Improved Simple Analytical Model and experimental study of a 100W β-type Stirling engine

A key issue in designing and optimizing Stirling engines is to build a precise thermodynamic model to predict the output power, thermal efficiency, and detailed performance properties and provide useful information for further improvement. In this study, a thermodynamic model called Improved Simple Analytical Model (ISAM) was proposed, carefully considering heat and power losses in Stirling engines. A 100W β-type Stirling engine was built and tested with helium and nitrogen when pressure and rotary speed ranging from 1.6MPa to 3MPa and 260r/min to 1380r/min, respectively. Experimental information on performance, such as PV diagrams and temperatures of the heater and cooler, was much detailed. Increasing rotary speed brings a “thin” PV diagram because it made compression and expansion processes become more imperfect, indicating heat transfer enhancement was necessary for compression and expansion chamber in a high speed Stirling engine. Shaft power reached the maximum value of 30.1W for helium and 21.0W for nitrogen at rotary speeds of 1000r/min and 650r/min, respectively. Improving the mean pressure of gas increased the indicated power, cycle efficiency, shaft power, and electrical power. The maximum indicated power and cycle efficiency were 165W and 16.5% for helium and 139W and 12.2% for nitrogen in the same working conditions of 2.96MPa and 1120r/min. The ISAM agrees well with the experimental data with a deviation of 4.3–13.4% for helium and 1–7.1% for nitrogen. Analysis of energy losses with ISAM indicated that helium had larger shuttle and seal leakage losses and smaller flow resistance and regenerator heat transfer losses than nitrogen under the same working conditions. Flow resistance and regenerator heat transfer losses, which increased much more rapidly than seal leakage or shuttle heat losses with the increase in rotary speed and pressure, played an important role and resulted in different performances with the two working gases. This study provides comprehensive understanding of the influence mechanism of rotary speed, pressure and working gas in the view of heat/power losses for Stirling engine performance, and recommends that more work (e.g., mechanisms of heat and power losses and PV diagrams) should be performed to improve the precision of second-order models.