How Free Piston Engine Works?

Free Piston Engine

Here you can get Free Piston Engine Working principle.

A free-piston engine is a linear, ‘crankless’ internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device (e.g., a piston in a closed cylinder) and a load device (e.g. a gas compressor or a linear alternator).

The purpose of all such piston engines is to generate power. In the free-piston engine, this power is not delivered to a crankshaft but is instead extracted through either exhaust gas pressure driving a turbine, through driving a linear load such as an air compressor for pneumatic power, or by incorporating a linear alternator directly into the pistons to produce electrical power.

What is Free Piston Engine

A free piston engine is the internal combustion engine wherein the crankshaft from a everyday I C engine utilized in vehicles is removed and the mechanical work is obtained just by the reciprocating motion of the piston or via way of means of a few different mean.

Generation of electricity is the principle reason of those type of pistons that may be received via way of means of any approach both via way of means of the exhaust gas pressure that may be used to force turbine or thru the linear movement of the piston that may be used as an air compressor for pneumatic electricity or via way of means of coupling the linear alternator with the transferring piston to generate electricity.

Working of Free Piston Engine

The application of the free piston engine is so wide so for the higher expertise of the operating of F P engine we’ve to speak about its
few applications that are-

1. Electricity Generator

The electricity generator is the device this is used to generate power with the help of the F P engine as an outside source of energy, for the generation of power a linear alternator is coupled as a loading device with the F P engine.

The working of this electricity generator is as follows-

  • The fuel enters in the combustion chamber of the engine in the expansion stroke and gets ignited at the end of the compression stroke either by the spark plug (gasoline engine) or by compression (diesel engine).
  • This combustion of the fuel inside the combustion chamber produces high stress pulses over the surface of the piston which in turn produces the reciprocating motion of the piston.
  • This reciprocating motion of the piston is then transferred to the linear alternator which is used as the loading device and is coupled with the piston.
  • Due to the reciprocating movement of the permanent magnet attached to the connecting rod of the piston, there is a fluctuation of the magnetic field takes which induces current and voltage in the coil and electricity is produced that is further stored in the accumulator (battery) used in electricity generator for the further use.

2. Air Compressor

It is the tool that’s used to compress or will increase the pressure of the air for the various purposes like pneumatic machines with the help of free piston engine as the external source of energy.

For the use of F P engine as a air compressor no loading device is used however there may be the coupling of air compressor cylinder with the plates
that are installed on the tail end of the piston.

The working of F P air compressor is as follows-

  • Same as the electricity generator fuel enters on the end of the expansion stroke and gets ignited at compression stroke of the F P engine respectively however there is the entry of the fresh air inside the air compressor cylinder throughout the expansion stroke through the inlet valve of the compressor cylinder.
  • Due to that combustion, reciprocating movement of the piston is produced which in turn compresses the air within the compressor with the help of the seizing plate mounted at the tail give up of the piston.
  • This compressed air is then taken out via the exhaust valve of the compressor for the in addition work.

Note- At end of the expansion stroke, the air from the compressor is enter into the cylinder at tail end and forces the piston to start the compression stroke again.

3. Turbine Rotation

The free piston engine is likewise used to rotate the turbine of the turbine electricity generator for the production of the electricity.

In this application of the F P engine instead of the reciprocating movement of the piston, exhaust pressure of the engine is used to apply pressure over the blades of the turbine which in turn reasons rotation of the turbine.

The working of the turbine electricity generator that uses F P engine as the source of energy is as follows-

  • The entry of fuel through the inlet port of the engine takes place at the end of expansion stroke of the engine.
  • After the entry of the fuel inlet port closes and the compression of the fuel due to the compression stroke occurs which in turn increases the pressure of the fuel inside the combustion chamber.
  • After this compression fuel gets ignited either by spark plug (gasoline engine) or by compression (diesel engine) depending upon the type of the F P engine used.
  • Due to this combustion of the fuel high pressure impulse is generated which in turn pushes the piston and the expansion of the gases produced during the combustion occurs.
  • The gases expanded during the expansion stroke are then exhausted with the high pressure through the exhaust port of the engine during the expansion stroke.
  • These exhaust gases having high pressure are blown over the blades of the electric generator turbine which in turn causes rotation of the turbine and the generation of the electricity takes place.

Main Components of Free Piston Engine

Free piston engine works on the same principle on which I C engine of an vehicle works i.e. the combustion of the air-fuel inside a closed cylinder produces reciprocating motion in the piston which is the acquired mechanical work. So the components of each the engines are also nearly identical. It is largely a stroke engine.

The main components of the F P engine are-

  1. Combustion chamber or cylinder- Same as the I C engine a combustion cylinder is the inflexible cylindrical chamber inside which the combustion of air-gasoline takes place, and also it is the housing inside which piston moves.
  2. Piston- It is the rigid cylindrical part of the F P engine that produces reciprocating motion in the combustion chamber due to the combustion of the air-gasoline mixture just like the I C engine.
  3. Engine head- It is the head of the engine  the spark plug or gasoline injector is attached, engine head is mounted over the combustion chamber similar to the I C engine.
  4. Spark plug or fuel injector- The spark plug is used to ignite the air-gasoline mixture and fuel injector injectects the diesel gasoline in the course of the compression of air which results into the combustion.
  5. Bounce cylinder: It is cylinder with a piston which is interconnected with the main piston. The major characteristic of the bounce cylinder is to saved the strength during expansion of the F P engine and use it on starts the compression stroke once more for the working.
  6. Loading devices- These are the devices that are utilized in free piston engine as the replacement of crankshaft of the IC engine, The choice of the load tool that’s to be used depends upon the required application of the  F P engine . for example
  • Linear alternator is coupled with the piston of the F P engine for the technology of the electricity.

Note – For some applications of F P engine like the air compressor, turbine rotation etc.  No loading device is used to obtain mechanical work.

7. Fuel – Of course just like an I C engine the most important part of an F P engine is the fuel that can be petrol or diesel depending upon the type of F P engine used i.e. Spark ignition F P engine or Compression ignition F P engine.

  • The fuel (air-fuel) is the chemical energy that is burned inside the combustion chamber to produce mechanical work i.e. reciprocating motion of the piston.


Potential advantages of the free-piston concept include:

  • Simple design with few moving parts, giving a compact engine with low maintenance costs and reduced frictional losses.
  • The operational flexibility through the variable compression ratio allows operation optimisation for all operating conditions and multi-fuel operation. The free-piston engine is further well suited for homogeneous charge compression ignition (HCCI) operation.
  • High piston speed around top dead centre (TDC) and a fast power stroke expansion enhances fuel-air mixing and reduces the time available for heat transfer losses and the formation of temperature-dependent emissions such as nitrogen oxides (NOx)


  • The free-piston engine is engine control, which can only be said to be fully solved for single piston hydraulic free-piston engines. Issues such as the influence of cycle-to-cycle variations in the combustion process and engine performance during transient operation in dual piston engines are topics that need further investigation. Crankshaft engines can connect traditional accessories such as alternator, oil pump, fuel pump, cooling system, starter etc.
  • Rotational movement to spin conventional automobile engine accessories such as alternators, air conditioner compressors, power steering pumps, and anti-pollution devices could be captured from a turbine situated in the exhaust stream


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