Modelling and Development of Integrated Electrical Machines in Linear Combustion Engines

A Free Piston Engine Generator (FPEG) system is a special type of combustion engine representing a new approach concerning the conversion of the chemical energy of fuel into electrical energy. Unlike conventional engines, this type of engine does not use a crankshaft, and generates electric energy directly by a linear movement of pistons.
The benefit of removing crankshaft and using linear electrical machine coupled directly to the piston is that, piston is free to move under the action of combustion process force. That means the movement of piston is not restricted by crankshaft any more. In other words, there is no need to convert linear motion of piston to rotary motion. Consequently, converting fuel to electricity can be achieved in more direct way with elimination of crankshaft. As a result, frictional loss and total system weight are reduced, and efficiency is increased significantly.
Permanent Magnet (PM) electrical machine has the best performance in terms of force/power density. Furthermore, efficiency is also higher due to using PMs instead of coils carrying current as well as PM electrical machines occupy less volume compared to other topologies for the same design power. Due to these reasons, PM synchronous electrical machine is chosen for this application. Tubular shaped linear electrical machine is a suitable candidate for integration with engine compared to flat shaped linear electrical machine, because it is more compatible with piston and cylinder shape.
Linear PM electrical machines exhibit some drawbacks: cogging forces and edge forces, disturbing the positional accuracy and cause oscillations and instabilities, and eccentricity increases the friction in linear bearings, causing losses and reducing the effective force. In order to decrease these detent forces, some strategies can be adopted, for example, by skewing or stepping the magnets and optimizing the PM dimension.
Primary objective of this project is feasibility of compact FPEG system to generate electrical power, for instance, charging electric batteries or supplying any load. The novel idea to combine the linear electrical machine with the compressor cylinder leads to a compact system design. It is proposed to integrate the linear electrical machine with the compressor cylinder, by using a set of coils circumferentially as a stator and embedding ring shaped PMs on the surface of connecting-rod-piston as a translator. Then linear movement of translator back and forth driven by engine process, generates electrical power. Furthermore, coupling the mechanical and electrical systems can be examined in Siemens LMS imagine Lab Amesim simulation software. Then optimal system performance (for instance electrical power generation) can be identified by modifying the key parameters of linear joule engine generator system.
What's more, there are three aims to be achieved by the optimization of the Linear Generator (LG). The first aim is to get a maximum electrical power. To reach a maximum of electric output power it is necessary to develop a LG with maximum axial force. So it is important to find a geometric structure which guarantees a maximum of axial force under consideration of certain boundary conditions. The second aim is to reduce the cogging force of the LG. This is important for the durability of the LG. The third aim is to reduce the weight of the mover. This is important to get an optimal engine performance. The base of all these optimizations is the FEA tool. By using this tool it is possible to calculate 2-D and 3-D FEA results for different types of LG.
In conclusion, FPEG system, generates power, then this generated power is fed into power electronic system for electrical power conversion purpose, hence leads to charge an on board battery or energising the motor in order to drive the wheels of an electric vehicle. This technology can also be used as a range extender in hybrid electric vehicles or providing the electrical power for aut