This paper presents the performance of biodiesel blends in a single-cylinder water-cooled diesel engine. All experiments were carried out at constant speed 1500？rpm and the biodiesel blends were varied from B10 to B100. The engine was equipped with variable compressions ratio (VCR) mechanism. For 100% Jatropha biodiesel, the maximum fuel consumption was 15% higher than that of diesel fuel. The brake thermal efficiency for biodiesel and its blends was found to be slightly higher than that of diesel at various load conditions. The increase in specific fuel consumption ranged from 2.75% to 15% for B10 to B100 fuels. The exhaust gas temperature increased with increased biodiesel blend. The highest exhaust gas temperature observed was 430°C with biodiesel for load conditions 1.5？kW, 2.5？kW, and 3.5？kW, where as for diesel the maximum exhaust gas temperature was 440°C. The CO2 emission from the biodiesel fuelled engine was higher by 25% than diesel fuel at full load. The CO emissions were lower with Jatropha by 15%, 13%, and 13% at 1.5？kW, 2.5？kW, and 3.5？kW load conditions, respectively. The emissions were higher by 16%, 19%, and 20% at 1.5？kW, 2.5？kW, and 3.5？kW than that of the diesel, respectively. 1. Introduction Diesel engines have provided power units for road transportation systems, ships, railway locomotives, equipment used for farming, construction, and in almost every type of industry due to its fuel efficiency and durability. However, Diesel engines are the major sources of and particulate matter emissions which are environmental concerns. For automotive industry the reduction of and PM emission is the most important task. National governments are imposing stringent emissions on automotive sector to reduce and PM emissions. Also global house warming gases (GHG) are going to receive more focus from future autosector. Therefore, the stringent emission regulation requirements give a major challenge to comply emission targets while maintaining its performance, drivability, durability, and fuel economy. The use of alternative fuels for internal combustion engines has attracted a great deal of attention due to fossil fuel crisis and also GHG impact. Alternative fuels should be easily available, environment friendly, and technoeconomically competitive. Successful alternative fuel should fulfill environmental and energy security needs without sacrificing engine operating performance . Renewable resources offer the opportunity to tap local resources and reduce dependency on fossil energy resources. Most biodiesel oils, particularly of the nonedible type
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