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Technical Paper

Experimental Characterization for Modelling of Turbocharger Friction Losses

Abstract Today turbochargers are used by car manufacturers on Diesel engines and on an increasing number of gasoline engines, especially in the scope of downsizing. This component has to be well understood and modeled as simulation is widely used at every step of the development. Indeed development cost and time have to be reduced to fulfill both customers’ wishes and more stringent emissions standards. Current turbocharger simulation codes are mostly based on look-up tables (air mass flow and efficiency) given by manufacturers. This raises two points. Firstly, the characteristics are known only in the same conditions as manufacturers’ tests. Secondly, the turbine efficiency given by turbochargers manufacturers is the product of the isentropic efficiency and the turbocharger mechanical efficiency. This global efficiency is suitable for the calculation of the power transferred to the compressor.
Technical Paper

Experimental Investigation of an In-Cylinder Sampling Technique for the Evaluation of the Residual Gas Fraction

Abstract Residual gas plays a crucial role in the combustion process of SI engines. It acts as a diluent and has a huge impact on pollutant emissions (NOx and CO emissions), engine efficiency and tendency to knock. Therefore, characterizing the residual gas fraction is an essential task for engine modelling and calibration purposes. Thus, an in-cylinder sampling technique has been developed on a spark ignition VVT engine to measure residual gas fraction. Two gas sampling valves were flush mounted to the combustion chamber walls; they are located between the 2 intake valves and between intake and exhaust valves respectively. In-cylinder gas was sampled during the compression stroke and stored in a sampling bag using a vacuum pump. The process was repeated during a large number of engine cycles in order to get a sufficient volume of gas which was then characterized with a standard gas analyzer.
Technical Paper

Experimental Study of Centrifugal Compressor Speed Lines Extrapolation for Automotive Turbochargers

Abstract Downsizing has nowadays become the more widespread solution to achieve the quest for reaching the fuel consumption incentive. This size reduction goes with turbocharging in order to keep the engine power constant. To reduce the development costs and to meet the ever tightening regulations, car manufacturers rely more and more on computer simulations. Thus developing accurate and predictable turbocharger models functioning on a wide range of engine life cases became a major requirement in industrial projects. In the current models, compressors and turbines are represented by look-up tables, experimentally measured on a turbocharger test bench, at steady point and high inlet turbine temperature. This method results in limited maps : on the one hand the compressor surge line and on the other hand the flow resistance curve behind the compressor. Mounted on an engine, the turbocharger encounters a wider scale of functioning points.
Technical Paper

Experimental Study of Automotive Turbocharger Turbine Performance Maps Extrapolation

Abstract Engine downsizing is potentially one of the most effective strategies being explored to improve fuel economy. A main problem of downsizing using a turbocharger is the small range of stable functioning of the turbocharger centrifugal compressor at high boost pressures, and hence the measurement of the performance maps of both compressor and turbine. Automotive manufacturers use mainly numerical simulations for internal combustion engines simulations, hence the need of an accurate extrapolation model to get a complete turbine performance map. These complete maps are then used for internal combustion engines calibration. Automotive manufacturers use commercial softwares to extrapolate the turbine narrow performance maps, both mass flow characteristics and the efficiency curve.
Technical Paper

Calibration Methodology in System Simulation to Predict Heat Transfer Along the Exhaust Line of a Diesel Engine

Abstract Emission regulations have become increasingly stringent in recent years. Current regulations need the development of a new worldwide driving cycle which gives greater weight to the pollutants emitted during transient phases or cold starts. Powertrains contain a large number of components such as multistage turbocharger systems; exhaust gas recirculation, after-treatment devices and sometimes an electric motor. In this context, 0D predictive models of heat transfer in the exhaust line, calibrated with experimental data, are particularly interesting. Many investigations are related to the development of precise control laws in order to optimize the light-off of after-treatment elements during the engine starting phase. A better understanding of the thermal phenomena occurring in the exhaust line is necessary. To study the heat transfer in the exhaust line of a Diesel engine during transient conditions, the temperature in the exhaust line must be known precisely.
Technical Paper

Intra-Pipe Restriction Non-Homentropic Boundary Resolution Method

A complete non-homentropic boundary resolution method for a flow upstream and downstream an intra-pipe restriction is considered in this article. The method is capable of introducing more predictable quasi-steady restriction models into the boundary problem resolution without adding artificial discharge coefficients. The traditional hypothesis of isentropic contraction, typically considered for the boundary resolution, is replaced by an entropy corrected method of characteristics (MOC) in order to be consistent with a non-homentropic formulation. The boundary resolution method is designed independently of the quasi-steady restriction models which allows obtaining a greater modeling flexibility when compared with traditional methods. An experimental validation at unsteady conditions is presented using different restriction quasi-steady models to illustrate the effectiveness of the proposed boundary resolution method in terms of predictability as well as flexibility.
Technical Paper

Optimized Air Intake for a Turbocharged Engine Taking into Account Water-Cooled Charge Air Cooler Reflective Properties for Acoustic Tuning

Unsteady intake wave dynamics have a first order influence on an engine's performance and fuel economy. There is an abundant literature particularly for naturally aspirated SI engines on the subject of intake manifolds and primary runner lengths aimed to achieve a tuned intake air line. A more demanding design for today's engines is to increase efficiency to meet the requirements of lower fuel consumption and CO2 emissions. Today's tendencies are downsizing the engine to meet these demands. And for drivability purposes, the engine is combined with a turbocharger coupled with a charge air cooler. However, when the engine's displacement is reduced, it will be very dependent on its boosting system. A particularly interesting point to address corresponds to the engine's operation in the low speed range and during transients where the engine has large pumping losses and poor boost pressure. This operation point can be optimized using acoustic supercharging techniques.
Technical Paper

