Dead Air Space
Another alteration we made was to reduce the ‘dead space’ in the system. This is a volume of air (or other working fluid) which is available for the expansion of the air before it starts to act on the moving power piston. In this instance it was the volume of the tubing connecting the two cylinders and was neither heated nor cooled. This volume of air is of no real purpose within the mechanical system and simply introduces unwanted friction. The best way of reducing this volume was to minimise the distance between the cylinders by altering the layout of the engine. In fact, this effect is exploited fully in the Beta-type engine where the displacer and power pistons are in the same cylinder, hence eliminating all dead space. On the original design we were looking at, the power piston was placed vertically next to the flywheel which meant there was a considerable length of tube running between this and the displacer cylinder. This has now been reduced by placing the power piston in a horizontal arrangement, parallel to the displacer cylinder. This has involved a complete redesign of the power piston and flywheel assembly to accommodate the new layout. The distance between the two pistons has been greatly reduced so the volume dead air space will now be less.
