Abstract
In this paper, a comparison of exergetic models between two hot air engines (a Gamma type Stirling prototype having a maximum output mechanical power of 500 W and an Ericsson hot air engine with a maximum power of 300 W) is made. Referring to previous energetic analyses, exergetic models are set up in order to quantify the exergy destruction and efficiencies in each type of engine. The repartition of the exergy fluxes in each part of the two engines are determined and represented in Sankey diagrams, using dimensionless exergy fluxes. The results show a similar proportion in both engines of destroyed exergy compared to the exergy flux from the hot source. The compression cylinders generate the highest exergy destruction, whereas the expansion cylinders generate the lowest one. The regenerator of the Stirling engine increases the exergy resource at the inlet of the expansion cylinder, which might be also set up in the Ericsson engine, using a preheater between the exhaust air and the compressed air transferred to the hot heat exchanger.
Highlights
The micro-combined heat and electrical power system is an emerging technology presenting a high global efficiency, which allows primary energy savings compared with a separated production of heat and electrical power
A Gamma type Stirling engine will be investigated in this study
For the Stirling engine, the working pressure is defined as the mean pressure in operation and for the Ericsson engine, it corresponds to the pressure in the hot heat exchanger
Summary
The micro-combined heat and electrical power system (micro-CHP) is an emerging technology presenting a high global efficiency, which allows primary energy savings compared with a separated production of heat and electrical power. The Stirling and the Ericsson hot air engines present high efficiencies (maximum theoretical thermodynamic efficiency of about 45%) for the power levels of the micro-cogeneration (under 50 kW) [2]. They are noiseless and not harmful to the environment (no direct pollutant emission by these engines), can operate with various sources of energy (especially renewable energy and coupled to cogeneration systems) and require a low maintenance. Martaj et al [16,17] investigated energy, entropy and exergy balances for each main element of a Stirling engine and for the complete engine They presented the irreversibilities due to imperfect regeneration and temperature differences between gas and wall in the hot and cold. Configurations of the Gamma Type Stirling Engine and the Open Cycle Ericsson Engines
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