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Nowadays, politicians are forced by air pollution prevention to demand zero emission vehicles (ZEV) in the form of pure electric vehicles. The poor capacity to weight factor of actual batteries compared to any kind of liquid or gaseous hydro-carbon fuel is the main reason for the retarded implementation of ZEV. Solutions offered by automobile manufacturers are mild to full hybrid powertrains based on the well established ICE platform. The difficulty of those approaches of electrification is to compete with the performance and benefit costumers expect from standard automobiles. Pure electric vehicles are rare and often disappointing regarding range and/or performance. Additionally the costs for such vehicles, which are mainly driven by the battery prices, are comparatively high, impeding their market entrance and acceptance. Low price electric city scooters are actually offered as pure electric vehicles in a wide variety of different models.

The continuous improvement of the numerical methods together with the increase of computer power allows the simulation of more and more complex technical problems even for increasing calculation domains. In order to get effective and significant results for the two-stroke two-cylinder engine, the simulation of the complete geometry with both cylinders and the complete exhaust port is required. However, the simulation requires several revolutions until the gas dynamic inside the exhaust port achieves a steady state. Hence, the simulation of a two-cylinder two-stroke engine consumes a lot of calculation time; nevertheless it is still acceptable in the development process of a new engine. This paper covers the discussion of the simulation of a two-stroke two-cylinder high-performance engine using the commercial CFD Code Fluent 6.3.26. The used settings for the simulation, like the turbulence model, injection settings, combustion model and reduced reaction mechanism are presented.

Computational Fluid Dynamic (CFD) is the state of the art tool for the development of an internal combustion engine (IC engine), especially for the scavenging process, internal mixture preparation, and combustion. CFD simulation is apt for the detailed simulation of the processes inside the IC engine and consequently it consumes a lot of computer resources. The time for a calculation can be decreased by a reduction of the full three-dimensional (3D) calculated domain. The omitted domain parts can be either replaced by a simplified model or by the smart exploitation of symmetry-conditions. The corresponding boundary conditions for the 3D domain often stem from one dimensional (1D) calculation, measurement data, or corresponding boundary values. In this paper, a new symmetry and time delayed boundary condition is introduced together with its application in a simulation of an internal combustion engine.

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 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.

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.