Free Piston Engine: Project Working


In some of our previous articles we talked about Stirling engines, their working, types and many project ideas based on Stirling engines. In this article we are going to learn about yet another type of Stirling engine known as Free Piston Engine.

A free piston engine? This must be the obvious question which must be coming  to your mind but yes, you read it correct. Ok let’s go into its detailed configuration and working with implications. A free piston engine is simply the Stirling engine where a diaphragm or liquid is used instead of the power piston unlike the internal combustion engine installed in your car or bike.

Working of Free Piston Engine Project

The basic steps of working of free piston are as follows:-

  • Hot gases as always expanded due to heating and push the power piston outward thus doing work and there is no role of gravity in the cycle.
  • The volume of the gases inside the engine increases and therefore the pressure reduces, which causes pressure gradient (difference) across the displacer towards the hot end. During the motion of the displacer, the piston almost remains stationary and hence the gas volume is constant. It results in the constant volume cooling process which reduces the pressure of the gas.
  • The reduced pressure now holds the outward motion of the piston and it begins to accelerate towards the hot end again and by its own inertia, compresses the cold gas which is cooled now residing in the cold space.
  • with the increase in pressure, an optimum point is reached where the pressure differential across the displacer rod becomes sufficient enough to begin to push the displacer rod towards the piston, collapsing the cold space and transferring the cold, compressed gas towards the hot side in an almost constant process. After arrival of the gas at hot side, the pressure increases and begins to move the piston outwards to initiate the expansion.

W.T. Beale was the one who invented this free piston version of Stirling engine to overcome the difficulty of lubricating the crank mechanism. There can be many project ideas based on free piston engine. If you want to know more about any project, leave your comments below. We would love to hear from you.


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