Exhaust gas emissions of ships have been and will be further restricted by the International Maritime Organisation (IMO) as well as by regional and national legislation for civil shipping. Despite the fact that Navies are not legally forced to fulfil these requirements, many Navies and Coast Guards already comply or intend to comply with the latest emission regulations. With IMO Tier 2 and Tier 3 emission limits in force or on the horizon, the requirement specifications for many new ship procurement programs demands compliance with this legislation. Public and political pressure to spend taxpayers' money on green technology is evident in both industrialised and emerging countries. This paper describes the current status of IMO's diesel engine emission limits and discusses the boundary conditions of IMO Tier 2 and IMO Tier 3 NO_x limits. It highlights the challenges that engine manufacturers face when developing engines for the new requirements and gives insight into the technological road map of MTU. Eventually the paper outlines the impact on ship designs such as superstructures and supply systems of the technologies under discussion, namely engine-internal technologies and exhausts gas after- treatment systems. The paper concludes with an outlook on alternative fuel concepts.
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