GASOLINE PARTIALLY PREMIXED COMBUSTION : HIGH EFFICIENCY, LOW NOX AND LOW SOOT BY USING AN ADVANCED COMBUSTION STRATEGY AND A COMPRESSION IGNITION ENGINE

Abstract

A VOLVO D5 was ran with Gasoline in order to demonstrate that high octane number fuels, in compression ignition engines, are able to achieve high efficiency, low NOx and low soot at the same time in the whole load range. An advanced injection strategy was developed to accomplish the target. It consisted in injecting most of the fuel very early in the compression stroke and then through the stratification created by the last injection the combustion is triggered. The load is controlled with the first injection while the combustion phasing with the last. Running the engine at 2000 rpm, an IMEP sweep was performed between 6 and 17 bar IMEP. Up to 8 bar IMEP no EGR are needed to keep NOx and soot below 27 ppm and 0.05 FSN respectively. After this load EGR is increased up to 50%, soot and NOx are still below the previously mentioned values while the gross indicated efficiency stays fairly constant at 47% throughout the sweep. In the second section of the paper, Diesel was compared with Gasoline. Slightly higher efficiency was obtained with the lower octane number fuel, NOx was comparable and soot steadily increased during the IMEP sweep up to 9 FSN. In the final part of the research, the commercial 140° UA nozzle was compared to the narrower one, 120°, that was used in the above mentioned experiments. Comparable values of soot and NOx are achieved on the other hand the efficiency deteriorates because the hot areas of the combustion move closer to the wall