Flames and Liquid Fuel in an SI Engine Cylinder during Cold Start

摘要

The flame propagations in the very first firing and subsequent cycles in an SIengine during cold start were studied to gain a better understanding of reaction fronts associated with liquid fuel (regular unleaded) in the cylinder. This work was performed using the Rutgers high-speed spectral infrared digital imaging system on a single-cylinder engine with optical access. The engine was mounted with a production engine head mated with a conventional pon fuel injection (PFI) system. In the study, four images in respective spectral bands were simultaneously obtained at successive instants of time, which was done for eight sequential cycles. This multiple-band successive-imaging was repeated in intervals of about two minutes over a period of more than twenty-five minutes after the engine start. During this experiment, the temperature changes at the intake port, the water jacket and the exhaust gas were monitored. In addition, pressure-time data was obtained from individual cycles in order to gain some insight into the overall in-cylinder reactions. The first firing cycle exhibited almost invariably weak flame propagation, which was followed by very intense flame fronts in the next cycle. Note that the flame propagation in the first cycle seems to only indicate consumption of the filel vapor available in the cycle. The flames in the third cycle were also intense in some cases, but mostly weaker than those in the second. Upon formation of the flame front in the beginning of combustion, some exceedingly strong local reactions started to grow, but no earlier than l5CA after TDC.