A review on atomization and exhaust emissions of a biodiesel-fueled compression ignition engine

In this article, the spray atomization characteristics, combustion performance, and emissions reduction characteristics of a biodiesel-fueled compression ignition (CI) engine are reviewed, including physical fuel properties such as the oxygen content, density, viscosity, and cloud point. Different fuel properties of biodiesel such as higher oxygen content and cetane number induce shorter ignition delay, improved combustion efficiency, and reduction of emissions. However, higher viscosity causes coarse atomization, and a higher cloud point indicates that the fuel injection system needs to be modified. A slightly shorter injection delay was observed due to the low compressibility of biodiesel, and the production of biodiesel spray is similar to that of diesel spray despite having different fuel properties. The higher surface tension of biodiesel results in a higher SMD distribution, and thus the droplet momentum of biodiesel, which is related to the spray velocity, is greater than that of diesel fuel. A lower maximum combustion pressure and indicated mean effective pressure (IMEP) were observed for biodiesel fuel due to its low heating value. Biodiesel combustion with exhaust gas recirculation (EGR) shows a higher combustion pressure and rate of heat release than those of diesel fuel due to its oxygen content. This oxygen content induces reduced HC, CO, and PM emissions, but there is an increase of NOx emission. However, a high EGR strategy can reduce the NOx emission in biodiesel-fueled Cl engines. (C) 2016 Elsevier Ltd. All rights reserved.