It's hard to believe that the mere presence of a constant low and high temperature can result in pulsating motion, but then along comes the genius mind of Robert Stirling. The inventor of the Stirling Engine.

What is the Stirling engine?

The Stirling engine is an engaging device that converts a temperature difference into mechanical work. Hot water near the hot side and room temperature on the cold side is enough to make it work.

How does Stirling Engine Work?

This exciting device is known as Stirling Engine. To understand how this device works or how Mr. Stirling's mind worked at the time of this invention. To start, separate the hot-cold plates, within the insulating material. Let's introduce a thick insulating cylinder called the displacer, if the displacer is at the bottom it will obviously prevent the heat flow from the bottom plate which means the majority of the air undergoes heat transfer you the upper cold plate, and the air volume approach is the surrounding air temperature. 

If the displacer is moved up the exact reverse will happen and the air will heat up when the air temperature inside this volume increases its pressure also increases. Robert Stirling's next brilliant idea was to use this high pressure to run a power system, the same power piston can move the displacer up or down. 

Mechanism of Stirling engine:

Let's see how he achieved it practically to achieve this objective Robert Stirling connected one more Crank on the same rotating shaft of the power piston, this time at a 90-degree offset to the first crank now this crank is connected to the displacer, he also added a flywheel in the shaft the use of which we will come to know later. Now let's see how this arrangement achieves the robot sterling's objectives when the bottom plate of the engine is heated up. 

Working of Stirling engine:

Let's start with the power piston's lowest position if you check the position of the displacer it is almost in the middle the air obviously gets heated so its pressure increases which move the piston up. While observing the displacer clearly during the upward piston motion the displacer moves up and supports the additional heat from the hot plate, the displacer prevents the cold heat transfer during this motion which means that during the upward piston motion the air's temperature and pressure keep increasing and the piston extracts the energy. 

However, after reaching the top the displacer is again in the middle which means that the heated air can lose heat to the cold plate obviously this process reduces the pressure of the air volume due to the momentum of a big flywheel, the piston will now start its downward journey during which the air loses progressively more heat and pressure, therefore, the piston is downward motion happens without much difficulty after the piston reaches the bottom position we are back at the starting point and the cycle repeats.

What happens when the Stirling engine is kept on a cube of ice?

It's a beautiful way of producing reciprocating motion, isn't it? Now you can predict how this machine will behave if we keep an ice block below it, here the inside air temperature and pressure become lesser than the atmospheric temperature and pressure the low pressure inside the chamber means the force acting on the piston will be in the downward direction, so the piston has to move down this way the engine rotates in the opposite direction. 

How efficient is the Stirling engine?

In short, this engine will keep on working unless and until there is a temperature difference between the two plates. The greater the temperature difference the greater the engine speed and power output. 

Compared to other internal combustion engines of the same power Stirling engines have more efficiency, and the thermal efficiency is comparable to small engines. Stirling engines have an amazing energy conversion efficiency. 

Why Stirling engines are not used?

The main reason is that Stirling engines are slow to respond to varying power demands to vary power output from a Stirling engine you have to control the upper and bottom plate temperatures and temperature control always takes time. Moreover, Stirling engines are heavier and costlier compared to their counterparts. 

Stirling Engine used in Solar power plants

However, we believe the Stirling engine can be an ideal candidate for solar power extraction, the Maricopa Solar Power Plant commissioned in 2010 was based on Stirling engine Technology and was capable of producing 1.5 MW of electricity, but this project was later banned due to environmental concerns.

Let's hope that modern engineers will find a suitable application for Robert's Stirling engine.