10 Control Systems For Stirling Engines

introduction

Control systems are necessary to regulate the power output (torque) and speed of a Stirling engine. Sometimes the engine speed is held constant whatever the load, i.e. stationary constant-speed fixed-frequency electric-power generators. Sometimes, as in automotive applications, wide ranges of both speed and load are encountered.

A rapid response of the engine to sudden changes in load is important in many applications. The eflicicncy of the engine is also important. Hngines operate most of the time at part-load, producing only a fraction of the maximum load of which they arc capable. In many cases, therefore, the efficiency at part load is of more concern than the efficiency at maximum rated power.

liy way of example, consider the hypothetical load/speed characteristics shown in Fig. 10.1. Diagram (a), representative of an electric-power generator, a pump, or a fan. shows the input power requirements as a function of speed for different levels of voltage or pressure. Diagram (b). representative of a Stirling engine, shows the power output as a function of speed at different levels of the mean pressure in the engine. If the engine be coupled directly to the load the characteristics will be superimposed as in diagram (c).

The engine output will be entirely absorbed to drive the load and the engine will thus assume a speed at which the output power is identical to the input required, say point A in Fig. It). 1(c). Increase in the engine mean cycle pressure will increase the power output from the engine. This will cause the engine to accelerate to a higher speed thereby increasing the load power requirement until ;i new balance is established at point B for example.

Engines in stationary applications are normally regulated to operate at constant speed and so would operate along the constant speed line C-D.

Automotive engines arc not coupled directly to the driving wheels of the vehicle. A transmission system is interposed which invariably includes a gearbox or other device for changing the ratio of engine shaft speed to vehicle road wheel speed. The input power/speed requirement of the load may then be represented as shown in Fig. 10.2(a). Note that the horizontal axis is the speed of the input shaft to the gearbox (output shaft of the engine). Changing the gear ratio between input and output shafts of the gearbox causes step changes in the load power requirements.

The engine output and load input power/speed characteristics may be

Speed <N) (a) Load Input
Speed (N) (h) Hngine Output
Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

Get My Free Ebook


Post a comment