CFD Driven Parametric Design of Air-Air Jet Pump for Automotive Carbon Canister Purging

Paper #:
  • 2017-01-1316

Published:
  • 2017-03-28
Abstract:
A jet pump, or an ejector, functions on the ability of a high velocity jet to entrain surrounding stationary fluid. When a high pressure flow from a primary inlet passes through a nozzle, it creates low pressure zone due to venturi effect. The low pressure zone allows flow entrainment from a secondary inlet. For a given pressure at primary inlet, it is desired to entrain maximum flow from secondary inlet. Jet pumps have been used in automobiles for a variety of applications such as: transferring liquid fuel between two halves of the saddle type fuel tank and entraining fresh coolant in the cooling circuit. Recently, jet pumps have been used in evaporative emission control system to remove gaseous hydrocarbons stored in carbon canister and supply it to intake manifold (canister purging). Naturally aspirated engines use vacuum pressure inside the intake manifold for canister purging. However, turbocharged engines operate at or above atmospheric pressure. Hence, a jet pump is used in which the high pressure air from turbo charger flows through a nozzle and creates necessary suction to facilitate canister purging. This paper describes the CAE driven parametric design process of such a jet pump. Flow velocity through nozzle is often in supersonic regime for this application. Hence, a CAE method needs to consider coupled flow along with local mesh refinements and additional boundary layer cells. For subsonic regime, results from the coupled flow solver were nominally same as less resource intensive segregated flow solver. However for supersonic regime, the difference was found to be up to 10% due to air compressibility effects. The paper also covers details about the CAE-test correlation. The validated CAE method is employed to understand effect of numerous geometrical parameters such as: nozzle shape, diameter, nozzle to diffuser area ratio and diffuser length. Performance curves (purge flow vs. turbocharger pressure) are developed for each of these parameters. Purge flow was specifically found to have an exponential dependency on the area ratio with lower area ratio providing significant performance improvement. In conclusion, this paper aims to show efficacy of the CAE method in the design process, selection of appropriate flow solver and effect of numerous geometrical parameters on the performance of the jet pump.
Also in:
  • SAE International Journal of Passenger Cars - Mechanical Systems - V126-6EJ
  • SAE International Journal of Passenger Cars - Mechanical Systems - V126-6
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