Project 16HS3: Controlled Stirling Power Unit Seth Thomas - - PowerPoint PPT Presentation

Georgia Institute of Technology | Marquette University | Milwaukee School of Engineering | North Carolina A&T State University | Purdue University | University of California, Merced | University of Illinois, Urbana-Champaign | University of Minnesota | Vanderbilt University

CCEFP Industry-University Summit College Station, TX | April 4 - 5, 2017

Project 16HS3: Controlled Stirling Power Unit

Seth Thomas Vanderbilt University Advisor: Dr. Eric Barth Photo

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Rationale

• Goal: Portable, untethered, high-energy-density power

supply for human-scale robotic applications.

Li-ion Batteries with Servomotors Hydrocarbons with Controlled Stirling Power Unit Fuel source energy density 700 kJ/kg Fuel source energy density 45,000 kJ/kg Efficiency of energy conversion and actuation via DC motors ~50% - 90% Efficiency of energy conversion, Stirling cycle, and hydraulic actuation (estimate) ~8% - 10% Specific mechanical

• utput

~350-630 kJ/kg Specific mechanical

• utput

~3600-4500 kJ/kg

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Stirling Engine Cycle

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Stirling Engine Variants

Displacer Piston Power Piston

Kinematic

Displacer Piston Power Piston

Dynamic

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Stirling Power Unit Design

heater head displacer piston Inconel engine cylinder cooling fins linear motor shaft coupling extension rod power connection ports (not shown)

Sealed Engine Section Return chamber

• Controlling displacer piston with

linear motor

• Return chamber is connected to

the engine section via an orifice plate

• Helium is used as the working

fluid - better heat transfer properties than air

• Electric heaters for accurate

temperature control

• Engine cylinder housing made

from Inconel

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Thermocompressor Principles

Stirling engine vs. Stirling Thermocompressor

Regenerator/ Displacer

hot side cold side

Regenerator/ Displacer

hot side cold side check valves power piston

Design of Stirling Power Unit

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Dynamic Model

Sealed Engine Section Return chamber

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Model Validation Setup

Cartridge heaters Temperature control PCB Pressure sensor Thermocouple Kulite Pressure sensor Motor leads 3 way ball valve Needle valve Helium inlet

heater head displacer piston Inconel engine cylinder cooling fins linear motor shaft coupling extension rod power connection ports (not shown)

Sealed Engine Section Return chamber

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Experimental Results

• Heater head temperature 250 C
• Average engine pressure 10 bar
• Displacer frequency of 2 Hz

Sinusoidal motion profile Square wave motion profile

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Experimental Results

• Heater head temperature 500 C
• Average engine pressure 20 bar
• Displacer frequency of 2 Hz

Sinusoidal motion profile Square wave motion profile

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Control Parameters - He

131 kPa 2,526 kPa

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Control Parameters - He

3.0 % 22.4 %

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2nd Generation Design

• Increase Frequency of Oscillating Displacer

Piston

– Limitations of current linear motor

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2nd Generation Design

• Streamlined Profile

– Ports for instruments unnecessary – Smaller, more compact design

• Difficulties in Managing Helium

– Costly and difficult to seal – Air is relatively easy to use

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Control Parameters - Air

102 kPa 1,102 kPa

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Control Parameters - Air

0.6 % 13.6 %

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Multi-Stage Model

Patm Tank

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Multi-Stage Simulation

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Multi-Stage Simulation

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Next Steps

• Continue to design the 2nd generation

prototype setup, using air as the working fluid.

• Fabricate 2nd generation prototype (late

May/early June) and experimentally characterize its performance. (Sept. 2017)

• Design and fabrication of hydrocarbon heater.

(Jan. 2018)

• Final high energy density Stirling device design
• complete. (May 2018)

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Conclusions

• Used validated model for simulation of control

parameter space and multi-stage design.

– High temperature difference is essential to high efficiency and high power output – High median engine pressure is largely responsible for large final pressure differences between high and low pressure tanks – Mid-to-low frequencies result in higher overall efficiencies, given current setup – Using air in a multi-stage design has potential

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Contact Information

• Seth Thomas

– benjamin.s.thomas@vanderbilt.edu

• Dr. Eric J. Barth

– eric.j.barth@vanderbilt.edu