Marine Low Speed 

Approved Methods Represent Best Solution for Environment and Shipowners

MAN B&W engine retrofits reduce emissions and fully meet IMO environmental legislation

While IMO guidelines are observed on a ‘voluntary’ basis by the international shipping community, their adoption becomes mandatory for certain vessels when an Approved Method for complying with the regulations is available. MAN Diesel & Turbo has developed Approved Methods for a number of its engines, requiring some shipowners to retrofit engines to follow IMO emission limits.

The legislation

The International Maritime Organisation (IMO) develops regulations and guidelines for international shipping. Its latest revision of emission regulations addresses NOx emissions on engines installed aboard ships built between 1990 – 1999 that are expected to be active in the global fleet for another 10 or 20 years, but that were not previously covered by any guidelines.

At the same time, certain port authorities and flag states have been very active in pushing for regulating emissions from the ‘old’, existing engine fleet in order to obtain significant emission reductions.

Thomas Knudsen, Senior Vice President Low-Speed, MAN Diesel & Turbo, said: “Our new Approved Methods require that shipowners running selected MAN B&W models retrofit these engines to meet Tier-I IMO emission requirements. These retrofits, essentially comprising the installation of modern, slide-type fuel valves, will significantly reduce exhaust emissions.

While MAN PrimeServ is aware that some shipowners will be thinking of their operational budgets and see the retrofits as being triggered by MAN Diesel & Turbo’s development of Approved Methods, the only other option is to wait for alternative legislation to be introduced locally worldwide. And that could well be a far costlier prospect.” He concluded: “This decision to introduce Approved Methods has not been taken lightly by MAN PrimeServ. However, injection valves are consumable parts that require regular replacement and, ultimately, we consider this decision as the best solution for our customers, bearing in mind that slide-type fuel valves also generally reduce the amount of on-board maintenance.”

The Approved Method project

MAN Diesel & Turbo’s Approved Method project has developed retrofits for the large number of engines covered by the new IMO legislation. The retrofits consist primarily of the replacement of engine fuel-injection valves with newly developed fuel-injection nozzles, as well as adjustment and certification of the engines.

MAN Diesel & Turbo selected three MAN B&W engine types as first priority for the development of Approved Methods based on their overall potential for emission reduction. In this respect, the company recently carried out an extensive testing and documentation programme with its licensees. As a result, the MAN B&W S70MC engine has now received final clearance as the first Approved Method.


MAN Diesel & Turbo currently has plans for three Approved Methods. It estimates that these will bring about the upgrade of approximately 800 engines over the next few years, resulting in reduced NOx emissions to the tune of 60,000 tonnes annually. The improved fuel-injection technology will also lower emissions of other exhaust gases including carbon monoxide, unburned hydrocarbons and particulates. In fact, many ship owners have already, voluntarily, installed this upgrade due to these benefits.

Encouragingly, the approved methods do not increase fuel-oil consumption and, due to the reduced formation of particulates, engine combustion-chambers and gas paths will be cleaner and require less maintenance. Furthermore, the low-load performance of the engine will be improved and visible smoke minimised. MAN Diesel & Turbo confirms that further Approved Methods are planned in due course.