Experimental study on the tuned operation of a free piston driver

Abstract.

An experimental study of the tuned operation of a free-piston driver is described. Two series of experiments were carried out. The first was performed to validate a theory which has been developed recently to predict the operation with a small free piston-driver named NAL-CTA. The driver has a transparent window at the end of the compression tube to allow observation of piston motion. In the second, a theoretically determined length of piston buffer was used to tune the operating condition. Piston collision speeds of less than 3 m/sec were observed. A quasi-one-dimensional numerical code including leakage of driver gas through the piston clearance gap was derived. The numerical result agreed well with the experimental result. It is concluded that tuned operation, by using an appropriate length of the piston buffer, can be extrapolated to large-size tunnels.