Weilin Zhuge

Development of an advanced turbocharger simulation method for cycle simulation of turbocharged internal combustion engines

Abstract An advanced turbocharger simulation method for engine cycle simulation was developed on the basis of the compressor two-zone flow model and the turbine mean-line flow model. The method can be used for turbocharger and engine integrated design without turbocharger test maps. The sensitivities of the simulation model parameters on turbocharger simulation were analysed to determine the key modelling parameters. The simulation method was validated against turbocharger test data. Results show that the methods can predict the turbocharger performance with a good accuracy, less than 5 per cent error in general for both the compressor and the turbine. In comparison with the map-based extrapolation methods commonly used in engine cycle simulation tools such as GT-POWER®, the turbocharger simulation method showed significant improvement in predictive accuracy to simulate the turbocharger performance, especially in low-flow and low-operating-speed conditions.

Comparative Study on Electric Turbo-Compounding Systems for Gasoline Engine Exhaust Energy Recovery

Electric turbo-compounding system attracts more attention in recent years with the advance of electronic control devices. There are mainly three kinds of electric turbo-compounding systems for internal combustion engines: System A has an electric-assisted turbocharger, System B has a turbo-generator that is in series with the turbocharger, and System C has a turbo-generator that is in parallel with the turbocharger. A comparative study on the performance of these three kinds of systems for a 1.8L turbocharged gasoline engine is presented. The comparative study has been carried out using 1D simulation methods. The gasoline engine is modeled with the GT-POWER software and the turbochargers and turbo-generators are modeled with turbo through-flow models. The GT-DRIVE software is used to evaluate the system performance under driving cycles. The performance comparisons of different systems have been carried out under US06 and FTP75 driving cycles. Results show that the performance of System C is better than those of the other two kinds of systems. The fuel economy improvement of System C is 4.0% under US06 driving cycle and 1.6% under FTP75 driving cycle, compared with the original prototype engine.Copyright

Numerical Simulation of a Transonic Centrifugal Compressor Blades Tip Clearance Flow of Vehicle Turbocharger

Flow induced by blade tip clearance is important for centrifugal compressor, especially for the high charging ratio transonic centrifugal compressor of the vehicle. Based on three-dimensional CFD method, the evolution and mechanism of tip clearance flow for the high charging ratio transonic centrifugal compressor are investigated. It is verified that shock waves have important effect on blade tip clearance flow. The original position and strength of leakage vortices depend on the position and intensity of shock waves. The tip leakage vortex (TLV) evolution is influenced by the evolution of passage vortex (PV), corner vortex (CV) and separated vortex (SV). Shock wave, adverse pressure gradient and casing boundary layer accelerate the leakage vortices breakdown. Leakage vortex loss is the most important factor of impeller loss. The research on the blades tip leakage flow of transonic centrifugal compressor for vehicle lays a foundation for transonic centrifugal compressor flow control.Copyright

Investigation of the Secondary Flow Structure in the Mixed Flow Turbine for a High Pressure Ratio Turbocharger

A numerical investigation into aerodynamic features of the mixed flow turbine used in a high pressure ratio turbocharger was conducted. The S-A turbulence model and Jameson’s center scheme have been applied in order to get good viscous resolution, accuracy and computing efficiency. Limiting streamlines on the wall surface as well as different flow characteristics, such as entropy generation of the cross sections, were evaluated, while detailed endwall flow and secondary flow structure were analyzed. The development of different vortex, especially the tip leakage vortex, passage vortex and horseshoe vortex were discussed. The results have shown that there is a great secondary flow feature and complicated vortex system in the mixed flow turbine.Copyright

A Matching Method for Two-Stage Turbocharging System

The turbine system of a two-stage turbocharger composed of high pressure turbine, low pressure turbine and by-pass valve decides distribution and utilization of exhaust gas energy and influence performance of two-stage turbocharger in whole operational conditions. Besides, characteristics of turbine is expressed by envelop line of characteristic lines in different speeds. So turbine can be conveniently selected compared with compressor with similarity theory. Therefore two-stage turbocharger matching begins from turbine system matching in the paper. In two-stage turbocharger, cooler efficiency, cooler loss and by-pass valve open besides turbochargers will influence turbocharging system performance and design of cooler and by-pass valve are important contents of turbocharging system matching. The paper matched inter cooler, by-pass valve open, compressors and turbines jointly. Calculation model for turbocharger matching was built, and turbine performance is get from reference turbine based on similarity theory; influence of compressor ratio distribution, cooler efficiency and pressure drop in cooler imposing on compressor work was analyzed; and influence of turbine flow capacity and by-pass valve imposing on output working in expanding process was studied; the method for matching of two-stage turbocharging system in whole operational condition is studied Matching analysis was made aiming at two-stage turbocharging system of a type of high power density diesel engine, and design for turbocharging system was finished. Matching result using the method is compared to matching result using traditional method. Analysis result proves that using the method matching points in different operational conditions are located in more reasonable zone of compressor MAP.Copyright

Study of Mechanism of Counter-rotating Turbine Increasing Two- Stage Turbine System Efficiency

