Air Induction Impact on Turbocharger Noise and Thermodynamic Performance

The trend to simultaneously improve fuel economy and engine performance has led to industry growth of turbocharged engines and as a result, the need to address their undesirable airborne noise attributes. This presents some unique engineering challenges as higher customer expectations for Noise Vibration Harshness (NVH), and other vehicle-level attributes increase over time. Turbocharged engines possess higher frequency noise content compared to naturally aspirated engines. Therefore, as an outcome, whoosh noise in the Air Induction System (AIS) during tip in conditions is an undesirable attribute that requires high frequency attenuation enablers. The traditional method for attenuation of this type of noise has been to use resonators which adds cost, weight and requires packaging space that is often at a premium in the under-hood environment. By improving our understanding of the root cause, we aim to develop AIS design strategies that can prevent unwanted noise from being generated at the source, while avoiding the need for traditional noise attenuation solutions. Additionally, a better understanding of any implication on compressor performance in terms of isentropic efficiency and pressure ratio will be investigated as a result of the noise being generated. A range of pipe configurations were designed to achieve specific swirl and flow uniformity metrics using inflow swirl devices and 90^o bends. Initial assessments were obtained from a gas stand and then verified during vehicle level testing on a gasoline turbocharged 2.0L vehicle. Acoustic and thermodynamic gas stand characterizations were completed for 80 operating points for a set of defined configurations. Particle Image Velocimetry (PIV) was used to map inlet flow conditions into the compressor. The outcome of the investigation has shown how specific flow conditions have degraded compressor efficiency up to ~2.6% and increased noise levels up to ~15 dB (A) at the compressor inlet.