Development of a Novel Energy Efficient Magnetic Scroll Air Motor

A scroll air motor, also known as a scroll expander is a relatively new concept to pneumatic actuators. Its unique structure features it many advantages as well as higher ability of energy conversion than other conventional pneumatic actuators, such as cylinders, vane-type air motors, etc. The scroll technique is now mainly and widely implemented in air conditioner and refrigeration compressors. The small, quiet, and highly compact design matches the requirement arising from designing refrigeration compressors. When a scroll air motor is running, the moving scroll wobbles inside the fixed scroll and it can revolve eccentrically with respect to the fixed one to form several sealed crescent chambers, and the motor goes successively and periodically. Recently, the concept was re-invented to build scroll air motors (expanders), which are immediately adopted to drive generators for electric power generation because of the scroll's inherent advantages. Such a scroll and generator combination has been successfully used in Micro Combined Heat and Power systems (Micro CHP) by a number of companies, such as Energetix Group Plc and Honda. Micro CHP is used to generate electric power while heating a house and invert surplus electric power to grid. It is claimed that up to 95% of available fuel energy can be used and the people could save 20% of gas and electricity bills by using the CHP system at home. In a CHP system, the scroll air motor serves as a driving force to drive the generator and also circulate the heat energy. On the other hand, the scroll air motor may be used for compressed air energy storage system to solve the problems of diffusion and intermittence associated with renewable resource electricity . It is well noticed that the instability and air leakage of air motor reduces the energy efficiency of a scroll. From our research, we observed that the energy efficiency will be dramatically reduced at lower compressed air supply pressures, for example, driving by exhaust compressed air. This characteristic will affect and limit many applications of the scroll, such as, recycling exhaust energy, fuel cell, and energy storage for renewable power generation. In this proposal, an inventive approach is proposed for improvement of scroll energy efficiency - development of a Magnetic Scroll, which will allow a scroll air motor to work at lower and variable air pressures. The key feature of the proposed approach is to make scroll spirals using magnetic materials. The magnetic scroll air motor consists of spirals made from permanent magnet inside the scroll motor. Each scroll is magnetized in one particular direction in the way that magnetic field arrangements of both scrolls are opposite to each other for their location inside the scroll air motor. For the magnetic scroll, the compressed air is supplied to produce mechanical force for scroll motion and the magnetized scroll will generate extra force at certain positions to drive the moving scroll to moving along its designed moving direction. From our initial simulation study, the following advantages of the proposed magnetic scroll will have: 1) to reduce the air leakage; 2) to improve energy efficiency of the scroll; 3) to allow the scroll to be able to work at a low compressed air supply. The total energy saving compared with the current scroll could be about 20% from our initial analysis. This proposal is to implement the idea by further simulation study and making a prototype of the scroll. A number of issues will be explored in the proposed research, such as, the suitable materials for the scroll, the scheme for magnetizing the scroll shaped material, assembly of the moving and fixed scroll, the mechanism of the magnetic field evolving along the scroll motion trajectory, control strategy for the scroll to get smooth movement, the quantified analysis for energy saving.