Turbocharger Applications Research Articles

Application of the passive turbocharger to PRHRS in integral PWR type SMR with an sCO2 power cycle

One of the potential design concepts for small modular reactor(SMR) is coupling an integral pressurized water reactor(IPWR) with a supercritical CO2(sCO2) power cycle to reduce the plant footprint. However, the passive safety systems of this SMR concept have not been well established compared to steam power cycle based SMRs. In this study, a passive turbocharger utilizing the unique characteristics of sCO2 is proposed as a way to improve the passive safety of sCO2 power cycle. This is the concept of installing a turbine-compressor set at the connection of passive residual heat removal system(PRHRS) to effectively remove the high level of residual heat in the early stages of an accident rather than relying only on natural circulation cooling. Based on the findings, it can be concluded that proposed sCO2 turbocharger concept has the potential to enhance performance of PRHRS and reduce the height of natural circulation loop leading to smaller volume.

Multi-Objective Numerical Optimization of Radial Turbines

Abstract The growing demand of high flexibility and wide operating ranges of radial turbines in turbocharger applications necessitates new methods in the turbomachinery design process. Often, design criteria such as high performance at certain operating conditions or low inertia contradict the requirement for high durability. This article demonstrates a newly developed optimization approach for radial turbines that allows to optimize for several design objectives. The presented approach is based on a parametric model of the turbine wheel geometry. On the one hand, the model is designed to capture the most important geometry and design features, and on the other hand, it is flexible for use on various machines. A surrogate model-based genetic algorithm is used to optimize the geometries with respect to several objectives, including efficiency, durability (HCF), low-cycle fatigue (LCF), inertia, and mass. Certain operating points or criteria can be particularly emphasized and specified constraints throughout the process allow for customized optimization. The simulations underlying the optimization are state-of-the-art computational fluid dynamics (CFD) and finite element (FE) analyses, involving the respective components. The newly developed and fully automated approach includes tasks of different disciplines. In the end, a selection of several promising geometries is examined more intimately to finally find a most suitable geometry for the given application. For the current study, this geometry has been manufactured and tested on a hot gas test facility to successfully validate the design process.

Determination of Mechanical Properties for Laser Welded Turbine Rotor Assemblies for Automotive Turbocharger Applications

To meet the demands of higher speeds, higher power density and the ability to adapt to harsh operating environments over a long period of time, structural designers use various materials to fabricate rotor parts for turbine assemblies. This introduces high requirements for stable rotation and rotor life. It is therefore important to analyse and determine the mechanical properties for a turbine rotor taking into account the manufacturing process. This paper focuses on laboratory mechanical testing for determination and analysis of turbine components consisting of a rotor, from 42CrMo4 (DIN EN 10083-3) and a turbine, made from Inconel 713C in laser welded assembly. The tests carried out consists of tensile testing for the turbine – rotor assembly, microhardness measurements, macro and microscopic examinations of the welded joint. The obtained results stand as a validation for the welding process technology used for this type of application ensuring the superior mechanical characteristics required for operation in harsh enviornments.

Three dimensional unsteady analysis of a miniaturized pressure probe for turbocharger applications

Downsizing and turbocharging are nowadays widely spread techniques in automotive small-size internal combustion engines aimed at reducing the specific fuel consumption without affecting the power output. Due to the device small dimensions and to the high temperature of the exhaust-gases feeding the turbine, a relevant amount of heat is customarily exchanged between the turbine and the compressor so that a classical adiabatic approach could lead to an inaccurate estimation of the performance. This paper preliminary investigates the feasibility of an experimental procedure aimed at computing the exchanged work as variation of the angular momentum via a three-hole probe located at the impeller outlet. Because of the very reduced machine dimensions, torque measurements could be difficult, as the intrusive nature of the measurement could significantly affect the accuracy of the collected data. For this reason, the influence of the probe finite-size onto the flow field is numerically analysed solving the Unsteady Reynolds-Averaged Navier Stokes equations with and without the probe installed at the diffuser inlet. The equations are closed via the k − ω SST turbulence model, while a density-based commercial CFD package is used to integrate the governing equation. Finally, the pressure distribution in the azimuthal direction is analysed to assess the probe intrusive effects which, in the proposed case, result in a 0.47% (resp. 0.69%) difference in the specific work when a miniaturized probe with a diameter of 1mm (resp. 1.5 mm) is employed.

