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Correct simulations of rotating wheels are essential for accurate aerodynamic investigations of passenger vehicles. Therefore, modern automotive wind tunnels are equipped with five-belt moving ground systems with wheel drive units (WDUs) connected to the underfloor balance. The pressure distribution on the exposed areas of the WDU belts results in undesired lift forces being measured which must be considered to obtain accurate lift values for the vehicle. This work investigates the parasitic WDU lift for various configurations of a crossover SUV using numerical simulations that have been correlated to wind tunnel data. Several parameters were considered in the investigation, such as WDU size, WDU placement, tyre variants and vehicle configurations. The results show that the parasitic lift is more sensitive to the width than the length of the WDU. However, the belt length is also important to consider, especially if the wheel cannot be placed centred.

Previous research on both small-scale and full-scale vehicles shows that base extensions are an effective method to increase the base pressure, enhancing pressure recovery and reducing the wake size. These extensions decrease drag at zero yaw, but show an even larger improvement at small yaw angles. In this paper, rear extensions are investigated on an SUV in the Volvo Cars Aerodynamic Wind Tunnel with focus on the wake flow and on the unsteady behavior of the surface pressures near the base perimeter. To increase the effect of the extensions on the wake flow, the investigated configurations have a closed upper- and lower grille (closed-cooling) and the underbody has been smoothed with additional panels. This paper aims to analyze differences in flow characteristics on the wake of an SUV at 0° and 2.5° yaw, caused by different sets of extensions attached to the base perimeter. Extensions with several lengths are investigated with and without a kick.

Pre-chamber combustion (PCC) has re-emerged in recent last years as a potential solution to help to decarbonize the transport sector with its improved engine efficiency as well as providing lower emissions. Research into the combustion process inside the pre-chamber is still a challenge due to the high pressure and temperatures, the geometrical restrictions, and the short combustion durations. Some fundamental studies in constant volume combustion chambers (CVCC) at low and medium working pressures have shown the complexity of the process and the influence of high pressures on the turbulence levels. In this study, the pre-chamber combustion process was investigated by combustion visualization in an optically-accessible pre-chamber under engine relevant conditions and linked with the jet emergence inside the main chamber. The pre-chamber geometry has a narrow-throat. The total nozzle area is distributed in two six-hole rows of nozzle holes.

Crash-test-data on local longitudinal and shear stiffness of the vehicle front is needed to estimate impact severity from car deformation in offset or pole impacts, and to predict vehicle acceleration and compartment intrusion in car-to-car crashes. Repeated full frontal crash-tests were carried out with a load-cell barrier to determine the local longitudinal stiffness with increasing crush. Repeated off-set tests were run to determine shear stiffness. Two single high-speed tests (full frontal and offset) were carried out and compared to the repeated tests to determine the rate sensitivity of the front structure. Four repetitions at 33.4 km/h provided equivalent energy absorption to a single 66.7 km/h test, when rebound was considered. Power-train inertial effects were estimated from highspeed tests with and without power-train. Speed effects averaged 2% per [m/s] for crush up to power-train impact, and post-crash measurements were a reasonable estimate of front-structure stiffness.

The need for a more complete understanding of the flow behavior in aerodynamic wind tunnels has increased as they have become vital tools not only for vehicle development, but also for vehicle certification. One important aspect of the behavior is the empty test section flow, which in a conventional tunnel should be as uniform as possible. In order to assess the uniformity and ensure consistent behavior over time, accurate measurements need to be performed regularly. Furthermore, the uncertainties and errors of the measurements need to be minimized in order to resolve small non-uniformities. In this work, the quantification of the measurement uncertainties from the full measurement chain of the new flow uniformity measurement rig for the Volvo Cars aerodynamic wind tunnel is presented. The simulation based method used to account for flow interference of the probe mount is also discussed.

In light of the drive for energy efficiency and low CO2 emissions, extensive research is performed to reduce vehicle aerodynamic drag. The wheels are relatively shielded from the main flow compared to the exterior of the passenger car; however, they are typically responsible for around 25% of the overall vehicle drag. This contribution is large as the wheels and tyres protrude into the flow and change the flow structure around the vehicle underbody. Given that the tyre is the first part of the wheel to get in contact with the oncoming flow, its shape and features have a significant impact on the flow pattern that develops. This study aims at identifying the general effects of two main tyre features, the longitudinal rain grooves and lateral pattern grooves, using both Computational Fluid Dynamics (CFD) and wind tunnel tests. This is performed by cutting generic representations of these details into identical slick tyres.

