With India being a major petroleum importing coun- try, the choice of feedstock for production of biodiesel within the geographical region is an economical viable option, as approximately 60–70 % of biodiesel cost is attributed to raw material (Demirbas 2007; Phan and Phan 2008)。 Higher Free Fatty Acid (FFA) crude rice bran oil is one of the potential sources for production of bio- diesel (Balat 2011; Ju and Vali 2005)。 It is extracted from rice bran which is a byproduct of rice processing indus- try (Kusum et al。 2011)。 Crude rice bran oil having lower FFA is used for production of edible grade rice bran oil。 India ranks among the leading rice producing countries in the world and is capable of producing around 6 mil- lion tonnes of oil。 Current production capacity is lim- ited to 0。4 million tonnes, half of it being from edible grade and rest being with higher FFA which is left unu- tilized (Kusum et al。 2011)。 For higher FFA content oils esterfication is carried out in two stages。 Firstly an acid catalyzed esterification followed by an alkali catalyzed trans-esterification isadopted(Gerpen2005;Leung et al。 2010; Canakci and Gerpen 2001; Ramadhas et al。 2005)。 Thus as a low cost feedstock, the unutilized rice bran oil can be used for biodiesel production and used as an alternative cheap and environmental friendly fuel in India。

Use of alternative environment friendly fuels along with improvements in the engine design can result in better engine performance and lower exhaust emissions。 Auto- mobile vehicles with diesel engine usually are operating with compression ratio in the range of 15–18。 Experi- mental work has been done (Sinha and Agarwal 2007; Lin et al。 2009; Saravanam et al。 2010) to study the engine characteristics of a diesel engine at a single compression ratio fuelled with blends of rice bran oil biodiesel。 Thus, realizing the importance and potential of rice-bran oil in catering to the energy needs and environmental issues of the country, an effort has been made in the present work to investigate the variation in engine performance and exhaust emission characteristics of a 4-stroke diesel engine fuelled with blends of crude rice bran biodiesel by varying compression ratio from 15 to 18。

Methods

Methanol, potassium hydroxide (KOH) and sulphuric acid (H2SO4) were used for carrying out a 2-step esteri- fication in water bath shaker。An acid catalyzedesterifi-

cation followed by an alkali catalyzed esterificationwas

carried out for higher FFA crude rice bran oil。 Figure 1 shows the transesterification process carried out for bio- diesel production from crude rice bran oil。 Table 1 shows the physical and chemical properties of crude rice bran oil and Table 2 shows the various properties of the pre- pared biodiesel。 Cetane index of diesel and biodiesel blends is calculated by a four variable equation as per ASTM D4737-10 (2010) standard test method。 Cetane index calculated for diesel, 10, 20 and 40 % vol。 crude rice bran biodiesel blends are 49。5, 51。4, 52。1 and 54 respectively。

A 4-stroke single cylinder variable compression ratio (VCR) compression ignition direct injection (DI) engine is used for the test。 The experimental set-up has the instrumentation (Piezo sensor) for measuring the cylin- der pressure variation with crank angle for every 1° incre- ment。 Lab-view® based software “Enginesoft” (http:// www。apexinnovations。co。in/) is used for acquiring the data which acts as interface between engine and the user。 The compatible multifunction data acquisition module for USB used is “NI USB-6210” (http://sine。ni。com/nips/ cds/view/p/lang/en/nid/203223)。 Each engine test data obtained is conditioned and processed for 10 cycles, which means that at a particular engine load condition

“Enginesoft” gives each reading after processing it for 10 cycles。 An eddy current dynamometer is used for meas-