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Measurements are presented of mean velocity and of turbulence intensity, energy spectrum, time scales and length scales in a ported engine with flat head and piston, motored at 1200, 1800 and 2400 RPM both with and without swirl. The measurements were made using laser Doppler velocimetry at data rates which were sufficiently high to allow the mean velocity in each cycle to be determined which enables one to separate the cyclic fluctuations of the mean velocity from the turbulence. The turbulence measurements near top dead center both with and without swirl showed relatively homogeneous turbulence intensity and time scales, approximately linear scaling of the turbulence intensity with RPM, decreasing time scales with increasing RPM and a shift in the turbulent energy spectrum to higher frequencies with increasing RPM. With swirl however, 25% to 50% greater turbulence intensity, higher frequency content and smaller cyclic fluctuations in the mean velocity were found.

Laser Doppler velocimetry has been used to make cycle-resolved velocity and turbulence measurements in a homogeneous-charge, spark-ignition engine. The engine had a ported intake and disc-shaped chamber with a compression ratio of 8 to 1. It was operated at a speed of 1200 rpm and with a TDC swirl number of 4. A stoichiometric propane-air mixture was used, and ignition was near the wall. The velocity measurements were made at three spatial locations at the midpoint of the clearance height. Tests were made to determine whether the presence of the flame affected the accuracy of the velocity measurements. It was found that the ensemble-averaged mean velocity shows a small deviation, and the rms fluctuation intensity is significantly influenced, but the effects appear to be confined to the flame zone. Data rates were sufficiently high in the preflame and postflame regions to determine the velocity history in each cycle (cycle resolved).

Results from an experimental study of the effect of incomplete fuel-air mixing on spark-ignited flame kernel growth in turbulent propane-air mixtures are presented. The experiments were conducted in a turbulent flow system that allows for independent variation of flow parameters, ignition system parameters, and the degree of fuel-air mixing. Measurements were made at 1 atm and 300 K conditions. Five cases were studied; a premixed and four incompletely mixed cases with 6%, 13%, 24% and 33% RMS (root-mean-square) fluctuations in the fuel/air equivalence ratio. The overall fuel/air equivalence ratio was unity in all cases. The flow characteristics were measured by LDV. The RMS fluctuation in the fuel/air equivalence ratio was characterized using NO2-based laser induced fluorescence. High speed laser shadowgraphy at 4,000 frames-per-second was used to record flame kernel growth following spark ignition, from which the equivalent flame kernel radius as a function of time was determined.