Soot particle size, particle concentration and volume fraction were measured by laser based methods in optically dense, highly turbulent combusting diesel sprays under engine-like conditions. Experiments were done in the Chalmers High Pressure, High Temperature spray rig under isobaric conditions and combusting commercial diesel fuel. Laser Induced Incandescence (LII), Elastic Scattering and Light Extinction were combined quasi-simultaneously to quantify particle characteristics spatially resolved in the middle plane of a combusting spray at two instants after the start of combustion. The influence that fuel injection pressure, gas temperature and gas pressure exert on particle size, particle concentration and volume fraction were studied. Probability density functions of particle size and two-dimensional images of particle diameter, particle concentration and volume fraction concerning instantaneous single-shot cases and average measurements are presented.

Due to stricter emission regulations and more environmental awareness, the powertrain systems are moving toward higher fuel efficiency and lower emissions. In response to these pressing needs, new technologies have been designed and implemented by manufacturers. As a result of increasing complexity of the powertrain systems, their control and optimization become more and more challenging. Virtual powertrain calibration, also known as model-based calibration, has been introduced to transfer a part of test bench testing into a virtual environment, and hence considerably reduce time and cost of product development process while increasing the product quality. Nevertheless, virtual calibration has not yet reached its full potential in industrial applications. Volvo Penta has recently developed a virtual test cell named VIRTEC, which is used in an ongoing pilot project to meet the Stage V emission standards.

The structure and evolution of cavitation in a transparent scaled-up diesel nozzle having a hole perpendicular to the nozzle axis has been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. Observations revealed that, at the inception stage, cavitation bubbles are dominantly seen in the vortices at the boundary layer shear flow and outside the separation zone. Cavitation bubbles grow intensively in the shear layer and develop into cloud-like coherent structures when viewed from the side of the nozzle. Shedding of the coherent cloud cavitation was observed. When the flow was increased further the cloud like cavitation bubbles developed into a large-scale coherent structure extending downstream of the hole. Under this condition the cavitation starts as a mainly glassy sheet at the entrance of the hole. Until this stage the spray appeared to be symmetric.

In the 1955 Le Mans race the worst crash in motor racing history occurred and this accident would change the face of motor racing for decades. After the crash numerous investigations on the disaster were performed, and fifty years after some interesting books were launched on the subject. However, a number of key questions remain unsolved; and one open area is the influence of aerodynamics on the scenario, since the Mercedes-Benz 300 SLR involved in the crash was equipped with an air-brake and its influence on the accident is basically unknown. This work may be considered as a first attempt to establish CFD as a tool to aid in resolving aerodynamic aspects in motor sport accidents and in the present paper, CFD has been used to investigate the aerodynamics and estimate the drag and lift coefficients of the Mercedes-Benz 300 SLR used in the Le Mans race of 1955.

A single-cylinder engine was operated in HCCI combustion mode with different kinds of commercial fuels. The HCCI combustion was generated by creating a negative valve overlap (early exhaust valve closing combined with late intake valve opening) thus trapping a large amount of residuals (∼ 55%). Fifteen different fuels with high octane numbers were tested six of which were primary reference fuels (PRF's) and nine were commercial fuels or reference fuels. The engine was operated at constant operational parameters (speed/load, valve timing and equivalence ratio, intake air temperature, compression ratio, etc.) changing only the fuel type while the engine was running. Changing the fuel affected the auto-ignition timing, represented by the 50% mass fraction burned location (CA50). However these changes were not consistent with the classical RON and MON numbers, which are measures of the knock resistance of the fuel. Indeed, no correlation was found between CA50 and the RON or MON numbers.

Approximately 25 % of a passenger vehicle’s aerodynamic drag comes directly or indirectly from its wheels, indicating that the rim geometry is highly relevant for increasing the vehicle’s overall energy efficiency. An extensive experimental study is presented where a parametric model of the rim design was developed, and statistical methods were employed to isolate the aerodynamic effects of certain geometric rim parameters. In addition to wind tunnel force measurements, this study employed the flowfield measurement techniques of wake surveys, wheelhouse pressure measurements, and base pressure measurements to investigate and explain the most important parameters’ effects on the flowfield. In addition, a numerical model of the vehicle with various rim geometries was developed and used to further elucidate the effects of certain geometric parameters on the flow field.

In a diesel engine, the combustion and emissions formation are governed by the spray formation and mixing processes. To meet the stringent emission legislations of the future, which will demand substantial reductions of NOX and particulate emissions from diesel engines, the spray and mixing processes play a major roll. Different fuel injection systems and injection strategies have been developed to achieve better performance and lower emissions from the diesel engine almost without investigating the influence of the injector nozzle orifices. A reduction in the nozzle orifice diameter is important for an increased mixing rate and formation of smaller droplets which is beneficial from emissions and fuel consumption point of view, as long as the local air-to-fuel ratio (AFR) is kept at a sufficiently lean level.

