Development of a new system for measuring the swirl ratio of an engine cylinder head under an unsteady flow condition

A new impulse-type swirl meter that measures the swirl ratio (R _s ) and flow coefficient (C _fmean ) during an intake air process for the intake port of an engine cylinder head under unsteady flow conditions was developed. The camshaft of the cylinder head was directly rotated by a step motor, allowing the valve lift to be adjusted automatically with the camshaft profile in the newly developed swirl measurement system. The measurements of the swirl ratio and flow coefficient were automated using a FPGA-DAQ board and a computer. The rotational speeds of the camshaft were held constant at steps of 90, 120, 150, 180 and 210 rpm during the measurement. As the camshaft rotation speed increased, the values of R _s tended to decrease while those of C _fmean tended to increase, implying that R _s and C _fmean depend on the engine speed. These results should be considered in the design of an intake port. With the newly developed swirl measurement system, it is possible to measure R _s and C _fmean repeatedly in a very short time. The repetitive measurement results of R _s and C _fmean were statistically processed. Through an uncertainty analysis, the values of the upper and lower bounds of R _s and C _fmean can be calculated for each camshaft rotation speed.