Energetic optimization of the performances of a hot air engine for micro-CHP systems working with a Joule or an Ericsson cycle

The micro combined heat and electrical power systems (micro-CHP) with hot air engines are well adapted for solid biomass upgrading, in particular, the Ericsson engines working with an open cycle and an external combustion. This paper presents a model of an Ericsson engine with a compression and an expansion cylinder which allows a thermodynamic optimization of the engine performances in a global approach. A sensitive analysis on the influent parameters is carried out in order to determine the optimal working conditions of the engine: temperature and pressure range, expansion cycle shape with a late intake valve closing or an early exhaust valve closing, heat transfers through the wall of the cylinders. This study, focused on thermodynamic aspects, is a first step in the design of an Ericsson engine.

► A model of Ericsson engine working with a Joule or Ericsson cycle is presented.
► Influent factors on the engine performances are investigated.
►  The heat exchanges in the cylinder wall must be avoided to improve the performances.
► Closing the intake valve late and the exhaust valve early enhances the performances.
► Efficiency, indicated mean pressure, specific work are thermodynamically optimized.