Impact of different levels of biodiesel oxidation on its emission characteristics

The oxidation of a Jatropha curcas-derived biodiesel was accelerated by the Rancimat method. The oxidation performance of the J. curcas-derived diesel was monitored by gas chromatography coupled with mass spectrometry (GC-MS), and the evolution of its physicochemical properties was further studied. Simultaneously, the combustion emissions of the J. curcas-derived biodiesel having different oxidation degrees were studied. The results revealed that the composition of the biodiesel sample was significantly altered during the oxidation process. Methyl linoleate, bearing multiple bis-allyl sites, was easily oxidized, while aldehydes, ketones, higher molecular weight oxygenated compounds, and soluble polymers were generated as a result of the oxidation process. The calorific value of the J. curcas-derived biodiesel decreased upon oxidation, whereas the acid value increased from 0.31 to 2.02 mg KOH/g. Both the density and the surface tension of biodiesel increased to a different extent with the oxidation time, while the CO2 emissions increased first and decreased thereafter. The maximum and minimum CO emissions were 321 and 120 ppm, respectively, while the NOx emissions increased up to 48 ppm upon oxidation from a minimum value of 14 ppm. (C) 2018 Energy Institute. Published by Elsevier Ltd. All rights reserved.