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The present paper deals with the development and evaluation of a new semi-empirical, pseudo-multi-zone model capable of estimating NOx emissions for various types of diesel engines and also different engine configurations. The specific model is physically based due to the use of the first thermodynamic law and the consideration of combustion chemistry and dissociation of the combustion products during the closed part of the engine cycle. The model estimates the fuel burning rate through Heat Release Rate Analysis of the measured cylinder pressure which is then coupled to a simplified multi-zone approach, assuming that each element of fuel burns individually at controlled conditions having from this point on its own history inside the combustion chamber. From this procedure, a simplified multi-zone semi-empirical model is developed, that accounts for the temperature distribution inside the combustion chamber and its evolution during an engine operating cycle.

During the past years most fundamental research worldwide has been concentrated on the direct injection diesel engine (DI). This engine has a lower specific fuel consumption when compared to the indirect injection diesel engine (IDI) used up to now in most passenger cars. But the application of the direct injection engine on passenger cars and light trucks has various problems. These are associated mainly with its ability to operate at high engine speeds due to the very low time available for combustion. To overcome these problems engineers have introduced various techniques such as swirl and squish for the working fluid and the use of extremely high pressure fuel injection systems to promote the air-fuel mixing mechanism. The last requires the solution of various problems associated with the use of the high pressure and relatively small injector holes.