Search Results

The subject of this work is 3D numerical simulations of combustion and soot emissions for a passenger car diesel engine. The CFD code STAR-CD version 3.26 [1] is used to resolve the flowfield. Soot is modeled using a detailed kinetic soot model described by Mauss [2]. The model includes a detailed description of the formation of polyaromatic hydrocarbons. The coupling between the turbulent flowfield and the soot model is achieved through a flamelet library approach, with transport of the moments of the soot particle size distribution function as outlined by Wenzel et al. [3]. In this work we extended this approach by considering acetylene feedback between the soot model and the combustion model. The model was further improved by using new gas-phase kinetics and new fitting procedures for the flamelet soot library.

The paper discusses the concept, design and final results from the ‘Ultra Boost for Economy’ collaborative project, which was part-funded by the Technology Strategy Board, the UK's innovation agency. The project comprised industry- and academia-wide expertise to demonstrate that it is possible to reduce engine capacity by 60% and still achieve the torque curve of a modern, large-capacity naturally-aspirated engine, while encompassing the attributes necessary to employ such a concept in premium vehicles. In addition to achieving the torque curve of the Jaguar Land Rover naturally-aspirated 5.0 litre V8 engine (which included generating 25 bar BMEP at 1000 rpm), the main project target was to show that such a downsized engine could, in itself, provide a major proportion of a route towards a 35% reduction in vehicle tailpipe CO2 on the New European Drive Cycle, together with some vehicle-based modifications and the assumption of stop-start technology being used instead of hybridization.

A turbocharger is currently widely used to boost performance of an internal combustion engine. Generally, a turbocharger consists of a compressor which typically is driven by an exhaust turbine. The compressor will influence how the low frequency engine pulsation propagates in the intake system. The compressor will also produce broad-band flow induced sound due to the turbulence flow and high frequency narrowband tonal sound which is associated with rotating blade pressures. In this paper, a practical simulation procedure based on a computational fluid dynamics (CFD) approach is developed to predict the flow induced sound of a turbocharger compressor. In the CFD model of turbocharger compressor, the unsteady, moving wheel, detached eddy simulation (DES) approach are utilized. In this manner, both the broad-band and narrow-band flow induced sound are directly resolved in the CFD computation.

Aero-vibro-acoustic prediction of interior noise associated with exterior flow requires accurate predictions of both fluctuating surface pressures across the exterior of a vehicle and efficient models of the vibro-acoustic transmission of these surface pressures to the interior of a vehicle. The simulation strategy used in this paper combines both CFD and vibro-acoustic methods. An accurate excitation field (which accounts for both hydrodynamic and acoustic pressure fluctuations) is calculated with a hybrid CAA approach based on an incompressible unsteady flow field with an additional acoustic wave equation. To obtain the interior noise level at the driver's ears a vibro-acoustic model is used to calculate the response of the structure and interior cavities. The aero-vibro-acoustic simulation strategy is demonstrated for a Mercedes-Benz S-class and the predictions are compared to experimental wind tunnel measurements.

Prediction of flow induced noise in the interior of a passenger car requires accurate representations of both fluctuating surface pressures across the exterior of the vehicle and efficient models of the vibro-acoustic transmission of these surface pressures to the driver’s ear. In this paper, aeroacoustic and vibro-acoustic methods are combined in order to perform an aero-vibro-acoustic analysis of a Mercedes-Benz A-class. The exterior aero-acoustic method consists of a time domain incompressible Detached Eddy Simulation (DES) and an acoustic wave equation. The method is extended in this paper to account for convection effects when modelling the exterior sound propagation. The interior vibro-acoustic model consists of a frequency domain Finite Element (FE) model of the side glass combined with a generalized Statistical Energy Analysis (SEA) model of the interior cabin.

To extend the operating range of a gasoline HCCI engine, the blowdown supercharging (BDSC) system and the EGR guide were developed and experimentally examined. The concepts of these techniques are to obtain a large amount of dilution gas and to generate a strong in-cylinder thermal stratification without an external supercharger for extending the upper load limit of HCCI operation whilst keeping dP/dθmax and NOx emissions low. Also, to attain stable HCCI operation using the BDSC system with wide operating conditions, the valve actuation strategy in which the amount of dilution gas is smaller at lower load and larger at higher load was proposed. Additionally to achieve multi-cylinder HCCI operation with wide operating range, the secondary air injection system was developed to reduce cylinder-to-cylinder variation in ignition timing. As a result, the acceptable HCCI operation could be achieved with wide operating range, from IMEP of 135 kPa to 580 kPa.

