working space: at the top end of the displacer cylinder dome (measuring expansion), at the top end of the power piston cylinder (measuring compression) and at the bottom end of the linear alternator housing (bounce spaces) (Fig. 2). The pressure data of 1024 points/cycle was averaged over 16 cycles through two FFT spectrum analyzers and then recorded. If the large bounce space is taken to be in an isothermal state, the power piston can reasonably be assumed to move in phase opposite to the variation in bounce pressure. This means that the peak bounce pressure takes place at the bottom dead center (BDC) of the piston stroke, while the minimum pressure happens at the top dead center (TDC). Any change in piston stroke can thus be determined from measuring the bounce pressure wave. Behavior of the NALSEM engine operation was monitored on a computer screen as shown in Fig. 5. Test Results Pressure Variations in the Engine Working Space It is well-known that generally pressure waves are smoothly sinuosoidal in any working space. Since the pressure drops due to the flow friction in internal heat exchangers, the pressure of the compression space is higher than that in the expansion space during the upwards motion of the power piston, while the exact opposite occurs during the downwards motion. Our test results, however, showed two significant differences when measuring the pressure waves in the NALSEM engine. First, two rapid changes in pressure occurred near both the BDC and the TDC of the power piston in low speed operations. Second, significant differences between the pressures of the expansion space and the compression space occurred when the output power was high. These operational problems will be discussed in more detail below. Figure 6 illustrates a cogging effect on ensemble-averaged pressure variations for low power operations. The bounce pressure waves are exactly in opposition with the power piston motions. In Fig. 6(a) a rapid drop in working pressure appears ahead of
RkJQdWJsaXNoZXIy MTU5NjU0Mg==