Measurements of Spatial Structure of BDC Turbulence in a Model IC Engine Using Flying Hot Wire

An investigation has been carried out to measure the spatial structure of the turbulence in a model IC engine at near to BDC, inlet stroke. Flying hot wire anemometer measurements have revealed details of the effect of the inlet port angle and valve lift on the spatial turbulence structure. Cycle resolved turbulence intensity and integral length scale are presented at three cutoff frequencies of 10 Hz, 100 Hz, and 1000 Hz. Although the situation is transient, conventional analysis methods are shown to be useful. The inhomogeneity of the intake turbulence is found to be considerable. It is also shown that high turbulence energy content occurs at lower frequencies. The flow also exhibits high cycle-to-cycle variation in the mean velocity although this variation was not sensitive to the cutoff frequency. At low cutoff frequency the integral length scale of BDC turbulence was found to be comparable with the valve lift. The rôle of the inlet jet flow is shown to be crucial.