Prieto et al. 1 propose a generic equation which should be applied to a wide variety of known kinematic Stirling Engines for the determination of the dimensionless value of the indicated and brake power as a function of the speed of the engine and of some dimensionless parameters and for different operating conditions. The magnitudes of and , in turn, depend on the parameters involved in the working process and the design dimensions of the machine. Prieto suggests that the approximate value of in Eq. (1) in the above discussion may be found from the Schmidt’s model and further, the parameters and should be calculated with the use of the experimental data obtained at the point when the engine operates with the maximum indicated power.
The above approach is only a small part of the extensive amount of work performed by these authors on deriving a complete system of dimensionless groups in order to represent the performance of different kinematic Stirling Engines. This approach is also known as the full dynamic similarity-scaling approach for the analysis and design of Stirling Engines (see 2,3,4) and it has been used by many researchers in the development of new engines and for the evaluation of their performance.
The Laboratory for Stirling Engines at the Physical-Technical Institute, Tashkent, Uzbekistan, has developed a wide range of kinematic Stirling Engines of different types and configurations for operation with the use of solar energy and fossil fuels and in our paper we have described some of the methods and the simplest computer simulation model which we use in the engine development process. It has not been our aim to define the influence of the speed of the engine on the indicated (or brake) power and on the mechanical losses in the frame of this publication.
We appreciate the importance of the dynamic similarity-scaling approach for the analysis and design of Stirling Engines. The use of these methods is, undoubtedly, very useful in the development of new machine designs. Unfortunately, our experience is that the above method may only be employed in the initial stages of the design and for the preliminary evaluation of the performance of the prospective engine. Extra precautions should be taken when new machines are under consideration which are not of a similar configuration to those that have been built and tested.
In our activity, we give preference and more reliance to an approach when an individual numerical simulation is performed for every engine we are working on. In doing so, different order of mathematical models are usually used in a sequential fashion. Such an approach allows us, for example, to take into account and analyze the influence of the working process parameters, geometrical dimensions, and the material properties of the guiding and sealing rings, etc. for the determination of the mechanical losses.
In our next paper, which we hope will follow this discussion, we will describe the use of CFD modelling for the analysis of the working process and the determination of the performance of the Stirling Engine.
Clearly, the individual numerical simulation, with the detailed analysis of the work of the Stirling Engine, and the use of the series of complex mathematical models is a time consuming process but in the end it gives more accurate predictions. In our opinion, it is essential to follow this approach when it concerns the costly development of a sophisticated piece of machinery such as Stirling Engines.