Application of Two-Color Particle Image Velocimetry to a Firing Production Direct-Injection Stratified-Charge Engine

A two-color Particle Image Velocimetry (PIV) technique has been applied for the first time to a firing, production, three-cylinder, two-stroke, direct-injection stratified-charge engine operated under realistic conditions. In comparison to single color PIV, two-color PIV can resolve the directional ambiguity of the velocity by cross-correlating two digitized photographic images of a particle-seeded flow field, acquired sequentially at two different light wavelengths. Such an approach is essential in complex, a priori unknown, flow fields, such as those of most I.C. engines. To gain optical access to the combustion chamber, the engine head was equipped with two optical windows in such a way that its original geometry was practically undisturbed. Although the field of view was relatively small, it covered a critical area of the combustion chamber. The measurements were made in the plane perpendicular to the engine longitudinal axis, within the crank angle range of 70 to 10 degrees BTDC. The engine was operated at 800 RPM and 10 lbs.-ft. The data consist of over 80 instantaneous velocity fields measured for selected crank angles. Flow patterns determined for the same crank angles are consistent despite some cycle-to-cycle variations. It was found that reliable velocity measurements could be made outside of the fuel injection sprays but not within the sprays. At 10 degrees BTDC, combustion manifests itself as blurring of the image due to the presence of hot combustion gases. No distinct flame front was observed. Beyond 10 degrees blurring was so severe that further velocity measurements were no longer possible.