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Investigations using novel fuel injection equipment, which allows fuel injection at highly elevated temperatures, were made to demonstrate the potential for improved mixture formation and exhaust particulate emission mitigation. Tests were carried out on a single cylinder gasoline spark ignition engine with direct fuel injection and operating in both homogeneous and stratified charge modes. Detailed measurements of the combustion characteristics, thermal efficiency and exhaust emissions were made. Particular attention was paid to particulate emission; measurements including smoke (FSN), particulate mass and particle count were made. Tests were carried out over a wide range of engine speed and load conditions to demonstrate that combustion performance is generally maintained. Particulate mass reduction in excess of 50% and particle count reduction of more than 90% were measured.

Transonic Combustion or TSCi™ is a novel combustion process based on the patented concept of injection-ignition of fuel. The process takes advantage of the improved mixing properties of supercritical fuel to achieve high yet controlled rates of heat release and high cycle efficiency. However, there is little science that documents the mixing process, ignition characteristics and combustion behavior of gasoline-like fuels in supercritical conditions, let alone the fluid transport properties. Thus, experimental studies and modeling efforts are necessary to enhance understanding of this combustion process and for effective development of this technology. This paper focuses on the model development and validation efforts for TSCi™ in an optical pressure chamber. An optically accessible pressure chamber was used to study the combustion of an injection-ignited supercritical fuel.

A novel combustion process has been developed utilizing supercritical gasoline injection-ignition for light-duty compression ignition engines known as Transonic Combustion or TSCi™. Previous publications have demonstrated results for improving fuel economy and emissions under light-load operating conditions typical of those for passenger car vehicles. The TSCi™ combustion process exhibits similarities with HCCI, LTC, PCCI and RCCI with high indicated thermal efficiencies (greater than 45%) and simultaneous reduction of NOx and PM at high EGR levels. The use of EGR at low and medium loads has shown a strong impact on NOx without compromising particulate emissions. However at higher loads with HCCI, LTC, PCCI and RCCI the operating range is limited by excessive pressure rise rates and control of combustion phasing, whereas the TSCi™ combustion process, due to its partially premixed and partially stratified mixture preparation, is not limited in the same manner.

Spark ignition gasoline engine efficiency is limited by a number of factors; these include the pumping losses that result from throttling for load control, spark ignition and the slow burn rates that result in poor combustion phasing and a compression ratio limited by detonation of fuel. A new combustion process has been developed based on the patented concept of injection-ignition known as Transonic Combustion or TSCi™; this combustion process is based on the direct injection of fuel into the cylinder as a supercritical fluid. Supercritical fuel achieves rapid mixing with the contents of the cylinder and after a short delay period spontaneous ignition occurs at multiple locations. Multiple ignition sites and rapid combustion combine to result in high rates of heat release and high cycle efficiency. The injection-ignition process is independent from the overall air/fuel ratio contained in the cylinder and thus allows the engine to operate un-throttled.