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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 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.

A major challenge in the development of future heavy-duty diesel engines is the reduction of NOx and particulate emissions with minimum penalties in fuel consumption. The further decrease of emission limits (i.e., EPA 2007-2010, Euro 5 and Japan 05) requires new, advanced approaches. The injection system of DI diesel engines has an important role regarding the fulfillment of demands for low pollutant emissions and high engine efficiency. One of the injection system parameters affecting fuel spray characteristics, fuel-air mixing and consequently, combustion and pollutant formation is the geometry of the nozzle hole. A detailed experimental investigation was conducted at UPV-CMT using three different nozzle hole types: a standard, a convergent and a divergent one to discern the effect of nozzle hole conical shape on engine performance and emissions.

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 last years a great effort has been made by many NATO nations to move towards the use of one military fuel for all the land-based military aircraft, vehicles and equipment employed on the military arena. This idea is known to as the Single Fuel Concept (SFC). The fuel selected for the idea of SFC is the JP-8 (F-34) military aviation fuel which is based upon the civil jet fuel F-35 (Jet A-1) with the inclusion of military additives possessing anti-icing and lubricating properties. An extended experimental investigation has been conducted in the laboratory of Thermodynamic and Propulsion Systems at the Hellenic Air Force Academy. This investigation was conducted with the collaboration of the respective laboratories of National Technical University of Athens and Hellenic Naval Academy as well.

Worldwide demand for reduction of automotive fuel consumption and carbon dioxide emissions results in the introduction of new diesel engine technologies. A promising technique for increasing the power density of reciprocating engines, improving fuel economy and curtailing engine exhaust emissions is the use of variable compression ratio (VCR) technology. Several automotive manufacturers have developed prototype vehicles equipped with VCR gasoline engines. The constructive pattern followed to alter the compression ratio varies with the manufacturer. The implementation of VCR technology offers two main advantages: the reduction of CO2 emissions due to optimal combustion efficiency in the entire range of engine operating conditions and the increase of power concentration due to high boosting of a small engine displacement (i.e., engine downsizing).

The diesel engine is currently the most efficient powertrain for vehicle propulsion. Unfortunately it suffers from rather high particulate and NOx emissions that are directly related to its combustion mechanism. Future emission legislation requires drastic reduction of NOx and particulate matter compared to present values. Engine manufacturers in their effort to meet these limits propose two solutions: reduction of pollutants inside the combustion chamber using internal measures and reduction at the tailpipe using aftertreatment technology. Currently there are various opinions considering the final solution. Taking into account information related to aftertreatment technology, an effort should be made to reduce pollutants inside the combustion chamber as much as possible. The last is obvious if we account for the even more strict emission limits to be applied after 2010 that will require a combination of aftertreatment and 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.

A method to curtail emissions of smoke and other pollutants from diesel engines is to enhance the oxygen supply to their combustion chamber. This can be accomplished by enriching either the intake air stream or the fuel stream with oxygen. Experimental studies concerning the oxygen-enrichment of intake air, have revealed large decrease of ignition delay, drastic decrease of soot emissions as well as reduction of CO and HC emissions while, brake specific fuel consumption (BSFC) remained unaffected and increasing of power output is feasible. However, this technique was accompanied by considerable increase of NOx emissions. Experimental and theoretical studies with oxygenated fuels have demonstrated large decrease of soot emissions, which correlated well with the fuel oxygen content. Reduction of CO and HC emissions with oxygenated fuels was also obtained. However, penalties in both BSFC and NOx emissions have been observed with oxygenation of diesel fuels.

In the past years various models have been proposed for the modelling of performance and pollutants emissions from DI diesel engines. These models range from complicated 3D detailed ones up to simple two zone phenomenological ones. The latter ones although simple offer solutions in engine study and are widely used due to their low computational cost and simplicity. In the present work a multi-zone model for direct injection diesel engines is presented together with its application on a direct injection diesel engine located at the authors laboratory. Multi-zone models usually fail to predict adequately both pollutants emissions and performance and thus focus mainly on pollutants emissions. Of course this is not acceptable since the formation of pollutants is strongly related to the combustion mechanism. In the present work an effort has been made to overcome this problem and predict both performance and emissions throughout the engine operating range.

