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There is a growing need for life-cycle data – so-called collectives – when developing components like elastomer engine mounts. Current standardized extreme load cases are not sufficient for establishing such collectives. Supplementing the use of endurance testing data, a prediction methodology for component temperature collectives utilizing existing 3D CFD simulation models is presented. The method uses support points to approximate the full collective. Each support point is defined by a component temperature and a position on the time axis of the collective. Since it is the only currently available source for component temperature data, endurance testing data is used to develop the new method. The component temperature range in this data set is divided in temperature bands. Groups of driving states are determined which are each representative of an individual band. Each of the resulting four driving state spaces is condensed into a substitute load case.

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.

A fuel cell system consists of a stack, a hydrogen fuel supply and an air supply system. This provides the required air flow and pressure which allows the stack to properly react on the cathode side to recombine Oxygen with the Hydrogen's protons and electrons resulting in water and heat. In addition the air flow and pressure are supporting directly or indirectly the water management. In this paper different air supply systems for automotive application developed by NuCellSys are compared: screw compressor and electrical turbo charger. Different technologies and control strategies allow the fuel cell system integrator to find the optimum between performances, weight, volume and cost. The authors describe the challenges and the new frontier of air supply systems for automotive fuel cell system application.

Rising oil prices and increasing strict emission legislation force vehicle manufacturers to reduce fuel consumption of future vehicles. In order to meet this target, the process of converting fuel into useable energy and the use of this energy by the different energy-consuming vehicle's subsystems have to be examined. Vehicles' subsystems consist of energy-supplying, energy-consuming, and in some cases energy-storing components. Due to the high complexity of these systems and their interaction, optimization of their energy efficiency is a challenging task. By introducing individual operational strategies for each subsystem, it is possible to increase the energy efficiency for a specific function. To further improve the vehicle's overall energy efficiency, holistic control strategies are introduced that distribute the energy between the subsystems intelligently.

The driving comfort influences the customer purchase decision; hence it is an important aspect for the vehicle development. To better quantify the comfort level and reduce the experiment costs in the development process, the subjective comfort assessment by test drivers is nowadays more and more replaced by the objective comfort evaluation. Hereby the vibration comfort is described by scalar objective characteristic parameters that correlate with the subjective assessments. The correlation analysis requires the assessments and measurements at different vehicle vibration. To determine the objective parameters regarding the powertrain excitations, most experiments in the previous studies were carried out in several test vehicles with different powertrain units.

Collective life-cycle data is needed when developing components like elastomer suspension mounts. Life-time prediction is only possible using thermal load frequency distributions. In addition to current extreme load cases, the Idle Load Case is examined at Mercedes-Benz Car Group as a collective load case for Vehicle Thermal Management (VTM) numerical simulations in early development stages. It combines validation opportunities for HVAC, cooling and transmission requirements in hot-country-type ambient conditions. Experiments in climatic wind tunnels and coupled 3D CFD and heat transfer simulations of the Idle Load Case have been performed. Measurements show steady conditions at the end of the load case. Decoupling of the torque converter, changes in ambient temperature and the technical implementation of a wind barrier for still air conditions exhibit influence on component-level results. Solar load, however, does not significantly change the examined component temperatures.

The overall efficiency of hybrid electric vehicles largely depends on the design and application of its energy management system (EMS). Despite the load coordination when operating the system in a hybrid mode, the EMS accounts for state changes between the different driving modes. Whether a transition between pure electric driving and internal combustion engine (ICE) powered driving is beneficial depends, among others, on the respective operation point, the route ahead as well as on the energetic expense for the engine start itself. The latter results from a complex interaction of the powertrain components and has a tremendous impact on the efficiency and quality of EMSs. Optimization based methods such as dynamic programming serve as benchmark for the design process of rule based control strategies. In case no energetic expenses are assigned to a state change, the resulting EMS suffers from being sub-optimal regarding the fuel consumption.

