In the last few years, both international and national legal requirements regarding the exhaust emissions of large-bore diesel engines have become much stricter. For marine diesel engines, these requirements focus primarily on the reduction of nitric oxides (NOx) and sulphur oxides (SOx). Recently, however, legal requirements for reducing the greenhouse gas carbon dioxide (CO2) have played an increasingly important role in the discussion.

For over 20 years, one of the prime concerns of MAN Diesel & Turbo’s development work has been the reduction of NOx emissions. Since the introduction of “IMO Tier I”, the first stage of the “IMO MARPOL 73/78 Annex VI” emissions regulations for marine diesel engines in 2000, we have significantly expanded our range of NOx-optimised engines.
 
The next stage of the IMO requirements, “Tier II”, came into force in 2011 and requires a further 20 percent reduction in NOx emissions compared to “IMO Tier I”.  Thanks to their advanced internal features all our engines are below this threshold.

 The third stage of the IMO emissions regulations, “IMO Tier III” is planned for 2016 and will be so strict that completely new measures and technical solutions will be required. We are well on track to providing these solutions and are already developing numerous primary and secondary measures to enable compliance with these highly demanding requirements. “Tier III” envisages a further reduction in NOx emissions in Emission Controlled Areas (ECAs) to 80 percent lower than the “Tier I” level.

ECAs are special zones where separate restrictions apply for SOx and particle emissions, NOx emissions, or both. Existing ECAs are currently the North and Baltic Seas, and further planned ECAs include the west and east coast of the USA, around Hawaii and in Canada.

In ECAs, the proportion of sulphur in fuel must not be more than 1.0 percent since 2010. After 1 January 2015, the proportion of sulphur will be limited to 0.1 per cent. Outside the ECAs, concentrations of 4.5 percent sulphur are still allowed in fuels until 1 January 2012; from 1 January 2020, the IMO stipulates a maximum of just 0.5 percent. From 2012, the IMO plans a reduction in the proportion of sulphur in fuel from 4.5 to 3.5 percent. As an alternative to compliance with these fuel regulations, ship operators can also use appropriate exhaust gas after-treatment systems that reduce SOx emissions accordingly.