Session: 06-04: Performance Systems Modeling and Design

Paper Number: 166543

166543 - Modeling Free-Piston Linear Generator 

Abstract: 

Free-Piston Linear Generators (FPLG) offer the potential benefit of high compression ratio (>25), low friction (< 1.0 bar FMEP) and reduced parts count (e.g. no crank shaft).  They are particularly interesting as range extending power plants for hybrid vehicles.  However, since the piston position is not controlled by a crank shaft, the free motion offers significant control challenges.  The model development will aid in the understanding and development of the power, air-spring, and generator controls.

In this study, a first principles model of a two-stroke, single-piston, double ended Free Piston-Linear Generator is developed including in-cylinder thermodynamics, piston dynamics and the linear generator electrical power generation.  The model is validated with experimental data from a prototype FPLG initially powered by air injection. 

A high fidelity GTpower model is built to enable further development.  Since the piston motion is free and not controlled like a conventional engine with a crank shaft, a major challenge of FPLG is controlling the combustion phasing. These models are used in a Control Oriented Modeling (COM) approach to understand controllability and develop a control strategy.  The control strategy includes control of the air-injection of the "air-spring" end to control the power-end compression motion and the power end injection.   

Presenting Author: Claire Daughtery University of Colorado - Boulder

Presenting Author Biography: Claire Daugherty is a mechanical engineer with a passion for clean energy technology and thermal systems. She earned her B.S. in Mechanical Engineering from Case Western Reserve University and went on to complete her M.S. in Mechanical Engineering at the University of Colorado Boulder. During her graduate studies, she worked with Dr. Greg Hampson to model a free piston linear generator engine, further deepening her expertise in energy systems.

Claire currently works as a structural engineer for the Department of Defense. Outside of work, she is an avid runner and hiker, always looking for the next trail to explore.

Authors:

Claire Daughtery University of Colorado - Boulder
Greg Hampson University of Colorado Boulder