Last Updated: Apr 2012
Increasing engine efficiency means that more energy for a quantity of fuel results in propulsion power. This can directly translate into reduced fuel consumption based on typical engine load levels, which equates to lower emissions across the board.
Engine upgrades to reduce NOx emissions can reduce such emissions by 20-30%, according to IMO figures. It also notes that Tier II NOx standards can be met with modifications to existing engine configuration but that meeting Tier III standards (80% NOx reductions) requires the use of additional technology such selective catalytic reduction (SCR).
Energy recovery systems can increase engine power in the range of 9-11%, according to IMO analysis. Systems are very large, requiring a difficult installation, and also require long pay-off times in terms of cost, from 5-11 years depending on engine size.
It has been noted that improvements to engine efficiency might be best combined with other design and operational changes such as improved propellers and slow-steaming to achieve substantial emissions reductions (see other articles on these technologies). According to MAN B&W, a "combination of a reduced ship speed and an increased propeller diameter and/or a changed number of propeller blades may reveal many new possible main engine selections not normally used for container ships. High efficiency, long-stroke MAN B&W two-stroke main engine types normally used for tankers may also be attractive solutions for the container ships of tomorrow, with around 30% reduced carbon dioxide (CO2) emissions per voyage compared with the ships of today."
Over the past two years, there has been increasing emphasis on the dual fuel engine, as it offers fuel flexibility and increases efficiency. Both Wartsila and MAN Diesel have been leading the trend.