Assessment of the unsteady performance of a turbocharger radial turbine under pulsating flow conditions: Parametric study and modeling

A characteristic of radial turbines for turbocharger applications subject to pulsating flow is the deviation of the turbine performance compared with corresponding continuous flow conditions, typically associated with gas-stand experiments. The performance deviations under pulsating flow generate a hysteresis loop that encloses the performance line obtained in gas-stand conditions and their intensity is demonstrated to grow with increasing pulse amplitude and frequency. Predicting the performance deviations is of great interest to improve the predictive capabilities of reduced-order models and enhance engine-turbocharger matching. In this work, the performance response of a turbocharger radial turbine is studied with respect to variations of the normalized pulse amplitude (between 0.4 and 1.6 ) and the pulse frequency (between 20 Hz and 100 Hz ). Results show that the hysteresis loop expands with increasing pulse amplitude and frequency, so that the turbine cannot be treated as a quasi-steady device. The characteristic trends of the turbine performance are also highlighted with respect to pulse amplitude and frequency variations. The expansion ratio is registered to improve by + 4.0 % with increasing pulse amplitude and decrease by - 1.3 % with increasing pulse frequency. An opposite trend is otherwise registered for the isentropic efficiency, which decreases by - 6.5 % for increasing pulse amplitude and increases by + 6.5 % for increasing pulse frequency. Finally, through a simple model, the deviations of the turbine performance from quasi-steady to pulsating flow conditions are demonstrated to depend on the time derivative of the pressure pulse and the residence time of the fluid particle rather than pulse amplitude and frequency.

TURBODYNA: A Generic One-Dimensional Dynamic Simulator for Radial Turbomachinery

AbstractThe turbocharged piston-driven engines are widely used in high altitude long endurance unmanned aerial vehicles (HALE UAVs). Repeated actions of engine pistons and valves give rise to engine pulsations resulting in intensive unsteady flows in the turbocharger. One-dimensional (1-D) modeling, which is computationally effective, plays a crucial role in evaluating turbocharger performance and conducting turbocharger-engine matching under pulsating conditions. The present work introduces a newly developed 1-D software (TURBODYNA) for the sake of improving traditional 1-D modeling's accuracy and generality. The advantages and capabilities of TURBODYNA are illustrated by applying it to three different and typical sorts of turbocharger applications: the single-entry turbine, the twin-entry turbine, and the centrifugal compressor. The unsteady testing conditions include high frequent pressure pulses for the single-entry turbine, out-of-phase pressure pulses for the twin-entry turbine, and rotating stall and surge for the centrifugal compressor. Results show that, by contrast to traditional 1-D modelings, the current 1-D modeling has achieved exceptional improvements in both accuracy and applicability. The novel and powerful tool provides a solid framework for assessing turbocharger unsteady performances and addressing turbocharger-engine matching.

Effect of housing size on the performance of a centrifugal compressor for turbocharger application: An experimental and numerical study

Currently, engine downsizing through turbocharging is widespread in the automotive industry to improve fuel economy and emissions. The engine downsizing demands compact and high performance centrifugal compressors for turbochargers. A compressor contains mainly an impeller and housing, which often uses a vaneless diffuser and an overhanging volute. High-speed flow from the impeller is decelerated in the diffuser and volute, to recover static pressure for boosting the engine. The volute flow characteristics and pressure recovery depend on the housing size, which determines the overall compressor performance and size. This study evaluates the effect of four different housing sizes viz., baseline, 12% scaled up, and 12% and 20% scaled-down geometrically, through experimental and numerical analysis. The experiments are conducted using different housing sizes with a given impeller to measure the compressor pressure ratio and efficiency. Also, steady-state numerical simulations are performed to examine the flow mechanisms causing pressure losses due to changes in housing size. Then, the simulation is also done for different volute surface roughness levels in each housing to establish its effect on compressor performance. From the results, it is found that there is no marked change in compressor efficiency between the baseline and 12% scaled-up housing. Whereas, the scaled-down housings (12% and 20%) showed efficiency drop of about 2–5 percentage points at near-choke flow rate. The CFD analyses of these scaled down housings with reduced cross-sectional area indicated substantial increase of meridional velocity, which results in higher swirl velocity in the volute causing more pressure losses. Besides, the increased volute surface roughness is realized to cause extra pressure loss due to higher wall shear stress. It amounts to additional efficiency reduction of 0.5–1 percentage points at the same near-choke flow.

