the BDC, while in Fig. 6(b) a rapid upward slope in the pressure was observed around the TDC. These are probably due to the cogging action of the magnet connected to the power piston, as mentioned earlier. When the piston moved towards the bottom/top of its stroke, the working gas was expanded/compressed by the additional acceleration in the same direction. This shows up as the distortion in pressure around the TDC/BDC. As noted, the accelerated force became comparatively stronger for low speeds of the piston. Without such a cogging effect, the pressure wave is expected to be sinusoidal, as shown in the figures by the dashed lines. It is, therefore, required to establish a dynamic matching of piston-to-magnet plunger coupling motion in a forced oscillation mode. Next consider the pressure variations for high output power operations. Figure 7 compared pressure waveforms for two different engine speeds (10 and 20 Hz). As mentioned earlier, the high-speed waveforms were different from that expected. The pressure of the expansion space (Pf) was higher than that of the compression space (Pc) for a phase range of about 90 to 180°. Pc was less than Pc for 270° to 360°. A possible cause for his may be as follows: When the piston moves from the TDC to the BDC, some of the working gas is transferred into the upper piston space from the bottom space. The gas is squeezed as it passes through the orifice, located at the entry to the transfer port. Therefore the pressure of the gas just prior to the orifice is nearly equal to the pressure of the expansion space. Due to contraction it becomes higher than the pressure of the compression space after it passes through the orifice. Pe is thus greater than PQ. The exact opposite occurs during the other half of the cycle, when the piston moves from the BDC to the TDC. During this part of the cycle, Pc>Pe. Such a hydrodynamic compression effect induces significant problems in engine operation when the engine speed is high, as evident from Fig. 7. It is expected that the magnitude of the pressure difference in front of and behind the orifice increases in proportion to the square of the engine speed. Thermodynamic Characteristics Expansion work tends to increase in proportion to the engine speed. Compression
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