Effects of variable-volume Helmholtz resonator on air mass flow rate of intake manifold

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The application of geometric modifications to the intake manifold to improve engine breathing provides positive results using different strategies. Helmholtz resonators (HR) are one of the most basic acoustic models and are widely used in engineering applications. Most of the works presented in the literature focus on the use of HR in the fields of acoustics. The present work experimentally investigates pulsating flow characteristics of the engine intake manifold and the effects of a Helmholtz resonator with variable internal volume. In this paper, acoustic studies were used to model the intake manifold and to develop a complex expression to determine the natural frequency of the system. The model included the primary and secondary intake pipes and the resonator. Experiments were conducted on a straight intake pipe connected to an engine cylinder head mounted on a test flow bench, especially designed for fluid dynamic studies of engine intake systems with unsteady flow conditions. Using electronic controls, the internal volume of the resonator was varied and adjusted according to the frequency of the valves as well as the natural frequency of the intake manifold. The natural frequency of the system was determined from a numerical model of the intake manifold. The results showed the internal volume of the resonator and frequency tuning affect the intake air mass flow rate at a wide range of camshaft velocities. For a fixed volume, the average increase of the mass flow rate was 17.8%, and when the volume was adjusted according to valve frequency, the average increase was 24.7%. The highest intake air mass flow rate was increased 31.5% when the resonator was tuned to the frequency of the system.