Flow visualization techniques are widely used in aerodynamics to investigate the surface trace pattern. In this experimental investigation, the surface flow pattern over the rear end of a full-scale passenger car is studied using tufts. The movement of the tufts is recorded with a DSLR still camera, which continuously takes pictures. A novel and efficient tuft image processing algorithm has been developed to extract the tuft orientations in each image. This allows the extraction of the mean tuft angle and other such statistics. From the extracted tuft angles, streamline plots are created to identify points of interest, such as saddle points as well as separation and reattachment lines. Furthermore, the information about the tuft orientation in each time step allows studying steady and unsteady flow phenomena. Hence, the tuft image processing algorithm provides more detailed information about the surface flow than the traditional tuft method.

Sulphur poisoning and regeneration of NOx trap catalysts have been studied in synthetic exhausts and in an engine bench. Sulphur gradually poisoned the NOx storage sites in the axial direction of the NOx trap. During sulphur regenerations, hydrogen was found to be more efficient than carbon monoxide in removing the sulphur from the trap. The sulphur regeneration became more efficient the richer the environment (λ<1) and the higher the temperature (at least 600°C). H2S was found to be the main product during the sulphur regeneration. However, it was possible to reduce the H2S formation and instead produce more SO2 by running with lambda close to one or by pulsing lambda. Even if a relatively large amount of sulphur was removed from the NOx trap, these methods gave a much less efficient regeneration per sulphur atom removed than when running relatively rich constantly. Finally, a model that could explain this observation was proposed.

The phenomenon of three-dimensional flow separation is and has been in the focus of many researchers. An improved understanding of the physics and the driving forces is desired to be able to improve numerical simulations and to minimize aerodynamic drag over bluff bodies. To investigate the sources of separation one wants to understand what happens at the surface when the flow starts to detach and the upwelling of the streamlines becomes strong. This observation of a flow leaving the surface could be captured by investigating the limiting streamlines and surface parameters as pressure, vorticity or the shear stress. In this paper, numerical methods are used to investigate the surface pressure and flow patterns on a sedan passenger vehicle. Observed limiting streamlines are compared to the pressure distribution and their correlation is shown. For this investigation the region behind the antenna and behind the wheel arch, are pointed out and studied in detail.

Maximum fuel injection pressures for GDI engines is expected to increase due to positive effects on emissions and engine-efficiency. Current GDI injectors have maximum operating pressures of 35 MPa, but higher injection pressures have yielded promising reductions in particle number (PN) and improved combustion stability. However, the mechanisms responsible for these effects are poorly understood, and there have been few studies on fuel sprays formed at high injection pressures. This paper summarizes experimental studies on the properties of sprays formed at high injection pressures. The results of these experiments can be used as inputs for CFD simulations and studies on combustion behavior, emissions formation, and combustion system design. The experiments were conducted using an injection rate meter and optical methods in a constant volume spray chamber. Injection rate measurements were performed to determine the injectors’ flow characteristics.

Gasoline direct injection (GDI) engines usually emit higher levels of particulates in warm-up conditions of a driving cycle. Thus, sources of soot formation in these conditions were investigated by measuring particulate numbers (PN) emitted from a single-cylinder GDI engine and their sizes. The combustion was also visualized using an endoscope connected to a high-speed camera. Engine coolant and oil temperatures were varied between 15 and 90oC to mimic warm-up conditions. In addition, effects of delaying the start of ignition (SOI) on the emissions in these conditions were examined. Coolant and oil temperatures were varied individually to identify which factor has most effect on PN emissions. While coolant temperature strongly influenced PN with cold oil, the oil temperature insignificantly affected PN at low coolant temperature. These findings indicate that PN emissions are heavily dependent on the engine block’s temperature, which is dominated by the coolant.

We describe experiments and numerical modeling of snow surface contamination on two simplified automotive bluff bodies: The Ahmed body and a wedge. The purpose was twofold: 1) To obtain well defined experimental results of snow contamination on simple geometries; 2) To propose a numerical modeling approach for snow contamination. The experiments were performed in a climatic wind tunnel using a snow cannon at −15 °C and the results show that the snow accumulation depends on the aerodynamics of the studied bluff bodies. Snow accumulates on surfaces in proximity to the aerodynamic wakes of the bodies and characteristic snow patterns are obtained on side surfaces. The numerical modeling approach consisted of an aerodynamic setup coupled with Lagrangian particle tracking. Particles were determined to adhere or rebound depending on an adhesion model combined with a resuspension criterion.

Simulations of a Direct Injection Spark Ignition (DISI) engine have been performed for both early injection with homogeneous charge combustion and for late injection with stratified charge combustion. The purpose has been to study flow characteristics, fuel/air mixing, combustion, and NOx and soot formation. Focus is put on the combustion modeling. Two different full load cases with early injection are simulated, 2000 rpm and 6000 rpm. One load point with late injection is simulated, 2000 rpm and 2.8 bar net MEP. Three different injection timings are simulated at the low load point: 77, 82, and 87 CAD bTDC. The spray simulations are tuned to match measured spray penetrations and droplet size distributions at both atmospheric and elevated pressure. Boundary conditions for the engine simulations are taken from 1-D gas exchange simulations that are tuned to match engine tests.