Influence of the manufacturing process tolerance on the swirl number of a low-capacity engine

We analyze the fluid-dynamic behavior of the cylinderhead of a low-capacity engine in the steady regime. Attention is paid to the influence of the manufacturing process tolerance on the variability of the swirl number generated by the intake port. Both the discharge coefficient and swirl number are measured for a number of cylinderheads manufactured in series. While the discharge coefficient values lie within the range specified by the manufacturer, most of the swirl number values fell outside that range. More importantly, the variability of the swirl number exceeds the prescribed limit. The influence of the manufacturing process tolerance on that variability is examined from numerical simulations. Specifically, we consider the position of the intake port with respect to the machined elements of the cylinderhead. The variation of that position in the range given by the manufacturing tolerance explains in itself the scattering of the swirl number observed in the experiments. To reduce the swirl number variability, we propose a procedure which combines advanced manufacturing techniques and fluid-dynamic simulation.