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The past decade significant research effort has concentrated on the DI diesel engine due to stringent future emission legislation which requires drastic reduction of engine tail pipe pollutant emissions, mainly PM and NOx, without significant deterioration of specific fuel consumption. Towards this effort, the important role of modeling to investigate and understand the impact of various internal measures on combustion and emissions has been widely recognized. Phenomenological models can significantly contribute towards this direction because they have acceptable prediction capability and the advantage of low computational time. This enables the production of results, on a cycle basis, that indicate the effect of various parameters on both engine performance and emissions. Therefore their use can significantly reduce engine development time (i.e. reduction of experimental effort) and cost.

A major challenge for researchers and engineers in the field of diesel engine development is the simultaneous reduction of both NOx and soot emissions from diesel engines to comply with strict future emission legislation. One of the promising internal measures that focus on the reduction of soot emissions is post fuel injection which does not have a serious effect on NOx emissions. The main parameters involved when using this technique are post fuel quantity and dwell angle between the main and the post fuel injection events. In the present work a detailed computational investigation has been conducted to determine the effect of post fuel injection on engine performance and pollutant emissions (NOx and soot). To this scope, a phenomenological multi-zone combustion model has been used, properly modified to take into account the interaction of post and main injected fuel amounts.

In the present work a sensitivity analysis is conducted using a multi-zone phenomenological model developed in the past by the author's, to estimate the effect of model's constants on engine performance and emissions. The constants used for this analysis are those embedded in the semi-empirical relations of the model, regarding air entrainment rate, combustion rate, ignition delay and evaporation rate. The model is applied on a heavy duty supercharged DI diesel engine and the effect of each of these constants on measurable engine parameters is defined. From the sensitivity analysis the relation between model constants and engine output data is derived. These results are used to define a constants determination procedure. The target is to define a limited number of adjustable constants so that the procedure can be of practical use. Following this, the calibration procedure is applied to determine the value of each constant, at various engine speeds and loads for the engine in question.

The model has already been applied on an old technology, naturally aspirated HSDI Diesel engine and on a heavy-duty turbocharged DI one equipped with a high pressure PLN fuel injection system, and the results were satisfying as far as performance and pollutant emissions (Soot and NO) are concerned. Taking into account that the main scope of engine simulation models is to assist engineers and researchers to understand the complex mechanisms involved in diesel engine combustion and pollutants formation and that through the continues engine development, new techniques are implemented, it is obvious that engine simulation models must always be enhanced with new features in order to be kept up-to-date. In this study the model has been modified to take into account the effect of EGR, since the latter one is a measure that will be used more extensively in the future to control NO emissions from turbocharged HDDI Diesel engines.

This work is a part of an extended investigation conducted by the authors to validate and improve a newly developed quasi-dimensional combustion model. The model has been initially applied on an old technology, naturally aspirated HSDI Diesel engine and the results were satisfying as far as performance and pollutant emissions (Soot and NO) are concerned. But since obviously further and more extended validation is required, in the present study the model is applied on a new technology, heavy-duty turbocharged DI Diesel engine equipped with a high pressure PLN fuel injection system. The main feature of the model is that it describes the air-fuel mixing mechanism in a more fundamental way compared to existing multi-zone phenomenological combustion models, while being less time consuming and complicated compared to the more accurate CFD models. The finite volume method is used to solve the conservation equations of mass, energy and species concentration.

The fundamental understanding of mixture formation and combustion process taking place in a DI diesel engine cylinder is an important parameter for engine design since they affect engine performance and pollutant emissions. Multi-dimensional CFD models are used for detailed simulation of these processes, but suffer from complexity and require significant computational time. The purpose of our work is to develop a new quasi-dimensional 3D combustion model capable of describing the air fuel mixing, combustion and pollutant formation mechanisms, on an engine cycle by cycle basis, needing reasonably low computational time compared to CFD ones, while describing in a more fundamental way the various processes compared to existing multi-zone phenomenological models. As a result, a number of problems associated with the application of multi-zone models are resolved.

The direct injection heavy-duty diesel engine is the main propulsion unit for trucks, lories and other heavy-duty vehicles mainly due to its superior efficiency when compared to other existing reciprocating engines. However, this engine suffers from relatively high particulate and nitric oxide emission levels. Considering current legislation for emissions and especially future limits, it seems that a great deal of research is required to satisfy these limits and maintain efficiency at a high level. As widely recognized, the fuel injection mechanism plays an important role for both engine performance and pollutant emissions. The major problem is to seek solutions that enable the control of major pollutants, nitric oxide and particulate matter. For this reason, various injection rate shapes have been proposed which require sophisticated fuel injection equipment and extremely high fuel injection pressures. Now two main categories are considered, common rail fuel injection system and PLN.

The purpose of this paper is to present an alternative method to predict the temperature and flow field in a motored internal combustion engine with bowl in piston. For the fluid flow it is used a phenomenological model which is coupled to a computational fluid dynamic method to solve the energy conservation equation and therefore the temperature field. The proposed method has the advantage of simplicity and low computational time. The computational procedure solves the energy conservation equation by a finite volume method, using a simplified air motion model (estimating axial and radial velocities) to calculate the flow field. The finite volume discretization employs the implicit temporal and hybrid central upwind spatial differencing. The grid used contracts and expands following the piston motion, and the number of nodes in the direction of piston motion vary depending on the crank angle.

The diesel engine is a thermal machine with very high efficiency when compared to other similar engines. But up to now its application for automotive purposes is limited due to the existing limits in power concentration, speed and noise. Up to now most diesel engines used for automotive applications are of the Indirect Injection type due to their ability to operate at relatively high rotational speeds and at low Air Fuel Ratios when compared to direct injection diesel engines. Currently the research is mainly concentrated to DI diesel engines due to their lower specific fuel consumption. Nevertheless it is not entirely clear that IDI diesel engines will be completely replaced. But if we consider in general the diesel engine regardless of its type, it is widely recognized that one of the major problems with their application on automobiles is the emission of particulates (smoke etc.).