Combustion Characteristics of Diesohol Using Biodiesel as an Additive in a Direct Injection Compression Ignition Engine under Various Compression Ratios

Abstract

An experimental investigation is carried out to study the combustion characteristics of diesel−biodiesel−ethanol blends in a single-cylinder four stroke direct injection variable compression ratio engine under the compression ratios 15:1, 17:1, and 19:1. As the ethanol is immiscible with diesel, biodiesel (jatropha methyl ester) is used as an additive to prevent the phase separation of the diesel−ethanol blends. The addition of ethanol decreases the cetane number of the blend, whereas the biodiesel addition improves the cetane number of the resultant mixture. The combustion characteristics of the stable fuel blends (D85B10E5, D80B10E10, D75B10E15, D70B10E20, and D65B10E25) are studied and compared with neat diesel by conducting experiments on the computerized variable compression ratio engine test rig. A piezoelectric pressure sensor and a crank angle encoder are used to record the cylinder gas pressure and a crank angle, respectively, to determine the combustion parameters. It is observed that the cylinder gas pressure, maximum rate of pressure rise, and heat release rate increase with higher ethanol concentration due to the longer ignition delay. Also it is found that the ignition delay decreases with the increase in compression ratio and brake mean effective pressure. The total combustion duration is longer as the total fuel consumption is higher for the diesel−biodiesel−ethanol blends than neat diesel. The exhaust gas temperature is found lower for the diesel−biodiesel−ethanol blends. The relative air fuel ratio is found higher for the diesel−biodiesel−ethanol blends than neat diesel and decreases with an increase in brake mean effective pressure. This research work established an insight on the fuel burning characteristics of the diesel−biodiesel−ethanol blends under various compression ratios and loading conditions.