Combustion Characteristics of Biodiesel Fuel Derived from Waste Edible Oil

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This report investigated the influence on diesel injection, engine performance, combustion characteristics, emissions, and other characteristics of combustion of single droplets of neat FAME fuels. The experiments used chemical reagents, methyl oleate (OME, C18:1), methyl Laurate (LME, C12:0), and mixtures of methyl palmitate (PME, C16:0) and OME or LME as the base fuels. Notable results obtained are as follows:(1) The bulk modulus was determined by measurements of the speed of sound under low fuel pressure conditions (>40MPa), and the results showed that the bulk modulus of OME was about 7% higher than gas oil. The delay in injection was examined by measuring the time difference between the start of the pressure rise in the injection pipe and the start of injection. With OME and LME there were shorter injection delays than with ordinary gas oil.(2) Engine experiments were carried out with biodiesel fuels derived from unused rapeseed oil, soybean oil, and palm oil. This elucidated the influence on engine performance, combustion characteristics and emissions of the three kinds of raw materials. Compared with gas oil, the FAME fuels showed similar brake thermal efficiencies at high loads, and the smoke densities were significantly lower under whole load conditions. The ignition characteristics were considerably improved when PME was blended with LME or OME.(3) With a suspended droplet combustion technique, the combustion characteristics of FAME droplets were analyzed with images taken by a high speed video camera. It was found that when PME is blended with OME the ignition delay shortens and the speed of combustion increases. During the combustion process, the formed soot was collected on a glass fiber filter and the mass was weighed by a micro balance. The results showed that the soot formation rate(defined as the mass ratio of soot to droplet) with OME is below 15% of that of gas oil droplets.