COMPARISON OF FLOW FIELD BETWEEN STEADY AND UNSTEADY FLOW OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE

Global decarbonizing efforts in transportation industry have forced the automotive manufacturers to opt for highly downsized high power-to-weight ratio engines. Since its invention, turbocharger remains as integral element in order to achieve this target. However, although it has been proven that a turbocharger turbine works in highly pulsatile environment, it is still designed under steady state assumption. This is due to the lack of understanding on the nature of pulsating flow field within the turbocharger turbine stage. This paper presents an effort to visualize the pulsating flow feature using experimentally validated Computational Fluid Dynamics (CFD) simulations. For this purpose, a lean-vaned mixed-flow turbine with rotational speed of 30000 rpm at 20 Hz flow frequency, which represent turbine operation for 3-cylinder 4-stroke engine operating at 800 rpm has been used. Results indicated that the introduction of pulsating flow has resulted in more irregular pattern of flow field as compared to steady flow operation. It has also been indicated that the flow behaves very differently between pressure increment and decrement instances. During the pressure decrement instance, flow blockage in terms of low pressure region occupies most of the turbine passage as the flow exit the turbine

Drawbacks on the application of nozzle vanes in turbocharger turbine under pulsating flow conditions

It is commonly agreed that a turbocharger turbine behaves differently between steady and pulsating flow operations. This is due in no small part to the flow field distribution within the turbine stage. The use of nozzle vanes has significantly increased the three-dimensional complexity of the flow field, although some argue that the use of such stator could lead to improved overall turbine performance. This research investigates the drawbacks on the circumferential flow angle distributions due to existence of nozzle vanes particularly during pulsating flow conditions. In achieving this objective, a validated full stage unsteady CFD model was built to gain insight of the flow field behaviour. The results indicate that application of nozzle vanes has favourable effect on flow angle distribution at the rotor inlet during steady state operations for both design and off-design conditions. This is achieved in such a way that the existence of nozzle vanes has reduced the fluctuation of flow angle as compared to the flow upstream the vanes. On the other hand, during pulsating flow turbine operation, the fluctuation amplitude has spiked almost 400% the level of its counterpart under steady state operation at the rotor inlet. This behaviour could potentially have adverse effect on flow field distribution within the turbine passage and as such, reducing unsteady turbine efficiency

Transient Thermal Modeling of an Axial Flux Permanent Magnet (AFPM) Machine Using a Hybrid Thermal Model

This paper presents the development of a hybrid thermal model for the EVO Electric AFM 140 Axial Flux Permanent Magnet (AFPM) machine as used in hybrid and electric vehicles. The adopted approach is based on a hybrid lumped parameter and finite difference method. The proposed method divides each motor component into regular elements which are connected together in a thermal resistance network representing all the physical connections in all three dimensions. The element shape and size are chosen according to the component geometry to ensure consistency. The fluid domain is lumped into one region with averaged heat transfer parameters connecting it to the solid domain. Some model parameters are obtained from Computation Fluid Dynamic (CFD) simulation and empirical data. The hybrid thermal model is described by a set of coupled linear first order differential equations which is discretised and solved iteratively to obtain the temperature profile. The computation involved is low and thus the model is suitable for transient temperature predictions. The maximum error in temperature prediction is 3.4% and the mean error is consistently lower than the mean error due to uncertainty in measurements. The details of the model development, temperature predictions and suggestions for design improvements are presented in this paper.Accepted versio

Turbocharger matching methodology for improved exhaust energy recovery

Current engine simulation codes rely on user-input turbine maps to predict the performance of turbocharged engines. These experimentally obtained maps are limited in range as they are typically obtained through the use of an aerodynamically limited turbine loading device, the compressor. In order to extend the range of the map for simulation, several fitting techniques are utilized in order to obtain the values of efficiency and mass flow over the entire range of pressure ratio for all speeds. This investigation compares predicted turbine maps, obtained from narrow ranges of pressure ratio with more reliable, wider maps obtained experimentally for the same turbines by replacing the compressor with a dynamometer. The outcome of this investigation can be used to improve the fitting of efficiency and mass flow rate curves in engine simulation software

Active Control Turbocharger for Automotive Application: An experimental evaluation

The current paper presents the results from a comprehensive set of experimental tests on a prototype active control turbocharger. This is a continuing series of test work as part of the development of this new type of turbocharger. Driven by the need to comply to increasingly strict emissions regulations as well as a continuing strive for better overall performance the active control turbocharger is intended to provide an improvement over the current state-of-the-art in turbocharging. In this system, the nozzle is able to alter the throat inlet area of the turbine according to the pressure variation of each engine exhaust gas pulse thus imposing a substantially more ‘active’ form of control of the conditions at the turbine rotor inlet

Non-adiabatic pressure loss boundary condition for modelling turbocharger turbine pulsating flow

This paper presents a simplified methodology of pulse flow turbine modelling, as an alternative over the meanline integrated methodology outlined in previous work, in order to make its application to engine cycle simulation codes much more straight forward. This is enabled through the development of a bespoke non-adiabatic pressure loss boundary to represent the turbine rotor. In this paper, turbocharger turbine pulse flow performance predictions are presented along with a comparison of computation duration against the previously established integrated meanline method. Plots of prediction deviation indicate that the mass flow rate and actual power predictions from both methods are highly comparable and are reasonably close to experimental data. However, the new boundary condition required significantly lower computational time and rotor geometrical inputs. In addition, the pressure wave propagation in this simplified unsteady turbine model at different pulse frequencies has also been found to be in agreement with data from the literature, thereby supporting the confidence in its ability to simulate the wave action encountered in turbine pulse flow operation

A new hollow fibre catalytic converter design for sustainable automotive emissions control

State-of-the-art catalytic converters need an ever-high amount of precious-metal catalysts to meet stringent emission regulations. This research reveals an alternative design based on micro-structured ceramic hollow fibre substrates, yielding high conversion of pollutants at low catalyst costs, as well as a unique benefit of low pressure-drop, leading to high engine performances