(562f) Experimental Investigation Towards the Uniformity of the Flow Field in Front of an Automotive MAF-Sensor

An MAF-Sensor (mass air flow) determines the mass of air flowing into a
vehicle's fuel injection intake system and is essential to prevent inefficient
burning. Therefore the main goal of the sensor is to provide a correct
fuel-to-air ratio to ensure at suitable combustion at specific working
conditions. Due to the very limited package space for the installation of the
air intake system the available space provides the basis for the sensor
position decision. As a consequence there is a mismatch between the optimal
position and the geometric needs which results in faulty values delivered by
the sensor. The incorrect data lead to a bad fuel-to-air ratio for the
particular condition followed by e. g. engine stall or at least lower
performance. To compensate this negative effect, especially in space limited
environments, investigations towards a correction factor for this sensor are
carried out. Due to the fact that invasive techniques disturb the flow especially
on small diameters to a great extend in downstream direction optical
measurement methods are used. Therefore stereoscopic 2D/3C-PIV and 2D-LDV
measurements are realized for the validation of the flow field in the zone of
influence in front of an MAF-Sensor. Additionally numeric simulations are
carried out due to comparison purpose and for further geometry benchmarking.

Figure 1: LDA/PIV comparison
(left), PIV/CFD comparison with uniformity index (right)

The results show a good agreement between the 2D/3C-PIV measurements and
LDV-measurements, see Figure 1. Especially for diameters smaller than -0.5 <
x/x_max < 0.5 the PIV data represents
the LDV in the area of interest with good agreement. In spite of the fact that
for the LDV measurements an optical refraction correction is used, the data in
the range of -0.5 < x/x_max > 0.5
should be examined with caution. The strong optical refraction is mainly
responsible for the deviation between the measurement techniques. As a result
it can be shown that the PIV measurement can deliver reasonable data for the
problem in the desired area and can be used for CFD data validation. Moreover
the PIV data is used as a basis for creating a uniformity index to describe the
flow in front of the MAF-sensor.

[1]            Raffel M ?Particle Image Velocimetry: A practical
guide? 2nd Edition Springer Heidelberg (2007)

[2]
           Westerweel J and Elsigna GE and Adrian
RJ ?Particle Image Velocimetry for Complex and Turbulent Flows? Annu. Rev. Fluid Mech. 45 (2013) pp.409-436