INTERNATIONAL JOURNAL OF ENERGY AND ENVIRONMENT Volume 2, Issue 6, 2011 pp.1141-1146 Journal homepage: www.IJEE.IEEFoundation.org ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2011 International Energy & Environment Foundation. All rights reserved. Effect of single double bond in the fatty acid profile of biodiesel on its properties as a CI engine fuel S. Saravanan 1 , G. Nagarajan 2 1 Department of Automobile Engineering, Sri Venkateswara College of Engineering, India. 2 Department of Mechanical Engineering, College of Engineering, Anna University, India. Abstract Fatty acid profile of the vegetable oil and animal fats plays a major role in determining the properties of biodiesel derived from them. Eventhough the type of fatty acids in vegetable oils are similar, their distribution is different. The percentage distribution of fatty acids differs by a significant magnitude with respect to the type of vegetable oil. In the present investigation the effect of single double bond fatty acids in the vegetable oil on its physical and chemical properties are investigated. Different vegetable oils based on the type and geography were selected and the properties of biodiesel derived from it were analysed with respect to its fatty acid of single double bond. From the results of the investigation it is inferred that the fatty acids with single bond plays an important role in determining the properties of biodiesel as a CI engine fuel. Copyright © 2011 International Energy and Environment Foundation - All rights reserved. Keywords: Biodiesel; Fatty acid profile; Double bond; Unsaturated fatty acids; Saturated fatty acids. 1. Introduction Biodiesel, a clean burning renewable fuel, has been paid more attention for the past two decades as an alternative fuel for petroleum diesel [1-8]. As per the ASTM standard 6751 biodiesel is a mixture of long chain fatty acid esters derived from vegetable oils and animal fats that contain only one alcohol molecule on one ester linkage[9]. Fatty acids with glycerine backbone present in the vegetable oil and animal fats are the major resources for the production of biodiesel. Each vegetable oil molecule is made up of a glycerin backbone of three carbons, and each of these carbon atoms is attached to a long chain fatty acid. Varieties of vegetable oils and animal fats (feedstock) which contain fatty acid in its structure are used to produce biodiesel. The chemistry of the feed stocks is similar and contain 10 common types of fatty acids with carbon atoms between 12-22. When comparing these carbon atoms it was found that over 90% are between 16-18. Some of these fatty acids are saturated while others are unsaturated. The level of unsaturation depends upon the number of double bonds present in it. For mono-unsaturation the number of double bonds is 1, and two or more for poly-unsaturation. Each feedstock contains different proportions of saturated, mono-unsaturated and poly-unsaturated fatty acids. The levels of this saturation will affect some of the biodiesel properties. This may also lead to a variation in the engine characteristics when biodiesel is employed as a CI engine fuel. A perfect biodiesel would be made only from mono- unsatuarted fatty acids [9]. Attempts have been made to predict the effect of saturation level on the properties of biodiesel [10]. In the present work attention was focused to investigate the effect of single double bond (mono-unsaturated fatty acids) present in the fatty acid profile of biodiesel on its properties.