CFD Driven Parametric Design of Air-Air Jet Pump for Automotive Carbon Canister Purging 2017-01-1316
A jet pump (also known as ejector) uses momentum of a high velocity jet (primary flow) as a driving mechanism. The jet is created by a nozzle that converts the pressure head of the primary flow to velocity head. The high velocity primary flow exiting the nozzle creates low pressure zone that entrains fluid from a secondary inlet and transfers the total flow to desired location. For a given pressure of primary inlet flow, it is desired to entrain maximum flow from secondary inlet. Jet pumps have been used in automobiles for a variety of applications such as: filling the Fuel Delivery Module (FDM) with liquid fuel from the fuel tank, 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 introduced in evaporative emission control system for turbocharged engines to remove gaseous hydrocarbons stored in carbon canister and supply it to engine 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 compressed air from the turbocharger flows through a nozzle and creates necessary vacuum 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 high subsonic or supersonic regime. 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 in performance 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 the effect of numerous geometrical parameters such as: nozzle diameter, area ratio of throat and nozzle, diffuser length, nozzle shape and purge port diameter. Performance curves (purge flow vs. turbocharger pressure) are developed for each of these parameters. Purge flow was specifically found to have a strong dependency on the area ratio and purge port diameter. Optimum area ratio of 0.04 and larger purge port provided significant performance improvement. In conclusion, this paper aims to develop performance curves and explore effect of several geometrical parameters on the performance of the jet pump to add to the existing knowledge base especially the automotive literature.