Investigation of single and split injection strategies in an optical diesel engine

Abstract

This study investigates the effects of a split injection strategy on combustion performance and exhaust emissions in a high speed direct injection optical diesel engine. The investigation is focused on the effects of injection timing, quantity, and the dwell angle between the injections using commercially available diesel fuel. Three different split injection strategies including 50:50, 30:70, and 70:30 have been investigated. Additionally, the effect of total injected fuel quantity using total fuel quantities of 10 mm3 and 20 mm3 has been investigated. Moreover, the effect of variable and fixed dwell angle in split injections has been examined for five different values between 5o CA and 25o CA in the case of variable and 10o CA for the fixed dwell timing. The last parameter investigated was the injection timing, nine injection timings have been tested for each of the strategies. A Ricardo Hydra single cylinder optical engine running at 1500 rpm was used in this investigation. Conventional methods such as direct in-cylinder pressure measurements and heat release rate analysis have been employed. In addition, optical techniques such as high speed video imaging and two-colour have been applied, aimed at in depth analysis of the effects of the aforementioned parameters on engine performance and emissions. Furthermore, a significant amount of effort was devoted to the development and application of the Laser Induced Excipex Fluorescence (LIEF) technique so that simultaneous fuel liquid and fuel vapour distribution could be visualised. This investigation concludes that split injection strategies have the potential to reduce diesel exhaust emissions while maintaining a good level of fuel economy, provided that injection timings and the dwell angle between injections are appropriately selected. Further investigations are required in order to examine the effect of split injection under different engine operating conditions and speeds. In addition, the effect of alternative fuels must be considered. Moreover, the application of LIEF technique for quantitative fuel vapour concentration measurement should be considered through further optimisation of the LIEF system and careful calibration experiments.