Creep behavior of conventional and Nb-modified as-cast MAR-M246 superalloy

Abstract Considering the lower cost of Nb and its chemical similarity to Ta, this work investigated the effect of complete replacement of Ta by Nb (in at.% basis) in MAR-M246 Ni-based superalloy for the automotive turbocharger applications. Conventional and Nb-modified polycrystalline MAR-M246 superalloys were prepared through vacuum induction melting and investment casting from commercial raw-materials. Creep tests were performed on the as-cast alloys in air, at 800 °C (475/500/550 MPa), 900 °C (300/350/400 MPa) and 1000 °C (150/200/225 MPa). Additional creep tests were carried out at 900 °C/350 MPa under high vacuum conditions to verify effects of oxidation on the creep behavior of the alloys. Both alloys presented similar creep behavior at 800 °C. At 900 °C and 1000 °C, the conventional alloy has shown better properties associated with less creep damages in the bulk and near the surface regions. Both alloys have a better creep life in high vacuum which revealed an important role of oxidation on the creep damage mechanisms of these alloys. The lower creep properties of Nb-modified alloy at T > 800 °C should be primarily associated with higher internal diffusivity in this alloy compared to the conventional one, leading to faster oxidation and microstructure degradation during the high temperature creep.

Performance and Losses Analysis for Radial Turbine Featuring a Multi-Channel Casing Design

Abstract A novel control technique for radial turbines is under investigation for providing turbine performance controllability, especially in turbocharger applications. This technique is based on replacing the traditional spiral casing with a multi-channel casing (MC). The MC divides the turbine rotor inlet circumferentially into a certain number of channels. Opening and closing these channels controls the inlet area and, consequently, the turbine performance. The MC can be distinguished from other available control techniques in that it contains no movable parts or complicated control mechanisms. Within the casing, this difference makes it practical for a broader range of applications. In this investigation, a turbocharger featuring a turbine with MC has been tested on a hot gas test stand. The experimental test results show a reduction in the turbine operating efficiency when switching from full to partial admission. This reduction increases when reducing the admission percentage. To ensure the best performance of the turbine featuring MC while operating at different admission configurations, it becomes crucial to investigate its internal flow field at both full and partial admission to understand the reasons for this performance reduction. A full 3D computational fluid dynamics (CFD) model of the turbine was created for this investigation. It focuses on identifying the loss mechanisms associated with partial admission. Steady and unsteady simulations were performed and validated with available test data. The simulation results show that operating the turbine at partial admission results in highly disturbed flow. It also detects the places where aerodynamic losses occur and which are responsible for this performance reduction. This operation also shows flow unsteadiness even when operating at steady conditions. This unsteadiness depends mainly on the admission configuration and percentage.

Radial Turbine Thermo-Mechanical Stress Optimization by Multidisciplinary Discrete Adjoint Method

This paper addresses the problem of the design optimization of turbomachinery components under thermo-mechanical constraints, with focus on a radial turbine impeller for turbocharger applications. Typically, turbine components operate at high temperatures and are exposed to important thermal gradients, leading to thermal stresses. Dealing with such structural requirements necessitates the optimization algorithms to operate a coupling between fluid and structural solvers that is computationally intensive. To reduce the cost during the optimization, a novel multiphysics gradient-based approach is developed in this work, integrating a Conjugate Heat Transfer procedure by means of a partitioned coupling technique. The discrete adjoint framework allows for the efficient computation of the gradients of the thermo-mechanical constraint with respect to a large number of design variables. The contribution of the thermal strains to the sensitivities of the cost function extends the multidisciplinary outlook of the optimization and the accuracy of its predictions, with the aim of reducing the empirical safety factors applied to the design process. Finally, a turbine impeller is analyzed in a demanding operative condition and the gradient information results in a perturbation of the grid coordinates, reducing the stresses at the rotor back-plate, as a demonstration of the suitability of the presented method.

