Investigation of Bulk In-Cylinder Stratification with Split Intake Runners

The mixing between the flows introduced through different intake valves of a four-valve engine was investigated optically. Each valve was fed from a different intake system, and the relative sensitivity to different flow parameters (manipulated with the goal of enhancing the bulk in-cylinder stratification) was investigated. Flow manipulation was achieved in three primary ways: modifying the intake runner geometry upstream of the head, introducing flow-directing baffles into the intake port, and attaching flow break-down screens to the intake valves. The relative merits of each flow manipulation method was evaluated using planar laser-induced fluorescence (PLIF) of 3-pentanone, which was introduced to the engine through only one intake valve. Images were acquired from 315° bTDC through 45° bTDC, and the level of in-cylinder stratification was evaluated on an ensemble and cycle-to-cycle basis using a novel column-based probability distribution function (PDF) contour plot. Results showed that geometric variations of the intake runner upstream of the head had little to no effect on the bulk in-cylinder stratification, whereas flow manipulation within the intake ports and at the intake valves could have a significant effect. The highest degree of bulk in-cylinder stratification (measured 45° bTDC) was produced with intake baffles that directed the intake stream towards the top portion of the intake valves, nearest to the peak of the pent-roof, seemingly a result of increased in-cylinder tumble.