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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.

The motivation for this paper is to predict the flow of water over exterior surfaces of road vehicles. We present simulations of liquid flows on solid surfaces under the influence of gravity with and without the addition of aerodynamic forces on the liquid. This is done using an implementation of a Coupled Level Set Volume of Fluid method (CLSVOF) multiphase approach implemented in the open source OpenFOAM CFD code. This is a high fidelity interface-resolving method that solves for the velocity field in both phases without restrictions on the flow regime. In the current paper the suitability of the approach to Exterior Water Management (EWM) is demonstrated using the representative test cases of a continuous liquid rivulet flowing along an inclined surface with a channel located downstream perpendicular to the oncoming flow.

Sensor selection for the control of modern powertrains is a recognised technical challenge. The key question is which set of sensors is best suited for an effective control strategy? This paper addresses the question through probabilistic modelling and Bayesian analysis. By quantifying uncertainties in the model, the propagation of sensor information throughout the model can be observed. The specific example is an abstract model of the slip behaviour of Selective Catalytic Reduction (SCR) DeNOx aftertreatment systems. Due to the ambiguity of the sensor reading, linearization-based approaches including the Extended Kalman Filter, or the Unscented Kalman Filter are not successful in resolving this problem. The stochastic literature suggests approximating these nonlinear distributions using methods such as Markov Chain Monte Carlo (MCMC), which is able in principle to resolve bimodal or multimodal results.

The two-dimensional, frictional tyre-road contact interaction is investigated. A transient contact algorithm is developed, consisting of an analytical belt model, a non linear sidewall structure and a discretized viscoelastic tread foundation. The relationship between the magnitude/shape of the predicted two-dimensional pressure distribution and the corresponding belt deformation is identified. The effect of vertical load and the role of sidewall non linearity are highlighted. The modal expansion/reduction method is proposed for the increase of the computational efficiency and the effect of the degree of reduction on the simulation accuracy is presented. The qualitative results are physically explained through the participation of certain modes in the equilibrium solution, offering directions for the application of the modal reduction method in shear force oriented tyre models.

A large contribution to the aerodynamic drag of a vehicle (30%(1) or more depending on vehicle shape) arises from the low base pressure in the wake region, especially on square-back configurations. A degree of base pressure recovery can be achieved through careful shape optimization, but the flow structures and mechanisms within the wake that cause these base pressure changes are not well understood. A more complete understanding of these mechanisms may provide opportunities for further drag reductions from both passive shape changes and in the future through the use of active flow control technologies. In this work surprisingly large changes in drag and lift coefficients of a square-back style vehicle have been measured as a result of physically small passive modifications. Tests were performed at quarter scale using a simplified vehicle model (Windsor Model) and at full scale using an MPV. The full scale vehicle was tested with and without a flat floor.

Various techniques to reduce the aerodynamic drag of bluff bodies through the mechanism of base pressure recovery have been investigated. These include, for example, boat-tailing, base cavities and base bleed. In this study a simple body representing a car shape is modified to include tapering of the rear upper body on both roof and sides. The effects of taper angle and taper length on drag and lift characteristics are investigated. It is shown that a significant drag reduction can be obtained with moderate taper angles. An unexpected feature is a drag rise at a particular taper length. Pressure data obtained on the rear surfaces and some wake flow visualisation using PIV are presented.

Particulate Matter (PM) emissions reduction is an imminent challenge for Direct Injection Spark Ignition (DISI) engine designers due to the introduction of Particulate Number (PN) standards in the proposed Euro 6 emissions legislation aimed at delivering the next phase of air quality improvements. An understanding of how the formation of combustion-derived nanoparticulates in engines is affected by the engine operating temperature is important for air quality improvement and will influence future engine design and control strategies. This investigation has examined the effect on combustion and PM formation when reducing the engine operating temperature to -7°C. A DISI single-cylinder optical research engine was modified to simulate a range of operating temperatures down to the proposed -7°C.

