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Many technologies are being developed to solve the trouble of the urban pollution. Among other solutions (improvements in engine control and combustion, electrical propulsion) one of the foreseen ways is the employment of low or zero carbon content fuels, such as hydrogen. In fact a nearly zero emission vehicle may be obtained through the hydrogen propulsion; in this case the only polluting agents are nitrogen oxides if an internal combustion engine is used. Though fuel cells are considered as the most promising solution in the long term, they are still in their prototypical phase and the use of the internal combustion engine use remains until today a relevant topic. It has been evident since the 80s that direct injection is the only method to get a high specific power without pre-ignition and backfire phenomena. However this technique shows a higher difficulty in getting a well-mixed charge.

The use of numerical techniques is widely accepted by manufactures in order to increase engine durability and performances and reduce emissions. The effective thermal load prediction is always considered a nodal point to correctly assess the coolant mass flow rate and jackets arrangement. In literature many approaches used to analyzed the in-cylinder heat transfer can be found and they can be classified as follows: methods based on the steady convective heat transfer, approaches based on the solution of the unsteady heat conduction equation by means of the knowledge of the temperature profile, approaches based on the energy conservation for the whole mass contained inside the cylinder. The purpose of this paper is to define a proper methodology to evaluate the thermal flow distribution and intensity inside the engine liner, head and coolant channel.

In this paper various methods of studying in-cylinder heat transfer in small displacement two-stroke engines are presented and compared. First of all, the mistakes that can be caused by the application of steady heat transfer models to the study of such a complex phenomenon are considered. After the demonstration that an ordinary convective heat transfer model determines mistakes in the evaluation of the thermal load, three-dimensional analysis and improved heat transfer models are considered. The multidimensional code Fluent is used for the 3-D fluid mechanics simulation. Numerical analysis evidences the importance of the non-uniformity of the gas temperature inside the cylinder. The improved models considers the fact that heat transfer during compression and expansion is out of phase with bulk gas-wall temperature difference and that the great part of the heat transfer is linked to the combustion.

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 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.