There will be many methods to get higher efficiency, but they will be found in future. Actually, flow resistance at various passages and leakage of valves give biggest loss today, which will be much improved in future. Also, any valves with wider inlet area are needed.
3. EXPERIMENTS BY SMALL MODEL STIRLING ENGINE
As already reported in (1), (2), first step experiments of at his engine were done with various conventional atmospheric model Stirling small engines made by the authors since 1980 years.
Compressed air was used instead of steam at first and rotary valves and or piston valves of many types including D-type valves were tried for comparison.
The records of representative experiments with SE-45, which is Sanden Companies' model Stirling engine designed by Isshiki and experimented at Ashikaga Inst. of Technology, will be shown here. As seen at Fig.3 a complicated piston type reciprocating carbon valve is installed to it, and into the cold side of the engine, compressed air of 0.2Mpa is injected and ejected timely to make expected cycle of this SSSE, and heater is heated by a gas burner.
One of the results of this engine for power output against rotational speed is shown at Fig.4. Power increase much more at heated hot heater case than cold air case.
Moreover one of the results of the measured power with various valve timing of this engine is shown at Fig.5. As seen in Fig. 4 and 5, the power of SE-45 reached near 27 watt, with 333℃ heater temperature, and 0.2Mpa air pressure.
This power is about three times of without air injection at same heater temperature but its speed at highest power went down.
By other several atmospheric conventional Stirling engine models have shown very similar results with power increase.
At fig. 6 the several examples of increase of no load rotation speed Nf by increase of head heater temperature Th, each at constant injection pressure of air between 0.06-0.2 Mpa.
These results prove that Stirling type head heaters work very effective to these engine.
Also, by these basic experiments of SSE with air injection and ejection, next many facts are known, that; (1) It is known that each model Stirling engine rotates very easily only by the injection of air as air expander without heating. This fact is quite different from conventional Stirling Engine which were sometimes very difficult in self running. (2) Then it has been known that D type valve needs more friction by one side air pressure than others. (3) Then carbon rotary valve is good at low temperature, but leakage increases by temperature increase by thermal expansion difference. So, carbon rotary valves could not be used for steam engine.
4. MINI SSSE AND ITS EXPERIMENTS
First for land use small double expansion SSSE engine was manufactured in 1999, named Mini SSSE, its section figure is shown at Fig.7.
It has a rotary valve made of brass, that is directly driven by the main shaft.
Although it is double expansion engine, but its second expansion cylinder has no DP. RG and Heater, so it is not yet the complete double expanding SSSE, as Fig.1. First, the rotating parts of the valve rotor was made by carbon, but with steam, steam leaks very much by the difference of thermal expansion between carbon and metal cylinder, so the rotor was changed to brass same to the valve cylinder. The output of at this engine was about 10 to 20 watt at 0.2Mpa (gauge) steam at 250℃ heater temperature with 400 rpm.
