2 research outputs found
Air induction noise investigation during turbocharger surge events in petrol engines
Turbocharging is used as a means to downsize petrol engines, thereby, producing more power for a
lower engine size, when compared with a naturally aspirated engine. Due to the presence of a throttle
valve in the intake system in petrol engines, flow is restricted at the outlet pipe of the compressor during
low load engine operation. For example, during transient tip out tip in maneuvers. Hence, there is a
chance of the turbocharger operating in near surge or surge conditions and, thus, generating surge noise.
This Thesis describes an experimental and simulation method to predict and measure the turbocharger
surge noise. Initially, experimental transient tip-in and tip-out maneuver was performed on a non
turbocharged car with a petrol engine. The measured noise level in the intake manifold, at a low
frequency of up to 1200 Hz, was analysed and was shown not to represent surge noise. Next, a one
dimensional simulation method was applied to simulate the noise of the engine and this demonstrated
an increase in the acoustic pressure level in the intake manifold during the tip in and tip out maneuver.
However, a surge noise pattern was not observed in the analysis of acoustic pressure signals in the
intake system using Short Time Fourier Transform (STFT). The simulation procedure was also used to
inform the design of an experimental rig to recreate the surge noise under laboratory conditions. An
experimental turbocharger noise rig, designed and built for this purpose, is explained in the Thesis.
Important component parts likely to be involved in the surge noise generation such as the intake system,
compressor, throttle body, compressor recirculation valve and measurement and control systems were
integrated into the test rig. Background noise contributions from the electric motor, AC mains,
supercharger pulley, throttle body, inverter fan, throttle body gearing and structural vibration of the
supporting structure were identified from the analysed frequency components of the signals from
surface microphone measurements taken at the intake system. This helped to clearly identify the surge
noise frequency components (3250 Hz) in the STFT analysis. The fundamental mechanism of noise
generation was identified using an analysis of the experimental results and a frequency calculation for
vortex shedding and the radial acoustic resonances. One of the main conclusions of the Thesis is that
the compressor recirculation valve (CRV) open or close position, the CRV delay time and the throttle
position are major contributing factors to the cause of the surge noise. Another major conclusion is that
the radial acoustic resonance may be a mechanism of surge noise generation. Finally, a passive solution
to reduce the surge noise is proposed. A pipe with cross ribs is designed as a passive solution using the
radial acoustic resonance calculation and the corresponding nodal patterns. This solution demonstrated
a measured intake system noise reduction of up to 10dB under compressor surge conditions
Turbocharger surge noise measurement and solution using experimental techniques
Turbocharging is used as a means to downsize petrol engines, thereby, producing more power for a lower engine size, when compared with a naturally aspirated engine. The introduction of a turbocharger means that a throttle body is included in the petrol engine downstream of the turbocharger
compressor. Due to the presence of this throttle valve, flow is restricted through the outlet pipe of the turbocharger during low load engine operation. For example, during transient tip out β tip in maneuvers.
Hence, there is a chance of the turbocharger operating in near surge or surge conditions. Surge noise generated during this stage is clearly audible and can also affect the durable life of the compressor and other rotor systems of the turbocharger. This paper describes an experimental method to
predict and measure the turbocharger surge noise. An experimental turbocharger noise rig, designed and built for this purpose, is explained. Using a time and frequency analysis of the measured data the fundamental mechanism of noise generation is identified. Finally, a passive solution to reduce the surge noise is proposed