A Study On Characteristic Of In-cylinder Flow Field In Four Valve SI Engine Under Low Valve Lift

The SI engine is now becoming the main powerplants for passenger cars.The study on the tumble motion will result in the improvement of combustion process and therefore that of engine performance. In this paper,PIV(Particle Image Velocimetry) is applied to study the characteristic of in-cylinder flow field under different valve lifts.This research tested and evaluated the abilities of tumble motion of the cylinder head in the steady flow test bench.The results show that with the lowering of valve lift , the flow ability was worse while the tumble intensity was enhanced .The flow ability and tunble ratio with one valve opening were better than that of dual-valves.In this paper, we completed the optimization of the optical SI engine and the set-up of the PIV system.70 image pairs were taken continually at one of 11 crankangles which were distributed equally during intake and compress stroke under three different engine speeds using PIV system.After each image pair being caculated by cross-correlation ,two-dimensional velocity distribution map were obtained and analysed.After the velocity distributions were postprocessed by Gaussian lowpass filter,the process of tumble motion: the formation,the expansion,the maintance and the distortion and breadup can be observed. The swirling strength analysis shows that stronger swirling strength in the measurement plane were found under lower valve lift ,and at 270o CA ATDC ,the swirling strength was the strongest By caculated the turbulence intensity and turbulence kinetic enery,the results showed that they were enhanced with the engine speed increasing.The turbulence intensity and turbulence kinetic energy are worse under higher valve lift than that of lower valve lift.In the early stage of intake stroke and end of compress stroke ,they were stronger than other crankangles.