A transparent model engine was developed which can generate an axially symmetrical flow field in the cylinder and which allows an easy access for optical measurement of the in-cylinder air motion. Experimental data on flow characteristics such as mean velocity, turbulent velocity and turbulent scale in the entire space of the cylinder obtained with this engine are expected to be available for evaluating the reliability of mathematical models popular at present. This paper describes the design concept and details of the construction of the engine, and offers some experimental data measured by both a flow visualization technique and Laser-Doppler anemometry.