Unsteady Gasoline Injection Experiments: Comparison of Measurements in Quiescent Air and in a Model Intake Port 950512

PDA-measurements of gasoline injection in a flow chamber and a simplified manifold-intake port configuration under constant air velocity have been performed. An acrylic glass model of an intake port without valves was mounted to a production manifold, equipped with a commercial plate-type gasoline injector. The PDA was set up in a 30° forward scatter arrangement to obtain dominant first order refracted light from the test gasoline droplets. The PDA-measurements could be synchronized with the injection cycle, thus achieving a simulated crank angle resolution in the engine.
Measurements were made 70 mm downstream of the injection nozzle in both the chamber and the intake port experiments. Due to the geometry of the intake port and the near forward scatter set-up of the PDA, the probe volume could be traversed through the center of the port to obtain radial profiles of mean droplet sizes and velocities. For the profile measurements 5000 samples were taken at each point. Furthermore, additional angular resolved measurements taking 50000 droplet events have been performed at specific locations of interest.
The measurement in the flow chamber yielded typical results for a non-swirl pressure atomizer. The maximum Sauter mean diameters around 175 μm were observed on the centerline of the spray. The maximum velocities at an axial distance of 70 mm were approximately 17 m/s. A strong positive size/velocity correlation existed due to the deceleration of small droplets.
The results of the mean quantities in the intake port exhibit a typical cross-flow situation with large mean diameters near the axis of propagation of the spray cone and smaller droplets following the air flow. Hence, bimodal size distributions could be obtained at some locations of the intake port, resulting from a superposition of a primary size distribution directly from the injector and a secondary distribution of small droplets that have been transported by the air flow.
Typically, the first droplets reach the measurement location approximately 20° after injection followed by a sharp increase of the droplet event rate. After 45° cam shaft angle, the event rate drops to near zero. The corresponding curves of the mean diameter D10 and the mean velocity indicate maximum mean diameters and velocities within the first droplets, which could be the result of a production of large droplets at injection start. In addition, these droplets are less decelerated due to their higher momentum. Later, only a few small droplets could be obtained with almost constant mean velocity near the air velocity. At 16 m/s air velocity, 99 % of the droplet mass appeared within the first 80° cam shaft angle.


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