A Case Study of Compressor Surge Related Noise on Turbocharged 2.0-L Gasoline Engine

Till recently supercharging was the most accepted technique for boost solution in gasoline engines. Recent advents in turbochargers introduced turbocharging technology into gasoline engines. Turbocharging of gasoline engines has helped in powertrains with higher power density and less overall weight. Along with the advantages in performance, new challenges arise, both in terms of thermal management as well as overall acoustic performance of powertrains. The study focuses mainly on NVH aspects of turbocharging of gasoline engines. Compressor surge is a most common phenomenon in turbochargers. As the operating point on the compressor map moves closer to the surge line, the compressor starts to generate noise. The amplitude and frequency of the noise depends on the proximity of the operating point to the surge line. The severity of noise can be reduced by selecting a turbocharger with enough compressor surge margin. There exists a challenge in defining the margin for compressor, since there is no standard practice for defining compressor surge margin. The study discusses on mechanism of noise generation, techniques to find root cause and resolve the noise. Some best practices are also presented which helps in alleviating surprises later in the project development. In this study three types of noises are discussed. They are termed as Tip-In noise, Tip-Out Noise and Turbocharger screech noise. During the study, test measurements were conducted on vehicle and various engine parameters were investigated to understand the noise. Both tip-in and turbo screech noise were found to be directly linked to surging of compressor. The source of tip-out noise was diagnosed as the operation of CRV (compressor re-circulation valve). Engine calibration parameters influencing the noise were identified and modified to understand the sensitivity on noise levels. In this study, various passive counter measures are presented for achieving the best noise results.