Power correlations as complementary tools for generalised analysis and preliminary design of Stirling engines

Abstract

The use of dimensionless variables facilitates the generalised analysis of Stirling engines and provides tools for preliminary design, validation of simulation codes and feasibility studies of energy conversion systems. This article provides correlations to estimate the dimensionless values of maximum indicated and brake power, as well as their corresponding speeds. The concept of effective pressure allows power correlations to be related to gas circuit models and mechanical efficiency calculations. Previous correlations based on data from eight very different prototypes are revised using the criterion of minimising the relative root mean square errors (RRMSE) and sensitivity analysis to select influential variables. The application of previously established performance models provided additional data from the M102C and ST05G engines for validation purposes. The procedure also allows detecting inconsistent measurements. Data deviations seem acceptable for most operating points of the 10 analysed engines. The errors inherent to the procedure, as well as the number and quality of experimental data, determine the following average values of accuracy indicators: RRMSE = 3.20% for the dimensionless maximum indicated power, RRMSE = 6.35% for the dimensionless speed corresponding to the maximum indicated power, RRMSE = 6.39% for the dimensionless maximum brake power, and RRMSE = 10.93% for the dimensionless speed corresponding to the maximum brake power.