| Two geometrically scaled, two-valve, optically accessible, single-cylinder research engines were designed and fabricated to study the fundamentals of engine size- and speed-scaling effects. All dimensions between the engines scale by the factor of 1.69. Two different port geometries and two different port orientations and both shrouded and non-shrouded intake valves were tested to vary the intake-generated flow. Prior to testing the engines, the different head configurations were tested on a steady flow bench. Flow, swirl, and tumble parameters were measured to quantify the performance of the engine heads.;The engines were motored at speeds ranging from 300--1200 RPM for the larger engine and from 600--1800 RPM for the smaller engine at an atmospheric intake pressure. Particle image velocimetry data were taken on a single plane, parallel to the piston surface, in the engines using both a low magnification to characterize the large-scale flow phenomena, and a high magnification to characterize the turbulence field. The low magnification data for conditions with higher levels of swirl were analyzed to determine the location of the swirl center and the angular velocity. The high magnification data (acquired at TDC) were investigated using both ensemble- and spatial-averaging to define a mean velocity field. The fluctuating velocity fields were used to calculate turbulence intensity, two-point fluctuating velocity correlations, and longitudinal and transverse integral length scales. Turbulence intensity measurements showed close agreement between the large and small engines. The longitudinal lengthscales were on average twice the transverse lengthscale, indicating a high level of isotropy in the flow. The longitudinal lengthscales, when normalized by the TDC clearance, showed good agreement between the large and small engines.;Turbulent kinetic energy spectra were calculated and were fit well by the model spectrum of Pope. The spectral analysis provided lengthscales ( L11) that were similar between the small and large engines when normalized by the TDC clearance. Kolmogorov scales between the small and large engines also showed similarity when compared at the same mean piston speed. Taylor-scale Reynolds numbers were calculated for all engine conditions and collapsed onto a single curve when plotted against an inlet valve Mach index. |
