Intake Port Flow in a Fired Two-Stroke Engine 930495

Velocity information was collected from an intake port of a single-cylinder piston-ported two-stroke engine by a Laser Doppler Velocimeter (LDV) system to better understand and quantify the behavior of intake flow exiting into the cylinder during the scavenging process. Ten measurement locations were chosen along a vertical line through the center of the port exit area. Motored and fired (skip-fired) radial velocity measurements were recorded at engine speeds of 600, 900, and 1200 RPM along with cylinder, intake (two positions), and exhaust pressure data. The ensemble-averaged mean radial velocities during motoring, when plotted versus crankangle, are generally flat over most of the port area and influenced by changes in the pressure differential between the intake and exhaust ports. During the initial phase of the port opening, a high velocity jet exits from the port causing a peak in the mean radial velocity profile. As the port opening area increases, the flow inside the port passage apparently separates from the wall resulting in near-zero velocities for the measurement points close to the top of the port. Mean velocities measured following the firing cycles are strongly affected by the expansion waves in the intake system which induce backflow of cylinder gases at 600 and 900 RPM. At 1200 RPM velocities for the motoring and firing cycles are very similar since the pressure differential between the intake and exhaust ports during the intake period are similar for the two cases. The root mean square (rms) of velocity fluctuations are generally higher in the fired engine over all the measured engine speeds.