Estimation of the performance of turbocharger compressors at extremely low pressure ratios

Abstract

Constant speed lines on turbocharger compressor performance maps usually have no test data at low pressure ratio and high flow. The engine, however, can force the turbocharger compressor to operate in this region and whole-engine simulation systems need to extend the test data in some way to include this region of the map. A physically based method of estimating the performance at low pressure ratios from measurements made in the rest of the map has been developed and is described in this article. The method requires no detailed geometrical information on the impeller and the stage but extracts the necessary information from the test data available; hence it can be applied to any measured compressor data.The test data over the measured range of speed and flow are used to estimate the work transfer and loss characteristics of the impeller, and the impeller throat area. The Euler equation justifies a linear extrapolation of the work input to higher outlet flow and a new technique based on the density ratio is used to extrapolate the losses. This accounts for choking at the impeller inlet in a similar way to choking at a one-dimensional duct of varying area, where losses are also a function of density ratio. The stage performance at low pressure ratios can then be obtained by recombining the extrapolated loss and work characteristics at higher flows. The method allows the measured performance map to be extrapolated to low pressure ratios on a sound physical basis and to identify physical aspects of the flow in this extreme off-design region, such as the location of increased risk of oil blow-by.

Theoretical and experimental study of mechanical losses in automotive turbochargers

“…At minimum compression ratios (i.e. 30 krpm and 50 krpm), the quasi-adiabaticity is difficult to achieve [18].…”

A surge and choke capable compressor flow model—Validation and extrapolation capability

“…The choke mass flow, assuming that choking occurs in the impeller and that the flow is isentropic, is modeled in Gravdahl and Egeland (1997) and Swain (2005), and is still an active field, see e.g. Casey and Schlegel (2010). Restriction compressor operation is discussed in a number of papers, see e.g.…”

“…Restriction compressor operation is discussed in a number of papers, see e.g. Shaaban (2004), Müller et al (2005), and Casey and Schlegel (2010), where the compressor is modeled as a typical turbine nozzle characteristic with poor efficiency.…”

“…Further, a single stage system can be operated with Π c below unity, e.g. during engine transients before it has overcome inertia effects (Casey & Schlegel, 2010). The, for multi-stage systems, commonly used passive high pressure stage (HP) by-pass (BP) valve (a spring pre-loaded valve that opens for a large enough pressure drop across it) will, in fact, force the HP stage compressor to operate at Π c o 1 when charging with the low pressure (LP) stage.…”

Modeling and Estimation of Unmeasured Variables in a Wastegate Operated Turbocharger

“…However, this introduces large errors due to linear interpolation and extrapolation [8,9]. Another problem associated with using maps provided by the compressor supplier is limited information at low compressor pressure ratios [9]. On the other side of the engine, there exist challenges with estimation of gas flow over the turbine and the WG when the WG is not 'Corresponding author.…”