Combustion Analysis of Esters of Soybean Oil in a Diesel Engine

The alkyl esters of plant oils and animal fats are receiving increasing attention as renewable fuels for diesel engines. These esters have come to be known as biodiesel. One objection to the use of the methyl and ethyl esters of soybean oil as a fuel in diesel engines is their high crystallization temperature. One solution to this problem is to use the isopropyl esters of soybean oil which have significantly lower crystallization temperatures. Another method to improve the cold flow properties of esters is to winterize them to sub-ambient temperature. This is accomplished by cooling the esters and filtering out the components that crystallize most readily.

Previous work has shown that when methyl, isopropyl and winterized ester blends were compared with No.2 diesel fuel, the isopropyl and winterized methyl esters had at least the same emission reduction potential as the methyl esters, with similar engine performance. This paper discusses those results using heat release analysis that shows all of the blends have shorter ignition delays, and lower premixed burn fractions than No.2 diesel fuel. All tested fuels except the isopropyl ester blends had similar combustion behavior. However, blends with isopropyl ester showed some abnormal combustion behavior, possibly due to high levels of monoglycerides.