| Reducing the cycle-to-cycle variability present in stratified charge engines is an important step in the process of increasing their efficiency. As a result of this cycle-to-cycle variability, fuel injection systems are calibrated to inject more fuel than necessary, to ensure the engine fires on every cycle. When the variability is lowered, the variation of work per cycle is reduced and the lean operating limit decreases, resulting in increased fuel economy.In this study an active flow control device is used to excite the intake flow of an engine at various frequencies. The goal of this excitation is to control the way in which vortices shed off of the intake valve, thus lowering the cycle-to-cycle variability. This method of controlling flow is investigated through the use of three engines. First, a single cylinder optically accessible engine is used to measure the in cylinder flow field. Next, a single cylinder firing engine with identical geometry to the optical engine is used to measure the engine performance. Finally, a four cylinder production engine is used to determine whether applying the flow control device improves the work output of a production engine.This study shows that the active flow control device did help to lower the cycle-to-cycle variability of the flow field however, the reduction did not translate to improved engine performance. Exciting the intake flow resulted in a reduction of velocity rms for many of the excitation frequencies with a maximum reduction of approximately 25%. Applying the same active flow control to both the single cylinder firing engine and the four cylinder firing engine resulted in no measurable increase in performance. |
