The tumble flow in modern spark ignition engines is assuming an evermore important role for fuel guiding, air/fuel mixing and the generation of turbulence kinetic energy to enhance the combustion process. This paper describes results obtained with laser Doppler anemometry in multiple vertical planes in the cylinder of a motored, tumble flow engine and looks at the post processed data in terms of tumble ratios and mean and turbulence kinetic energies.
The tumble results indicate very different flow fields in parallel planes lying in the main tumble direction, showing the complex nature of the flows in the cylinder. A simple method of integrating the tumble ratios from the different planes is suggested, leading to a tumble ratio more in line with those expected from an integrated method of measuring tumble, albeit these results are crank angle dependent. The tumble in a perpendicular plane shows unexpected asymmetries and values for the tumble.
The kinetic energy data shows evidence of a decaying mean kinetic energy contributing to the turbulence kinetic energy and is most obvious in plots of the percentage of total kinetic energy contained in the turbulence component of the energy. The mean kinetic energy also suggests that the asymmetries observed in the tumble in the cross tumble plane are likely to be due to the positions of the counter rotating vortices, rather than the magnitude of the velocities in these vortices.
One of the major conclusions from this piece of work is that a simple integrated tumble ratio is unlikely to yield much information on the expected engine performance given the complex nature of the in-cylinder flows.