Effect of Split Injection on the Combustion and In-Cylinder Soot Formation Characteristics of Low Compression Ratio Neat Gas-To-Liquid-Fueled DI Diesel Engine

This work capitalizes on the investigation of the effect of split injection on the combustion and in-cylinder soot formation performance of low Compression Ratio GTL-fueled DI diesel engine. An optically-accessed Rapid Compression Machine was deployed allowing the application of optical diagnostics. A shadowgraph imaging was used to analyze spray development and detect ignition zones while imaging of soot incandescence was used to determine the temporal and spatial development of soot. In addition the rate of heat release was calculated for the analysis of the combustion characteristics. It has been found that split injection shortens sprays length while increases their penetration velocity. It alters the combustion from fully premixed to two-mode, premixed and non-premixed. Soot with split injection was, therefore, significantly larger while combustion noise was reduced by factor of 4. Surprisingly, split injection has no effect on the time at which cylinder pressure peaks and the time between first and second injection was found to have no influence on the ignition delay of the second injection as a result varying pilot injection timing with split injection in the combination of low CR and GTL fuel requires no combustion phasing. Split injection did, however, altered the air-mixing quality. A quadratic relation governed this time to soot formation which was found to be inversely proportional to Lift-Off-Length. Interestingly, close split could utilize cooling effect which extended premixed combustion mode yielding lowest soot level, highest rate of heat release and combustion noise two times larger than far split.