Abstract
Characterisation of Internal Flow Conditions in GDI Injectors by Means of Spray-Hole-Individual Mass Flow Rate and Momentum Flux Measurements
Highlights
The multi-hole design commonly used for gasoline direct injection (GDI) injectors grants a high degree of freedom for the adaptation and optimisation of the spray targeting to the specific requirements of a given engine and its associated combustion strategy
To retrieve individual mass flows from each spray hole, and to separate the discharge coefficient into a velocity and an area coefficient, an approach that has been suggested and demonstrated by Payri and co-workers [2] is to deduce the spray-hole-individual flow rates from momentum flux measurements normalised by the total flow rate
The comparison with mass flow rate results obtained with n-heptane as a more common and realistic gasoline surrogate instead of diesel calibration oil (Figure 5, left) shows that, at the high pressure differences relevant for GDI, the flow conditions are very similar for both liquids in terms of the contraction coefficient cC
Summary
The multi-hole design commonly used for GDI injectors grants a high degree of freedom for the adaptation and optimisation of the spray targeting to the specific requirements of a given engine and its associated combustion strategy. The assumption that needs to be made is that the flow through all holes is relatively similar This approximation is well justified for typically symmetric layouts of diesel injectors but might no longer be accurate in a typical GDI situation. Combining spray-hole-individual mass flow rate measurements, obtained from our recently presented extension of the hydraulic pressure rise method [3], with spray-hole-individual momentum flux measurements overcomes this limit. It makes a detailed characterisation of the bulk flow properties in highly asymmetric injectors possible. To the best knowledge of the authors, this work is the first one in which this experimental approach was used on a hole-tohole basis and on GDI injectors
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