Design and Performance Analysis of Mixed Flow Turbine Rotors With Extended Blade Chord

Abstract Mixed flow turbines offer additional design freedom compared with conventional radial turbines. This is useful in the automotive turbocharger application to reduce rotor inertia, which can be very beneficial for the transient response of a highly boosted downsized passenger car powertrain. A previously published study from the authors analyzed a series of nine mixed flow turbine rotors with varying blade cone angle and inlet blade angle. This paper reports an extension of that study with two further mixed flow turbine rotors where the chord length of the rotor blade was extended. The aim of this work was to understand both the aerodynamic and mechanical impacts of varying the chord length, particularly for the turbocharger application where off-design performance and transient response are very important. The baseline mixed flow rotor for this study had a blade cone angle of 30 deg and an inlet blade angle of 30 deg. Two further variations were produced; one with the trailing edge (TE) extended in the downstream direction across the entire blade span. In the second variation, the chord was extended at the hub corner only, while the shroud corner of the TE remained unchanged, with the aim of achieving some aerodynamic improvement while meeting mechanical requirements. When the blade was extended at both the hub and shroud, the inertia and stress levels increased significantly and the blade eigenfrequencies reduced. There was a significant improvement in peak efficiency, but the mechanical performance was unfavourable. The improvement in peak efficiency was mainly due to better exhaust diffuser performance and, therefore, would not be realized in most turbocharger installations. The blade that was extended at only the hub corner incurred very little additional inertia, and the centrifugal stresses and blade eigenfrequencies were improved. Consequently, it was possible to reduce the blade thickness at the TE in order to achieve a more aerodynamically optimized design. In this case, the mechanical performance was acceptable and there were efficiency improvements of up to 1.1% points at off-design conditions, with no reduction in peak efficiency or maximum mass flowrate. Therefore, the blade that was extended only at the hub produced some improvement within acceptable mechanical limits. The flow field features were considered for the three rotor geometries to explain the changes in loss and efficiency across the operating range.

Application of variable geometry turbine turbochargers to gasoline engines- A review

An ideal engine today is considered to be one with low emission, low fuel consumption and high specific power output. Engine downsizing by turbocharging provides an answer toall the three. Though the traditional problems of poor low end torque and inadequate transient response have been overcome to a great extent using variable geometry turbine turbocharger in diesel engine, the application of variable geometry turbine turbocharger is in quite a nascent stage when it comes to gasoline engine. This article primarily describes all the important aspects of application of VGTs to gasoline engines right from when VGT’s were restricted to only very expensive research prototypes to the very recent application in cost sensitive production engines. Also at the same time,it highlights the need and development in the flow range of the turbocharger compressor, addressing problems of choke and surge in the turbo chargers compressor.

Study of microstructure and mechanical properties of γ-Ti-46.5Al-2Cr-(3.5 & 5.0) Nb alloys

γ-TiAl alloys are used in high temperature aero-engine as well as in turbocharger applications in high performance cars etc. These alloys have very good oxidation and creep resistance and favorable specific strength but have poor ductility. The wrought γ-TiAl alloys have been designed to increase the hot workability of these alloys. In the present study, the effect of Nb on the microstructure and mechanical properties of wrought compositions have been investigated. Two γ-TiAl alloys, Ti-46.5Al-2Cr-3.5Nb-0.3B (at.%) and Ti-46.5Al-2Cr-5.0Nb-0.3B (at.%) were studied. The microstructure after a standard heat treatment has been characterized and the phases present were identified through SEM and XRD. The three phases viz. α2, γ and β/B2 have different morphologies in these alloys. The compression properties at room temperature as well as high temperature (25 °C & 800 °C) and creep properties at 800 °C & 300 MPa of applied stress were evaluated. The increase in Nb content results in the increase in βphase fraction and the creep properties were found to improve, whereas not much significant change in the compression strength was observed.

