Velocity Field Measurements with High Speed Structural Image Velocimetry in the Primary Atomization Region of Future Diesel Fuels

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Abstract
Fuel spray breakup in combustion engines and hence all following processes are determined by the primary atomization. Due to high optical densities as well as high velocities and structures in the μm-range, the measurement of sprays in the near nozzle region is extremely challenging. Therefore, the processes of the primary breakup are not fully understood yet, although these processes are very important for simulation of spray atomization. One important property of a spray is the velocity distribution close to the nozzle outlet. With the newly developed Structural Image Velocimetry (SIV) technique it is possible to visualize spray structures in the near nozzle region and track them via cross-correlation algorithms, so that two-dimensional velocity fields of the spray can be derived. The initial SIV technique is improved with a new high-speed setup, allowing to observe also the temporal behavior of the spray velocities during the injection. Within this work, velocities of potential future diesel fuels were measured under engine relevant conditions with a variation of fuel pressure, fuel temperature and gas pressure based on the ECN Spray A conditions. Velocity fields of Oxymethlyenether 3-5 (OME) as an E-Fuel and Hydrogenated Vegetable Oil (HVO) as a Bio-Fuel were measured and compared with Gas-to-Liquid Diesel (GTL) as a reference fuel. For constant fuel pressures, the velocity distribution for OME shows significantly different values than for GTL and HVO, having about 15 % lower values and much lower deceleration behavior in downstream direction. Obviously the OME spray has a weaker air-fuel interaction. This can be attributed to a lower density leading to reduced nozzle outlet velocities and a lower Weber number.

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