In the 19th century, engineers began to look for a safe alternative to steam engines of the time, whose boilers often exploded due to high steam pressures and inappropriate materials for their construction. And such a replacement appeared thanks to the Canadian priest Robert Stirling, who invented and on September 27, 1816 patented (English patent No. 4081) a new type of external combustion engine that converts any temperature difference into work.
The basic principle of operation of the Stirling engine is to constantly alternate heating and cooling of the working fluid in a closed cylinder. Usually air acts as a working medium, but hydrogen and helium are also used.
The cycle of the Stirling engine consists of four phases and is divided by two transitional phases: heating, expansion, transition to a cold source, cooling, compression and transition to a heat source. Thus, when passing from a warm source to a cold source, the gas in the cylinder expands and contracts. At the same time, the pressure changes, due to which useful work can be obtained. Since theoretical explanations are the lot of pundits, listening to them at times is tedious, so let's move on to a visual demonstration of the Sterling engine.
How a Stirling engine works
- An external heat source heats the gas at the bottom of the heat exchange cylinder. The generated pressure pushes the working piston upward.
- The flywheel pushes the displacement piston downward, thereby transferring the heated air from the bottom to the cooling chamber.
- The air cools and contracts, the working piston moves down.
- The displacement piston is lifted upward, thereby moving the cooled air to the bottom. And the cycle repeats.
In a Stirling machine, the movement of the working piston is shifted 90 degrees relative to the movement of the displacement piston. Depending on the sign of this shift, the machine can be a motor or a heat pump. At 0 degrees of shift, the machine does not perform any work (other than frictional losses) and does not generate it.
Another invention of Stirling that increased the efficiency of the engine was a regenerator, which is a chamber filled with wire, granules, corrugated foil to improve the heat transfer of the passing gas (in the figure, the regenerator is replaced by cooling radiator fins).
In 1843, James Stirling used this engine in a factory where he was working as an engineer at the time. In 1938, Philips invested in a Stirling engine with more than two hundred horsepower and over 30% efficiency.
Stirling Engine Merits:
1. Omnivorous. You can use any fuel, the main thing is to create a temperature difference.
2. Low noise level. Since the work is based on the pressure drop of the working fluid, and not on the ignition of the mixture, the noise is significantly lower compared to the internal combustion engine.
3. Simplicity of design, hence a high margin of safety.
However, all these advantages in most cases are crossed out by two large disadvantages:
1. Large dimensions. The working fluid must be cooled, and this leads to a significant increase in mass and size due to the increased radiators.
2. Low efficiency. Heat is supplied not to the working fluid directly, but only through the walls of the heat exchangers, respectively, the efficiency losses are large.
With the development of the internal combustion engine, the Stirling engine has gone ... no, not into the past, but into the shadows. It is successfully used as auxiliary power plants on submarines, in heat pumps at thermal power plants, as converters of solar and geothermal energy into electricity, space projects are associated with it to create power plants operating on radioisotope fuel (radioactive decay occurs with the release of temperature, who did not know) Who knows, maybe one day the Stirling engine will have a great future!