General discussions of the Stirling engine
On thermodynamics, it can explain that Stirling engine is an regeneratable external combustion engine using Stirling cycle. Stirling cycle is composed by constant volume heating process, isothermal expansion process, constant volume cooling process, and isothermal compression process. For heat efficiency of this cycle, by using heat, which is discharged to the engine outside by constant volume cooling, for a constant volume heating, as being equal to a thermal efficiency of Carnot cycle that have theoretically highest thermal efficiency. Also, this means Stirling cycle is a reversible cycle. Then it is able to make engines, which driven with an outside power, work as a refrigeration machine.
A general Stirling engine makes gas go and return between two space attached temperature differences and make a pressure variation occur. These two space are ideally sealed up, and then there isn't gas exchange with the outside. As being able to work anywhere, if there is a temperature difference, Stirling engine is expected various applications in future.
The Stirling cycle
Characteristics of the Stirling engine
Stirling engine has the following characteristic
Diversity of heatsources
Internal combustion engines, like gasolin or Diesel engines, can only use volatile fuels. For Stirling engines on the other hand, not only can fuel like this be used, but any combustible things like charcoal and wood may also be use as fuel. In addition, many non-fuel heat sources such as terrestrial heat, hot springs, or sunlight can be used to power Stirling engines. At present, research on Solar powered Stirling engine designs is being carried out worldwide.
Clean exhaust gas
For Stirling engines that is an external combustion engine, naturally, combustion of fuel is done on the outside of the engine. For this reason, the combustion can be controled easily compared with an internal combustion engine. As a result, exhaust gas after combustion is very clean compared with the exhaust gas of the internal combustion engine.
With internal combustion engines, because the pressure variation in the engine occurs by an explosion, an occurrence of vibration and noise isn't avoidable by any means. For Stirling engines, the pressure variation in the engine is very gentle, and they are also very quiet, because there isn't any complicated valve mechanism.
High theoretical thermal efficiency
The thermal efficiency of Stirling cycle that is used for Stirling engine is equal to that of Carnot cycle which is theoretical higiest efficiency. Expression of Carnot efficiency is follows.
Th : Higher temperature in the cycle
Tc : Lower temperature in the cycle
This means as to be large for a temperature difference, theoretical heat efficiency are higher. Among Stirling engine developed, the engine to achieve a thermal efficiency 40 % exists.
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