Turbocharger Heat Transfer Research Articles

An analytical user-friendly methodology to transform compressor and turbine supplier characterization maps dedicated to 1D engine simulation: Modelling of turbocharger heat transfer and friction losses

Available turbocharger characterization maps are usually obtained on a gas stand where the turbine intake temperature is high, resulting in heat transfer affecting both the compressor and turbine. A correction is then mandatory to take into account heat transfer and calculate the real amount of work produced or consumed.An experimental campaign is conducted to characterize heat transfer and friction losses on two different turbochargers. Then, semi-empirical correlations are developed minimizing the sum of square errors of a multiple regression to modelize these two phenomena. Compared to existing methodologies, these correlations minimize the requested input data: only the supplier maps are required whereas no additional test or calibration is needed.The methodology to transform efficiencies and model heat transfer is presented. A gain of 10 % is observed on the confidence interval +/−3 °C on the compressor outlet temperature calculation (passing from 42.2 to 53 %), beside the turbine outlet temperature +/−10 °C interval is improved by around 20 %. These improvements are observed on two engine 1D models using two different turbochargers. The second engine's turbocharger is not involved in the establishment of the correlations and then demonstrates the good predictability of the proposed methodology.

Water cooled turbocharger heat transfer model initialization: Turbine and compressor quasi-adiabatic maps generation

Water cooled turbochargers used in gasoline engines present a difficulty in studies due to heat transfers in both the turbine and the compressor. Data available for users is usually measured in stable operating conditions with high temperature gradients on the turbine side which affects the compressor and the whole turbocharger. The heat transfers between the different elements are not quantified. Heat transfer models are necessary to quantify the amount of heat exchanged with an element and calculate then the real amount of work produced or consumed. A lumped mass heat transfer model is presented in this paper where every element of the turbocharger is considered as a thermal mass. Three main elements are represented: the turbine, the compressor and the central housing. The heat transfer model is then used to generate compressor and turbine quasi-adiabatic maps using supplier maps and geometrical data without more complicated tests. An experimental campaign is conducted to validate the model and show the effect of the water cooling on the thermal transfer between the turbocharger elements. In this model, the compressor and the turbine are treated separately and the water cooling is considered as a thermal barrier between the two. No coupling between the compressor and the turbine heat transfer models is needed which simplifies the calculation compared to other models.

A holistic consideration of turbocharger heat transfer analysis and advanced turbocharging modeling methodology in a 1D engine process simulation context

The focus on transient engine operation will increase to fulfill future emission requirements in the commercial vehicle sector. Accordingly, the transient turbocharger matching process is becoming increasingly important. The one-dimensional fluid dynamics (1D-CFD) simulation is established as an important development tool for matching the exhaust gas turbocharger to a combustion engine. The optimization of the modeling methodology of the combustion process and the turbocharger modeling are two key parameters to improve the reliability of the dynamic engine process simulation. In this paper, the advanced turbocharger (TC) methodology is described. This includes the determination of the adiabatic turbocharger performance from conventional hot gas test stand (HGS) measurement data, the derivation of an one-dimensional (1D) turbocharger heat transfer model and a method to physically extend the turbine map range. The adiabatic efficiencies of the turbocharger are determined with a model-based heat transfer correction of the conventional measured efficiencies from HGS measurement data. These adiabatic efficiency maps were used as a baseline to extend the conventional TC model with a heat transfer model taking into account of the engine boundary conditions in terms of temperature, pressure and mass flow rate. To assess the temperature distribution and the thermal inertia of the TC main components, in both stationary and transient engine operations, the variable geometry turbine (VGT) turbocharger hardware, installed on a medium-duty diesel engine, was equipped with several thermocouples on all accessible surfaces to make comprehensive surface temperature surveys. A 1D lumped capacitance heat transfer model (HTM) of the VGT TC was developed and validated against the experimental data from the engine test bench. To complete the advanced TC modeling, the turbine map is extended using experimental measurement data, based on extended HGS measurements, in combination with mathematically supported extrapolation. The results from the advanced turbocharger simulation methodology significantly improves the prediction of the temperature drop over the turbine in comparison to the conventional adiabatic TC simulation methodology. The validated heat transfer model also allows the analysis of the heat flow breakdown of the turbocharger. Based on the advanced turbocharger model, a tool for the improved transient turbocharger-engine matching process is given.

Turbocharger Heat Transfer Determination With a Power-Based Phenomenological Approach and a Conjugate Heat Transfer Validation

This investigation represents work on a model to determine heat flows on turbochargers. Recently, a power-based method has been developed to compare adiabatic and hot gas tests from radial turbines and compressors. Moreover, this method has shown the ability to correct standard measurements in terms of heat flows. In this investigation, a wastegate turbocharger has been investigated from a small gasoline engine. For validation purposes of the isentropic efficiencies, a conjugate-heat-transfer (CHT) simulation has been carried out on the turbine. Results have shown that isentropic efficiencies fit well for values of turbine inlet temperatures of 600 °C between corrected data and the simulation. For other temperatures, the differences between the determined values and CHT are greater. The differences rise with higher temperatures generally. So, the objective of the investigation is to improve the existing method for determining turbocharger heat transfers. Hence, an additional dependency of turbine inlet temperatures has been implemented in the approach and tested for T3 = 400 °C, 600 °C, 800 °C, and 950 °C. The modification has shown better results and smaller differences to CHT simulation. Especially, at low speeds where the former approach has had big differences, the modification improves the distribution for the investigated turbine inlet temperatures.

