Predictive Simulation Strategies for the 2-Stroke Scavenging Process within the Scope of the Development Process

摘要

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 second one is a predictive simulation which is required to determine basic engine parameters in order to shorten the development time. The detailed simulation is usually done with the use of 3D-CFD-simulation codes which are able to model complex geometries and to simulate e.g. the combustion process and fuel spray. Unfortunately the 3D-simulation is rather dedicated to evaluation and analysis, as measurement data for initial conditions are required and the model-build up and calculation times are relatively high. This leads to the fact that most times the simulation status does not correspond with the development progress and/or the simulation results are not achieved before the prototype phase begins. Regarding gas dynamics, the 1D-simulation seems to be more applicable for predictive simulation as the model is simpler and therefore requires less computational time compared to the 3D-approach. This means that a high number of iterations can be calculated in order to get a converged solution which lowers the demands on initial conditions. Detailed understanding of the thermodynamic processes and correct prediction and optimization of power carried out within the time frame of the development process is the only possibility to achieve future emission levels while maintaining high power. For these rising demands on predictive and detailed simulation strategies a combination of the two approaches is necessary. In the present paper, the existing 0D-, 1D- and 3D-simulation techniques and the current approaches of a combination or coupling of the 0D-, 1D- and 3D-simulation will be described in detail including a discussion of their advantages and disadvantages. A comparison of their integration possibilities into the developmental process is also performed and special focus will be put on the determination of the proper simulation approach for the single domains of the simulation model (the cylinder itself, for example, requires a different simulation approach than the exhaust or intake part). The paper will describe experiences with these simulation strategies within the development process and presents examples of performed simulation tasks. Finally, a new strategy for an integrated and optimized 1D- and 3D-simulation will be presented. This new approach will enable an effective and accurate simulation of the 2-stroke scavenging within the development process, its impact on development time and prediction quality will be considered in future publications.