Laser Doppler Velocimetry Measurements in Valved and Ported Engines 840375
Measurements are presented of bulk velocity and its cyclic variation and of turbulence intensity in IC engines with combustion chambers of open shape. Engines with both ported* and valved intakes were tested. The ported engine was tested both with and without swirl and the valved engine without swirl only. The ported engine was motored at 1200, 1800 and 2400 RPM and the valved engine at 600, 1200 and 1800 RPM. In both engines the shape of the combustion chamber was such as not to introduce strong organized gas motion during compression. Thus the in-cylinder gas motion, including turbulence, was due primarily to the intake process. The measurements were made using laser Doppler velocimetry at data rates which were sufficiently high to determine the bulk velocity in each cycle and thereby separate the cyclic fluctuations of the bulk velocity from the turbulence. Such measurements are called cycle-resolved and have not previously been made in either valved or ported engines at practical engine speeds using LDV. The measurements were made at numerous spatial locations in the ported engine and at a single location in the valved engine, in both cases on a plane centered within the clearance height over a crankangle interval of sixty-four degrees around TDC.
It is shown that the ensemble averaged velocity is proportional to engine speed in the ported engine with swirl, whereas no such trend was found in either the ported or valved engines without swirl. The cyclic variation of the bulk velocity is shown to increase with engine speed and to decrease with swirl; trends which are consistent with the results of other studies of cyclic peak pressure and flame propagation variations. An ensemble averaged analysis of the turbulence, which includes the contribution of the cyclic variation in the bulk velocity, was found to overestimate the cycle resolved turbulence intensity by as much as 100% in the ported engine without swirl and by as much as 300% in the valved engine without swirl; however, in the case of the ported engine with swirl this difference was less than 10%. In all cases the turbulence intensity was found to be nearly proportional to engine speed and in the ported engine, with and without swirl, the turbulence intensity was found to be approximately homogeneous. In both the valved and ported engines without swirl, TDC turbulence was also found to be isotropic within ±20%. These findings support the hypothesis that, for open combustion chambers, different intake designs influence the intensity of the TDC turbulence (and, possibly, its scale) but not its homogeneity, isotropy or proportionality to engine speed.