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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Increasing Fast Refill of Compressed Natural Gas by Active Heat Removal

Guoyu Zhang
The University of British Columbia, Okanagan Campus, Kelowna, Canada, V1V 1V7

Joshua Brinkerhoff
The University of British Columbia, Okanagan Campus, Kelowna, Canada, V1V 1V7

Ri Li
School of Engineering, University of British Columbia, 1137 Alumni Avenue, Kelowna, British Columbia V1V1V7, Canada

Chris Forsberg
Agility Fuel Systems, Kelowna, Canada

Abstract

Heavy duty vehicles powered by compressed natural gas (CNG) have large CNG tanks onboard. The tanks need to be fast refilled at CNG stations whenever the gas storage is low. The refill stops when the pressure inside the tank exceeds the rated pressure, and at the same time the temperature inside the tank is higher than the ambient by around 30K. The pressure goes down when the temperature reaches the equilibrium with the ambient. Defining the ratio of the filled natural gas to the actual onboard storage capacity as the refill efficiency, the refill efficiency is only about 80%. The driving range of the heavy duty CNG vehicles can be increased if the refill efficiency can be improved. An active heat removal method based on a liquid cooling loop is proposed to improve the fast refill of CNG vehicles. In this research, analytical and numerical models of the filling process with and without active heat removal inside a type III cylinder is developed. In the analytical study, the mass and energy conservation equations are coupled with an ideal-gas equation of state and orifice flow equations to predict the heat generation rates during fast fill. The influence of heat removal via a cooling coil inserted in the cylinder on the fill efficiency and fill time is quantified. The results show that although it takes more time to fill a cylinder with the cooling coil, the cylinder can carry more mass of natural gas so that the vehicle's range can be increased. The analytical study is compared against numerical simulations employing a two-dimensional axisymmetric computational fluid dynamics (CFD) model for unsteady, compressible turbulent flow with and without active heat removal. Dynamic average temperature, pressure and mass curves and local temperature distribution in the cylinder are obtained at different time instances during the fill. The results of the analytical/numerical study achieve good agreement with published experimental data and illustrate the benefit of heat removal from the cylinder as a means of improving fast fill efficiency.

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