Effect of Exit Pressure Pulsation on the Performance and Stability Limit of a Turbocharger Centrifugal Compressor

Abstract

It is well known that compressor surge imposes a significant limit on the flow range of a turbocharged internal combustion engine. The centrifugal compressor is commonly placed upstream of the inlet manifold and hence, it is exposed to the intermittent flow regime of the inlet valves. Surge phenomena has been well studied over the past decades, there still remains limited information with regards to the unsteady impact caused by the inlet valves. This study presents an experimental evaluation of such a situation. Engine representative pulses are created by a downstream system comprising a large volume, two rotating valves, a throttle valve and the corresponding pipe network. Different pulsation levels are characterized by means of their frequency and the corresponding amplitude at the compressor inlet. The stability limit of the system under study is evaluated with reference to the parameter B proposed by Greitzer [7–9]. B describes the dynamics of the compression system in terms of volume, area, equivalent length and compressor tip speed as well as the Helmholtz frequency of the system. For a given compressor, as B goes beyond a critical value, the system will exhibit surge as the result of the flow instability progression. The reduced frequency analysis shows that the scroll-diffuser operates in an unsteady regime, while the impeller is nearly quasi-steady. In the vicinity of the surge point, under a pulsating flow, the instantaneous operation of the compressor showed significant excursions into the unstable side of the surge line. Furthermore, it has been found that the presence of a volume in the system has the greatest effect on the surge margin of the compressor under the unsteady conditions.

Investigation of the influence of pulsating boundary conditions generated by an internal combustion engine on compressor operating near surge

“…These authors carried out tests on a HGTR at steady state boundary conditions. If the compressor is operated under pulsating boundary conditions, similar measurement techniques are used to determine the surge limit (Barrera-Medrano et al, 2019, 2017Galindo et al, 2013Galindo et al, , 2009Marelli et al, 2013Marelli et al, , 2012.…”

“…For this reason, the effects of the experimental setup, especially the configuration of the inlet and outlet duct of the compressor, have been the subject of numerous investigations. The volume downstream the compressor outlet has the most significant influence on the position of the surge margin (Barrera-Medrano et al, 2017;Fink et al, 1992;Galindo et al, 2006;Greitzer, 1976;Grigoriadis, 2008;Müller, 2008). In addition, Haeckel et al (Haeckel et al, 2023) show in detail that other influencing factors, such as the inlet pressure into the compressor or the throttle characteristics, must also be taken into account.…”

“…Due to the opening and closing of the engine inlet valves and the associated pressure fluctuations, the compressor experiences a pulsating backpressure. These pulsations influence compressor performance as well as shift the position of the surge onset (Barrera-Medrano et al, 2019, 2017Galindo et al, 2013Galindo et al, , 2009Marelli et al, 2012). For this reason, it is extremely important for the design of centrifugal compressors to take this influence into account.…”

Investigation on the unsteadiness of centrifugal compressor exposed to pulsating backpressure

“…Some experimental researches have been carried out on the topic of compressor performance exposed to pulsating backpressure. 5,7,8 A pulse generator is applied downstream the compressor to replicate the pressure waves in the intake manifold on a real engine. The compressor instantaneous pressure ratio versus mass flow rate is confirmed to form a hysteresis loop, encapsulating the steady performance curve.…”