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College of Science & Engineering > Department of Mechanical Engineering

Compressed Air Approach for Wind Energy Storage



Research: Machine Design                                                


igh Efficiency Variable Displacement Hydraulic Transformer: A hydraulic transformer is needed to control the liquid piston during compression and expansion. The trajectory of this liquid piston requires that the transformer operate at a low displacement for large portions of the cycle. This project is being headed by Dr. James Van de Ven with research assistance from Hao Tian and Shawn Wilhelm .

Design Challenges: 
At low displacements, conventional variable displacement hydraulic pumps are fairly inefficient. This is due to their fixed losses occurring at a lower output power. These loses are due to mechanical friction and volumetric losses due to leakage. We attempt to address these issues in our transformer design.


Adjustable linkage Design and Optimization : Friction is addressed by using a pinned linkage to vary the displacement. Pins are inherently more efficient than the prismatic joint used in current technology. An adjustable sixbar linkage was designed and optimized for transmission angles and footprint. This mechanism also addresses volumetric losses by always returning to top dead center. Also, the pin joints require less lubrication than current technology. A mechanical pumping mechanism was made to validate the linkage design.

High-Speed Cylinder Valves:  For a liquid piston based compressed air energy storage (CAES) system, the central energy conversion unit, the variable displacement linkage pump/motor, requires a high speed valve with low transitional loss, low leakage, and low activation energy.

Hydraulic Transformer Applications:
  Pumping and motoring actions are the two basic functions (modes) of the hydraulic transformer. To enable the variable displacement linkage pump/motor to act as a pump, traditional check valves along will be sufficient. However, for the motoring mode, active valve control is required to precisely time the opening and closing of the pressure and tank ports relative to the piston position.

Challenges and Modifications: To maximize efficiency, the valve must transition between states rapidly, have minimal leakage, and require low activation energy.  A proposed design is an axial flow continuously rotating disc type valve.  Currently, an experimental system is under development to characterize the leakage and the mechanical efficiency as a function of valve clearance, rotational speed, and sealing materials on the rotating disc surface.  These results will be used to validate the valve model.


New Hybrid Valve Prototyping: To minimize transitional loss and provide better sealing, a novel poppet-rotary hybrid valve is proposed and is currently being investigated. The new valve features a combination of advantages of both poppet valves and rotating axial flow valves. The force applied by compression spring provides improved sealing and the torque generated by the torsion spring further reduces the transition time between On/Off states.


  Contact: Prof. Perry Li
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