The work presented investigates the effect of road gradient, head-wind, horizontal road curvature, changes in tyre rolling radius, vehicle drag co-efficient and vehicle weight on real-world emission levels of a modern EURO-IV vehicle. A validated steady-state engine performance map based vehicle modeling approach has been used for the analysis. The results showed that a generalized correction factor to include the effect of road-gradient on real-world emission levels might not yield accurate results, since the emission levels are strongly dependent on the position of the vehicle operating parameters on the engine maps. In addition, it also demonstrated that the inclusion of horizontal road curvature such as roundabouts and traffic islands are essential for the estimation of the real-world emission levels.

A qualitative FMEA study of Polymer Electrolyte Fuel Cell (PEFC) technology is established and presented in the current work through a literature survey of mechanisms that govern performance degradation and failure. The literature findings are translated into Fault Tree (FT) diagrams that depict how basic events can develop into performance degradation or failure in the context of the following top events; (1) activation losses; (2) mass transportation losses; (3) Ohmic losses; (4) efficiency losses and (5) catastrophic cell failure. Twenty-two identified faults and forty-seven frequent causes are translated into fifty-two basic events and a system of FTs with twenty-one reoccurring dominant mechanisms. The four most dominant mechanisms discussed that currently curtail sustained fuel cell performance relate to membrane durability, liquid water formation, flow-field design, and manufacturing practices.

Various studies have shown that the level of wind noise experienced inside cars on the road in unsteady conditions can be substantially different from that measured in wind tunnel tests conducted using a low turbulence facility. In this paper a simple geometric body representing the cabin of a passenger car has been used to investigate the effects of free stream turbulence, (FST), on the A-pillar vortex flowfield and the side glass pressure distribution. Beneath the A-pillar vortex, both mean and dynamic pressures are increased by FST. The unsteady pressure can be associated with wind noise and the flow visualization shows the peak unsteadiness is related to the separation of the secondary vortex.

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).

This paper presents the findings from a numerical study of a gasoline direct injection engine flow using the Large Eddy Simulation (LES) modelling technique. The study is carried out over 30 successive engine cycles. The study illustrates how the more simple but robust Smagorinsky LES sub-grid scale turbulence model can be applied to a complex engine geometry with realistic engineering mesh size and computational expense whilst still meeting the filter width requirements to resolve the majority of large scale turbulent structures. Detailed description is provided here for the computational setup, including the initialisation strategy. The mesh is evaluated using a turbulence resolution parameter and shows the solution to generally resolve upwards of 80% of the turbulence kinetic energy.

Short tapered sections on the trailing edge of the roof, underside and sides of a vehicle are a common feature of the aerodynamic optimization process and are known to have a significant effect on the base pressure and thereby the vehicle drag. In this paper the effects of such high aspect ratio chamfers on the time-dependent base pressure are investigated. Short tapered surfaces, with a chord approximately equal to 4% of the overall model length, were applied to the trailing edges of a simplified passenger car model (the Windsor Body) and base pressure studied via an array of surface pressure tappings. Two sets of configurations were tested. In the first case, a chamfer was applied only to the top or bottom trailing edge. A combination of taper angles was also considered. In the second case, the chamfer was applied to the side edges of the model base, leaving the horizontal trailing edges squared.

The injection timing of a Diesel internal combustion engine typically follows a prescribed sequence depending on the operating condition using open loop control. Due to advances in sensors and digital electronics it is now possible to implement closed loop control based on in cylinder pressure values. Typically this control action is slow, and it may take several cycles or at least one cycle (cycle-to-cycle control). Using high speed sensors, it becomes technically possible to measure pressure deviations and correct them within the same cycle (intra-cycle control). For example the in cylinder pressure after the pilot inject can be measured, and the timing of the main injection can be adjusted in timing and duration to compensate any deviations in pressure from the expected reference value. This level of control can significantly reduce the deviations between cycles and cylinders, and it can also improve the transient behavior of the engine.

