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Fouling phenomenon is a key issue for EGR cooler operation. In spite of the fact that soot deposition is imposed by the characteristics of the exhaust gases flow, the design of the EGR cooler has a significant impact for effect on the engine. New combustion modes corresponding to new engine developments and combination of EGR system with other post-treatment devices make that fouling conditions for future generations of EGR coolers can be significantly different from previous applications from Euro 3 to Euro 5. An investigation has been performed in order to characterize the response of different EGR coolers designs for different conditions of the exhaust gases. As for the design, the technology selected has been tube-and-fin heat exchanger, which is a high performance technology that fits Euro 6 customer specifications. The variations in design have been made through modifications in fin characteristics, both in configuration and geometric dimensions.

This work presents a study to characterize and quantify the mechanical losses in small automotive turbocharging systems. An experimental methodology to obtain the losses in the power transmission between the turbine and the compressor is presented. The experimental methodology is used during a measurement campaign of three different automotive turbochargers for petrol and diesel engines with displacements ranging from 1.2 l to 2.0 l and the results are presented. With this experimental data, a fast computational model is fitted and used to predict the behaviour of mechanical losses during stationary and pulsating flow conditions, showing good agreement with the experimental results. During pulsating flow conditions, the delay between compressor and turbine makes the mechanical efficiency fluctuate. These fluctuations are shown to be critical in order to predict the turbocharger behaviour.

The influence of turbine inlet gas temperature on turbocharger performance is a topic discussed recently by many authors. Some studies present results on adiabatic operation by insulating the turbocharger from ambient conditions and report significant differences in compressor isentropic efficiency. Other authors perform non-adiabatic tests and report a significant influence on compressor isentropic efficiency only at the lowest turbocharger speed. In present work two different levels of gas temperature at the inlet of a Variable Geometry Turbine (VGT) have been tested at two different vane positions and two different corrected turbine speeds. Temperatures have been measured in the outer cases of turbine and compressor in order to determine the radiated power and their relative importance with respect to different power definitions obtained from turbocharger operative variables. The obtained results show the influence on both compressor and turbine isentropic efficiency.

Surge phenomenon is becoming a limitation of the low end torque for downsized turbocharged Diesel engines. The stable operation of centrifugal compressors is limited at low flow rates because of the occurrence of surge. In the present work a CFD analysis of the flow inside automotive centrifugal compressors near the surge line is carried out. For this purpose, the actual geometry of a compressor -including its inducer, rotor, diffuser and volute- has been modelled with a CFD code. Initially, steady calculations have been performed to have a first approximation of the flow characteristics inside the compressor. In these calculations, a source term is imposed in the momentum equations to simulate the movement of the rotor and its effects on the air when it passes through it.

The paper analyses a procedure, based on thermodynamics concepts, to calculate the isentropic outlet temperature taking into account the changes in specific heat during the thermodynamic process; the results obtained were compared whit those given by the traditional methods. Besides, using data from tests, performed in a specific turbochargers test bench, the differences in isentropic efficiency have been evaluated and compared too. Moreover, another factor related with the influence of the gas specific heat on turbocharger performance is the effect that the humidity contents on gas has on the efficiency calculations. Normally, ambient conditions are taken into account just to obtain the corrected values of the main variables in compressor calculations, however the humidity ratio is not included and its effect is neglected. This study presents also a theoretical- experimental analysis about the effect of taking into account this factor.

The growing concerns about emissions in internal combustion engines, makes necessary a good prediction of the after-treatment inlet temperature in fast one-dimensional engine simulation codes. Different simple models have been developed during the last years which improve the prediction of the turbocharger heat transfer phenomena. Although these models produce good results when computing the turbine outlet temperature, those models focus on the axial heat transfer paths and lack the capability of producing detailed results about the internal thermal behavior of the turbocharger. In this work, a new version of heat transfer model for automotive turbochargers is presented. This model discretizes the turbocharger in both the radial and axial directions, and computes the heat transfer and temperature at different parts of the machine. Aiming for a low computational cost, it was designed to be compatible with fast one-dimensional engine simulations as a replacement of previous models [1].

0D-1D codes allow researchers to obtain a prediction of the behavior of internal combustion engines with little computational effort. One of the submodels of such codes is devoted to the centrifugal compressor. This model is often based on the compressor performance maps, therefore requiring the extrapolation of the maps so that all possible operating conditions are covered. Particularly, a suitable extrapolation of isentropic efficiency map is sought. This work first examines different available methods for compressor efficiency extrapolation into off-design conditions. No method is found to provide satisfactory results at all extrapolated regions: low and high compressor speeds and low compression ratio at measured speeds. Hence, a new method is proposed and its accuracy is assessed with the aid of compressor off-design measurements.

Surge occurrence in automotive engine turbochargers is known to be dependent on the installation conditions. It is proven that the flow pattern produced by the inlet ducting at the compressor inducer modifies surge margin. But also the engine intake line acoustics, both compressor upstream and downstream, affects turbocharger surge. In the paper the effect of different parameters in the intake line geometry on compressor surge is investigated. Modifications in the air filter volume, compressor inlet geometry and compressor outlet length have been considered. Surge limit obtained on a steady gas-stand is compared to those measured on the engine test bench using two different methodologies. Testing results show significant differences in term of surge line shift and the corresponding engine low end torque. A 1D model of the engine has been built using a non-steady compressor model able to predict surge occurrence.