Papers

As world-wide exhaust legislation for diesel powered vehicles becomes more and more rigorous, extensive measures inside and outside the engine are necessary. This includes a cooled exhaust gas recirculation (EGR), which makes possible substantial reduction of nitrogen oxide emissions. Thereby, the EGR process can be implemented in a conventional high pressure EGR loop or in a low pressure EGR loop. In the latter case, part of the exhaust gas is extracted after the turbine and the diesel particulate filter to be recirculated and mixed with fresh air before the compressor. The present contribution describes the fundamental advantages and disadvantages of these two EGR systems and supplies a simulation model for a vehicle, which was generated using KULI®, a one-dimensional simulation software package. This model permits the computation of the charge air inlet temperature to the engine and the thermodynamic effects on the involved heat exchangers (EGR cooler, Charge air cooler and Radiator). It shows that in case of unchanged components a substantial thermal advantage for the low pressure EGR loop can result. For the boundary conditions of the selected basis case the engine intake air temperature could be reduced around 5.1K without penalizing the coolant side. An additional parametric study examines the influence of fresh air mass flow, air compression ratio, exhaust gas temperature, EGR rate and coolant rate in the EGR cooler.

The engine warm-up after a cold start depends not only on the engine, the driving cycle and on the vehicle itself, but also on the behavior of systems like cooling circuit and power train. The individual systems stand in interaction both with the engine as well as with the other systems. This requires for the simulation of the thermal management system that all relevant subsystems are simulated simultaneously and that the interaction between the individual systems is being considered in a correct way. Therefore, a generic simulation platform was developed. The main advantage of the platform is in being able to couple the simulation models without the need of special interfaces between the individual programs. Based on an example, the modeling of the individual subsystems of the vehicle is shown. For the verification of the single subsystems experimental measurements on a vehicle dynamometer have been performed. The comprehensive vehicle model is verified with the measurement data of a ‘real-world’ driving cycle. Key parameters such as coolant temperature, engine temperature, and cabin temperature are compared therefore. Based on an example, the modeling of the individual subsystems of the vehicle is shown. For the verification of the single subsystems experimental measurements on a vehicle dynamometer have been performed. The comprehensive vehicle model is verified with the measurement data of a ‘real-world’ driving cycle. Key parameters such as coolant temperature, engine temperature, and cabin temperature are compared therefore.

The engine warm-up after a cold start depends not only on the engine, the driving cycle and on the vehicle itself, but also on the behavior of systems like cooling circuit and power train. The individual systems stand in interaction both with the engine as well as with the other systems. This requires for the simulation of the thermal management system that all relevant subsystems are simulated simultaneously and that the interaction between the individual systems is being considered in a correct way. Therefore, a generic simulation platform was developed. The main advantage of the platform is in being able to couple the simulation models without the need of special interfaces between the individual programs. Based on an example, the modeling of the individual subsystems of the vehicle is shown. For the verification of the single subsystems experimental measurements on a vehicle dynamometer have been performed. The comprehensive vehicle model is verified with the measurement data of a ‘real-world’ driving cycle. Key parameters such as coolant temperature, engine temperature, and cabin temperature are compared therefore. Based on an example, the modeling of the individual subsystems of the vehicle is shown. For the verification of the single subsystems experimental measurements on a vehicle dynamometer have been performed. The comprehensive vehicle model is verified with the measurement data of a ‘real-world’ driving cycle. Key parameters such as coolant temperature, engine temperature, and cabin temperature are compared therefore.

Shortening of development times in the automotive industry with simultaneous rise of complexity, efficiency and product variety require more effective, faster and “robust” simulation methods. In this research we focus on computation of cooling packages for vehicles in the concept phase. We extended conventional methods, which proceed from purely deterministic results, by a stochastic computation and CFD calculation, in order to be able to consider the effects of uncertain estimates of boundary conditions and/or the fluctuations, occurring in measurements. The goal is a robust simulation method assisting the cooling package design engineers in the very early concept and development phase, respectively.

Heat management of a vehicle and especially the heat-up characteristic of the combustion engine can strongly influence fuel consumption.
In the development process of new vehicle parts, numerical simulation is indispensable to uncover the effects on the vehicle heat-up in an early stage. Thus, a framework for the virtual product development of innovative thermal management components has been developed.
In the beginning, comprehensive thermal measurements of a vehicle on a roller test bench are performed. On this basis a 1D simulation of the various fluid circuits and components is built up. A thermal engine model is included as well as all necessary circuits for coolant, engine oil, transmission oil, cooling air and charge air. In this framework different product concepts and operating strategies can be compared and the impact on fuel consumption can be revealed for various driving cycles.
The paper shows the working process for a turbo-charged passenger car with special attention to the NEDC and FTP72/75 emission cycles.

Intelligent heat management of conventional vehicle propulsion systems can lead to further reduction of fuel consumption. Especially, the application of variable pumps, actuators and sensors establishes new possibilities. Simulation can help to evaluate different thermal management measures. Control strategies can be developed and the influence on the engine heat-up can be analyzed.

In a first step, comprehensive thermal measurements on a test vehicle are performed and serve as groundwork for fluid-thermal simulations of the operating fluid circuits and the included components.

Based on this 1D fluid-thermal simulation model, solutions for a demand-controlled coolant flow, directed use of heat sources and the intelligent reduction of thermal masses in the warm-up phase are discussed and virtually tested. With emphasis on the NEDC and FTP driving cycles, the impact on fuel consumption reduction is calculated.

In the past few years hybrid vehicles have been in the center of automotive engineering efforts, in particular in the field of passenger cars. But hybrid powertrains will also be important for commercial trucks. This focus on hybrid vehicles leads to high demands on thermal management since the additional components in a hybrid vehicle need appropriate cooling or even heating.

In the given paper the simulation of a complete cooling system of a hybrid commercial vehicle will be explained. For this virtual examination the commerical 1D thermal management software KULI will be used, a co-simulation with several programs will not be done deliberately. Yet all aspects which are relevant for a global assessment of the thermal management are considered.

The main focus is put on the investigation of appropriate concepts for the fluid circuits, including low and high temperature circuits, electric water pumps, etc. Moreover, also a refrigerant circuit with a chiller for active battery cooling will be used, the appropriate control strategy is implemented as well.

For simulating transient profiles a simple driving simulation model is included, using road profile, ambient conditions, and various vehicle parameters as input. In addition an engine model is included which enables the investigation of fuel consumption potentials.

This simulation model shows how the thermal management of a hybrid vehicle can be investigated with a single program and with reasonable effort.

This paper presents a method for a cool down simulation of passenger compartments. Main targets were the reduction of modelling effort, limited CPU-time consumption, high accuracy, allowing the prediction of temperature diffusion in the cabin for parameter studies for transient analysis. The process is based on a 1D model, while 3D effects like diffusion fields and mass flow fields are implemented from CFD data. For a given flow field, the transport of heat and humidity are computed. The simulation model contains a specifically developed multi zone cabin model, which can deal e.g. with multiple inlets into the cabin, solar radiation, and recirculation for pre-defined cabin types. Different materials for the cabin walls, like doors, floor, roof and windows are considered by a multi-layer model. To describe the transient cool down behaviour of the HVAC air-path, the simulation was done with a full AC circuit, consisting of evaporator, condenser, TXV and compressor. The transient thermal behaviour of walls and internal masses is considered. The AC system is combined with a 1D model of the engine cooling package. The simulation of the AC circuit is based on the transient behaviour of the cabin. The presented paper covers the definition and the description of the workflow as well as the verification with test data.