The purpose of this study is to determine the upper-bound energy storage capacity of gas-charged hydraulic accumulators and to assess the accumulator size and total mass for use in a hydraulic-hybrid passenger car. At pressures commonly encountered in a hydraulic accumulator (up to 41.48 MPa, absolute (6000 psig)), thermodynamic properties of nitrogen depart significantly from ideal gas behavior. To determine the best equation of state for accumulator calculations, predictions of the ideal gas law, the Beattie-Bridgeman equation, the Benedict-Webb-Rubin (BWR) equation, and Sandri's equation of state were compared with nitrogen data published by the National Bureau of Standards. The BWR equation of state is shown superior to other proposed equations and is, consequently, selected for accumulator analysis. A hydraulic accumulator operating at a constant temperature will have the maximum possible energy storage capacity. A conventional accumulator can be 'isothermalized' by the insertion of an appropriate elastomeric foam into the gas enclosure. This will minimize entropy generation in the accumulator and virtually eliminate the thermal losses.
Sizing energy storage units for hydraulic hybrid vehicle applications
Auslegung der Energiespeicheranlagen für hydraulische Hybridfahrzeuge
1993
16 Seiten, 25 Bilder, 4 Tabellen, 22 Quellen
Conference paper
English
Sizing Energy Storage Units for Hydraulic Hybrid Vehicle Applications
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