NAME
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Eric J. Barth |
PROJECT
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2B: Free Liquid-Piston Engine Compressor with External Combustion Chamber |
ABSTRACT
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This paper presents the design and test results of a resonating Free Piston Compressor (FPC) equipped with a built-in external combustion chamber. The FPC is a proposed device that utilizes combustion of a hydrocarbon fuel to compress air into a high-pressure supply tank, thus potentially serving as a portable power supply candidate for untethered pneumatic systems of human-scale power. The energetic merits of the FPC have been outlined and demonstrated in previous work, and this new design aims at meeting its intended power density, all while maintaining a high energy density in a compact and simple device. In this new design, the free "piston" consists of a slug of water (or other incompressible fluid) trapped between two high-stiffness elastomeric diaphragms, thus providing perfect blow-by sealing and near zero friction, while adequately presenting the dynamic elements needed for smooth, continuous operation at desired resonant frequencies. The device is essentially a tuned resonator whereby the inertia of the liquid piston and the elasticity of the diaphragms are selected to achieve a given resonant frequency. The passive dynamics of the engine are exploited to achieve efficiency through over-expansion, and to enable a return stroke with the small investment made in elastic energy with each power stroke. Additionally, the implementation of an external combustion chamber – along with built-in, actuated, high-flow, intake and exhaust valves – ensures the feasibility of such desired frequencies by decoupling the injection dynamics from the free-piston dynamics. |