Stirling engine gadgets

Running with the heat of your hand

The American Stirling Company manufacturers Stirling engine gadgets and models for educational and demonstration purposes. Their newest model is the MM-7, powered by the heat from your hand. It needs only a 4 °C temperature differential to run. The FAQ page of their Web site presents a very clear explanation of the working principle of the Stirling engine, as well as comprehensive facts on its history and applications.

Stirling engines hardly qualify as new technology. Robert Stirling received a patent for his first air engine all the way back in 1816. At that time however, the only readily available metal was cast iron, which oxidizes rapidly when left in a very hot flame. So Stirling engines started life with a metallurgical if not technological disadvantage.

Prototypes of Stirling engine-powered cars have been developed, but have had the significant drawback that they need to warm up before they will move. Up to now, Stirling engines have only been used commercially in very specific applications such as submarines and cryocoolers (appliances for reaching extremely low temperatures). An important future use of the Stirling engine could be in domestic CHP units (see previous blog post). Other potential uses include applications in the maritime and aviation industries.

In fact, Stirling engines deserve a great deal more attention since they are very efficient. They can reach up to 80 per cent of the Carnot cycle efficiency, which is exceptionally high. Moreover they are very silent. So silent, it seems, that not only do you seldom hear them while they are running, you seldom even hear ABOUT them. And that is precisely what the American Stirling Company wants to change by promoting their gadgets.