Experimental Investigation to Study Convective Mixing, Spatial Uniformity, and Cycle-to-Cycle Variation During the Intake Stroke in an IC Engine

Abstract

The work described in this paper focuses on experiments to quantify the initial fuel mixing and gross fuel distribution in the cylinder during the intake stroke and its relationship to the large-scale convective flow field. The experiments were carried out in a water analog engine simulation rig, and, hence, limited to the intake stroke. The same engine head configuration was used for the three-dimensional PTV flow field and the PLIF fuel concentration measurements. High-speed CCD cameras were used to record the time evolution of the dye convection and mixing with a 1/4 deg of crank angle resolution (and were also used for the three-dimensional PTV measurements). The captured sequences of images were digitally processed to correct for background light non-uniformity and other spurious effects. The results are finely resolved evolution of the dye concentration maps in the center tumble plane. The three-dimensional PTV measurements show that the flow is characterized by a strong tumble, as well as pairs of cross-tumble, counter-rotating eddies. The results clearly show the advection of a fuel-rich zone along the wall opposite to the intake valves and later along the piston crown. It also shows that strong out-of-plane motions further contribute to the cross-stream mixing to result in a relatively uniform concentration at BDC, albeit slightly stratified by the lean fluid entering the cylinder later in the intake stroke. In addition to obtaining phase-averaged concentration maps at various crank angles throughout the intake stroke, the same data set is processed for a large number of cycle to extract spatial statistics of the cycle-to-cycle variability and spatial non-uniformity of the concentration maps. The combination of the three-dimensional PTV and PLIF measurements provides a very detailed understanding of the advective mixing properties of the intake-generated flow field. [S0742-4795(00)00103-4]