Control oriented modeling of a radial turbine for a turbocharged gasoline engine

This paper presents a control oriented model for predicting turbine major variables in a turbocharged spark ignition engine. The turbine is simulated as a two-nozzle chamber where the pressure ratio over the two nozzles is not the same. A convex nonlinear estimation algorithm is formulated to determine the relation between these pressure ratios. The new model is experimentally validated with transient and steady state data collected from a 1.7 liter gasoline engine. The results show the new model can predict the turbine mass flow with an average error of 1.4%. In addition, the application of the turbine model is illustrated for the design of a nonlinear observer to estimate the turbocharger non-measured variables. The designed observer is tested against experimental data and the results confirm the observer capability to estimate the turbine rotor speed, flow over the compressor and temperature downstream the compressor.