Effect of biodiesel unsaturated fatty acid on combustion characteristics of a DI compression ignition engine Sukumar Puhan a, *, N. Saravanan b , G. Nagarajan c , N. Vedaraman d a Department of Mechanical Engineering, Veltech Engineering college, Avadi, Chennai, India b ERC Engines, Tata Motors, Pimpri, Pune, India c Department of Mechanical Engineering, Anna University, Chennai, India d Chemical Engineering Division, Central Leather Research Institute, Adyar, Chennai, India article info Article history: Received 20 January 2008 Received in revised form 12 February 2010 Accepted 20 February 2010 Available online 23 March 2010 Keywords: Linum usitatissimum Cocos nucifera Jatropha integerrima Compacta Combustion Performance Emission abstract Several research works have been carried out on biodiesel combustion, performance and emissions till today. But very few studies have been made about the chemistry of biodiesel that affects the diesel engine operation. Biodiesel is derived from vegetable oil or animal fats, which comprises of several fatty acids with different chain length and bonding. The present work focuses on the effect of biodiesel molecular weight, structure (Cis & Trans), and the number of double bonds on the diesel engine operation characteristics. Three types of biodiesel with different molecular weight and number of double bond were selected for the experimental studies. The biodiesels were prepared and analyzed for fuel properties according to the standards. A constant speed diesel engine, which develops 4.4 kW of power, was run with biodiesels and its performance was compared with diesel fuel. The results show that Linseed oil methyl ester with high linolenic (unsaturated fatty acid ester) does not suit best for diesel engine due to high oxides of nitrogen emission and low thermal efficiency. ª 2010 Elsevier Ltd. All rights reserved. 1. Introduction The concept of using vegetable oil as a fuel for the compres- sion ignition engine is not a new idea. Rudolph Diesel used peanut oil to fuel the diesel engine during the late 1800. Petroleum based diesel fuel has been the fuel of choice for the diesel engines for many years due to abundant supply and low fuel prices. However, methyl esters of animal and vegetable oils (biodiesel) are again being re-evaluated for use as a fuel for diesel engines due to their clean burning tendencies, envi- ronmental benefits, and energy security reasons. The Euro- pean emission limits is shown in Table 1 and Indian exhaust emission standards for heavy duty diesel vehicles is given in Table 2. Different biodiesels derived from different sources have been tested in diesel engines for several years. All these biodiesels perform differently in diesel engines in terms of performance, emissions and combustion. Because the phys- ical and chemical properties of biodiesel derived from different sources are not same, these properties have a strong relation with the fatty acid composition of biodiesel. The structure of the fatty compounds can also affect other prop- erties of biodiesel such as density, cetane number, heating value and low temperature properties. On the other hand, the need for standardization of biofuel’s physical and chemical properties has been widely recognized [1]. It has become that only the existence of standards and norms may allow engine manufacturers to endorse the use of biofuels in vehicles and provide consumer confidence. Currently, several European * Corresponding author. Mobile: þ91 9444489013. E-mail address: sp_anna2006@yahoo.co.in (S. Puhan). Available at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 34 (2010) 1079–1088 0961-9534/$ – see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2010.02.017