Study of Parallel Turbocompounding for Small Displacement Engines

In order to reduce greenhouse gases and respect stringent pollutant emission regulations, the modern engine is increasingly required to incorporate energy recovery systems to enhance performance and increase efficiency. This paper deals with the exhaust energy recovery through turbocompounding. Both series and parallel turbocompounds are discussed. In the first part of the document, literature on turbocompounding is introduced. Then a simulation study carried on AMESim software, using a 2L Diesel engine model is presented. The parallel turbocompounding is simulated by expanding a part of the exhaust gases in a converging nozzle instead of the turbocharger turbine. The power produced is evaluated as a function of the pressure drop in case a turbine is mounted instead of the nozzle. A global study over the entire engine map is described, and two steady state points 2000 rpm, 8 bar and 3500 rpm, 7 bar are chosen.
Technical Paper

Potential of Exhaust Heat Recovery by Turbocompounding

Energy recovery of internal combustion engines has proved to be of primary interest to increase engine global efficiency. The motivation behind is to meet future fuel economy requirements and more stringent emissions regulations. Among all engine waste, research has shown that exhaust energy is the most promising solution due to its high availability. In this context, this paper deals with the analysis of the potential of exhaust heat recovery, especially by a turbocompound system. Turbo-compounding is already established in heavy-duty engines, in which an additional stage of expansion is made through an exhaust recovery turbine. This technique is now being studied for small displacement engines. In the first part of this document, a short history on turbocompounding is presented. Then we present a simulation study conducted on AMESim software, using a 0D 2L diesel engine model, calibrated to fit real engine test bench results.
Technical Paper

Transfer Matrix Computation for Intake Elements with Large Pressure Fluctuations under Mean Flow Conditions

A new methodology for modeling engine intake has been presented; it is based on a transfer function relating pressure response and mass flow rate that makes use of the corresponding frequency spectrum obtained on the so-called “dynamic flow bench”. This new approach provides a way to obtain fast and robust results, which take into account all the phenomena inherent to compressible unsteady flows. Recently the potential of this method has been explored by incorporating it in a GT-Power model to produce a coupled frequency - time domain simulation of a naturally aspirated engine. The method exhibited promising results. One strategy utilized to combat the increasingly stringent emissions standards and reduce fuel consumption is to employ downsized turbocharged engines equipped with charge air coolers (CAC). Therefore, research and development must focus not only on naturally aspirated engines but also on turbocharged ones.
Technical Paper

An Experimental Evaluation of 1-D Valve Models under Dynamic Conditions

The influence of unsteady flow in engine pipes system is a first order parameter to take into account when designing an engine. Wave motions being relatively well described by a 1-D model, these types of algorithm are very common. Logically, the boundary conditions have to use the same formulation. The importance of valve models is thus demonstrated. The aim of this paper consists of a comparison between two valve models. In order to obtain the discharge coefficient, algorithms have been coded and tested in a stationary test bench. Different computation methods of coefficient have been used. Then, a dynamic test has been performed to determine which valve model coupled with a test analysis method gives the best result. This work shows that each tested models give good results. As a consequence this kind of experimental setup can be used in order to study the fluid behavior under dynamic excitation and to study the temperature effect on the models.
Technical Paper

Variable Inlet Guide Vanes in a Turbocharger Centrifugal Compressor: Local and Global Study

Engine downsizing is potentially one of the most effective strategies being explored to improve fuel economy. A main problem of downsizing using a turbocharger is the small range of stable functioning of the turbocharger centrifugal compressor at high boost pressures. Several stabilization techniques were studied to increase the compressor operating range without sacrificing the compressor efficiency. The paper presents an experimental study of one of these techniques, the axial variable inlet guide vanes (VIGV). Test rigs were put up to conduct two different experiments. The first was to study the effect of pre- rotation generated by VIGVs on the overall compressor performance and the second to determine the pressure loss through the VIGVs and to analyze the flow downstream the VIGV system using LDA (laser Doppler Anemometry) measurement.
Technical Paper

Heat Transfer Analysis in a Turbocharger Compressor: Modeling and Experiments

Usually, the simulation of a turbocharger included in a diesel engine model relies typically on the assumption of adiabaticity for the compressor. However experiments on a turbocharger test bench show that the heat transfers from the turbine to the compressor have a major influence on the compressor performances. So the manufacturers maps must be modified or used with a new method taking into account heat transfers. The methods proposed are a simple way to take into account heat transfers when the performance maps are used. They give results in relative good agreement with experimental measures in comparison to their easiness of use.
Technical Paper

Comparison of Different Methods for the Determination of Pressure Wave in the Inlet and Exhaust Systems of Internal Combustion Engine

Unsteady flow in the inlet and exhaust systems of Internal Combustion Engines can be simulated with multi-dimensional simulation codes. Due to their computational time, other methods are widely used and give the opportunity of coupling it with a model of the complete engine. This paper reports on an investigation undertaken to compare the accuracy of the method of inertia, the acoustic method and the one-dimensional method for modeling the gas flow in pipe systems. Results of this study give the advantage and disadvantage of each approach. The comparison shows good agreement between one-dimensional and experimental results while the calculation time is kept acceptable.