This paper investigates the pressure drop with and without condensation inside a charge air cooler. The background to this investigation is the fact that the stored condensate in charge air coolers can be torn into the combustion chamber during different driving states. This may result in misfiring or in the worst-case lead to an engine failure. In order to prevent or reduce the accumulated condensate inside charge air coolers, a better understanding of the detailed physics of this process is required. To this end, one single channel of the charge air side is investigated in detail by using an experimental setup that was built to reproduce the operating conditions leading to condensation. First, measurements of the pressure drop without condensation are conducted and a good agreement with experimental data of a comparable heat exchanger reported in Kays and London [1] is shown.

Aerodynamic design and thermal management are some of the most important tasks when developing new concepts for the flow around tractor-trailers. Today, both experimental and numerical studies are an integral part of the aerodynamic and thermal design processes. A variety of studies have been conducted how the aerodynamic design reduces the drag coefficient for fuel efficiency as well as for the construction of radiators to provide cooling on tractor-trailers. However, only a few studies cover the combined effect of the aerodynamic and thermal design on the air temperature of the under hood flow [8, 13, 16, 17, 20]. The objective of this study is to analyze the heat transfer through forced convection for a scaled Cab-over-Engine (CoE) tractor-trailer model with under hood flow. Different design concepts are compared to provide low under hood air temperature and efficient cooling of the sub components.

This paper summarizes a common project of Mercedes-Benz and FKFS (Research Institute of Automotive Engineering) to apply numerical methods to thermal soak issues in a very early stage of the development phase of a new car. “Thermal soak” results from driving the vehicle at high load followed by shutting off the engine and a cool down phase. After stopping, the underhood flow is only driven by natural convection. The thermal soak behaviour is discussed in principal and the numerical challenges are summarized. Four different issues are identified: the need for a transient computation including transient thermal load pattern, a method to compute natural convection in the underhood after the shutdown of the engine, the complex geometry and the lack of a single computational program to consider all three modes of heat transfer, which results in a coupled numerical approach.

The electric turbocharger is a promising type of air supply unit for future automotive fuel cell drive systems. It comprises of a centrifugal compressor, a variable geometry turbine and a permanent magnet synchronous motor assembled on a single shaft. Compared to other types of vehicular fuel cell air supplies, like for example a screw or roots compressor, it needs less installation space and has lower weight while also causing less noise and vibration. This paper presents a validated mechanistic model of the electric turbocharger. The stationary compressor model is based on a set of aerodynamic loss models with surge and stone wall line prediction capability. Similarly, the stationary variable axial turbine is a detailed station based model derived from aerodynamic losses at the turbine wheel and the stator blades. The aerodynamic losses incorporated in the compressor and the turbine models are implemented under MATLAB/Simulink and show a good correlation with the experimental data.

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.

Fuel cells convert a fuel together with oxygen in a highly efficient electrochemical reaction to electricity and water. Automotive fuel cell systems mainly use compressed onboard stored hydrogen as fuel. Oxygen from ambient air is fed to the cathode of the fuel cell stack by an air supply subsystem. For its current and next generation air supply subsystem NuCellSys has employed screw type compressor technology, which in the automotive area initially was developed for supercharged internal combustion (IC) engines. As NVH expectations to fuel cell vehicles differ very much from IC-engine driven vehicles, specific efforts have to be taken to address the intense noise and vibration profile of the screw compressor. This paper describes different counter measures which have been implemented into the NuCellSys next generation air supply subsystem.

An accurate model to predict the formation of fogging and defogging which occurs for low windshield temperatures is helpful for designing the air-conditioning system in a car. Using a multiphase flow approach and additional user-defined functions within the commercial CFD-software STAR-CCM+, a model which is able to calculate the amount of water droplets on the windshield from condensation and which causes the fogging is set up. Different parameters like relative humidity, air temperature, mass flow rate and droplet distributions are considered. Because of the condition of the windshield's surface, the condensation occurs as tiny droplets with different sizes. The distribution of these very small droplets must be obtained to estimate numerically the heat transfer coefficient during the condensation process to predict the defogging time.

