Numerical simulation for the design analysis of kinematic Stirling engines

Abstract

The Stirling engine is a closed-cycle regenerative system that presents good theoretical properties. These include a high thermodynamic efficiency, low emissions levels thanks to a controlled external heat source, and multi-fuel capability among others.However, the performance of actual prototypes largely differs from the mentioned theoretical potential. Actual engine prototypes present low electrical power outputs and high energy losses. These are mainly attributed to the complex interaction between the different components of the engine, and the challenging heat transfer and fluid dynamics requirements. Furthermore, the integration of the engine into decentralized energy systems such as the Combined Heat and Power systems (CHP) entails additional complications. These has increased the need for engineering tools that could assess design improvements, considering a broader range of parameters that would influence the engine performance when integrated within overall systems. Following this trend, the current work aimed to implement an analysis that could integrate the thermodynamics, and the thermal and mechanical interactions that influence the performance of kinematic Stirling engines. In particular for their use in Combined Heat and Power systems. The mentioned analysis was applied for the study of an engine prototype that presented very low experimental performance. The numerical methodology was selected for the identification of possible causes that limited the performance. This analysis is based on a second order Stirling engine model that was previously developed and validated. The simulation allowed to evaluate the effect that different design and operational parameters have on the engine performance, and consequently different performance curves were obtained. These curves allowed to identify ranges for the charged pressure, temperature ratio, heat exchangers dimensions, crank phase angle and crank mechanical effectiveness, where the engine performance was improved. In addition, the curves also permitted to recognise ranges were the design parameters could drastically reduce the brake power and efficiency. The results also showed that the design of the engine is affected by the conditions imposed by the CHP interactions, and that the engine could reach a brake power closer to 832 W with a corresponding brake efficiency of 26% when the adequate design parameters were considered. On the other hand, the performance could also be very low; as the reported in experimental tests, with brake power measurements ranging 52-120 W.

Comparative study on the performance of different drive mechanisms used in a beta type Stirling engine through thermodynamic analysis

“…Cheng et al investigated the thermal efficiency in a Stirling engine with beta type slider crank drive mechanism by using a numerical model, and designed the engine by making the theoretical analyses [28]. Araoz et al investigated theoretically the numeric simulation that included all of the thermodynamic, thermal and mechanical interactions of a Stirling engine with slider crank drive mechanism, and compared the results with experimental analyses [29]. Barreto et al analyzed theoretically the dynamic simulation and optimization of a beta type Stirling engine with slider crank drive mechanism that run with solar energy by using a parabolic aerial, and investigated the effects on engine performance [30].…”

Stirling Engine Configuration Selection

“…In the case of the beta configuration, by solving Equation 7, we find that S 1 = 360 = 0[deg] and S 2 = 180[deg], then, the compression ratio can be simply expressed by Equation (11).…”

“…More recently, applications like power generation in space for earth and deep space exploration uses [9] and atmospheric CO 2 capture to mitigate anthropogenic climate change [10] have been proposed, demonstrating an active interest in the technology. Due to several factors few of these attempts have succeeded and reached a commercial stage, of these factors the main are their inherent low power to weight ratio if compared with internal combustion machines, their poor empirical performance compared with their theoretical performance [11], and the lack of policies Table 1. Different configurations are applied to meet similar objectives.…”

A transient one-dimensional numerical model for kinetic Stirling engine

“…The mechanical efficiency η mech is determined by, The correlations for the friction factor of tube channels for laminar flow and turbulence flow are given by Eqs. (24) and (25), respectively [50,64]:…”

“…Though the accuracies were still low, these models laid a good foundation for the follow-up developments of second-order methods. More studies were then conducted by either directly adopting Urieli and Berchowitz's models [21,22] or modifying the ideal adiabatic model [23][24][25][26][27][28][29][30], quasi-steady model [31] or simple analysis model [32][33][34][35][36][37]. These models were improved by considering more internal or external losses [23][24][25][26][27][28][29][30][31][32][33][34][35], introducing the concept of finite speed thermodynamics [28,35], or changing the treatments of compression/expansion processes in working spaces [36,37].…”