Transient Discharge from a Cylinder at High Rates of Volume Expansion

Experiments are described in which compressed air is suddenly released through circular square edge orifices mounted co-axially in a cylinder and simultaneously a piston in the cylinder is moved at speeds comparable to that in an engine. Under these conditions, discharge coefficients are affected by the rate of volume expansion. The discharge coefficients are independent of the orifice length/diameter ratio and are equal to those of sharp edge orifices (1/d < 0.05) under conditions of decaying upstream pressure without piston motion. The experiments simulate partly the blowdown process in two stroke-cycle engines.