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.

With the increasing public interest in energy supply and the environment, attention has focused on the development of ecological and efficient combustion technologies. One of these technologies could be the use of natural gas as supplement fuel for diesel fuel in DI diesel engines. The great availability at attractive prices and the clean nature of combustion are the most important advantages of natural gas compared to conventional diesel fuel. In the present work are given theoretical and experimental results for the combustion mechanism of natural gas in a compression ignition environment, with special emphasis on the combined heat release rate of natural gas and diesel fuel, the duration of combustion and the ignition delay period. Results are also provided for the formation history of pollutants inside the combustion chamber of a DI diesel engine operating in dual fuel mode (with natural gas fuelling).

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.).

A great deal of research is taking place at the present time in the field of diesel engines, especially regarding the emission of gaseous pollutants and soot. This research is essential for engine manufacturers since it is difficult for diesel engines to meet current standards regarding soot and nitric oxide emissions. The problem will become even more severe when the new legislation will be applicable requiring a 50% reduction of existing levels. Many manufacturers and researchers feel that engines will be difficult to meet this criterion without the use of other techniques such as gas aftertreatment or newly developed fuels (low sulfur content, etc.). The aim of this research is to examine the effect of fuel composition and physical properties on the mechanism of combustion and pollutants formation.

In this paper, the results are presented from the analysis of the second stage of an experimental investigation with the aim to provide insight to the cyclic, instantaneous heat transfer phenomena occurring in both the cylinder head and exhaust manifold wall surfaces of a direct injection (DI), air-cooled diesel engine. Results from the first stage of the investigation concerning steady-state engine operation have already been presented by the authors in this series. In this second stage, the mechanism of cyclic heat transfer was investigated during engine transient events, viz. after a sudden change in engine speed and/or load, both for the combustion chamber and exhaust manifold surfaces. The modified experimental installation allowed both long- and short-term signal types to be recorded on a common time reference base during the transient event.

An experimental analysis is carried out to investigate several heat transfer characteristics during the engine cycle, in the combustion chamber and exhaust manifold walls of a direct injection (DI), air-cooled, diesel engine. For this purpose, a novel experimental installation has been developed, which separates the engine transient temperature signals into two groups, namely the long-and the short- term response ones, processing the respective signals in two independent data acquisition systems. Furthermore, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an innovative, object-oriented, control code for fast data acquisition have been designed and applied. Experimentally obtained cylinder pressure diagrams together with semi-empirical equations for instantaneous heat transfer were used as basis for the calculation of overall heat transfer coefficient.

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).

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.

During recent years, the deterioration of greenhouse phenomenon, in conjunction with the continuous increase of worldwide fleet of vehicles and crude oil prices, raised heightened concerns over both the improvement of vehicle mileage and the reduction of pollutant emissions. Diesel engines have the highest fuel economy and thus, highest CO2 reduction potential among all other thermal propulsion engines due to their superior thermal efficiency. However, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are comparatively higher than those emitted from modern gasoline engines. Therefore, reduction of diesel emitted pollutants and especially, PM and NOx without increase of specific fuel consumption or let alone improvement of diesel fuel economy is a difficult problem, which requires immediate and drastic actions to be taken.

During the last years a great deal of effort has been made for the reduction of pollutant emissions from direct injection Diesel Engines. Towards these efforts engineers have proposed various solutions, one of which is the use of gaseous fuels as a supplement for liquid diesel fuel. These engines are referred to as dual combustion engines i.e. they use conventional diesel fuel and gaseous fuel as well. The ignition of the gaseous fuel is accomplished through the liquid fuel, which is auto-ignited in the same way as in common diesel engines. One of the fuels used is natural gas, which has a relatively high auto-ignition temperature. This is extremely important since the CR of most conventional diesel engines can be maintained. In these engines the released energy is produced partially from the combustion of natural gas and from the combustion of liquid diesel fuel.