Taking the next steps in emissions reduction for large 2-stroke engines

摘要

All low speed 2-stroke engines produced for ships constructed after 1st January 2000 are complying with the IMO regulation specifying emissions limits, for NO_x in particular, in Annex VI of Marpol 73/78. After this regulation has come into force in May 2005, discussions have been started within IMO for a next step in emissions reduction with the target of formulating new limits to be valid from probably 2010 onwards. The currently applied technologies are reviewed and today's potentials for further reducing emissions by means of adjustments of the thermodynamic layout and of further optimisation of fuel injection are shown. The key technology enabling exploitation of all these possibilities is the RT-flex system, which has become the preferred option on new Waertsilae 2-stroke engines. For achieving substantial additional reductions of NO_x emissions, most likely wet technologies will have to be applied. Based on the former promising testbed results with NO_x reductions up to 50% a direct water injection equipment has been developed and installed the first time on a large bore engine in ship operation. Target is to accumulate experience of the system in long term operation at regular service conditions. A completely new approach to reduce not only NO_x but also all other emissions simultaneously can be seen in the application of the waste heat recovery (WHR) concept. This technology has been developed for improving the overall efficiency of the engine by increasing its output. Simultaneously, as this is done without modifying the thermodynamic layout of the combustion cycle, hence also without alterations of the exhaust gas amount and composition, the power specific emission rate is reduced in accordance with the overall efficiency increase. The challenge in the WHR system development was to use as much as possible of the "wasted" energies from the engine and transform them into power via a generator driven by a powerturbine and/or a steam turbine. So several steps can be taken in order to improve the gain in overall fuel efficiency. These individual solutions, all requiring additional investments into the engine room installation, are discussed. The systems realised so far allow a recovery of 11% with today's available technologies leading to an equivalent reduction of all the exhaust gas emissions. For reducing both hydrocarbon and particulate emissions, the reduction of lubricating oil consumption has come into focus in the car and truck engine industries. Also in large bore engines, lowering the lubricating oil feed rates is considered a promising means of reducing those emissions. Over the past few years, new lubricating systems have been developed and tested in operation. Common to all these systems is the use of electronic control allowing a more precise timing of the lubricating oil injection into the engine.