Thermodynamic Model for Performance Analysis of a Stirling Engine Prototype

Abstract

In this study, the results of simulations generated from different thermodynamic models of Stirling engines are compared, including characterizations of both instantaneous and indicated operative parameters. The aim was to develop a tool to guide the decision-making process regarding the optimization of both the performance and reliability of Stirling engines, such as the 2.9 kW GENOA 03 unit—the focus of this work. The behavior of the engine is characterized using two different approaches: an ideal isothermal model, the simplest of those available, and analysis using the ideal adiabatic model, which is more complex than the first. Some of the results obtained with the referred ideal models deviated considerably from the expected values, particularly in terms of thermal efficiency, so a set of modifications to the ideal adiabatic model are proposed. These modifications, mainly related to both heat transfer and fluid friction phenomena, are intended to overcome the limitations due to the idealization of the engine working cycle, and are expected to generate results closer to the actual behavior of the Stirling engine, despite the increase in the complexity derived from the modelling and simulation processes.

A Theoretical and Experimental Study of Moderate Temperature Alfa Type Stirling Engines

“…• C up to maximum tested level (6 bar) for 400 • C. It can be concluded that further rise of charge pressure should simultaneously increase the indicated work produced by the engine for 350 as well as Energies 2020, 13, 1622 6 of 21 400 • C. Unfortunately, the sealing system used in the prototype engine is not suitable for such a level of pressure. The increase of the indicated work, due to heating temperature rise, is in line with the theoretical description of a Stirling engine cycle [22][23][24], the higher temperature difference between upper and lower heat source, the higher efficiency of the engine, which means more work for the given thermal energy impact. The effect of rising efficiency is, at the same time, amplified by the increase of thermal energy transmitted by the heater to the working gas, which comes also from the higher heating temperature.…”

“…For example, between the heater -expansion spaces, during the flow from the expansion space the temperature is lower, and during the flow from the heater, the temperature is higher and corresponds to that in the heater. On this basis, the adiabatic work has been calculated (19) and, after taking pumping loss (22) into account the net adiabatic work (23) has been also calculated. For further considerations regarding the impact of selected design features of the system on the efficiency and power, the authors decided to use the simplified characteristics of the regenerator effectiveness taking into account only the effect of charge pressure:…”

“…For example, between the heater -expansion spaces, during the flow from the expansion space the temperature is lower, and during the flow from the heater, the temperature is higher and corresponds to that in the heater. On this basis, the adiabatic work has been calculated (19) and, after taking pumping loss (22) into account the net adiabatic work (23) has been also calculated.…”

“…Assuming that the conditions W = 0 and V = 0 are met for the heat exchanger we obtain for the cooler: The theoretical Stirling cycle is a highly idealized thermodynamic cycle [22,29], therefore, its use is not recommended for quantitative analyses [20,30]. For practical analyses, the isothermal or adiabatic model [23,[31][32][33][34] is most often used, which allows the functional separation of engine working spaces into: compression space, cooler, regenerator, heater and expansion space. Unfortunately.…”

Experimental comparison of sinusoidal motion and non-sinusoidal motion of rise-dwell-fall-dwell in a Stirling engine

“…Simulation work enables detailed study of Stirling engine design parameters [5]. It is used for the task of optimization [6 -13], exploration of new design or concept [14 -19] as well as parametric study of Stirling engines [5,20,21]. Experimental study focuses on validation and performance testing of existing or new Stirling engine design [9,16].…”