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A comprehensive structural analysis simulation model is used for describing the thermal condition of a four-stroke, air-cooled, DI diesel engine under steady and transient operation. Two- and three- dimensional finite element analyses are implemented for the representation of the complex geometry metal components (piston, liner, cylinder head), in a way that the temperature and heat flux variations are calculated during any transient event. A detailed thermodynamic simulation model of engine operation is utilized for the determination of boundary conditions on the combustion chamber sides of each component. During an engine transient, processing of experimental cylinder pressure diagrams on a cycle to cycle basis resulted in the estimation of heat resease rate and boundary conditions (gas temperature, heat transfer coefficient) variation from the initial to the final engine thermodynamic state. Consequently, the power and specific fuel consumption curves can be accurately determined.

The reduction of brake specific consumption and pollutant emissions are issued as future challenges to diesel engine designers due to the depletion of fossil fuel reserves and to the continuous suppression of emission regulations. These mandates have prompted the automotive industry to couple the development of combustion systems in modern diesel engines with an adequate reformulation of diesel fuels and have stirred interest in the development of “clean” diesel fuels. The use of oxygenated fuels seems to be a promising solution towards reducing particulate emissions in existing and future diesel motor vehicles. The prospective of minimizing particulate emissions with small fuel consumption penalties seems to be quite attractive in the case of biodiesel fuels, which are considered as an alternative power source. Studies conducted in diffusion flames and compression ignition engines have shown a reduction of soot with increasing oxygen percentage.

During the past years, extensive research efforts have led to the development of diesel engines with significantly improved power concentration and fuel efficiency as compared to the past. But unfortunately, the increase of engine thermal efficiency is accompanied by a sharp increase of peak cylinder pressure. At the moment, peak pressures in the range of 230-240 bar have been reported. Naturally, a question remains as to whether such increased peak pressures could have an overall detrimental impact on mechanical efficiency. Initially, it was expected that these would have a negative impact and this was the motive for conducting the present work and developing a detailed friction model. Up to now, various correlations have been proposed that provide the friction mean effective pressure as a function of engine speed and load mainly, neglecting the effect of peak pressure or using data up to 130-140 bar.

The compression ignition engine of the dual fuel type has been employed in a wide range of applications to utilize various gaseous fuel resources while minimizing soot and oxides of nitrogen emissions without excessive increase in cost from that of conventional direct injection diesel engines. The use of natural gas as a supplement for liquid diesel fuel could be a solution towards the efforts of an economical and clean burning operation. The high auto-ignition temperature of natural gas is a serious advantage since the compression ratio of most conventional diesel engines can be maintained. In the present work a comparison between experimental and theoretical results is presented under dual fuel operation. For the theoretical investigation a computer simulation model has been developed which simulates the gaseous fuel combustion processes in dual fuel engines.

Diesel engine manufacturers have succeeded in developing engines with high power concentration and thermal efficiency without disregarding to comply with the continuous stringent emission regulations. Nowadays, several techniques such as injection control strategies, EGR and exhaust after treatment devices have been used to reduce diesel emissions. However, emission control alternatives are often accompanied by fuel consumption or cost penalties and also, the request for improving the pollutant emissions behavior of the existing diesel vehicle fleet has become mandatory. Thus, research scientists and engineers have focused also on the area of fuel composition for the reduction of pollutant emissions. Of major importance seems to be the use of oxygenated additives to reduce particulate emissions. According to recent studies, soot emissions are decreased following the increase of oxygen percentage.