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B iodiesel is gaining recognition as a renewable alternative to diesel fuel. One step toward commercialization of biodiesel is establishing how well it stores and what affect storing for long periods has on the performance of the fuel. The problems of fuel deterioration with biodiesel during storage are expected to be more severe than for commercial diesel fuel. Although vegetable oils contain natural antioxidants, their high degree of unsaturation makes them susceptible to gum formation. Since fuel deterioration occurs mainly by oxidative polymerization leading to gum formations one purpose of this study was to determine the rate of oxidative polymerization for different fatty acid esters prepared from rapeseed, as effected by container types, and environments. Peroxide values measure the levels of the oxidation products in the samples. Another purpose of this study was to use short term engine coking and torque test procedures to determine whether the presence of the oxidation products affected the engine performance.

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Comprehensive tests were performed on an on-road vehicle in cooperation with the Los Angeles County Metropolitan Transit Authority emissions test facility. All tests were with a transient chassis dynamometer. Tests included both a double arterial cycle of 768 s duration and an EPA heavy duty vehicle cycle of 1,060 s duration. The test vehicle was a 1994 pickup truck with a 5.9-L turbocharged and intercooled, direct injection diesel engine. Rapeseed methyl (RME) and ethyl esters (REE) and blends were compared with low sulfur diesel control fuel. Emissions data includes all regulated emissions: hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), oxides of nitrogen (NOx), and particulate matter (PM). In these tests the average of 100% RME and 100% REE reduced HC (52.4%), CO (47.6%), NOx (10.0%), and increases in CO2 (0.9%) and PM (9.9%) compared to the diesel control fuel. Also, 100% REE reduced HC (8.7%), CO (4.3%), and NOx (3.4%) compared to 100% RME.

Test quantities of ethyl and methyl esters of four renewable fuels were processed, characterized and performance tested. Canola, rapeseed, soybean oils, and beef tallow were the feedstocks for the methyl and ethyl esters. Previous results have shown methyl esters to be a suitable replacement for diesel fuel; however, much less has been known about the ethyl esters. A complete set of fuel properties and a comparison of each fuel in engine performance tests are reported. The study examines short term engine tests with both methyl and ethyl ester fuels compared to number 2 diesel fuel (D2). Three engine performance tests were conducted including an engine mapping procedure, an injector coking screening test, and an engine power study. The gross heat contents of the Biodiesel fuels, on a mass basis; were 9 to 13 percent lower than D2. The viscosities of Biodiesel were twice that of diesel. The cloud and pour points of D2 were significantly lower than the Biodiesel fuels. The Biodiesel fuels produced slightly lower power and torque and higher fuel consumption than D2. In general, the physical and chemical properties and the performance of ethyl esters were comparable to those of the methyl esters. Ethyl and methyl esters have almost the same heat content. The viscosities of the ethyl esters is slightly higher and the cloud and pour points are slightly lower than those of the methyl esters. Engine tests demonstrated that methyl esters produced slightly higher power and torque than ethyl esters. Fuel consumption when using the methyl and ethyl esters are nearly identical. Some desirable attributes of the ethyl esters over methyl esters were: significantly lower smoke opacity, lower exhaust temperatures, and lower pour point. The ethyl esters tended to have more injector coking than the methyl esters and the ethyl esters had a higher glycerol content than the methyl esters.