Combustion Analysis of Diesel Engine for Unmanned Aerial Vehicle Applications

Abstract

Computational fluid dynamics tools play an important role in the diesel engine analysis, design and development. A CFD tool gives the detailed analysis about invisible in-cylinder process of diesel combustion, which is very complex in nature. It provides better guidance for the engine designs in terms of fuel economy and power output. In this present work reacting flow simulations were performed in a four cylinder direct injection diesel engine with improved version ECFM-3Z (Extended Coherent Flame model - 3 Zones) model using ES-ISE and STAR-CD codes. The closed cycle combustion process is studied in an angular sector model which is determined by the number of injector holes which reduces the computational time. The important combustion parameters like pressure variation, temperature variation, heat release rate, percentage evaporation burnt are plotted against crank angle of the engine. Parametric study of some parameters like injector location, injector nozzle hole diameter, cetane number of the diesel has been carried out. Combustion characteristics were analysed by changing the location of injector to find the best suitable location for the engine. It is found that injector location that is closer to cylinder head gives better performance due to better mixing of the fuel by avoiding the wall impingement and turbulence loss due to injector obstruction. The peak firing pressure in the diesel engine is indirectly proportional to injector nozzle hole diameter. The suitable diameter of the injector hole was found to be 85 microns beyond which the choking of the injector happens and can be declared as impractical. Performance of diesel engine also depends on the quality of fuel where higher cetane number fuel gives better performance. The study to find the best suitable number of holes in an injector was carried out and found that the healthy range for this particular engine to give best performance is 6 to 10. Best suitable combination was obtained using Minitab software.