Surge Limit Prediction for Automotive Air-Charged Systems

Abstract

Compressor surge has been investigated and predicted since the early days of turbomachinery research. Experimental testing of turbomachinery applications is still needed to determine whether stable compressor operation is possible in the expected application regime. Measuring compressor maps and operating ranges on hot gas test stands is common. The test benches are designed and optimized to ensure ideal inflow and outflow conditions as well as low measurement uncertainty. Compressor maps are used to match turbocharger and application. However, a shift in surge limit, caused by the piping system or application, can only be adequately addressed with full engine tests. Ideal measurements use the corresponding piston engine in the charged-air system. This can only take place in the development process, when surge detection is unfavorable from an economic perspective. The surge model for turbochargers presented here is an extension of the Greitzer’s surge model, which considers the effect of inlet throttling. Application components, such as air filters, pipe elbows and flow straighteners, reduce pressure in front of the compressor and flow conditions might differ from those in laboratory testing. Experimental results gathered from the hot gas test stand at TU Darmstadt indicate strong variation in surge limit, influenced by inlet throttling. An extension to the surge model is developed to explain the observed phenomena. The model was validated using extensive experimental variations and matches the experienced surge limit shift. Additional measurements with a piston engine downstream of the turbocharger demonstrated the validity of the surge model. The results also show that surge is a system-dependent phenomenon, influenced by compressor aerodynamics and boundary conditions.

Determination of a Numerical Surge Limit by Means of an Enhanced Greitzer Compressor Model

“…Taking only the part of the equation of the damping ratio which can be smaller than zero results in the stability criterion D S in Equation (2). Further details on the derivation can be taken from [19,20].…”

“…The initial approach has been extended in-house at TU DARMSTADT to consider the compressor inlet system. Further details about the development and the underlying equations have been published by Bühler et al in [19,20].…”

Assessment of Variable Geometry Orifice Compressor Technology Impact in a New Generation of Compression Ignition Powertrains at Low-End and Transient Operation

“…Surge mitigation is possible by changing piping geometry or using air filters, flow straighteners, or inlet air throttling upstream of the compressor. Researchers from [3] presented an extended version of the Greitzer surge model, and results show that surge is a system-dependent phenomenon influenced by compressor aerodynamics and boundary conditions. Extensive research in the transonic state has also been carried out, experimentally and using calculation, to explain the lower compressor performance.…”