UBC Theses and Dissertations
Development of a CNG intensifier for high pressures Aichinger, Christoph
A CNG intensifier has been designed to compress natural gas from a variable, elevated-pressure storage source (20 - 200 bar) to a constant high discharge pressure (200 bar). The intensifier delivers variable amounts of gaseous fuel (5 - 43 kg/hr) at a maximum required pressure ratio of 10:1 for fueling a heavy duty bus diesel engine which is converted to a gas-diesel engine. Based on a study of alternative intensifier concepts, a single-stage and a two-stage reciprocating crank-shaft driven intensifier prototype was built. The bore and stroke dimensions of both intensifiers are 31.75 mm and 82.55 mm, respectively. The stage volume ratio of the two-stage intensifier is 2.78:1. The performance of the intensifier prototypes was measured at pressure ratios between 6:1 and 12:1 while keeping the discharge pressure constant at 200 bar. Taking into account volumetric efficiency and the need to limit compression temperature for satisfactory life of the elastomer seals, the performance of the intercooled two-stage intensifier prototype proved to be decisively superior, providing volumetric efficiencies of 92 per cent, isentropic efficiencies of 77 per cent and maximum operating temperatures of 120°C with air cooling at design pressure ratio (10:1). A bore-to-valve area ratio of 16:1 or less was found to be adequate to limit the valve flow velocity to Mach numbers less than 0.1. The test results of the proposed two-stage intensifier indicate a potential for efficient intensifier operation at pressure ratios exceeding 10:1. However, the crank-shaft actuation of the intensifier can lead to friction- and alignment-related problems at higher piston frequencies and it is suggested that a variable displacement, hydraulic actuator could be utilized to further improve efficiency and to offer better controlability.
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