Effects of autooxidation on the fuel spray characteristics of Karanja biodiesel

Abstract

A significant obstacle to utilize biodiesel fuel for automotive engine applications is its poor oxidative stability. In the present work, oxidation and spray characteristics of Karanja biodiesel stored for one year are studied. The fuel physical properties that influence the spray characteristics, viz. density, kinematic viscosity, and surface tension, are increased by 0.38%, 12.74%, and 3.95%, respectively, after a one-year storage period. The macroscopic spray characteristics of fresh and aged Karanja biodiesels are compared with that of diesel. The spray penetration length, spray cone angle, and the projected spray area are measured at chamber pressures of 20, 30, and 40 bar and injection pressures of 300, 600, and 900 bar. The results showed reduced mass flow rate at lower injection pressures with fresh and aged biodiesels than diesel. At 300 bar injection pressure, spray penetration length is longer with diesel during the initial injection period, but later the spray slows down. There are no appreciable differences in the spray penetration length and the spray cone angle between diesel, fresh, and aged biodiesels at all the injection pressures. The projected spray area is higher for diesel than biodiesels indicating a denser spray with biodiesels. The study concludes that although biodiesel's long-term storage results in variations in physical and chemical properties, there are no significant variations in the macroscopic spray characteristics. Analysis of atomization characteristics of fresh and aged biodiesels also revealed similar results.