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United States Department of Agriculture

Agricultural Research Service

Title: The Influence of Various Oxygenated Compounds on the Cetane Numbers of Fatty Acids and Esters

Authors
item Knothe, Gerhard
item Bagby, Marvin - RETIRED
item Ryan, Iii, Thomas - SOUTHWEST RES INSTITUTE

Submitted to: Liquid Fuels from Renewable Resources Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 17, 1996
Publication Date: N/A

Interpretive Summary: Similar to the octane number of gasoline, diesel fuel has a quality indicator termed the "cetane number". Alternative diesel fuels derived from vegetable oils ("biodiesel") and their component fatty acids and esters also possess cetane numbers. The work in this paper reports that several additives have been found which improve the cetane numbers of fatty acids and esters. The results may be crucial for improving combustion and emissions of biodiesel.

Technical Abstract: The ignition delay times of four C18 fatty acids of varying unsaturation and their methyl, ethyl, propyl and butyl esters were determined in a Constant Volume Combustion Apparatus (CVCA). These values were used to calculate some preliminary relative cetane numbers (CN). The CN range from 80.1 for butyl stearate to 20.4 for linolenic acid. In fatty compounds, there are positive correlations between CN and the number of CH(2) groups as well as between CN and the saturation of the hydrocarbon chains. In addition, the CN of numerous oxygenated compounds with different functional groups were determined. These compounds are possible cetane-improving additives in biodiesel and perhaps for petroleum-based diesel fuel. One neat material had ignition delay characteristics suggesting a CN of 234. These compounds were investigated in different concentrations with the various fatty compounds. The effectivity of these compounds varied with concentration, some being more effective at higher concentrations, some at lower concentrations. The compounds had different effects on diesel fuel. One selected compound markedly enhanced the CN of acids in contrast to the esters.

Last Modified: 4/18/2014
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