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The in-cylinder flow field of a Schnürle (loop) scavenged two-stroke engine has been examined under conditions simulating both blower and crankcase driven scavenging. Measurements of the radial component of velocity were obtained along the cylinder centerline during fired operation at delivery ratios of 0.4, 0.6, and 0.8. Both mean velocity profiles and root mean square velocity fluctuations near top center show a strong dependence on the scavenging method. Complementary in-cylinder pressure measurements indicate that combustion performance is better under blower driven scavenging for the engine geometry studied. IN THE PAST TEN YEARS the engine research and development community has demonstrated a renewed interest in two-stroke engine technology. Many manufacturers have new engine designs operating on test stands and in prototype vehicles being road tested.

A hot-wire anemometer was used to study the air motion in a motored i.c. engine. Measurements were made of the mean velocity, turbulence intensity, and integral scales of turbulence. The engine speed was varied from 500 to 2500 rpm, and the hot-wire probe was traversed both across the combustion chamber clearance volume and down into the piston sweep volume. The latter traverse was accomplished by probe-accommodating “wells” built into the piston crown, which were subsequently shown to severely disrupt the flow during the compression and expansion strokes. The results show the mean velocity and turbulence intensity to vary linearly with engine speed, and the turbulence scales to be a function of geometry only. The structure of turbulence was found to be inhomogeneous in the clearance volume and the upper portion of the sweep volume.

A variety of diagnostic techniques useful for the study of cold start phenomena are presented. Although the tools are demonstrated in a port fuel-injected engine, they are also suitable for direct-injection gasoline engines. A very useful technique, seemingly forgotten in the literature (and applicable to diesel engines as well), is the use of a short focal-length lens inside a Bowditch piston to expand the field-of-view. Rather than being limited by the clear aperture of the window in the piston, this technique permits the entire combustion chamber and the top section of the cylinder liner to be seen. Results using this technique are presented for the imaging of pool fires and laser-induced fluorescence of fuel films.