Impact of Mixed Flow Turbines on the Efficiency of Automotive Turbocharger Applications

Impact of Mixed Flow Turbines on the Efficiency of Automotive Turbocharger Applications

Centrifugal Compressor Design for a Gasoline Engine Turbocharger

With increasing challenges in both fuel consumption and emission, the turbochargers have played a very important role for gasoline engines. Turbochargers can increase engine power density, reduce physical dimensions and reduce engine weight. Most of the turbochargers have a rotor system including a centrifugal compressor and a turbo turbine. Centrifugal compressors is a turbomachine which increases the gas pressure with the help of a turbine. Centrifugal compressors dominate the turbocharger applications. Centrifugal compressor performances are very critical for turbocharger performance. Gasoline engines need compressor not only to have high efficiency at whole operating range but also have a wide operating range. This paper discussed a centrifugal compressor design for gasoline engine turbocharger. The modern compressor design process developed recently was used for this new compressor design. The performance of the new design was compared with original compressor in CFD (Computational Fluid Dynamics) analysis, gas stand test and engine test. It demonstrated that the newly developed compressor has better performance and also meet the engine operating needs from both numerical analysis and test. The new centrifugal compressor development is successful.

The effect of three-lobed bearing shapes in floating-ring bearings on the nonlinear oscillations of high-speed rotors

Floating-ring bearings are widely used in automotive turbocharger machinery because of their robustness, low cost and their suitability under extreme rotation speeds. This type of bearings, however, can become a source of noise due to oil whirl/whip instability. The stabilizing effect of lobed bearing shape is known in the literature, which encourages the researchers to substitute plain cylindrical full floating bearings with lobed geometries in their outer and inner clearances to prevent the rotor-bearing system from developing oil whirl/whip instability or to reduce its amplitude of response when oil whirl/whip instability takes place. In this study, a novel concept of a floating-ring bearing with three-lobed clearances in its inner and outer films is modelled. In order to perform transient simulations, a very time-efficient approximate solution for the Reynolds equation to the geometry of three-lobed bearings is presented. Using the run-up simulation method, the nonlinear dynamic behaviours of a real turbocharger rotor supported by the novel concept of three-lobed floating-ring bearings are systematically investigated. The newly obtained results show that the sub-synchronous vibrations can be thoroughly suppressed with high preload factor at the cost of a moderate increase in the synchronous vibrations. Hence, the three-lobed floating-ring bearings design is an attractive alternative to plain cylindrical floating-ring bearings for automotive turbocharger applications.

Dynamic behaviors of a high-speed turbocharger rotor on elliptical floating-ring bearings

Floating-ring bearings are commonly used in automotive turbocharger applications due to their low cost and their suitability under extreme rotation speeds. This type of bearings, however, can become a source of noise due to oil whirl-induced sub-synchronous vibrations. The scope of this paper is to examine whether the concept of a floating-ring bearing with an elliptical clearance might be a solution to suppress sub-synchronous vibrations. A very time-efficient approximate solution for the Reynolds equation to the geometry of elliptical bearings is presented. The nonlinear dynamic behaviors of a turbocharger rotor supported by two concepts of elliptical floating-ring bearings are systematically investigated using run-up simulations. For the first concept of elliptical floating-ring bearings i.e. the outer bearing of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(b) in the article), some studies have pointed out that its steady-state and dynamic performances are superior to plain cylindrical floating-ring bearings but, the nonlinear run-up simulation results shown that this type of elliptical floating-ring bearings is not conducive to reduce the self-excited vibration levels. However, for the second type of elliptical floating-ring bearings i.e. both the inner and outer films of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(c) in the article), it is shown that the sub-synchronous vibrations have been considerably suppressed. Hence, the second noncircular floating-ring bearing design is an attractive measure to suppress self-excited vibrations.[Figure: see text]

Ultra-High Speed Switched Reluctance Motor-Generator for Turbocharger Applications

This paper proposes technical guidelines, modelling, and control of an ultra-high-speed-switched reluctance motor- generator for automotive turbo-charged assistance and energy recovery. Creation of an ideal model using electromagnetic finite element analysis and conducting a low cost/ low scale experiment is proposed. The first objective focuses on the transient simulation process. The second objective focuses on an investigation of the proposed control criteria. The modelling and analysis of a “Switched Reluctance Motor” (SRM) is an initial task for the selection of the coupled mover. Two controllers are selected for the experiment which consists of a generally low-cost solution and an optimized development board for prototyping optimization. The low-cost control solution is implemented with an Arduino Uno and an assortment of relays configured into an asymmetrical half bridge. The second controller is the “Digilent Zed Board Zynq-7000 ARM/FPGA SoC Development Board” (Zed board). ANSYS 2D, 3D modelling, data simulation for the stator and rotor are implemented. Current, voltage, and flux for all phases waveforms are included. Rotor dynamic simulation, machine transient simulations, and some other characteristics are depicted through 3D figures.

