An investigation of in-cylinder tumbling motion in a four-valve spark ignition engine

Abstract

The formation and break-up of the tumble in the cylinder were studied in a single-cylinder four-valve spark ignition engine using laser Doppler anemometry (LDA) measurements and multidimensional numerical simulations. The flow structure generated by the tumble break-up was also analysed using the cycle-resolved LDA data processing method. These results show that, during the intake stroke, two counter-rotating vortices are generated in the cylinder by the intake flow along the two sides of the cylinder. They then gradually evolve into the tumble vortex at the initial stage of the compression stroke. Tumble motion can be strengthened by increasing the intake flow going along the surface of the exhaust valves and/or decreasing the intake flow descending directly along the cylinder wall on the side of intake valves. Although a partially decayed tumble vortex still exists in the central part of the combustion chamber near the end of compression, in other parts of the combustion chamber the tumble distorts and breaks up into small vortices and eddies so that the root mean square velocity fluctuation increases. The flow structure generated by the tumble break-up has a characteristic of lower frequency and larger eddy scale.