The flow visualization technique was used to measure the in-cylinder flow of an internal combustion engine. Many papers have been published about flow velocity in a cylinder determined with a laser-Doppler velocimeter or hot-wire anemometer to analyze the flow characteristics, but the data are generally for only one point of the cylinder. In this study, metaldehyde was used as a tracer particle for the gas flow and was supplied to an engine specially designed for flow visualization. To photograph the particle path, an electrooptical shutter (PLZT) was adopted because of its electrical controllability. The flow velocity obtained by this measuring system and with laser-Doppler anemometry were compared to examine the measuring system. The trends were almost in agreement, which demonstrates the validity of the measuring system. Two examples of the measured velocity were shown. One is that in-cylinder flow varies cyclically and differences in velocity exist on the same radius at the same moment. The other is that the axis of the swirl center changes considerably during each stroke. The swirl center of the flow was calculated from each particle path, and it was found that the swirl center nearly coincides with the cylinder center near top dead center though it does not at the compression or expansion stroke. Further examinations are required to adapt this technique to three-dimensional flow fields as the system is applicable to the two-dimensional plane. © 1991.
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