A Three-Zone Modeling Approach for Centrifugal Compressor Slip Factor Prediction

Accurate estimation of slip factor is of paramount importance to ensure centrifugal compressor work input is adequately predicted during the preliminary design process. However, variations in the flow field at impeller exit in both the pitchwise and spanwise directions complicate the evaluation procedure considerably. With the increasing implementation of engine downsizing technologies in the automotive sector, achieving a wide operating range has become a factor of prime importance for centrifugal compressors used in automotive turbocharging applications. As a result of the design features required to achieve this aim, modern impeller geometries have been shown to exhibit an approximately parabolic variation in slip factor across their respective operating maps. By comparison, traditional slip correlations typically exhibit a constant, or at best monotonic, relationship between slip factor and impeller exit flow coefficient. It is this lack of modeling fidelity which the current work seeks to address. In order to tackle these shortcomings, it is proposed that the impeller exit flow should be considered as being made up of three distinct regions: a region of recirculation next to the shroud providing aerodynamic blockage to the stage active flow, and a pitchwise subdivision of the active flow region into jet and wake components. It is illustrated that this hybrid approach in considering both spanwise and pitchwise stratification of the flow permits a better representation of slip factor to be achieved across the operating map. The factors influencing the relative extent of each of these three distinct regions of flow are numerous, requiring detailed investigations to successfully understand their sources and to characterize their extent. A combination of 3D computational fluid dynamics (CFD) data and gas stand test data for six automotive turbocharger compressor stages was employed to achieve this aim. Through application of the extensive interstage static pressure data gathered during gas stand testing at Queen's University Belfast, the results from the 3D CFD models were validated, thus permitting a more in-depth evaluation of the flow field in terms of locations and parameters that could not easily be measured under gas stand test conditions. Building on previous knowledge gained about the variation in shroud side recirculation with geometry and operating condition, the characteristic jet/wake flow structure emanating from the active flow region of the impeller was represented in terms of area and mass flow components. This knowledge allowed individual slip factor values for the jet and wake to be calculated and combined to give an accurate passage average value which exhibited the distinctive nonlinear variation in slip across the operating map which is frequently absent from existing modeling methods. Fundamental considerations of the flow phenomena in each region provided explanation of the results and permitted a modeling approach to be derived to replicate the trends observed in both the experimental data and the CFD simulations.

Energy Harvesting Technology for turbocompounding automotive engines with waste-gate valve

The reduction of CO2 and, more generally, GHG (Green House Gases) emissions imposed by the European Commission (EC) and the Environmental Protection Agency (EPA) for passenger cars has driven the automotive industry to develop technological solutions to limit exhaust emissions and fuel consumption, without compromising vehicle performance and drivability. In a mid-term scenario, hybrid powertrain and Internal Combustion Engine (ICE) downsizing represent the present trend in vehicle technology to reduce fuel consumption and CO2 emissions. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory for both Spark Ignition (SI) and Diesel engines. Following this aspect, the possibility to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world. One method to recover exhaust gas energy from ICEs is the adoption of turbo-compounding technology to recover sensible energy left in the exhaust gas by-passed through the waste-gate valve. In the paper, an innovative option of advanced boosting system is investigated through a bladeless micro expander, promising attractive cost-competitiveness. The numerical activity was developed on the basis of experimental data measured on a waste-gated turbocharger for downsized SI automotive engines. To this aim, mass flow rate through the by-pass valve and the turbine impeller was measured for different waste-gate settings in steady-state conditions at the turbocharger test bench of the University of Genoa. The paper shows that significant electrical power can be harvested from the waste-gate gases, up to 94 % of compressor power, contributing to fuel consumption reduction.