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Technical Paper

Three-Dimensional Multi-Scale Simulation for Large-Scale Proton Exchange Membrane Fuel Cell

2019-04-02
2019-01-0381
PEMFC (proton exchange membrane or polymer electrolyte membrane fuel cell) is a potential candidate as a future power source for automobile applications. Water and thermal management is important to PEMFC operation. Numerical models, which describe the transport and electrochemical phenomena occurring in PEMFCs, are important to the water and thermal management of fuel cells. 3D (three-dimensional) multi-scale CFD (computational fluid dynamics) models take into account the real geometry structure and thus are capable of predicting real operation/performance. In this study, a 3D multi-phase CFD model is employed to simulate a large-scale PEMFC (109.93 cm2) under various operating conditions. More specifically, the effects of operating pressure (1.0-4.0 atm) on fuel cell performance and internal water and thermal characteristics are studied in detail under two inlet humidities, 100% and 40%.
Technical Paper

Experimental and Computational Study of the Flow around a Stationary and Rotating Isolated Wheel and the Influence of a Moving Ground Plane

2019-04-02
2019-01-0647
This study investigates the aerodynamic behavior of the flow around a rotating and stationary 60% scale isolated wheel, with and without the use of a moving ground plane. The aim of this research was to improve the understanding of the fundamental aerodynamic flow features around a wheel and to examine how rotation and moving ground planes modify these and affect the production of drag. A bespoke rotating wheel rig was designed and wind tunnel tests were performed over a range of pre to post critical Reynolds numbers. Force coefficients were obtained using balance measurements and flow field data were obtained using Particle Image Velocimetry (PIV). The unsteady flow field data generated was used to validate unsteady CFD predictions. These were performed using STAR-CCM+ and a k-ω SST Improved Delayed Detached Eddy Simulation (IDDES) turbulence model. This was seen to outperform other models by capturing an increased amount of finer detailed, high frequency vortical structures.
Technical Paper

Towards In-Cylinder Flow Informed Engine Control Strategies Using Linear Stochastic Estimation

2019-04-02
2019-01-0717
Many modern I.C. engines rely on some form of active control of injection, timing and/or ignition timing to help combat tailpipe out emissions, increase the fuel economy and improve engine drivability. However, development of these strategies is often optimised to suit the average cycle at each condition; an assumption that can lead to sub-optimal performance, especially an increase in particulate (PN) emissions as I.C. engine operation, and in-particular its charge motion is subject to cycle-to-cycle variation (CCV). Literature shows that the locations of otherwise repeatable large-scale flow structures may vary by as much 25% of the bore dimension; this could have an impact on fuel break-up and distribution and therefore subsequent combustion performance and emissions.
Technical Paper

Application of Multi-Objective Optimization Techniques for Improved Emissions and Fuel Economy over Transient Manoeuvres

2019-04-02
2019-01-1177
This paper presents a novel approach to augment existing engine calibrations to deliver improved engine performance during a transient, through the application of multi-objective optimization techniques to the calibration of the Variable Valve Timing (VVT) system of a 1.0 litre gasoline engine. Current mature calibration approaches for the VVT system are predominantly based on steady state techniques which fail to consider the engine dynamic behaviour in real world driving, which is heavily transient. In this study the total integrated fuel consumption and engine-out NOx emissions over a 2-minute segment of the transient Worldwide Light-duty Test Cycle are minimised in a constrained multi-objective optimisation framework to achieve an updated calibration for the VVT control. The cycle segment was identified as an area with high NOx emissions.
Technical Paper

Experimental Design for Characterization of Force Transmissibility through Bearings in Electric Machines and Transmissions

2018-06-13
2018-01-1473
With the increasing stringent emissions legislation on ICEs, alongside requirements for enhanced fuel efficiency as key driving factors for many OEMs, there are many research activities supported by the automotive industry that focus on the development of hybrid and pure EVs. This change in direction from engine downsizing to the use of electric motors presents many new challenges concerning NVH performance, durability and component life. This paper presents the development of experimental methodology into the measurement of NVH characteristics in these new powertrains, thus characterizing the structure borne noise transmissibility through the shaft and the bearing to the housing. A feasibility study and design of a new system level test rig have been conducted to allow for sinusoidal radial loading of the shaft, which is synchronized with the shaft’s rotary frequency under high-speed transient conditions in order to evaluate the phenomena in the system.
Technical Paper