In the digital prototype development process of a new Mercedes-Benz, thermal protection is an important task that has to be fulfilled. In the early stages of development, numerical methods are used to detect thermal hotspots in order to protect temperature sensitive parts. These methods involve transient full Vehicle Thermal Management (VTM) simulations to predict dynamic vehicle heat-up during critical load cases. In order to simulate thermal control mechanisms, a coupled 1D to 3D thermal vehicle model is built in which the coolant and oil circuit of the engine, as well as the exhaust flow are captured in detail. When performing a transient 3D VTM analysis, the conduction and radiation phenomena are simulated using a transient structure model while the convective phenomena are co-simulated in a steady state fluid model. Both models are brought to interaction at predetermined points by an automatized coupling method.

Air-cooled fin and tube heat exchangers are used as a condenser in the conventional automotive Heating Ventilation & Air-Conditioning (HVAC) systems. In this study, the use of liquid cooled plate heat exchanger as a condenser in the automotive HVAC systems has been investigated. In the proposed configuration, the cabin heat absorbed by the refrigerant in HVAC system is rejected to the coolant through a liquid cooled condenser and then to the ambient air through a low temperature radiator. Hence, the proposed configuration combines heat rejection from HVAC system with a low temperature radiator circuit of power train cooling. Mixture of Ethylene glycol & Water (coolant), which is used in power train cooling system, is used as secondary fluid in the condenser.

A raise of efficiency is the strongest selling point concerning the total cost of ownership (TCO), especially for commercial vehicles (CV). Accompanied by legislations, with contradictive development demands, satisfying solutions have to be found. The analysis of energy losses in modern engines shows three influencing parameters. Wall heat transfer (WHT) losses are awarded with the highest optimization potential. Critical for the occurrence of these losses is the WHT, which can be described by representing coefficients. To reduce WHT accompanying losses a decrease of energy transfer between combustion gas and combustion chamber wall is necessary. A measurement of heat fluxes is necessary to determine the WHT relations of the combustion chamber in an engine. As this has not been done for a Heavy-Duty (HD) engine, with peak pressures up to 250 bar, an increased in-cylinder turbulence and high exhaust gas recirculation (EGR)-rates before, it is presented in the following.

In the proposed work the transient thermal modeling of a vehicle cabin has been performed. Therefore, a reduced model has been developed based on a one-node discretization of the cabin air. The conduction in the solid parts is accounted for by a one-dimensional heat transfer approach, the radiation exchange between the surfaces is based on view factors adopted from a 3D reference and the convective heat transfer from the cabin surfaces to the cabin air is conducted with the help of heat transfer coefficients calculated in a 3D reference simulation. The cabin surface is discretized by planar wall elements, including the outer shell of the cabin and inner elements such as seats. Each wall element is composed of several homogeneous material layers with individual thicknesses. Investigations have been conducted on the temporal and spatial resolution of the layer structure of these wall elements, for the 3D model as well as for the reduced one.

The need for a consistent and reliable calculation of thermodynamic property of refrigerants has been a topic of research since the past decade. This paper reports a study of various cubic equations of state for a refrigerant being used in automotive air-conditioning applications. The thermodynamic property of refrigerant 1,1,1,2 tetrafluoroethane (commercially known as R134a) is estimated for this purpose. A comparative analysis is made on three sets of equations of state. They are Redlich Kwong equation (RK), Peng Robinson equation (PR) and Patel Teja equation. It is found that the Patel-Teja and Peng-Robinson equations are accurate in the operating region of automotive air-conditioning system. Using these literature based equations and Maxwell correlations, thermodynamic models are developed. They estimate thermodynamic properties of saturated liquid/vapor, sub-cooled liquid and superheated vapor phases.

In this paper the latest status of the Vehicle Thermal Management (VTM) simulation at the Mercedes-Benz Car Group is shown. First of all VTM is nowadays a routine simulation application and secondly it is embedded in a standard process which starts with the CAD data collection and ends with standard reporting of the simulation results and thirdly VTM is now an integrated simulation application in terms of VTM includes the classical underhood-underbody analysis, the analysis of electric/electronic components, the brake temperature analysis and last not least the thermal comfort of passengers. There is also a close link to the tests of vehicle hardware. Beside the operational simulation process there is a process installed which guarantees good quality of the results.