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Free Piston Engine
In order to better present potentials of the linear vane pump technology, different concepts of the free piston engines will be presented and analyzed.
At free piston engine combustion piston is directly connected with pump piston or linear electric actuator. Crankshaft and rods, as frictional losses connected with them, are removed so more energy and cost-effective source of hydraulic and/or electric energy is possible.
This concept is especially interesting for hydraulic systems because standard combination of the Diesel engine and hydraulic pump has two transformations connected with friction losses, translation-rotation and rotation-translation, that can be avoided by the free piston engine.
Dynamical Analysis of the Free Piston Engine.
The free piston engine is internal combustion engine where the energy developed by the fuel combustion is directly transformed to the hydraulic, pneumatic and/or electric energy by simple linear motion of the engine moving part. Next figure presents basic concept o the free piston engine, aimed to generate hydraulic energy.
As the pump piston section is constant and stroke is fixed by the stroke of the combustion piston control of the free piston engine is special challenge. This will be shown through the mathematical modeling.
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About Free Piston Engine Analysis
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Initially, mathematic modeling, based on this basic free piston engine concept with double cylinder will be performed. Analysis will continue through the comparison of the free piston engine concepts using developed mathematical modeling. Comparison will be started with the explanation of the limits of the basic concept. It will be continued with the analysis of the four advanced concepts, in order as they are presented in following image
At the end, in conclusion, it will be explained why fourth concepts, that is result of the advanced research study of this project, is considered as most promising solution, especially regarding synergy between hydraulic and electric technology / system:
Dynamical Analysis of the Free Piston Engine.
The free piston engine is internal combustion engine where the energy developed by the fuel combustion is directly transformed to the hydraulic, pneumatic and/or electric energy by simple linear motion of the engine moving part. Next figure presents basic concept o the free piston engine, aimed to generate hydraulic energy.
It is double cylinder (A and B), two stroke internal combustion engine directly connected to a hydraulic pump (P). The pump is formed from hydraulic cylinder connected to the passive check valves. Hydraulic accumulators are used to damp pressure and flow fluctuations. As there is only one moving part it is evident that this engine is much simpler than standard engines with crankshaft and rotational output.
Simplicity of the concept will result with engine thait is more cost and energy efficient than standard solutions but with increased demand regarding moving part motion control.
Mathematical Modeling
Motion of the moving part of the free piston engine is determined by the balance of the forces acting on it. In the order to briefly compare few, recently proposed, concepts of the free piston engine, simplified simulation model will be presented. As the guideline three SAE papers will be used (SAE papers 2004-01-187, 2001-01-0280, 2002-01-1739), with appropriate modifications/simplifications. As main point of the simulation is to show potentials of the different control strategies on to the basic dynamical behavior of the engine, all effects that are similar for all compared concepts, so that they aren’t essential for comparison, like friction, heat rele)) ase and heat transfer. will be excluded from the modeling. Therefore, only major forces produced by the pressure of ideal fluid in combustion chamber and pressure of the hydraulic oil in pump chamber will be used to determine the force balance of the moving part. Dynamic modeling with mentioned simplifications is presented by Newtons second law;
