The temperature difference of entrance and exit of the cooling water increases similarly to the heat source in high revolution. So, increment of heat rejection is confirmed. The gas temperature of the high-temperature space is about 105℃, which is about 15℃ lower than the heat source temperature. The gas temperature tends to be lower as engine speed rises. The gas temperature of the low temperature space is near about 25℃, so that the temperature difference of working gas of both space is about 80℃ only.
Figure 4 shows engine performance in the different conditions of the buffer pressure. From this figure, both indicated power and shaft power are drastically improved, when the buffer pressure is raised. The maximum speed of this engine is nearly 180rpm. And the engine speed which gives maximum shaft power is about 90-100rpm. So there is a proper condition which gives maximum shaft power.
Figure 5 shows maximum indicated power and maximum shaft power with the relation to the buffer pressure. From this figure, indicated power increases as the buffer pressure is raised, and it is about 350W at the buffer pressure of 2atm. Shaft power is about 205W at the buffer pressure of 1.5atm, and about 244W at 2atm. It increases rapidly by raising the buffer pressure. From this result, the improvement of output power can be expected by giving optimum operating condition of high buffer pressure.
Figure 6 shows maximum shaft power and various efficiency in relation to the buffer pressure. The mechanical efficiency rises when the buffer pressure is raised. Indicated thermal efficiency and brake thermal efficiency are improved when the buffer pressure is raised from the atmospheric pressure to 1.5atm. However, these are slightly decreased at the buffer pressure of 2atm. We had been able to verify a possibility of developments of the practical model from a successful experiences on the trial manufacturing of 300W class low temperature difference Stirling engine. To obtain the practical power from about 100℃ temperature difference, it was found that engine must be operated in high buffer pressure and high engine speed .
Fig. 5 Maximum Indicated Power and Maximum Shaft Power
Fig. 6 Variously Efficiency in Maximum Shaft Power
