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Free Piston Engine Seminar Report

Free-piston engine is a linear ‘crankless’ engine, in which the reciprocating motion of piston is determined by the balancing of various forces acting on it.The piston is coupled directly with a linear load device such as hydraulic pump, air compressor, electric generator or gas generator.They are under investigation by a number of research groups worldwidedue to their potential advantages in terms of fuel efficiency and engine emissions over conventional engines. The accurate control of piston motion along with the variable stroke length may provide extensive operation optimization and multi-fuel possibilities. They are having wide applications in the fields of heavy machineries, lift trucks, electric-hybrid vehicles etc. The experimental analysis on free piston engines shows better performance than the conventional internal combustion engines in terms of in-cylinder gas pressure, heat transfer losses etc.

1. What is HCCI?
HCCI stands for Homogeneous Charge Compression Ignition. HCCI engines operate on the principle of having a dilute, homogeneous, premixed charge that reacts and burns volumetrically throughout the cylinder as it is compressed by the piston. Unlike other engines, the combustion occurs simultaneously throughout the volume rather than in a flame front. This important attribute allows combustion to occur at much lower temperatures, dramatically reducing engine emissions of NOx. HCCI incorporates the best features of both spark ignition (SI) and compression ignition (CI) modes.

2. What is PPM?
PPM stands for Pulse Pause Modulation. It is used to control the piston operating frequency. The control is achieved by pausing the piston motion at BDC, at the end of expansion stroke, by regulating the flow of compression oil from the accumulator. Thus the piston dwells at BDC.

3. Why the maximum pressure rise rate occurs before the peak value of in-cylinder gas
pressure? Towards the end of compression stroke, the high piston velocity results in large gas turbulence, which increases the in-cylinder pressure rapidly. As the piston decelerates close to TDC, the rate of pressure rise drops. The high turbulence results in the premixed combustion of the charge, in which most of the fuel burns. Thus the in-cylinder gas pressure reaches the peak value, just after TDC.

4. What about the economic feasibility of FPE?
The Free Piston Engine is economically viable since there is few number of moving parts compared to conventional engine, and this reduces the manufacturing cost and the need for periodic maintenance.

5. Is FPE suitable for automobile applications?
Free Piston Engine is not found to be suitable for automobile applications since it produce reciprocating motion only.

6. What is bounce chamber?
A bounce chamber is used to provide the necessary rebounding force to the piston at the end of expansion stroke and this will commence the compression stroke. By regulating the bounce pressure, the piston motion can be accurately controlled.

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