I have heard Mat a diesel engine maker is experimenting
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with a tuned inlet manifold. Could you explain the meaning of "'tuned" in this instance?
ABecause of the opening and closing of the inlet valves the air in the inlet manifold of any piston engine pulsates as it flows through the manifold passages on its way to the cylinders. Consequently there are alternate areas of high and relatively low pressure, the position of which in relation to the inlet valves varies according to the speed of the engine.
It is desirable that the pressure should be as high as possible in the vicinity of the valves when they open so that the maximum amount of air will enter the cylinder during the intake stroke. The rate of air flow and the length of the pulses depend upon the size of the passages and configuration of the manifold. The higher the rate of flow the lower the average pressure but the greater the ram effect. When the air changes direction the rate of flow is reduced and eddy currents may be produced.
These comments show that designing a manifold to give optimum flow rates is a very complex exercise, particularly as uniform distribution between the cylinders is a priority consideration.