LDV Measurements of Intake Port Flow in a Two-Stroke Engine with and without Combustion 920424
To better understand the complex scavenging process in ported two-stroke engines, velocity measurements were taken at the exit of an intake port of a motoring and firing single-cylinder propane-fueled two-stroke engine by Laser Doppler Velocimetry (LDV). The radial velocity component was measured at the center of one port at engine speeds of 600, 900, and 1200 rpm. Cylinder pressure was also recorded for both motoring and firing cycles. When plotted versus crankangle, it was observed that the intake flow ensemble-averaged mean velocities have a characteristic two-end-peak profile with peaks occurring just after the piston exposes or is about to block the measurement volume. The two peaks occurred at approximately the same crankangle in both the motoring and firing engines. At 600 rpm the two velocity end peaks in the fired engine are larger than the corresponding motored values by a factor of 1.73 to 2.26. The root mean square (rms) of velocity fluctuations are approximately equal for the motoring and firing engines within 20 degrees both sides of Bottom Dead Center (BDC). During the rest of the measurement period the firing rms values are greater. At 900 rpm the first peak in the fired engine is larger in magnitude by a factor of about 1.4 with the second peak being less than the corresponding motored engine values. The rms of velocity fluctuations is larger for the most part in the fired engine. At 1200 rpm the ensemble-averaged mean velocities for the two cases are similar in shape with the magnitude being larger for the fired engine in the first half of the intake process. The rms of velocity fluctuations is higher when fired. A backflow into the intake was observed at 600 rpm which decreased in strength and shifted in crankangle at 900 rpm. At 1200 rpm no backflow was observed.