Possibilities of the power optimization in the Stirling cogeneration engine fuelled by the natural gas

Abstract

As the energy efficiency is at the heart of the integrated European Union energy policy, which aims to protect the environment through various research projects, the application of the Stirling engine for diffused electricity generation is one of the possible paths for low-carbon application. That is today particularly topical, just looking at the major interest paid at European level at the energy communities, also in terms of incentives and policies facilitating and supporting such initiatives. Although the tested engine V-160 runs on natural gas, its emissions can be neglected in comparison with the internal combustion engines, due to the much more favourable external combustion under the lower pressures and temperatures, as well as to the working medium, which is helium. Next step, becoming every day more and more relevant, will be using hydrogen as a clean (and green) fuel. A major advantage of the proposed engine for use in power generation is the constant speed under different loads. According to the thorough parametric analysis after 200 hours of operation of the engine at the University of Rome La Sapienza, new evidence of the possibilities of performance improvement was obtained. Compared to the Stirling engine with low temperature difference, it has a much lower Schmidt factor of about 21%, which means that a real thermodynamic efficiency of the cycle could be improved. The scope of the analysis was to determine the power that is changed due to the mass of helium and the power that is changed due to the temperature difference. Based on the experimental data, it is found that the temperature difference and the mass of the working medium have a reciprocal relationship. In such a working condition, the engine power is simultaneously increased due to the greater mass of helium, but at the same time decreased due to the decrease in the temperature difference, which is not valid for other types of Stirling engines. The resulting power can be optimized according to a new expression, presented in the paper.