Synthesis of the 1D modelling of turbochargers and its effects on engine performance prediction

Abstract

Low fuel consumption is one of the main requirement for current internal combustion engines for passenger car applications. One of the most used strategies to achieve this goal is to use downsized engines (smaller engines while maintaining power) what implies the usage of turbochargers. The coupling between both machines (the turbocharger and the internal combustion engines) presents many difficulties due to the different nature between turbomachines and reciprocating machines. These difficulties make the optimal design of the turbocharged internal combustion engines a complicated issue.In these thesis a strong effort has been made to improve the global understanding of different physical phenomena occurring in turbochargers and in turbocharged engines. The work has been focused on the 1D modelling of the phenomena since 1D tools currently play a major role in the engine design process. Both experimental and modelling efforts have been made to understand the heat transfer and gas flow processes in turbochargers. Previously to the experimental analysis a literature review has been made in which the state of the art of heat transfer and gas flow modelling in turbochargers have been analysed.The experimental effort of the thesis has been focused on measuring different turbochargers in the gas stand and the engine test bench. In the first case, the gas stand, a more controlled environment, has been used to perform tests at different conditions. Hot tests with insulated and not insulated turbocharger have been made to characterise the external heat transfer. Moreover, adiabatic tests have been made to compare the effect of the heat transfer on different turbocharger variables and for the validation of the turbine gas flow models. In the engine test bench full and partial load tests have been made for model validation purposes.For the models development task, the work has been divided in heat flow models and gas flow models. In the first case, a general heat transfer model for turbochargers has been proposed based on the measured turbochargers and data available from previous works of the literature. This model includes a procedure of conductive conductances estimation, internal and external convection correlations and radiation estimation procedure. In the case of the gas flow modelling, an extended model for VGT performance maps extrapolation for both the efficiency and the mass flow has been developed as well as a model for discharge coefficient prediction in valves for two stage turbochargers.Finally, the models have been fully validated coupling them with a 1D modelling software simulating both the gas stand and the whole engine. On the one hand, the results of the validation show that compressor and turbine outlet temperature prediction is highly improved using the developed models. This results prove that the turbocharger heat transfer phenomena are important not only for partial load and transient simulation but also in full loads. On the other hand, the VGT extrapolation model accuracy is high even at...

Experimental characterization and mean line modelling of twin-entry and dual-volute turbines working under different admission conditions with steady flow

“…In the present thesis, the development steps of some of the equations used for doubleentry turbine modelling and heat transfer characterization are based on the PhD dissertations of Reyes-Belmonte [19] and Dombrovsky [20]. Therefore, to follow better the logic behind the development of models described in this thesis, in the following sections, a summary of previous works is added.…”

“…Equation 4. 23 shows the parameter that accounts for average flow deviation from the calculated rotor inlet angle (Equation 4.21) and imposed metal angle at the rotor outlet [20]. These are the only 'losses correction' of Equation 4.15 model, apart from the discharge coefficients accounted by the flow model.…”

“…The thesis of Reyes-Belmonte [19] deals with the problems related to the internal heat transfers and extrapolation modelling of turbine maps and in a physical methodology. Dombrovsky [20], further improved the models of Reyes-Belmonte [19] to enhance engine simulation using commercial 1D tools like GT-POWER T M and also studied the effects of external heat transfers in turbochargers. Inhestern [21] focused his study at the extreme off-design working conditions of radial turbines experimentally.…”

“…Equation 4.2 can be used to express the isentropic expansion between station 0 and 3, as shown in Equation 4. 20. It can be noted that the coefficient 'd' in Equation 4.20 comes from the reduced mass flow fitting, and it represents the expansion ratio in the rotor concerning the total turbine expansion ratio.…”

A contribution to the global modeling of heat transfer processes in Diesel engines

“…The development of the turbocharger heat transfer model is described in [192]. In the model, geometry is simplified to a set of coaxial cylinders, see Fig.…”