The excellent efficiencies in large Diesel motors emanate from high combustion temperatures during the combustion in the cylinder. These result in reduced specific fuel consumption and formation of CO₂. On the other hand, high gas temperatures and air-fuel ratios increase substantially  NO_x formation. The resulting conflict has a particularly profound impact on the development of  marine diesels. Through the stricter regulatory framework on land (TA-Luft) the relative contribution of marine motors on global air pollution has increased rapidly. Indeed, one assumes that the current contribution of ca. 8% of total NO_x emissions by shipping will almost double in the coming decade.

In May 2005 new regulations of the International Maritime Organization (IMO) came in force, which determine the maximum allowable NO_x emissions limits for ships commissioned after the 1.1.2000. In addition to these regulations also national and regional directives exist. For example a Swedish directive offers financial incentives for reducing air pollution in marine propulsion. These successful measures are based on step-wise increases in harbour charges, depending on the emissions of the ship. Ships from Norway with reduced exhaust emissions receive tax reductions.

In-motor measures for reducing emissions are suitable for meeting the applicable IMO regulations without deteriorating substantially the operating costs. To meet more stringent regulations, however, such as the Swedish regulation or the planned further tightening of the IMO emission limits, requires much more and in-motor interventions alone, targeted at the optimisation of constructive and operational parameters, would not be sufficient.

For the purpose of dropping the temperature by simultaneously reducing the oxygen surplus in the flame one may introduce in the combustion chamber inert substances with high specific heat capacities. To this aim research is conducted on the injection of preconditioned water in the combustion chamber (DWE), the injection of Fuel/water mixtures (KWE) or the targeted moistening of the intake air with untreated seawater (HAM). The maximum achievable NO_x reduction can reach up to ca. 50%.

Such low NO_x-emissions can be obtained at present only through post-processing of the exhaust gases. Given the high air/fuel ratio in large diesel motors only Selective Catalytic Reduction (SCR) may here be applicable. In such an application the motor can be designed to deliver minimum fuel consumption without regard for the resulting emissions. This approach has been used widely in power stations. By introducing a reducing agent the NO_x is converted in the catalyst to N₂ and water. NO_x reduction rates of more than 90% can be achieved. However, due to the relatively short life of the catalyst and the extremely large space requirement, the capital and operational costs are significant to such an extent as to prevent the widespread marketability of this process in ships.

Within the framework of this research project the practical options and limitations of the various emission control concepts will be investigated and consistently compared with each other. In this manner Shipowners, Shipbuilders and Motor Manufacturers can have an objective basis for the optimal selection and conceptual design of drivetrains, in an economically-sound and as close to practice manner as possible.