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The present experimental investigations deal with the spark plug location and its effect on the performance and emission of a 100% raw biogas-fueled variable compression ratio engine. Different measurements of performance, combustion, and emission parameters are used to analyze the effect of four spark locations protruded inside the clearance volume (viz. 0, 2, 5, and 10 mm). The protrusion of the spark plug by 2 mm is observed to be optimum for compression ratios 8, 9, and 10. For this optimum spark plug location, engine efficiency and fuel economy are found to be higher. Faster combustion, in this particular case, has led to early and higher peak cylinder pressure and burnt gas temperature. Lower emissions of hydrocarbons and carbon monoxide have verified the optimality of 2 mm protrusion location of the spark plug for all the compression ratios. Thus, present investigations recommend minor protrusion of the spark plug to assist the combustion process, to enhance the performance and lowering the emission of a biogas-fueled engine.

Currently, more than 95% of biodiesel is being produced from edible vegetable oils which may affect the sustainability of biodiesel industries. Rubber seed oil (RSO) is one of the promising non-edible oil for biodiesel synthesis. Higher free fatty acid content of RSO was reduced by ultrasonic assisted esterification reaction. Non-conventional techniques, ultrasonic horn and ultrasonic bath for transesterification of esterified RSO (ERSO) were studied to enhance the yield of rubber seed oil methyl esters (ROME). The effect of transesterification parameters; molar ratio (MR) of methanol/ERSO (3:1-13:1), reaction time (5-50min) and heterogeneous catalyst Ba(OH) 2 ·8H 2 O (2-10wt%of feedstock) on conversion of RSO were investigated and optimized for maximum yield of ROME. The physico-chemical properties of ROME and its various blending with diesel (RDXX) were estimated to suite diesel engine for efficiency (BTE) was achieved at 80% load with RD10 (28.36%) compared to neat diesel (24%) and a drastic improvement of overall 13% increase at all loads. Maximum exhaust gas temperatures for biodiesel blends were found to be lower than neat diesel with rise in pressure by about 4% which ultimately shows slight improvement in the net heat release rate. The emissions of CO, CO 2 and NO X were reduced with the use of ROME blends.