Parametric Study of Asymmetric Side Tapering in Constant Cross Wind Conditions

2018-04-03
2018-01-0718
Sports Utility Vehicles (SUVs) often have blunt rear end geometries for design and practicality, which is not typically aerodynamic. Drag can be reduced with a number of passive and active methods, which are generally prioritised at zero yaw, which is not entirely representative of the “on road” environment. As such, to combine a visually square geometry (at rest) with optimal drag reductions at non-zero yaw, an adaptive system that applies vertical side edge tapers independently is tested statically. A parametric study has been undertaken in Loughborough University’s Large Wind Tunnel with the ¼ scale Windsor Model. The aerodynamic effect of implementing asymmetric side tapering has been assessed for a range of yaw angles (0°, ±2.5°, ±5° and ±10°) on the force and moment coefficients.
Technical Paper

The Development of Skutterudite-Based Thermoelectric Generators for Vehicles

2018-04-03
2018-01-0788
With the continuing improvements to thermoelectric (TE) materials and systems, their potential for both energy recovery and thermal management is increasingly apparent. Recent developments in materials and notably Skutterudites have allowed materials to be matched much more closely to the working temperatures of a light duty power-train. The choice of TE materials remains a substantial question in the design of a thermoelectric generator (TEG). While the quest for improvements in materials performance continues, the work reported in this paper is characterized by the decision to focus on the refinement of one class of TE materials: Skutterudites. In parallel, the engineering work on the integration of the TE materials into a heat exchanger could continue and be focused on the properties of this class of material. Skutterudites offer the combination of a high working temperature and a competitive electrical output (defined by ZT, the figure of merit).
Journal Article

A Drag Coefficient for Test Cycle Application

2018-04-03
2018-01-0742
The drag coefficient at zero yaw angle is the single parameter usually used to define the aerodynamic drag characteristics of a passenger car. However, this is usually the minimum drag condition and will, for example, lead to an underestimate of the effect of aerodynamic drag on fuel consumption because the important influence of the natural wind has been excluded. An alternative measure of aerodynamic drag should take into account the effect of nonzero yaw angles and a variant of wind-averaged drag is suggested as the best option. A wind-averaged drag coefficient (CDW) is usually derived for a particular vehicle speed using a representative wind speed distribution. In the particular case where the road speed distribution is specified, as for a drive cycle to determine fuel economy, a relevant drag coefficient can be derived by using a weighted road speed.
Technical Paper

Towards Optimal Performance of a Thermoelectric Generator for Exhaust Waste Heat Recovery from an Automotive Engine

2018-04-03
2018-01-0050
Thermoelectric generator has very quickly become a hot research topic in the last five years because its broad application area and very attractive features such as no moving parts, low maintenance, variety of thermoelectric materials that total together cover a wide temperature range. The biggest disadvantage of the thermoelectric generator is its low conversion efficiency. So that when design and manufacture a thermoelectric generator for exhaust waste heat recovery from an automotive engine, the benefit of fuel consumption from applying a thermoelectric generator would be very sensitive to the weight, the dimensions, the cost and the practical conversion efficiency. Additionally, the exhaust gas conditions vary with the change of engine operating point. This creates a big challenge for the design of the hot side heat exchanger in terms of optimizing the electrical output of the thermoelectric generator during an engine transient cycle.
Technical Paper

Tribodynamics of a New De-Clutch Mechanism Aimed for Engine Downsizing in Off-Road Heavy-Duty Vehicles

2017-06-05
2017-01-1835
Clutches are commonly utilised in passenger type and off-road heavy-duty vehicles to disconnect the engine from the driveline and other parasitic loads. In off-road heavy-duty vehicles, along with fuel efficiency start-up functionality at extended ambient conditions, such as low temperature and intake absolute pressure are crucial. Off-road vehicle manufacturers can overcome the parasitic loads in these conditions by oversizing the engine. Caterpillar Inc. as the pioneer in off-road technology has developed a novel clutch design to allow for engine downsizing while vehicle’s performance is not affected. The tribological behaviour of the clutch will be crucial to start engagement promptly and reach the maximum clutch capacity in the shortest possible time and smoothest way in terms of dynamics. A multi-body dynamics model of the clutch system is developed in MSC ADAMS. The flywheel is introducing the same speed and torque as the engine (represents the engine input to the clutch).
Technical Paper

