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Considering future emission legislation for HD diesel engines it is apparent that it will be probably necessary to employ A/T devices to achieve them. The main problem concerns the simultaneous control of both NOx and particulate emissions at an acceptable fuel penalty. Concerning particulate matter the use of particulate traps is considered to be a proven technology while for NOx emission control; various solutions exist mainly being the use of SCR catalysts or LNT devices. But LNT traps require periodical regeneration, which is accomplished by generating reducing agents i.e. CO and H2. The present investigation focuses on the regeneration of LNT devices through the engine operating cycle. This can be achieved using two techniques, additional injection of fuel at the exhaust manifold (external measures) or operation at low lambda values in the range of 1.0 or lower (internal measures).

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.

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.

Engineers use phenomenological simulation models to determine engine performance. Using these models, we can predict with reasonable accuracy the heat release rate mechanism inside the engine cylinder, which enables us to obtain a prediction of the pressure history inside the engine cylinder. Using this value and the volume change rate of the combustion chamber, we can then estimate the indicated power output of the engine. However, in order to obtain the brake engine power output we must have an indication for the mechanical losses, a great part of which are friction losses. Up to now various correlations have been proposed that provide the frictional mean effective pressure as a function mainly of engine speed and load. These correlations have been obtained from the processing of experimental data, i.e. experimental values for the indicated and brake power output of engines.

During the recent years, extensive research conducted worldwide in the field of Heavy Duty Diesel engines has resulted to a significant improvement of engine performance and emissions. These efforts have been assisted from simulation models providing good results. Towards this direction a multi-zone model developed by the authors has been used in the past to examine the effect of injection pressure on DI diesel engine performance and emissions. The attempt was challenging since no experimental data existed when the calculations were conducted, to support the findings. Eventually, experimental data concerning engine performance and emissions became available using slightly different operating conditions and injection pressure data. In the present study an attempt is made to evaluate the prediction ability of the multi zone model by comparing the theoretical results with experimental data and explain any discrepancies between them.

Homogeneous Charge Compression Ignition (HCCI) engines have the potential of reducing NOx emissions as compared to conventional Diesel or SI engines. Soot emissions are also very low due to the premixed nature of combustion. However, the unburned hydrocarbon emissions are relatively high and the same holds for CO emissions. The formation of these pollutants, for a given fuel, is strongly affected by the temperature distribution as well as by the charge motion within the engine cylinder. The foregoing physical mechanisms determine the local ignition timing and burning rate of the charge affecting engine efficiency, performance and stability. Obviously the success of any model describing HCCI combustion depends on its ability to describe adequately both the chemistry of combustion and the physical phenomena, i.e. heat and mass transfer within the cylinder charge. In the present study a multi-zone model is developed to describe the heat and mass transfer mechanism within the cylinder.

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.

Simulation models are widely used from research engineers to investigate the combustion mechanism of DI diesel engines. These models can be used, as tools to either comprehend information provided by experimental data or to perform predictions and assist the development process. As widely recognized a valuable source of information for engine performance and emissions studies is the cylinder pressure trace. It can provide after processing information concerning the combustion rate of fuel injected inside the combustion chamber. Often it is also used to calibrate simulation models or even to derive correlations to represent the combustion rate of fuel inside the combustion chamber. The present research team has during the development process of a simulation model for the description of DI diesel engine performance and emissions realized that there exists a serious problem.

During the last years a great deal of efforts have been made to reduce pollutant emissions from Direct Injection Diesel Engines. The use of gaseous fuel as a supplement for liquid diesel fuel seems to be one solution towards these efforts. One of the fuels used is natural gas, which has a relatively high auto - ignition temperature and moreover it is an economical and clean burning fuel. The high auto - ignition temperature of natural gas is a serious advantage against other gaseous fuels since the compression ratio of most conventional diesel engines can be maintained. The main aspiration from the usage of dual fuel (liquid and gaseous one) combustion systems, is the reduction of particulate emissions. In the present work are given results of a theoretical investigation using a model developed for the simulation of gaseous fuel combustion processes in Dual Fuel Engines.

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 direct injection diesel engine is one of the most efficient thermal engines known to man. For this reason DI diesel engines are widely used for heavy-duty applications and especially for the propulsion of trucks. Even though the efficiency of these engines is currently at a high level there still exist possibilities for further improvement. One way to accomplish this is by increasing the injection timing which usually improves, depending on the operating conditions, the indicated efficiency of the engine. On the other hand advanced injection timing has a negative effect on peak pressure causing a serious increase of its value, a negative effect on NO emissions which are also seriously increased and a positive effect on Soot emissions which are reduced. In the present work a theoretical and experimental investigation is presented to determine the effect of more advanced injection timing on engine performance and pollutant emissions.

Pollutant emissions and specifically NO and soot are one of the most important problems that engineers have to face when developing heavy duty DI diesel engines. Two main strategies exist as options for their control, reduction inside the engine cylinder using advanced combustion and fuel injection technologies and use of after-treatment systems. In the present work it is examined the use of EGR to control the formation of NO inside the cylinder of an engine with extremely high peak pressure. The work is applied on a single cylinder truck test engine developed under a project funded by the European Community focusing on the improvement of heavy duty DI diesel engine efficiency using increased injection timing. Use is made of a simulation model to predict the effect of more advanced injection timing on engine performance and emissions. The model has been modified to include the effect of EGR used to c ontrol the formation of NO which is considerably increased at high injection timings.

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 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 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.

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.

Cylinder pressure measurements are common practice for internal combustion reciprocating engines during field or lab applications for the purpose of combustion analysis, condition monitoring etc. The most accurate method is to measure cylinder pressure using a crank angle encoder as a trigger source to guarantee cylinder pressure measurement at predefined crank angle events. This solution, even though favorable, presents a number of practical difficulties for field applications and increased cost, for this reason its use is practically restricted to lab applications. Therefore a commonly used approach for ad hoc measurements is to digitize samples at fixed time intervals and then convert time into crank angle assuming a constant rotational speed. But if engine rotational speed is not constant within the engine cycle this may result to incorrect cylinder pressure CA referencing.

Diesel engine manufacturers are currently intensifying their efforts to meet future emission limits that require a drastic reduction of NOx and particulate matter compared to present values. Even though several after-treatment techniques have been developed for tailpipe NOx reduction in heavy duty diesel engines, the in-cylinder control of NOx formation still remains of utmost importance. Various methods have been used to control NOx formation in diesel engines such as retarded injection timing and EGR providing each one of them very promising results. However, use of these techniques is accompanied by penalties in specific fuel consumption and exhaust soot. A promising technology for NOx reduction especially for heavy-duty diesel engines and mainly large scale ones is the addition of water to the combustion chamber to reduce peak combustion temperature that obviously affects NOx formation.

During the recent years, extensive research is conducted worldwide for the purpose of tailpipe emission reduction from diesel engines. These efforts resulted in the achievement of very low emission levels for today's diesels. But considering the future legislation it is required a further drastic reduction. Towards this direction, a multi-zone combustion model is used in the present study to investigate the effect of fuel injection pressure level on the performance and pollutant emissions from a Heavy Duty DI diesel engine. For this purpose it is made use of injection pressure histories obtained from a detailed simulation model at various engine operating conditions. The increase of injection pressure is accomplished by increasing the injector opening pressure from 400 up to 1600 bar.

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.