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In order to develop modern two-stroke engines with low fuel consumption, respectively with low exhaust emissions, two alternative development areas - the mixture formation and the scavenging system - have been correlated. For a satisfying mixture formation without fuel losses by scavenging, the direct injection seems to be one of the best solution for the high speed two-stroke engine of the future. On the other hand the modern development of two-stroke scavenging systems shows a large field of application and improvement methods of cross and loop scavenging [1]. Based on the specific optimisation factors of the injection system, respectively of the scavenging system, the aim off this common work of the Universities of Pisa and Zwickau is to correlate both the optimisation fields in an advantageous mixture formation process.

The heat transfer process has always played an important role in internal combustion engine design. An area of importance is the thermal loading of engine structural components, and the optimisation of engine cooling system. The engine cooling system of a vehicle makes up a significant portion of the total component cost. It also places demands on other vehicle systems, and the quality of its design is evident to the customer in terms of the power that it consumes that for a two-stroke engine with forced convection air cooling can be also the 10% of the total brake power. An area of importance is the calculation of the thermal load of engine structural components, and the optimisation of engine cooling system. Optimisation of engine cooling requires the solution of the coupled problem of heat transfer from gases to walls and of heat convection from the structure (generally a finned surface) to the external environment.

World-wide attention to environmental issues in recent years has resulted in a greater demand for cleaner engines, especially with regards to the two-stroke. Considering the techniques for reduction of exhaust emissions the direct injection of fuel into the combustion chamber adapted for a loop scavenged cylinder seems to be an advantageous method. This paper describes the application of advanced experimental and computational techniques to evaluate mixture formation produced on a commercial engine by means of a direct fuel injection strategy, namely a ram-tuned injection system. The injection system data are experimental while air flow and fuel air mix for the direct injection engine are calculated using a turbulent model of the three dimensional code FLUENT. Extension of a first work in this field is presented. In particular two possible strategies to simulate direct injection are tested. The influence of different boundary conditions on the scavenging process was examined too.

The chief aim of the work concerns the optimisation of a forced convection air cooling system and particularly of the external heat exchange surfaces, applied on a small internal combustion two-stroke engine. At the present time in the industrial practice, the design of cooling system and of fin arrays is developed by means of simple technical criteria, starting fiom the assumption to consider the thermal loading of engine about 30% of the power furnished by fuel. This paper describes an approach that combines theoretical and simulation techniques with experimental methods. Attention is primarily focused on the most important input data of this kind of optimisation represented by the thermal load of the engine. Then attempts are made to establish some general criteria for the optimum design. The proposed calculation methods have carried out the creation of a PC software, useful instrument for the design phase of a new engine or for the improvement of an old one.

The future development of two-stroke engines will be conditioned by the drastic reduction of pollutant emission, especially of hydrocarbon. This goal is not achievable only by scavenging improvement, rather a new quality of mixture formation using direct injection is imposed. However, the internal mixture formation in a large range of speed and load, considering the scavenge flow particularities of two-stroke engines as well, appears as an extremely complex process. Thereby a numerical simulation is in this case very effective for the adaptation of a direct injection method at the engine. The paper presents a concept for modeling and optimization of the mixture formation process within a high-speed two-stroke engine with liquid fuel injection system. The injection system generates a pressure pulse which is not dependent on the engine speed.