A review on Free piston engines

-An alternative to conventional engine

CONTENTS:

INTRODUCTION.

FREE PISTON ENGINE BASICS .1) SINGLE PISTON.2) DOUBLE PISTON.3) OPPOSED PISTON .

FIRST GENERATION .1) AIR COMPRESSORS.2) GAS COMPRESSORS.

APPLICATIONS. ADVANTAGES & DIS-ADVANTAGES. CONCLUSION.

INTRODUCTION. Extensive use of fossil fuels as an energy source for both sea and

land based transport leads to significant amounts of co2 and other pollutants being produced.

Fuel cell engines were invented .But not reached the requirements.

Free piston engines are being investigated by a no of research groups world wide as an alternative to conventional engine generator sets or for generating hydraulic power in off-highway vehicles.

In free piston engines , the stroke of the piston is used directly to produce Hydraulic , Pneumatic or Electrical energy .

FREE PISTON ENGINE BASICS .

The Free-piston term is most commonly used to distinguish a linear engine from a rotating crankshaft engine.

The piston is ‘free’ because its motion is not restricted by the position of a rotating

crankshaft, as known from conventional engines, but only deter-mined by the interaction between the gas and load forces acting upon it.

This gives the free-piston engine some distinct characteristics, including (a) variable stroke length and (b) the need for active control of piston motion. Other important features of the free-piston engine are potential reductions in frictional

losses and possibilities to engine operation using the variable compression ratio.

a ) Single piston engine b ) Dual piston engine c ) Opposed piston engine

Single piston :

This engine essentially consists of three parts a combustion chamber, a load device , and a rebound device to store the energy required to compress the next cylinder charge .

Cylinder serves as both load and rebound device.

Rebound device is used to store the energy required to compress the next charge.

Dual piston:

The dual piston engine configuration eliminates the need for a rebound device. This allows a simple and compact device with higher power to weight ratio. The control of piston motion , particularly in stroke length and compression ratio has proved difficult.

Opposed piston:

It consists of two single piston units with a common combustion chamber .each piston requires a rebound device, and load device may be coupled to both of the pistons.

First generation of FPE Free piston Air Compressor:-

The first successful application of the free-piston engine concept was as air compressors. In these engines, air compressor cylinders were coupled to the moving pistons, often in a multi-stage configuration. Some of these engines utilized the air remaining in the compressor cylinders to return the piston, thereby eliminating the need for a rebound device.

Free-piston air compressors were in use among others by the German Navy, and had the advantages of high efficiency, compactness and low noise and vibration .

Free Piston Gas Generator:

This are the free pistons feeding hot gases to a power turbine.

These are used in some large scale marine and stationary power plants

in themid-20th century , and attempts were made to use this principle

in Automotive applications.

Modern Applications

Hydraulic free-piston engines.Free piston engine generators.

Advantages: Optimized combustion through variable compression ratio.

High load efficiency.

Multi fuel operation.

Reduced frictional losses due to simple design with few moving parts.

Disadvantages:

The control of piston motion , in particular stroke length and compression ratio has difficult in dual piston.

Misfiring

Conclusion; The basic design and features of the free piston

engines have been discussed.mny reports conclude that more research is required to investigate potential advantages over conventional technology.

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