Seed contains about 35-40 % oil (Kandpal and Madan 1995; Jongschaap et al. 2007), which can be extracted by pressure, heat, or solvents. One hectare of Jatropha plantation can produce about 900 kg of oil. Raw seed oil of J. curcas has been exten­sively studied because of its promising potential to substitute fossil diesel (Achten et al. 2008). J. curcas raw oil is cost effective, environmentally safe, renewable non­conventional source of energy and has fuel properties comparable to fossil diesel (Table 17.1).

These properties, particularly calorific value of J. curcas oil which is akin to fossil diesel and greater than coal (Gubitz et al. 1999; Rosenblum 2000; Sotolongo et al. 2009), vindicates its use both in unmodified and modified diesel engines as a substitute for petro-diesel.

However the high kinematic viscosity of raw oil 49.93 mm2 s-1 compared to die­sel fuel which is 1.3-4.1 mm2 s-1 results in less satisfactory use of raw oil in diesel engines (Shahid and Jamal 2008; Kywe and Oo 2009) as it causes several problems in diesel engines such as increasing fuel spray and reduction in fuel atomization, which causes choking of injectors, engine deposits, thickening of lubricating oil, and piston ring sticking (Shahid and Jamal 2008; Kywe and Oo 2009). Notwithstanding these problems, raw oil is used with success in slow-speed station­ary diesel engines such as generators and pumps (Tomomatsu and Brent 2007). Prasad et al. (2000) reported that use of raw J. curcas oil in diesel engine results in lower GHG emissions than fossil diesel which is beneficial for environment. To improve the use of raw Jatropha oil as fuel, its viscosity is reduced by either blend­ing raw oil with fossil diesel or preheating it (Achten et al. 2008). Apart from trans­portation fuel, raw oil also finds its use in lamps and cooking stoves. Thus, the most common uses of raw J. curcas oil are lighting lamps combustion, in stationary die­sel engines and cooking stoves; however to counter low absorbance capacity and high viscosity of oil, they have to be modified slightly.

Jatropha seed oil in raw form without any modification can be used directly in agri­cultural machinery. However, conversion to biodiesel first, will result in very little long-term problems (Harwood 1984). High content of unsaturated fatty acids (78— 84 %) makes J. curcas seed oil suitable for biodiesel production (Salimon and Abdullah 2008). Pure biodiesel and its blends with petro-diesel can be used in any petroleum diesel engine without the need for modification. The oil can be used in machines and engines as a direct replacement for fuel, in addition to many other commercial and industrial uses (Cerrate et al. 2006; Ndong et al. 2009).

The most common technology to produce biodiesel J. curcas oil is Trans­esterification (Meher et al. 2006). The J. curcas oil in trans-esterified form gives comparable results to fossil diesel (Prasad et al. 2000). The suitability of Jatropha oil for trans-esterification into biodiesel has been demonstrated (Achten et al. 2008; Shahid and Jamal 2008). In trans-esterification process, under heat using alcohol and a strong base usually NaOH as catalyst, J. curcas oil is converted to esters and glycerine. The ester usually formed is methyl esters (Singh et al. 2008). The process involves three successive reversible reactions. In the first reaction diglycerides are formed from triglycerides, and then former is converted to monoglycerides which finally forms glycerine. In all the three reactions, esters are produced. Raw oil type, temperature of reaction, alcohol to ratio, catalyst type and quantity, and mixing intensity are different variables in process of trans-esterification (Marchetti et al. 2007). Acids, alkali, lipases, or supercritical alcohol all can be used as catalysts. The stoichiometric ratio of oil and alcohol is usually 1:3 (Marchetti et al. 2007). Ethanol is preferred usually as it is CO2 neutral and also renewable. Trans­esterification transforms 92-98 % of the original oil to biodiesel and also reduces its viscosity from 49.93 to 4.59 mm2 s-1. Thus one hectare of Jatropha plantation can produce about 828 kg biodiesel, representing about 32 GJ ha-1 energy. The eco­nomic evaluation showed that the production of biodiesel from Jatropha oil is prof­itable provided the by-products of production process are also commercialized as valuable energy products (Eisa 1997; Foidl and Eder 1997).