Piston compression rings are thin, incomplete circular structures which are subject to complex motions during a typical 4-stroke internal combustion engine cycle. Ring dynamics comprises its inertial motion relative to the piston, within the confine of its seating groove. There are also elastodynamic modes, such as the ring in-plane motions. A number of modes can be excited, dependent on the net applied force. The latter includes the ring tension and cylinder pressure loading, both of which act outwards on the ring and conform it to the cylinder bore. There is also the radial inward force as the result of ring-bore conjunctional pressure (i.e. contact force). Under transient conditions, the inward and outward forces do not equilibrate, resulting in the small inertial radial motion of the ring.

Low temperature combustion (LTC) in diesel engines offers attractive benefits through simultaneous reduction of nitrogen oxides and soot. However, it is known that the in-cylinder conditions typical of LTC operation tend to produce high emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO), reducing combustion efficiency. The present study develops from the hypothesis that this characteristic poor combustion efficiency is due to in-cylinder mixture preparation strategies that are non-optimally matched to the requirements of the LTC combustion mode. In this work, the effects of three key fuel path parameters - injection fuel quantity ratio, dwell and injection timing - on CO and HC emissions were examined using a Central Composite Design (CCD) Design of Experiments (DOE) method.

It has been recognised that the ideal flow conditions that exist in the modern automotive wind tunnel do not accurately simulate the environment experienced by vehicles on the road. This paper investigates the effect of varying one flow parameter, freestream turbulence, and a single shape parameter, leading edge radius, on aerodynamic drag. The tests were carried out at model scale in the Loughborough University Wind Tunnel, using a very simple 2-box shape, and in the MIRA Full Scale Wind Tunnel using the MIRA squareback Reference Car. Turbulence intensities up to 5% were generated by grids and had a strong effect on transcritical Reynolds number and Reynolds sensitivity at both model scale and full scale. There was a good correlation between the results in both tunnels.

This paper deals with experimental investigations of the in-cylinder flow structures under steady state conditions utilizing Particle Image Velocimetry (PIV). The experiments have been conducted on an engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and different inlet valve configurations at two pressure drops, 250mm and 635mm of H2O that correlate with engine speeds of 2500 and 4000 RPM respectively. From the two-dimensional in-cylinder flow measurements, a tumble flow analysis is carried out for six planes parallel to the cylinder axis. In addition, a swirl flow analysis is carried out for one horizontal plane perpendicular to the cylinder axis at half bore downstream from the cylinder head (44mm). The results show the advantage of using the planar technique (PIV) for investigating the complete flow structures developed inside the cylinder.

In this paper the effects of a rough underbody on the rear wake structure of a simplified squareback model (the Windsor model) is investigated using balance measurements, base pressure measurements and two and three component planar PIV. The work forms part of a larger study to develop understanding of the mechanisms that influence overall base pressure and hence the resulting aerodynamic drag. In the work reported in this paper the impact of a rough underbody on the base pressure and wake flow structures is quantified at three different ground clearances. The underbody roughness has been created through the addition of five roughness strips to the underbody of the model and the effects on the wake at ground clearances of 10.3%, 17.3% and 24.2% of the model height are assessed. All work has been carried out in the Loughborough University Large Wind Tunnel with a ¼ scale model giving a blockage ratio of 4.4% for a smooth under-body or 4.5% with the maximum thickness roughness strips.

An expedient route to improving in-vehicle fuel economy in 4-stroke cycle engines is to reduce the swept volume of an engine and run it at a higher BMEP for any given output. The full-load performance of a larger capacity engine can be achieved through pressure charging. However, for maximum fuel economy, particularly at part-load, the expansion ratio, and consequently the compression ratio (CR) should be kept as high as possible. This is at odds with the requirement in pressure-charged gasoline engines to reduce the CR at higher loads due to the knock limit. In earlier work, the authors studied a pressure-charging system aimed at allowing a high CR to be maintained at all times. The operation of this type of system involves deliberately over-compressing the charge air, cooling it at the elevated pressure and temperature, and then expanding it down to the desired plenum pressure, ensuring a plenum temperature which can potentially become sub-atmospheric at full-load.