Experimental analysis of the influence of diesel-used cooking oil methyl ester blends on efficiency, emissions and combustion process in a diesel engine

An extended investigation on the application of blends between diesel oil and used cooking oil methyl esters (UCOME) was developed on an automotive turbocharged diesel engine. Two commercial diesel oils were considered as reference fuels, the first with the conventional content of biodiesel (7%), the second with an increased amount (15%). Then, increased levels of UCOME were added, on a volumetric basis (20%, 40%, 55 or 60%), to analyze the influence of biodiesel content on engine behavior. Three part load engine operating conditions were selected for tests, measuring average engine parameters and indicated pressure diagrams. Their processing allowed to calculate the most important operating, energy and environmental engine quantities, rate of heat release and related combustion parameters. A proper management of the exhaust gas recirculation circuit, variable nozzle turbine and injection system was applied thanks to the availability of an open electronic control unit. An optimal UCOME content (40%) was identified, leading to highest values of brake thermal efficiency (with maximum increase around 5% referring to baseline fuels) and lowest levels of NOX emissions. Soot emissions were always reduced when increasing biodiesel content.