2021 Volume 33 Issue 2 Pages 114-126
There has been no example of the development of a low-temperature Stirling engine for heat-source temperature of 5℃ to 20℃ on the low-temperature side and of 95℃ on the high-temperature side, where temperatures differ by 75℃ to 90℃. In our previous paper*1, we proceed with sensitivity analysis and optimization for all variables. As a result, the amount of calculation become enormous, while some of the variables are roughly dealt with. The accuracy of the assumed calculation process with assumed constants does not require high precision of estimation to be tested by experiment, remaining concerns over sensitivity analyses and optimization for some variables. In this estimation, in order to reduce manufacturing costs of the experimental machine, dimensions are reduced while maintaining the graduality to mass-produced machines.
This report examines the conrod-stroke ratio, pressure ratio of a crank chamber to working gas, cylinder-PTFE overlap thickness, and phase difference, which have a large effect on friction loss and working-gas heat-capacity, aiming at eliminating the concern these sensitivity analyses. The examination resulted in the conrod-stroke ratio of 6.4 (3.84 in the previous design), the crank-chamber working-gas pressure-ratio of 1.0 (to be optimized by experiment in the previous design), and the cylinder- PTFE overlap-thickness of 0.02 mm and 0.10 mm on the high and low temperature side, respectively (both 0.05 mm in the previous design), and phase difference of 6.0°and 8.7°in the experimental and practical environment, respectively (2°to 3°in the previous design, whose sensitivity was to be confirmed and optimized in the experiment). With reduction of friction loss and work in one cycle, maximization of the revolution number and the working-gas heat-capacity makes output of 283W (237W in the previous design, in experimental environment), power-generation efficiency of 8.9% (8% in the previous design), and in the practical environment, output of 11.8% and 12.1% for power-generation efficiency of 3kW and 10kW, respectively, so that we achieve the target*2 of 12%.
