Fig.7 Experimental results as a function of operating time

Fig.8 Engine Speed and indicated work as a function of expansion space gas temperature

　

In the figure, it is shown that the engine starts to run just after the start of heating, and engine speed increases to about 800 rpm after 30 minutes. Then, engine speed decreases slowly, and keep about 600 rpm after 1.5 hours. After then, engine speed increases with increasing heat input, Q_in, temporally. However, it decreases with time. The power in this operating condition is smaller than that of rated operation. Therefore, it is considered that the effects of friction loss in mechanical devices and gas leakage from the power piston were relatively bigger.

Figure 8 shows the relationship between expansion space gas temperature, T_E, engine speed, N, and indicated work, W_i, at a steady state. The calculated result of indicated work, W_i, was derided from an isothermal analysis[4] with considerations of pressure loss in the regenerator and gas leakage from the power piston. Calculated conditions were based on the experimental results approximately. In the case of the experiment, engine speed, N, and indicated work, W_i, increased with increasing of expansion space gas temperature, T_E. The calculated result of indicated work, W_i, is similar to that of the experimental result comparatively, though the calculated result is about 7% lower than the experimental result. Thus, it is confirmed that the prototype engine works correctly under atmospheric condition.

　

3.2 MEASUREMENT OF MECHANICAL LOSS

In order to measure mechanical loss, the prototype engine was driven by an electric motor as shown in Fig.6. Mechanical loss, L_m, and friction torque, T_qm(= 60 L_m/2πN), were derived from driving torque of the electric motor and indicated work of the engine. In this experiment, the lip seal was set at the output shaft, and working space and buffer space (behind the power piston) were pressurized to 1 MPa maximum with nitrogen. The prototype engine was not heated in this experiment, and working space temperature kept room temperature approximately.

Figure 9 shows the relationship between angular speed, ω (= 2πN/60), and friction torque, T_qm. In the figure, friction torque, T_qm, increases with increasing of angular speed, ω, linearly. In a research by the author[4], it was continned that if mechanical loss consisted of the Coulomb friction loss that depends on vertical force and the viscosity friction loss that depends on speed, viscosity coefficient, then c_v, was equivalent to an inclination of this line. The inclination was constant at various pressure, and viscosity coefficient, c_vi, was determined to be 2.03 × 10^-4(Nms) from Fig.9. On the other hand, in the range of higher engine speed, such as N＞2000 rpm, a noise was generated periodically from a hot side of the cylinder. It was caused by a collision between the displacer and the cylinder, because the Rhombic mechanism of this engine did not have high assembling accuracy.

Figure 10 shows the experimental and calculated results of the relationship between mean pressure, P_m, and friction torque, T_qm.

　

Fig.9 Experimental result of friction torque

Fig.10 Friction torque as a function of mean pressure

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