Research Papers

The High Inertance Free Piston Engine Compressor—Part I: Dynamic Modeling

[+] Author and Article Information
Eric J. Barth

e-mail: eric.j.barth@vanderbilt.edu
Department of Mechanical Engineering,
Vanderbilt University,
Nashville, TN 37235

Contributed by the Dynamic Systems Division of ASME for publication in the Journal of Dynamic Systems, Measurement, and Control. Manuscript received March 18, 2011; final manuscript received January 17, 2013; published online April 29, 2013. Assoc. Editor: Nabil Chalhoub.

J. Dyn. Sys., Meas., Control 135(4), 041003 (Apr 29, 2013) (12 pages) Paper No: DS-11-1078; doi: 10.1115/1.4023759 History: Received March 18, 2011; Revised January 17, 2013

Free piston engine compressors have recently been investigated for the purpose of providing a high pressure air supply for untethered, pneumatically actuated robotic systems. Given that free piston engine performance is highly dependent on the dynamic characteristics of the piston, this paper presents the idea of incorporating a liquid piston whose geometry can be manipulated to achieve the desired piston dynamics while maintaining the compactness and light weight necessary for applications in the power output range of 100 W. An inertance-based dynamic model of the liquid piston is developed and validated experimentally. The piston model is incorporated into a complete system dynamic model of a proposed high inertance free liquid piston compressor (HIFLPC). Critical model parameters for individual components and subsystems of a proposed HIFLPC prototype are experimentally characterized. Simulation results for the proposed prototype are shown and discussed.

Copyright © 2013 by ASME
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Fig. 3

Three regions of a generic liquid piston contained by diaphragms or sliding pistons on both ends. The dashed lines show the idealized shapes used for model development.

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Fig. 2

Schematic of the high inertance free liquid piston compressor (HIFLPC)

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Fig. 1

FLPC major features

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Fig. 4

Diagram of the HIFLPC control volumes and mass flows

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Fig. 7

Diaphragm stiffness test setup

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Fig. 8

Volume displaced by the diaphragm for given pressure differentials, and the least squares fit of Eq. (33)

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Fig. 15

(a) Pump check valve piston and spring. (b) Check valve location in compression chamber.

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Fig. 16

(a) Control volume pressures for simulated HIFLPC cycle. (b) Volumes of the combustion and compression chamber during cycle.

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Fig. 17

Mass flow from compression chamber to reservoir

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Fig. 18

Energy storage in HIFLPC cycle

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Fig. 5

Experimental setup used to validate the liquid piston model

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Fig. 6

Experimental piston response compared to the liquid piston dynamic model (for isentropic adiabatic and isothermal models of the response chamber)

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Fig. 13

Measured versus modeled response of the air and fuel injectors for a driving pressure of 431 kPa (47.9 psig)

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Fig. 14

Empirical determination of metal-flap check valve influence on air and fuel injectors

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Fig. 9

Bosch 0 280 150 846 CNG fuel injector

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Fig. 10

(a) Injectors mounted to combustion head. (b) Injector check valve flaps (one in place, the second removed revealing one of the injector ports).

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Fig. 11

Air/fuel injection test setup

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Fig. 12

Measured versus modeled response of the air and fuel injectors for a driving pressure of 647 kPa (79.2 psig)




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