The purpose of this paper is to characterise barrel swirl behaviour in a production four-valve engine with pentroof chamber. Steady flow analysis showed that the insertion of tubes into the cylinder head's induction tracts increased the tumbling ratio of the in-cylinder flow field at intake valve closure. A comparison of LDA measurements, conducted along the spark plug axis, for tubes and no tubes inserted yielded the following conclusions.The results indicated that the barrel swirl generated was not efficiently breaking down into turbulence but forming two counter-rotating vortices in the horizontal cylinder plane. The turbulence levels and cycle-to-cycle flow variations towards the end of the compression stroke increased with tumbling ratio. The former suggested faster combustion rates if applied to a lean burn engine, however, the latter suggested greater cyclic combustion instability and may limit lean burn capability. Both the rotational sense of the vortices and their cyclic stability appeared to be sensitive to tumbling ratio.
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