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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 the feasibility of the application of a system conceived by Järvi to a 125 cm3, four strokes motorcycle engine built by Piaggio Company is investigated. This study was carried out using a one-dimensional model built with the well known CFD 1D code Wave and validated in a previous work. An analytical study was performed on the kinematic scheme of the mechanism in order to establish the relationship between control ramp and valve lift. The control ramp shape was then optimized accordingly with the results of the fluid dynamic analysis performed through the above mentioned Wave model.

A very stringent problem in most of European cities is the individual mobility. This problem is mainly caused by traffic jam and arising from this are two particularly interesting environmental issues: pollution and noise [1]. Use of two wheeler vehicles does not represent the final solution to these problems, nevertheless they can supply a useful aid to ease them. Recently, two stroke engines are being replaced with four stroke engines. For small capacity engines this means a true reduction in exhaust emissions, especially unburned hydrocarbons (HC), but, on the other hand it involves a performance reduction, particularly for sudden accelerations, which constitute an essential requirement for these vehicles [2, 3, 4, 5]. Hybridisation can help to fill the gap between two stroke engines and cleaner, but less performing four stroke engines [6]. At the same time, it can help to lower fuel consumption, by means of a reduction in the revolution speed [2, 5].

The development trends of advanced automobile engines towards high power-to-volume and power-to-mass ratios are partially in contradiction with the requirements regarding drastically reduced fuel consumption and pollutant emission. The development way of the engine between customer acceptance and limitations by law is mainly determined by the optimization of scavenging, mixture formation and combustion characteristics, as functional base for the engine design. The paper presents a new direct injection concept and its optimization correlated with the scavenging process. The process simulation - as a base for the engine development - was carried out using concomitantly two CFD codes - FIRE and VECTIS. The main optimization parameters were the combustion chamber design, the injector location, the spray characteristics, the spark location, the injection timing and duration.

The paper presents the results of a down-sizing concept implicating gasoline direct injection, which is applied to a four-stroke four-valve SI engine with a displacement of 500 ccm per cylinder. The typical features of a down sized engine such as a high level of engine speed, high power density at low fuel consumption and a low level of pollutant emission form the main targets of this study. Numerical models of the process stages have been developed in 1D and 3D CFD codes. The accurateness of the models has been proved using experimental results. The main work consisted on the application of a direct injection system to the engine. The compact engine design and the high compression ratio have been maintained resulting in a combustion chamber design without any cavities or bowls. To obtain accurate results, the simulation work has been carried out using two different CFD-codes (FIRE and VECTIS); the results have been analyzed and compared.

The spray characteristics are determining factors for the quality of mixture formation respectively for the combustion, when applying GDI. Their variation with load and speed is a basic criterion for the adaptability of an injection system type to an engine with known requirements. CFD models of the fluid flow dynamics, mixture formation and combustion are a determining condition for such adaptation. The paper presents the development results of a GDI four-stroke, four-valve, single cylinder engine. The pressure pulse injection system involved in this application is analyzed and presented from the fluid-dynamic behavior up to the obtained injection spray characteristics. The mixture formation and combustion processes are simulated for different load and speed values, respectively for favorable combinations of parameters, such as the injection system configuration, the opening pressure of the applied mechanical injector and the injection duration.

The fuel direct injection in SI engines is demonstrating a remarkable potential regarding the reduction of consumption and pollutant emission. Nevertheless, the management of the mixture formation “in-cylinder” - in conditions of a short duration and of a complex fluid dynamic configuration imposes both an accurate modeling and an exact control of the process. The problem gains on complexity when considering the use of alternative fuels which becomes more and more a subject of actuality. The paper presents a comparative analysis of mixture formation process and engine performances, when applying direct injection of gasoline, respectively of ethanol in a four-stroke single cylinder SI engine. The modulation of the injection rate shape is the result of a fuel high pressure wave, generated in a pressure pulse direct injection system.