Biodiesels: Oxidizing enhancers to improve CI engine performance and emission quality

Biodiesels, renewable fuels derived from biomass, animal fat, algae, wastes or residues, are amongst potential candidates to improve energy security and to reduce greenhouse gas emissions. Different from fossil diesel which mainly consists of hydrocarbons, biodiesels are oxygenated fuels. Oxygen contained in biodiesels, as an oxidizing enhancer, plays a crucial role in improving the auto-ignition quality. The oxygen enrichment coming from biodiesels causes the fuel-air mixture in the auto-ignition zone where the mixture is quite rich to become leaner, consequently improving combustion and emission quality. As such, a quantitative analysis of the impact of oxygen content in biodiesel-diesel blends in engine combustion and emission concentrations is crucial in giving key clues to fuel manufacturing as well as to internal combustion engine modeling. This study aims to establish a link between the oxygen content and engine performance as well as emission concentrations when using biodiesel blends B0, B10 and B20 (0%, 10% and 20% of biodiesel by volume in biodiesel-diesel mixtures, respectively). The biodiesel was derived from residues of the manufacturing process of palm cooking oil using methanol transesterification with the aid of a high hardness solid ceramic metal catalyst. The engine used in this test is a modern common-rail, single-cylinder engine operating under a fixed injection condition (injection timing, pressure and duration) but with a wide range of engine speeds. The results show that the oxygen enrichment coming from the fuel blends tested in this study lowers the engine power which is attributable to lower heating values of the biodiesel blends compared with that of the fossil diesel. However, the oxygen contained in the blends suppresses particle formation and decreases hydrocarbon and carbon monoxide concentrations. © 2015 Elsevier Ltd. All rights reserved.