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In this work, a quasi-dimensional, multi-zone combustion model is analytically presented, for the prediction of performance and nitric oxide (NO) emissions of a homogeneous charge spark ignition (SI) engine, fueled with biogas-H2 blends of variable composition. The combustion model is incorporated into a closed cycle simulation code, which is also fully described. Combustion is modeled on the basis of turbulent entrainment theory and flame stretch concepts. In this context, the entrainment speed, by which unburned gas enters the flame region, is simulated by the turbulent burning velocity of a flamelet model. A flame stretch submodel is also included, in order to assess the flame response on the combined effects of curvature, turbulent strain and nonunity Lewis number mixture. As far as the burned gas is concerned, this is treated using a multi-zone thermodynamic formulation, to account for the spatial distribution of temperature and NO concentration inside the burned volume.

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.

A computer analysis is developed for studying the energy and exergy performance of a turbocharged diesel engine, operating under transient load conditions. The model incorporates some novel features for the simulation of transient operation, such as detailed analysis of mechanical friction, separate consideration for the processes of each cylinder during a cycle (“multi-cylinder” model) and mathematical modelling of the fuel pump. The model is validated against experimental data taken from a turbocharged diesel engine, located at the authors' laboratory, operated under transient load conditions. The availability terms for the diesel engine and its subsystems are analyzed, i.e. cylinder for both the open and closed parts of the cycle, inlet and exhaust manifolds, turbocharger and aftercooler.

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.

In the present work a multi-zone combustion model, initially developed for naturally aspirated, high-speed, direct injection diesel engines, is used for studying the performance and emission characteristics of large scale, slow-speed marine diesel engines. Up to now pollutant emissions was not considered a problem in the field of marine engines, since no specific legislation existed. However, the International Maritime Organization (IMO) is forwarding a legislation that will be applicable in the next years concerning soot and nitric oxide (NO) emissions. This legislation will make it impossible for vessels to enter the native waters into countries where this legislation applies. Due to this fact, engine manufacturers are making serious efforts to design new engine builds with reduced soot and nitric oxide emissions using new designs and exhaust gas aftertreatment systems.

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.