Dynamic balancing of multiple independent stirling engines

NASA Tech Briefs, Apr 2001 by White, Maurice A, Penswick, Laurence B, Qiu, Songgang

Vibrations are minimized without sacrificing redundancy.

Experiments have shown that an assembly of multiple free-piston Stirling engines can be designed and constructed in such a way as to both (1) make the vibrations of the engines balance each other to minimize the overall level of vibration, and (2) enable the engines to operate independently of each other, so that if one fails, the others) can continue to provide power. Prior to these experiments and to the research and development effort that preceded them, it was not possible to achieve both redundancy and suppression of vibrations: The only previously demonstrated method to balance out vibrations of multiple Stirling engines was by use of counter-oscillating pistons coupled to each other via a common thermodynamic hot space, with the engines driving linear alternators connected electrically in series. This older scheme precludes redundancy because the common thermodynamic interaction and the series electrical connection causes both engines to fail when one fails.

In the present scheme, the multiple Stirling engines in a given assembly are thermodynamically independent of each other. For coupling of vibrations between the engines, the housings of the engines are rigidly connected to each other at their cold ends in an opposed arrangement (see figure). A tuning capacitor is connected in series with the linear alternator of each engine to compensate for the alternator inductance in order to obtain a near unity power factor.

The experiments were performed on a two-engine assembly operating at a frequency =60 Hz and output-power levels =

When the ac connection is closed after having been open, the engines come back into synchronization with opposing piston motions, so that vibrations are once again suppressed. When so synchronized, the engines remain synchronized even in the presence of wide variations in charge pressure or hot-- end temperature of one engine relative to the other. No significant transient overstrokes or other potentially damaging behavior was observed.

This work was done by Maurice A. White, Lawrence B. Penswick, and Songgang Qiu of Stirling Technology Co. for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Commercial Technology Office, Attn: Steve Fedor, Mail Stop 4-8, 21000 Brookpark Road, Clever land, Ohio 44135. Refer to LEW-16823.

John H. Glenn Research Center, Cleveland, Ohio