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. A significant obstacle to utilize biodiesel fuel for automotive engine applications is its poor oxidative stability. The present work examined the impact of biodiesel oxidation on physical and chemical properties relevant to automotive engine applications. The impact of changes in the biodiesel's physical properties due to oxidation on its fuel spray characteristics is studied with the parame ters: spray penetration length, spray cone angle, spray projected area and evaporation index. The effect of variations in biodiesel's properties due to oxidation on automotive engine characteristics is studied through critical fuel injection, ignition, combustion, and emission parameters. The impact of alcohol addition to oxidized biodiesel on mitigating higher oxides of nitrogen (NOx) emissions is also examined in this research work.
The spray penetration length, spray cone angle, and 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 physical and chemical properties variations, there are no significant variations in the macroscopic spray characteristics. Accelerated oxidation tests of Karanja biodiesel are also carried out to increase the viscosity beyond ASTM limit, and its influence on spray characteristics studied. The study concludes that despite significant variations in the kinematic viscosity of fresh and oxidized biodiesels, there are no significant differences in the macroscopic spray characteristics. The effects of oxidation of Karanja biodiesel on the combustion and emission characteristics of a heavy-duty truck diesel engine are studied. The results 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 NOx and lower smoke emissions than diesel. Blending with alcohol simultaneously reduces smoke and NOx emissions of oxidized biodiesel. The mechanisms behind these inferences are discussed in my presentation.