A Comparison of Four Modelling Techniques for Thermoelectric Generator

2017-03-28
2017-01-0144
The application of state-of-art thermoelectric generator (TEG) in automotive engine has potential to reduce more than 2% fuel consumption and hence the CO2 emissions. This figure is expected to be increased to 5%~10% in the near future when new thermoelectric material with higher properties is fabricated. However, in order to maximize the TEG output power, there are a few issues need to be considered in the design stage such as the number of modules, the connection of modules, the geometry of the thermoelectric module, the DC-DC converter circuit, the geometry of the heat exchanger especially the hot side heat exchanger etc. These issues can only be investigated via a proper TEG model. The authors introduced four ways of TEG modelling which in the increasing complexity order are MATLB function based model, MATLAB Simscape based Simulink model, GT-power TEG model and CFD STAR-CCM+ model. Both Simscape model and GT-Power model have intrinsic dynamic model performance.
Technical Paper

The Potential of Thermoelectric Generator in Parallel Hybrid Vehicle Applications

2017-03-28
2017-01-0189
This paper reports on an investigation into the potential for a thermoelectric generator (TEG) to improve the fuel economy of a mild hybrid vehicle. A simulation model of a parallel hybrid vehicle equipped with a TEG in the exhaust system is presented. This model is made up by three sub-models: a parallel hybrid vehicle model, an exhaust model and a TEG model. The model is based on a quasi-static approach, which runs a fast and simple estimation of the fuel consumption and CO2 emissions. The model is validated against both experimental and published data. Using this model, the annual fuel saving, CO2 reduction and net present value (NPV) of the TEG’s life time fuel saving are all investigated. The model is also used as a flexible tool for analysis of the sensitivity of vehicle fuel consumption to the TEG design parameters. The analysis results give an effective basis for optimization of the TEG design.
Technical Paper

MIMO (Multiple-Input-Multiple-Output) Control for Optimising the Future Gasoline Powertrain - A Survey

2017-03-28
2017-01-0600
This paper surveys publications on automotive powertrain control, relating to modern GTDI (Gasoline Turbocharged Direct Injection) engines. The requirements for gasoline engines are optimising the airpath but future legislation suggests not only a finely controlled airpath but also some level of electrification. Fundamentals of controls modelling are revisited and advancements are highlighted. In particular, a modern GTDI airpath is presented based on basic building blocks (volumes, turbocharger, throttle, valves and variable cam timing or VCT) with an example of a system interaction, based on boost pressure and lambda control. Further, an advanced airpath could be considered with applications to downsizing and fuel economy. A further electrification step is reviewed which involves interactions with the airpath and requires a robust energy management strategy. Examples are taken of energy recovery and e-machine placement.
Journal Article

Off-Road Tire-Terrain Interaction: An Analytical Solution

2016-09-27
2016-01-8029
A novel semi-analytical solution has been developed for the calculation of the static and dynamic response of an off road tire interacting with a deformable terrain, which utilizes soil parameters independent of the size of the contact patch (size-independent). The models involved in the solution presented, can be categorized in rigid and/or pneumatic tires, with or without tread pattern. After a concise literature review of related methods, a detailed presentation of the semi-analytical solution is presented, along with assumptions and limitations. A flowchart is provided, showing the main steps of the numerical implementation, and various test cases have been examined, characterized in terms of vertical load, tire dimensions, soil properties, deformability of the tire, and tread pattern. It has been found that the proposed model can qualitatively capture the response of a rolling wheel on deformable terrain.
Technical Paper

Optimization of the Number of Thermoelectric Modules in a Thermoelectric Generator for a Specific Engine Drive Cycle

2016-04-05
2016-01-0232
Two identical commercial Thermo-Electric Modules (TEMs) were assembled on a plate type heat exchanger to form a Thermoelectric Generator (TEG) unit in this study. This unit was tested on the Exhaust Gas Recirculation (EGR) flow path of a test engine. The data collected from the test was used to develop and validate a steady state, zero dimensional numerical model of the TEG. Using this model and the EGR path flow conditions from a 30% torque Non-Road Transient Cycle (NRTC) engine test, an optimization of the number of TEM units in this TEG device was conducted. The reduction in fuel consumption during the transient test cycle was estimated based on the engine instantaneous Brake Specific Fuel Consumption (BSFC). The perfect conversion of TEG recovered electrical energy to engine shaft mechanical energy was assumed. Simulations were performed for a single TEG unit (i.e. 2 TEMs) to up to 50 TEG units (i.e. 100 TEMs).
Technical Paper

