The primary problems associated with using straight soybean oil as a fuel in a compression ignition internal combustion engine are caused by high fuel viscosity. Transesterification of soybean oil with an alcohol provides a significant reduction in viscosity, thereby enhancing the physical properties of the renewable fuel to improve engine performance. The ethyl and methyl esters of soybean oil with commercial diesel fuel additives revealed fuel properties that compared very well with diesel fuel, with the exception of gum formation, which manifested itself in problems with the plugging of fuel filters. Engine performance using soybean ester fuels differed little from engine performance with diesel fuel. A slight power loss combined with an increase in fuel consumption were experienced with the esters, primarily because of the lower heating value of the esters than for diesel fuel. Emissions for the 2 fuels were similar, with nitrous oxide emissions higher for the esters. Measurements of engine wear and fuel‐injection system tests showed no abnormal characteristics for any of the fuels after the 200‐hr tests. Engine deposits were comparable in amount, but slightly different in color and texture, with the methyl ester engine experiencing greater carbon and varnish deposits on the pistons.

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