Two-stage turbocharging is an important way to raise engine power density, to realize energy saving and emission reducing. At present, turbine matching of two- stage turbocharger is based on MAP of turbine. The matching method does not take the effect of turbines’ interaction into consideration, assuming that flow at high pressure turbine outlet and low pressure turbine inlet is uniform. Actually, there is swirl flow at outlet of high pressure turbine, and the swirl flow will influence performance of low pressure turbine which influencing performance of engine further. Three-dimension models of turbines with two-stage turbocharger were built in this paper. Based on the turbine models, mechanism of swirl flow at high pressure turbine outlet influencing low pressure turbine performance was studied and a two-stage radial counter-rotation turbine system was raised. Mechanisms of the influence of counter-rotation turbine system acting on low-pressure turbine were studied using simulation method. The research result proved that in condition of small turbine flow rate corresponding to engine low-speed working condition, counter-rotation turbine system can effectively decrease the influence of swirl flow at high pressure turbine outlet imposing on low pressure turbine and increases efficiency of the low-pressure turbine, furthermore increases the low-speed performance of the engine.

STABILITY IMPROVEMENT OF TURBOCHARGER CENTRIFUGAL COMPRESSOR BY ASYMMETRIC VANELESS DIFFUSER TREATMENT

The asymmetric flow field induced by the volute has considerable influence on the performance of a turbocharger centrifugal compressor, especially through its effect on the stability. In this paper, a novel asymmetric vaneless diffuser treatment with a circumferentially non-axisymmetric diffuser width distribution was firstly developed to enhance the stability of a centrifugal compressor for turbocharger. Design principle of the asymmetric diffuser was proposed based on the asymmetric flow in the compressor. The objective of the asymmetric vaneless diffuser design is to alleviate the flow asymmetry in the diffuser, which requires that the phase of the maximal diffuser width is coincident with the phase of the minimum static pressure in the diffuser. The results of the numerical simulation showed that the designed asymmetric diffuser was able to decrease the magnitude of the pressure distortion induced by the volute and therefore alleviated the negative effect of the volute on compressor stability. Experimental results showed that the designed asymmetric diffuser extended the stable flow range by 28.3% at designed speed compared to the prototype with symmetric diffuser.Copyright

Investigation of Influence of Two-Stage Turbocharging System on Engine Performance Using a Pre-Design Model

As the result of increasingly strict emission regulations and demand of fuel reduction, current light and medium duty engines are being highly boosted with complex two-stage turbocharging systems. The purpose of this work is to investigate the influence of two-stage turbocharging system parameters on the engine performance and the optimization of these parameters.An analytical pre-design model of the series two-stage turbocharging system for an internal combustion engine was developed, which builds the relationship between total pressure ratio, total expansion ratio and other two-stage turbocharging system parameters. Considering total expansion ratio as a function of expansion ratio between HP and LP turbine, minimum total expansion ratio can be determined using this model. The ratio of total pressure ratio to total expansion ratio, engine brake thermal efficiency and total heat exchange of coolers are considered as the parameters for engine performance evaluation. Influence of two-stage turbocharging system parameters, such as efficiency of compressors and turbines, cooling water temperature, cooler efficiency, pressure loss of coolers, EGR rate and bypass gas rate of wastegate, etc., on engine performance was analyzed respectively.Results show that the performance of a two-stage turbocharging engine is impacted mainly by LP turbocharger efficiency, intercooler performance and air filter performance.Copyright

Numerical Investigation of the Effect of Rotor Blade Leading Edge Geometry on the Performance of a Variable Geometry Turbine

Variable geometry turbines are more and more widely used in diesel engines to meet the requirements of the stringent emission standards. The VGTs mostly operate at off-design conditions. At highly off-design conditions, there exist complex secondary flow structures and severe flow separation in the rotor passage, which deteriorate the turbine performance largely.The influence of rotor blade leading edge geometries on the VGT performance was studied by CFD simulations. The blade angle distribution along the leading edge was varied while keeping the radial-fiber rotor construction. The effects of inlet sweep angle distribution and lean angle of the blade leading edge on the turbine flow fields and performance were investigated under different operating conditions.Results show that the turbine with backswept leading edge has better performance at low U/C, while the turbine with forward swept leading edge has a higher efficiency under high flow rate conditions. With the same sweep angle distribution, the leading edge lean affects the flow fields in the rotor passage as well as the turbine performance significantly. The influence of blade lean on the turbine performance varies according to different swept blading and operating conditions.Copyright

TURBOCHARGER DESIGN FOR A 1.8 LITER TURBOCHARGED GASOLINE ENGINE USING AN INTEGRATED METHOD

Turbocharging is playing an increasingly vital role in the development of gasoline engines to reduce fuel consumption and CO2 emissions. Turbocharger design is a key technique used for improving the gasoline engine’s performance. In this study, a new turbocharger design method is proposed by integrating a turbocharger through-flow model with a gasoline engine model for better turbocharger matching. The integrated method was applied to design a new turbocharger according to the performance requirements of a 1.8L turbocharged gasoline engine. Compared to the original prototype, the engine with the new turbocharger designed with the integrated method can achieve a better power and torque curve with about a 4% reduction of fuel consumption at the rated engine speed.Copyright