The paper presents a simulation approach to Li-Ion batteries based on geometrically resolved electrodes. This means that solid particles and the space occupied by electrolyte are not overlapping but are represented by contiguous, arbitrarily shaped volumes. The solid-electrolyte interface is explicitly resolved and thus allows detailed modeling of electro-chemical processes that are essential for studying performance of the battery cell. Finite volume method is used to solve the equations governing the mass and thermal energy conservation in solid and electrolyte, as well as the distribution of electric potential. The solution domain is discretized in contiguous control volumes of arbitrary polyhedral shape, with conformal interface between solid and fluid regions. Butler-Volmer equation is used to describe the kinetics of solid-electrolyte interface.

Though some practitioners consider the simulation process for sunroof and side window buffeting to be mature, there remain considerable uncertainties and inefficiencies as how in predictive methodologies to account for interior panel flexibility, vehicle structural stiffness, seals leakages and interior materials surface finish. Automotive OEMs and component suppliers rightly target flow simulation of open sunroofs and passenger windows with a view to reducing the severely uncomfortable low-frequency booming disturbance. The phenomenon is closely related to open cavity noise experienced also in other transportation sectors; for example in Aerospace, landing gear and store release cavities, and in Rail Transportation, cavities for HVAC intakes and the bogie environment. Recent studies published by the author demonstrate that the uncertainties can be correctly quantified by modeling.

A transient interactive flamelet model and a transient flamelet library based model are used to model a medium-duty diesel fueled engine operating in PCCI mode. The simulations are performed with and without the source term accounting for evaporation in the mixture fraction variance equation. Reasonable agreement is found with the experiments with both models. The effect of the evaporation source term in the mixture fraction variance equation is different for the different transient flamelet approaches. For the transient interactive flamelet model the ignition onset is delayed as a consequence of the higher mixture fraction variance, which leads to a higher scalar dissipation rate. The evaporation source term does not affect the global characteristics of the ignition event for the transient flamelet progress variable model, but locally the initial combustion is occurring differently.

The transport industries face a continuing demand from customers and regulators to improve the acoustic performance of their products: reduce noise heard by passengers and passersby; avoid exciting structural modes. In both the aerospace and automotive areas, flow-induced noise makes a significant contribution, leading to the desire to understand and optimize it through the use of simulation. Historically, the need for time-consuming, computationally expensive transient simulations has limited the application of CFD in the field of acoustics. In this paper are described efficient simulation processes that, in some instances, remove the requirement for transient analyses, or significantly reduce the total process time through intelligent pre-processing. We will outline this process and provide both automotive and aerospace industrial examples, including analyses of highly complex geometries found in real life.

Fuel level sensors are used to indicate the amount of fuel in the tank of an automobile. The most common type of fuel level sensor is the float-arm sensor in which a float is connected to a resistance band via an arm. The fuel volume inside the tank sets the height of the float which in turn is converted to a resistance value. This resistance value is converted into gauge reading that is displayed on the dashboard. Whereas this method is widely popular due to its low cost and durability, fuel slosh phenomenon imposes a major challenge. The fuel slosh waves under numerous driving maneuvers impose dynamic drag/lift forces on the float which result into fluctuations in its position (i.e. float height). Under severe acceleration or braking maneuvers, the float can actually submerge inside the liquid and fail to predict location of the free surface. These fluctuations can cause erroneous fuel indication.

A system for controlled heat generation in exhaust pipeline is studied, consisting of fuel injector and oxidation catalyst (plus connecting pipes). A 3D-CFD software (StarCD) coupled with a tailored 1D model of catalytic monolith channel (XMR) are employed for simulations of realistic, fully 3D system geometry. Exhaust gas flow, fuel injection, and distribution at the catalyst inlet is solved by 3D-CFD, while the processes inside individual representative channels are simulated by the effective 1D model. The 3D-CFD software calls iteratively the 1D channel model with proper boundary conditions and solves 3D temperature profile over the monolith, utilizing local enthalpy fluxes (including gas-solid heat transfer and reaction enthalpy) calculated by the 1D channel model. Seven representative hydrocarbons are used for characterisation of Diesel fuel composition with respect to catalytic oxidation kinetics.