The Influence of Thermoelectric Materials and Operation Conditions on the Performance of Thermoelectric Generators for Automotive

2016-04-05
2016-01-0219
An automotive engine can be more efficient if thermoelectric generators (TEG) are used to convert a portion of the exhaust gas enthalpy into electricity. Due to the relatively low cost of the incoming thermal energy, the efficiency of the TEG is not an overriding consideration. Instead, the maximum power output (MPO) is the first priority. The MPO of the TEG is closely related to not only the thermoelectric materials properties, but also the operating conditions. This study shows the development of a numerical TEG model integrated with a plate-fin heat exchanger, which is designed for automotive waste heat recovery (WHR) in the exhaust gas recirculation (EGR) path in a diesel engine. This model takes into account the following factors: the exhaust gas properties’ variation along the flow direction, temperature influence on the thermoelectric materials, thermal contact effect, and heat transfer leakage effect. Its accuracy has been checked using engine test data.
Journal Article

Design and Optimisation of the Propulsion Control Strategy for a Pneumatic Hybrid City Bus

2016-04-05
2016-01-1175
A control strategy has been designed for a city bus equipped with a pneumatic hybrid propulsion system. The control system design is based on the precise management of energy flows during both energy storage and regeneration. Energy recovered from the braking process is stored in the form of compressed air that is redeployed for engine start and to supplement the engine air supply during vehicle acceleration. Operation modes are changed dynamically and the energy distribution is controlled to realize three principal functions: Stop-Start, Boost and Regenerative Braking. A forward facing simulation model facilitates an analysis of the vehicle dynamic performance, engine transient response, fuel economy and energy usage.
Technical Paper

Optimal Control Inputs for Fuel Economy and Emissions of a Series Hybrid Electric Vehicle

2015-04-14
2015-01-1221
Hybrid electric vehicles offer significant fuel economy benefits, because battery and fuel can be used as complementing energy sources. This paper presents the use of dynamic programming to find the optimal blend of power sources, leading to the lowest fuel consumption and the lowest level of harmful emissions. It is found that the optimal engine behavior differs substantially to an on-line adaptive control system previously designed for the Lotus Evora 414E. When analyzing the trade-off between emission and fuel consumption, CO and HC emissions show a traditional Pareto curve, whereas NOx emissions show a near linear relationship with a high penalty. These global optimization results are not directly applicable for online control, but they can guide the design of a more efficient hybrid control system.
Technical Paper

The Characterisation of a Centrifugal Separator for Engine Cooling Systems

2015-04-14
2015-01-1693
It is an engineering requirement that gases entrained in the coolant flow of an engine must be removed to retain cooling performance, while retaining a volume of gas in the header tank for thermal expansion and pressure control. The main gases present are air from filling the system, exhaust emissions from leakage across the head gasket, and also coolant vapour. These gases reduce the performance of the coolant pump and lower the heat transfer coefficient of the fluid. This is due to the reduction in the mass fraction of liquid coolant and the change in fluid turbulence. The aim of the research work contained within this paper was to analyse an existing phase separator using CFD and physical testing to assist in the design of an efficient phase separator.
Journal Article

Aerodynamic Drag of Passenger Cars at Yaw

2015-04-14
2015-01-1559
The aerodynamic drag characteristics of a passenger car are typically defined by a single parameter, the drag coefficient at zero yaw angle. While this has been acceptable in the past, it may not allow a true comparison between vehicles with regard to the impact of drag on performance, especially fuel economy. An alternative measure of aerodynamic drag should take into account the effect of non-zero yaw angles and some proposals have been made in the past, including variations of wind-averaged drag coefficient. For almost all cars the drag increases with yaw, but the increase can vary significantly between vehicles. In this paper the effect of various parameters on the drag rise with yaw are considered for a range of different vehicle types. The increase of drag with yaw is shown to be an essentially induced drag, which is strongly dependent on both side force and lift. Shape factors which influence the sensitivity of drag with yaw are discussed.
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