Observations on the Effects of Intake-Generated Swirl and Tumble on Combustion Duration

Intake-generated flow fields and subsequent combustion characteristics were studied respectively in a reciprocating piston water analog flow apparatus and in firing engines. Three 1.6L, I4, 4-valve engine cylinder heads were tested with and without one intake port blocked to generate six distinctly different inducted flow fields. Fluid velocity distributions and flow field structure (“zero mean motion”, “swirl”, and “tumble”) were determined at BDC of the induction stroke using 2-D or 3-D particle tracking velocimetry. Swirl ratios based on steady-flow data were also obtained. The burn duration for each case was determined from cylinder pressure data.

The results show that burn duration decreased with increases in tumble or swirl strength. Previously observed correlations between burn duration and swirl hold if swirl is the major component of the large-scale motion. Further, the correlation between burn duration and swirl is better when based on swirl ratios measured in the reciprocating water analog rig rather than with a steady-flow angular momentum flux meter. In addition, notable three-dimensional characteristics can be observed in BDC flow fields. For example, one of the flow fields exhibited “tipped swirl” with its axis of rotation at a 30° angle to the cylinder axis.