Rapid industrialization and economic growth of developing countries increase the diesel fuel demand for automotive and standby power generation applications. The projected demand for diesel fuel is 21% higher than gasoline by 2025. Thus, it is imperative to search for alternative fuels for diesel. Among the various alternative fuels, biodiesel has emerged as the most promising fuel due to its renewable, non-toxic, and biodegradable nature. It has similar fuel properties as diesel and bi-directional oxides of nitrogen (NOx) and particulate matter (PM) trade-off reduced to unidirectional higher NOx emission problem. A significant obstacle to utilize biodiesel fuel for automotive engine applications is its poor oxidative stability. Biodiesel autooxidation upon long-term storage results in variations in composition and properties, leading to fuel quality degradation. Fuel property variation influences the fuel spray, evaporation and engine characteristics. The present study aims to understand the effects of gradual and accelerated oxidation of Karanja biodiesel on the fuel spray and engine characteristics. To understand the effects of gradual autooxidation, the variations in fuel properties and macroscopic spray characteristics of Karanja biodiesel stored for one year are studied.
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 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. However, it is worth noting that the variations in fuel properties of Karanja biodiesel are within the maximum allowable limits specified by the ASTM standards. Based on this observation, accelerated oxidation tests of Karanja biodiesel are carried out to increase the viscosity beyond ASTM limit, and its influence on spray characteristics studied. The study concludes that even though there are significant variations in the kinematic viscosity of fresh and oxidized biodiesels, there are no significant differences in the macroscopic spray characteristics.
Analysis of atomization characteristics of fresh and oxidized fuels also revealed similar results. The effects of oxidation of Karanja biodiesel on the combustion and emission characteristics of a heavy-duty truck diesel engine is studied. The results obtained show that compared to diesel, the start of fuel injection of fresh and aged biodiesels advanced by ~2-degree crank angle and the ignition delay time is shorter. The ignition delay of oxidized biodiesel is shorter than fresh biodiesel. Both fresh and aged biodiesels produced higher oxides of nitrogen (NOx) and lower smoke emissions compared to diesel. Interestingly, with an increase in the oxidation rate of biodiesel, NOx emission decreases. The mechanisms behind these inferences are discussed in my presentation.