work increases in proportion to the square of engine speed due to friction losses. This implies that the indicated work has a peak at a specific operating speed, which also depends on the kind of working fluid used. This also results in a drop of efficiency of power conversion for high speeds of the engine. Figure 8 shows typical performance when varying the engine speed. The compression work deviated at high speeds from the square law given above. This is due to the above mentioned contraction effect by the transfer port orifice. Any increase in work was thus largely due to rapid increases in the expansion work. As observed from the pressure waveforms, the measured compression work is higher than the actual work, since Pcp>Pcd during the compression period. This difference (△ IT) can be expressed as: On the other hand, in the expansion cycle the displacer motion is considered to induce additional work through the substantial gas compression in the bottom section of the displacer. Apparently, this energy is converted into the part of the expansion work, with the final result being the total expansion work having increased, for higher engine speeds, the measured expansion work may be noticeably higher than the actual work due to the increased displacer driving power. As can be seen from Fig. 9, the efficiency of the internal power conversion increased for higher engine speeds. In the case of low initial pressures, efficiency levels were kept almost constant over a wide range of speed, characteristic of conventional kinematic engine operations. Figure 10 represents the different energy flows occurring
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