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CFD has been widely used to predict the flow behavior inside 2-stroke engines over the past twenty years. Usually a mass flow profile or a simple 0D model is used for the inlet boundary condition, which replaces the complete intake geometry, such as reed valve, throttle, and air box geometries. For a CFD simulation which takes into account the exact reed valve geometry, a simulation of all above mentioned domains is required, as these domains are coupled together and thus interact. As the high speed of the engine affects the opening dynamic and closure of the reed valve, the transient data from the crank case volume and the section upstream the reed valve have an important influence on the reed petal dynamic and therewith on the sucked fresh air mass of the engine. This paper covers a methodology for the transient CFD simulation of the reed petals of a 2-stroke engine by using a 2D model.

The two stroke engine has a wide range of application, especially in the field of recreational vehicles, handheld products and small two-wheelers. This is due to the advantages of the two stroke working principle: high power density, low weight, and low costs. In order to reduce the system-inherent disadvantages of the loop-scavenged two stroke engine developments using latest methods are necessary. One of these methods is the CFD simulation of the scavenging process, the high pressure cycle and the injection process. Reliable predictive simulation in the early development phase of a new engine is required to shorten the development time and to reduce prototype and test bench costs. In previous investigations (1) [SAE 2005-32-0099; JSAE 20056552] the strategies for the simulation and the requirements for a predictive simulation were discussed. Finally a new methodology which bases on the combination of 3-dimensional (3D) and 0/1-dimensional (0/1D) CFD simulation was presented.

Research and development engineers have paid much attention to coupling commercial tools for examining complex systems, recently. The purpose of this paper is to demonstrate an automated coupling of a CFD program with a commercial thermal radiation tool. Based on a previous work the coupling behaviour of a parallelized CFD code is being demonstrated. The automation thus speeds up the calculation procedure even for transient simulations not relying on codes of just one vendor. The simulation is then compared with measurements of temperatures of an actual SUV and conclusions are drawn.

CFD simulation (Computational Fluid Dynamics) is a state of the art tool for the development of internal combustion engines, especially for internal mixture preparation, scavenging process and combustion. Simulation offers an array of information in the early development phase without the need of building a prototype engine. It shortens the development time, reduces the number of prototypes and therewith test bench costs. In previous investigations [SAE 2005-32-0099] and [SAE 2007-32-0030] a new coupling methodology which bases on the combination of three-dimensional (3D), one-dimensional (1D), and zero-dimensional (0D) CFD calculation has been presented. This methodology uses a new multidimensional interface technology and is able to handle 3D-0D, 3D-1D and 3D-3D connections. The special feature of this methodology is the capability of being placed on any position in the 3D CFD mesh.

The exhaust system design has an important influence on the charge mass and the composition of the charge inside the cylinder, due to its gas dynamic behavior. Therefore the exhaust system determines the characteristics of the indicated mean effective pressure as well. The knowledge of the heat transfer and the post-combustion process of fuel losses inside the exhaust system are important for the thermodynamic analysis of the working process. However, the simulation of the heat transfer over the exhaust pipe wall is time consuming, due to the demand for a transient simulation of many revolutions until a cyclic steady condition is reached. Therefore, the exhaust pipe wall temperature is set to constant in the conventional CFD simulation of 2-stroke engines. This paper covers the discussion of a simulation strategy for the exhaust system of a 2-cylinder 2-stroke engine until cyclic steady condition including the heat transfer over the exhaust pipe wall.

The advantages of 2-stroke engines, high power and low weight, are in conflict with their disadvantages, high emissions and bad fuel economy. As these disadvantages are caused by the scavenging process, a reason for the problem can be analyzed by using three dimensional computational fluid dynamics simulation (3D CFD simulation). The scavenging losses can be dramatically reduced with a high pressure fuel injection strategy. The purpose of this strategy is to prevent a fuel concentration in the incoming charge and to reduce the fuel concentration inside the exhaust system. These advantages can only be successfully exploited with the application of an optimal injection strategy. This paper covers a spray study for a gasoline direct injection (GDI) high performance 2-stroke engine using the commercial CFD Code Fluent.

Recent trends in computer aided engineering (CAE) and optimization (CAO), seem to be introducing more and more simulation techniques based upon the combination of two ore more simulation tools in order to accomplish a common task. One factor that led to this co-simulation trend is the ongoing development of computational resources which enable the working-together of different simulation tools which are of themselves usually complex enough and finishing the designated tasks within acceptable time limits. This paper deals on the one hand with an independent coupling integration approach and on the other hand with some basic assumptions regarding the synchronization in the time domain which form the very basics of each co-simulation process.

The present paper is part of a more comprehensive study concerning the surface flow in the engine compartment and focuses on the fluid flow of a cooling system in a modern vehicle. The complexity of this field needs to further optimization in the integration of 3D CFD (Computational Fluid Dynamics) methods. An important focus lies on the modeling of radiators and fans. A new simulation method needs to be validated. For this purpose a component test bench was built. This paper shows the results oft the simulation on the test bench and the CFD analysis. All the fan and radiator model configurations have been studied by means of a commercial CFD package. The comparison of the results gives a better understanding of the total system performance for a faster and more reliable preliminary design.

The wide variety of applications of the loop scavenged 2-stroke engine is based on 3 advantages which emerge from the 2-stroke working principle: the high power density, the low weight, and the low production costs. An important aim of research activities in the field of 2-stroke engines is to optimize these advantages while minimizing the known disadvantages of high emissions and fuel consumption. Important tasks of the research work within the development process are the prediction of power and emissions of engine concepts and the simulation with special regard to the scavenging process and the high pressure cycle. In this area of research two state of the art simulation approaches exist. The first one is a detailed simulation of the scavenging and combustion process which is necessary to understand and optimize the fundamentals of the 2-stroke engine.

The development and optimization of two stroke engines, especially the development of internal mixture preparation and the combustion process, require effective and reliable simulation in order to shorten the development time and to reduce prototype and test bench costs. CFD (Computational Fluid Dynamics) is a state of the art tool to optimize and visualize the fluid processes, e.g. scavenging, in-cylinder charge motion, spray formation, mixture preparation or combustion. The drawback of full 3D CFD simulation is the required time for grid generation and calculation of the model, especially for the simulations in the early development phase or in the concept phase as the available time for simulation is limited. Additionally, two stroke specific models e.g. for the reed valve, are not available in commercial 3D CFD codes. In previous investigations [SAE 2005-32-0099] the strategies and the requirements for a predictive simulation have been discussed.