporate quickly, the lubricating oil is left behind. If this lubricating oil consisted largely of biodiesel, it would be nontoxic and biodegrade in just a few days.