Slow streaming is a process of deliberately reducing the speed of cargo ships to cut down fuel consumption and carbon emissions.  The major benefits of slow steaming have been:
 Higher fuel savings  Reduction in carbon emissions (CO2, NOx and Sox)  Improved reliability  Increased efficiency

Slow steaming and ultra slow steaming has helped many ship owners and companies during high bunker cost period and financial recession.
But running engines on slow or reduced MCR brings many disadvantages to the smooth operation of engines which are designed for optimum running. Manufacturers always suggest to run the engines on their optimum MCR. Marine engineers have following concerns regarding the slow steaming of the engines:
1) Increased scavenge and under piston inspection
2) Over lubrication
3) Carbon deposits on the fuel valves decreasing their efficiency
4) Fouling of turbochargers
5) Frequent fouling of exhaust gas economisers
6) Turbochargers running outside their designed range and thus supplying less air for combustion
7) Due to improper combustion, reduced maintenance period
8) Chances of scavenge fire

To overcome the above challenges some of the engine builders have come with retrofits for efficiently running the engines at slow speed or ultra slow speed. MAN B&W has suggested following retrofits:-
1) Turbocharger cut-out:- The Turbocharger Cut-Out system is designed to lower the fuel oil consumption and improve the main engine performance during low load operation. This can be archived in two different ways, either by installing Gate valves on the TC Air outlet and TC exhaust Gas inlet or by installing Blinding plates on the TC Air outlet, TC exhaust Gas inlet and outlet.

2)Slide fuel valves:- This new type of valve reduces the amount of waste products and gives better combustion properties. The elimination of the sac volume also saves fuel, as fuel used to drip from the sac on to the piston topland.

3)Alpha Lubrication system:- The Alpha ACC (Adaptive Cylinder Oil Control) is based on an algorithm controlling the cylinder oil dosage proportional to the sulfur content in the fuel. To explore the potential savings with the Alpha ACC, a large-scale testing program was initiated on MAN Diesel & Turbo’s MC and MC-C engines in service for a number of owners.

4) De-rating:- A vessel’s engine and propeller are optimized and designed for a given operational and max. speed. If the operational speed of the vessel is generally lower than the one originally optimized for, it may be beneficial to consider derating of the main engine and propeller. Derating as a retrofit product offers reduction of the total fuel consumption by improving the match between the operational speed and optimization speed. Derating is usually an attractive option for fuel oil savings if a reduction of 10-15% of the max. speed at SMCR can be accepted. A standard derating calculation made by MAN Diesel & Turbo takes into account the benefit gained from exchanging the original propeller with a new propeller having an optimized diameter designed for the required optimizing speed and reduced max. speed.

5) MAN EcoCam:- MAN EcoCam is a hydraulically regulated variable exhaust timing solution enabling a variable cam profile without any mechanical modification of the camshaft. When MAN EcoCam is active, the engine can run at a lower load with reduced fuel consumption. It can be deactivated whenever necessary, allowing the engine to run at full load.


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