Applying neural networks (NN) to the improvement of gasoline turbocharger heat transfer modeling

Precise prediction of turbine outlet temperature is important for the design of after-treatment systems, two-stage turbochargers and exhaust energy recovery. An accurate turbocharger model is necessary for the prediction of turbine outlet temperature. Turbine and compressor models are important for the behavior of both engine and turbocharger predicting. An predicted of turbine outlet temperature using a related model is significantly different from the actual turbine outlet temperature due to the neglect of turbocharger heat transfer [1]. In this study, we developed an improved method for correcting a turbocharger simulation model by considering turbocharger heat transfer. The differences between the predicted and actual turbine outlet temperatures depend on three parameters: turbocharger speed, turbine expansion ratio, and the turbine inlet temperature. A neural network was used to correct turbocharger heat transfer based on these three parameters, and then it coupled with a one-dimensional (1D) turbocharger model in the GT-Power software. Further, this method was validated by performing additional experiments. The predictions of turbine outlet temperature were improved, the errors are less than 15 K when the turbocharger detailed geometry model and heat transfer coefficients is not clear, and the NN method is more easier than the traditional 1D turbocharger heat transfer model.

Turbocharger heat transfer and mechanical losses influence in predicting engines performance by using one-dimensional simulation codes

The exhaust energy can represent up to 40% of the fuel chemical energy in turbocharged internal combustion engines. In order to calculate properly the available energy of the exhaust gases, a critical parameter is the temperature downstream the turbine. The prediction of this temperature will also benefit the two-stage turbochargers and after-treatment modelling that affects brake specific fuel consumption, exhaust gases emissions and the scavenging process.In this paper, turbocharger heat transfer losses have been modelled using a lumped capacitance model coupled with one-dimensional whole-engine simulation software. The data from the simulations of a turbocharged Diesel engine, with and without the turbocharger heat transfer model, have been compared with experimental measurements performed in an engine test bench. The analysis is focused on studying the influence in turbocharger outlet temperatures and predicting the engine performance. The main result of the study is the improvement in the prediction of both compressor and turbine outlet temperatures (up to an improvement of 70 K). The results from the model allow analysing how heat transfer losses are split in the turbocharger and quantifying the importance of heat transfer phenomena in turbocharger efficiency, at full load conditions and as a function of engine speed.

Analysis and Methodology to Characterize Heat Transfer Phenomena in Automotive Turbochargers

In the present work a comprehensive study of turbocharger heat transfer phenomena is discussed, showing their relevance compared to gas enthalpy variations through the turbomachinery. The study provides an experimental methodology to consider the different heat fluxes in the turbocharger and modeling them by means of a lumped capacitance heat transfer model (HTM). The input data required for the model are obtained experimentally by a proper combination of both steady and transient tests. These tests are performed in different test benches, in which incompressible fluids (oil) and compressible fluids (gas) are used in a given sequence. The experimental data allows developing heat transfer correlations for the different turbocharger elements. These correlations take into account all the possible heat fluxes, discriminating between internal and external heat transfer. In order to analyze the relative importance of heat transfer phenomena in the predictability of the turbocharger performance and the different related variables; model results, in hot and cold conditions, have been compared with those provided by the standard technique, consisting on using look up maps (LUM) of the turbocharger. The analysis of these results evidences the highly diabatic operative areas of the turbocharger and it provides clearly ground rules for using hot or cold turbocharger maps. In addition, paper discussion advises about using or not aHTM, depending on the turbocharger variables and the operative conditions that one desires to predict. Paper concludes that an accurate prediction of gas temperatures at turbine and compressor outlet and of fluid temperatures at water and oil ports outlet is not always possible without considering heat transfer phenomena in the turbocharger.

Turbocharger Heat Transfer Modeling Under Steady and Transient Conditions

In the field of automotive propulsion, environmental issues (need for drastic reduction of greenhouse gases) and diminishing fossil fuels supplies enhance the need to reduce fuel consumption. To reach this goal, a possible solution is downsizing. Unfortunately, the degradation of the transient performance of the engine limits the expected benefits of downsizing. Engine manufacturers try to improve turbocharger matching using simulation. However, the literature and experiments on a turbocharger test bench show that, contrary to general opinions, heat transfer can influence the turbocharger performance. Thus it seems essential to determine and correlate the different types of heat transfer phenomena occurring in a turbocharger. First a complete experimental characterization of turbocharger heat transfer is performed in steady and transient conditions. The experimental results are used to correlate turbocharger heat transfer coefficients. Then, the equivalent heat transfer resistance method is explained. The correlations obtained are then used in this method to calculate all heat transfer interactions within the turbocharger and transferred to the surroundings in steady and transient conditions. In each case, comparisons between numerical and experimental results are performed to verify the quality of the method proposed.