Study notes of turbocharger theory

The new map is based on the use of conservative parameters as turbocharger power and turbine mass flow to describe the turbine performance in all VGT positions. The curves obtained are accurately fitted with quadratic polynomials and simple interpolation techniques give reliable results.

Downsizing is a trend in engine development that allows better efficiency and lower emissions based on the increase of power output in reduced displacement engines. In order to achieve this high output it is necessary to increase boosting pressure. In the last decade, variable geometry turbocharger (VGT) technologies have spread to all engine displacements and all segments of the market, and nowadays, new turbocharging technologies are been evaluated such as variable geometry compressors, sequentially turbocharged engines or two-stage compressed engines.

The right design and coupling of the turbocharging system to the internal combustion engine have capital importance for the correct behavior of the whole engine. More specifically, it is fundamental in the gas exchange process and during the engine transient evolution, and it will influence in an important way the engine specific consumption and pollutant emissions.

The turbine characteristics are accurately fitted with quadratic polynomial functions. These functions have the particularity to be continuously differentiable and without discontinuities. The differences between turbines behavior under steady or under pulsating flow conditions, as well as heat transfer phenomena across the turbine are still under investigation. Nowadays, it does not exist simple solution to solve these problems in 0D codes. The new representation uses conservative parameters which are less sensitive to their effects. So the interpolated results are more reliable and the accuracy of the whole engine simulation is improved.

Reference

J. Galindo, H. Climent, C. Guardiola, A. Tiseira, J. Portalier, Assessment of a sequentially turbocharged diesel engine on real-life driving cycles, Int. J. Veh. Des. 49 (1/2/3) (2009).