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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).

Considering future emission legislation and the global thermal problem, two are the main issues that are of specific concern for the future of the diesel engine, specific gaseous pollutants and CO2 emissions. Both parameters are related to engine bsfc consumption directly or indirectly. The last is becoming even more important considering current fuel prices and the projection for the future indicating a trend for increasing fuel prices. The last decade significant improvement have been accomplished in the field of diesel engine efficiency that has resulted to considerable reduction of engine bsfc. It is obvious that despite improvements in diesel engine efficiency still a considerable amount of energy is rejected to the environment through the exhaust gas. Approximately 30-40% of the energy supplied by the fuel is rejected to the ambience.

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.

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).

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.

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 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.

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).

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.

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.