A Novel Approach to Optimize the Resonators for Air Induction System 2016-01-1320
The Air Induction system (AIS) must provide sufficient and clean air to the engine for its desired combustion thus enhancing engine performance. The critical functions which effect the performance are pressure restriction and acoustic performance. The ideal design of AIS effectively reduces the engine noise heard at snorkel, which contributes to the cabin noise. Good acoustic expertise and several tests are required to optimize the design of AIS. Multiple resonators are commonly used in passenger cars to attenuate the noise. This paper emphasize on One Dimensional (1D) approach to optimize the resonators in the AIS to meet the functional requirements. In AIS, the flow happens from the snorkel to the engine air intake whereas the engine noise propagates in the opposite direction. The unsteady mass flow through the intake valves causes pressure fluctuations in the intake manifold and these propagate to intake orifice and are radiated as noise which is heard at snorkel. Air Induction system operates in a wide frequency range (0Hz to 600Hz). Suitable design of ducts, air filter box and resonators are required to attenuate the snorkel noise to meet the Sound Pressure Level (SPL) targets. Resonator is a component of small air volume which shall be added to AIS components. A Helmholtz Resonator is a common type of resonator which is widely used and is tuned to attenuate a single frequency. AIS may need multiple resonators tuned to desired frequencies to attenuate engine noise in broad band and it’s a challenge to engineers to choose the optimum number of resonators during the design stage. In this paper a detailed methodology is developed to study the characteristics of multiple resonators with different geometries and their impact on noise attenuation at different frequency levels. The attenuation of noise is studied in terms of Transmission Loss (TL) plot. A commercial tool GT-POWER® is used to build the 1D model of the AIS and measure TL. GEM 3D is used as a preprocessor. The internal flow volume of the AIS is properly discretized and TL is calculated using four pole transfer matrix method and subsequently snorkel noise is predicted using plane wave theory . A graph is plotted between Frequency (Hz) vs TL (dB). The effect of TL in different frequencies is studied. Higher the TL better will be the attenuation of snorkel noise. Several combinations of resonators are tried to obtain higher TL throughout the frequency range and optimum resonator combinations are derived. The TL plot is found to be in good correlation with 3D simulation and test results. 1D acoustic mode analysis result is also capable of predicting the optimum location of resonator on AIS as compared to conventional 3D modal analysis or testing which is more time consuming. The optimized design of AIS is tested and found good correlation with snorkel noise. This optimization technique shall be useful for future programs which reduces development time and cost.