Demand for a high thermal performance heat exchanger with good durability in a small packaging space can be very challenging. For the durability testing, the typical thermal cycle test in the lab with the fixed temperature cycles can be very time consuming and costly. In order to shorten the product development time and cost, CAE tools have been explored for the radiator thermal cycle simulation. Due to the nature of the most common failure mode, it is imperative to develop reliable methodologies so that the transient temperature, stress, and corresponding fatigue life for the product can be predicted. This paper focuses on the prediction of the metal temperature during the radiator thermal cycle using computational fluid dynamics (CFD) with conjugate heat transfer. To verify the developed temperature prediction method in CFD, thermal cycle tests were performed for three radiator samples. The test procedure and some of the test results are reviewed.

It has been shown that internal transmission of wind noise is dependent on the external aerodynamic and acoustic excitation around the automobile. Flow over the A-pillar and side-view mirror induces strongly convecting turbulence and associated acoustics which excite the side-glass. A useful tool to understand and quantify these physics is to perform temporal Fourier analysis (auto-spectra) and spatial Fourier analysis (cross-spectra and wave-number decomposition). This study demonstrates the uses of wave-number decomposition to quantify the mechanisms associated with turbulent convection and acoustical propagation. A CFD computation using the commercial codes STAR-CCM+ is performed for the flow over a generalized side-view mirror in a freestream of 38m/s. LES-enabled turbulence is solved in a fully compressible framework so as to capture all the local acoustical propagation well beyond 3kHz.

The interior noise in a vehicle that is due to flow over the exterior of the vehicle is often referred to as ‘windnoise’. In order to predict interior windnoise it is necessary to characterize the fluctuating surface pressures on the exterior of the vehicle along with vibro-acoustic transmission to the vehicle interior. For example, for greenhouse sources, flow over the A-pillar and side-view mirror typically induces both turbulence and local aeroacoustic sources which then excite the glass, and window seals. These components then transmit noise and vibration to the vehicle interior. Previous studies by the authors have demonstrated validated CFD (Computational Fluid Dynamics) techniques which give insight into the flow-noise source mechanisms. The studies also made use of post-processing based on temporal and spatial Fourier analysis in order to quantify the amount of energy in the flow at convective and acoustic wavenumbers.

In this paper a new numerical methodology to compute component temperatures of a rotating cardan shaft is described. In general temperatures of the cardan shaft are mainly dominated by radiation from the exhaust gas system and air temperatures in the transmission tunnel and underbody. While driving the cardan shaft is rotating. This yields a uniform temperature distribution of the circumference of the shaft. However most simulation approaches for heat protection are nowadays steady-state computations. In these simulations the rotation of the cardan shaft is not considered. In particular next to the exhaust gas system the distribution of the temperatures of the cardan shaft is not uniform but shows hot temperatures due to radiation at the side facing the exhaust gas system and lower temperatures at the other side. This paper describes a new computational approach that is averaging the radiative and convective heat fluxes circumferentially over bands of the cardan shaft.

With the increasing focus on the use of lithium ion batteries for traction applications the ability to simulate electrochemical and thermal performance of such batteries is of great interest. This paper details a multi-length scale approach which is used to simulate a single lithium ion pouch cell and compare against some previously published experimental work. This approach is then extended and used as a building block to a much more complex simulation using multiple cells within a battery pack. This technology also simulates the cooling system performance and the inherent coupled behavior of the battery's operation and its thermal environment.

Several emission performance tests like Butane Working Capacity (BWC), Cycle Life, and ORVR load tests are required for the certification of a vehicle; these tests are both expensive and time consuming. This paper presents a test process based upon analytical simulation of BWC of an automotive carbon canister in order to greatly reduce the cost incurred in physical tests. The computational model for the fixed-bed system of a carbon canister is based upon non-equilibrium, non-Isothermal, and non-adiabatic algorithm to simulate the real life loading/purging of hydrocarbon vapors from this device.

One of the major reason for lower efficiency and higher unburned hydrocarbon and carbon monoxide emission for two stroke engine is short circuit losses during the scavenging process. An attempt has been made in this study to understand and improve this phenomenon. A three dimensional transient CFD model is developed for a loop scavenged, Schnullar type, 70 cc two stroke engine. Three major processes, namely, blow down (expansion); scavenging and compression have been modelled. The model is validated with PIV measurement done in motoring mode. Model is also validated with experimental data for trapping efficiency with Watson method and for in-cylinder pressure during expansion, blow down and intake events. A good correlation is observed between experimental and simulation results. CFD model is used to quantify various parameters, such as, delivery ratio, trapping efficiency, scavenging efficiency, and amount of fresh mass short circuit at different load and speed points.