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Oxidation stability of biodiesel and its effects on diesel combustion and emission characteristics

Abstract The current paper describes two topics. The first is a study of the effect of fatty acid methyl ester content in biodiesel on characteristics of oxidation stability as quality parameters, including peroxide value, acid value, kinematic viscosity, and induction period obtained from a Rancimat test. The second is a study of the effect of biodiesel oxidation on diesel combustion and emission characteristics. An accelerated oxidation stability test was conducted by the Rancimat test method on methyl esters with different unsaturated fatty acid components. The unsaturated fatty acid components exert a large influence on oxidation deterioration as well as thermal and auto-oxidation stability. In addition, characteristics of oxidation were obtained from a thermal oxidation test using a tank equipped with an injection system test rig. These experiments clarified relationships between oxidation quality parameters. The autoignition characteristics of deliberately oxidized biodiesel were analysed by means of the constant-volume combustion method. Engine bench tests were also conducted on a single-cylinder engine. These experiments employed methyl ester made from soya bean oil as biodiesel. Use of an oxidized biodiesel was found to increase combustion pressure and temperatures, resulting in increased NO x emission; however, CO emission and smoke are decreased without any loss in fuel consumption rate.