PIV In-Cylinder Flow Measurements of Swirl and the Effect of Combustion Chamber Design

Particle Image Velocimetry (PIV) experiments were performed on single-cylinder versions of a 0.375 L/cylinder and a 0.5 L/cylinder engines from the same engine class to determine the differences in swirl flow between the two engines. Two engine speeds (750 and 1500 rpm), manifold pressures (75 kPa and 90 kPa) and valve timings (maximum overlap and with the intake valve 20° retarded from the max overlap position) were examined. The swirl ratio (SR) and mean velocity (|V|) were calculated at BDC for every case in the mid-stroke plane and the fluctuation velocity (U') calculated for the 1500 rpm / 90 kPa / maximum overlap case. The in-cylinder velocities do not differ by the expected ratio of mean piston speed caused by differences in the engine stroke. The smaller engine was expected to have lower in-cylinder velocities and SRs due to a shorter stroke and lower piston speeds but instead has SR and |V| levels that are the same or higher than the larger engine.

In addition, the fluctuation velocities between the two engines are essentially identical. The values of U´ exhibit the proper scaling with engine speed but show only minor differences between the two engines. Examination of the flow fields show that the intake jet from the smaller engine is stronger. The smaller intake valves of the 0.375 L engine cause higher velocities in the intake flow. Also, the position of the intake valves and the relative spacing of the valve edges lead the smaller engine to have an advantage in swirl formation.