Highly promising results in terms of cylinder oil savings, lower particle emissions and reduced combustion chamber wear figures are emerging from large-scale testing of a wide range of MAN B&W MC/MC-C two-stroke engines equipped with Alpha Adaptive Cylinder Oil Control (Alpha ACC).
The aim of the testing programme --based on engines in service with various shipowners- is to verify the savings in cylinder oil consumption delivered by the electronically-controlled Alpha Lubricator System. Such savings reduce operating costs and the environmental impact of ships, and the system fosters more uniform and optimal cylinder liner wear rates.
Large bore engines for both container ship (K-MC/MC-C) and VLCC (S-MC/MC-C) propulsion are covered in the current programme, along with small and medium bore MC/MC-C engines.
Alpha ACC allows the cylinder oil dosage (g/bhph) to be controlled in such a way that it is proportional to the amount of sulphur (g/bhph) entering the cylinder with the fuel.
This is achieved by making the cylinder oil dosage proportional to the sulphur percentage in the fuel and to the engine load (fuel amount).
The main element of cylinder liner wear is of a corrosive nature, and the amount of neutralising alkalinic components needed in the cylinder will therefore be proportional to the amount of sulphur (which generates sulphurous acids) entering the cylinders.
A minimum cylinder oil dosage is set in order to satisfy other requirements of a lubricant, such as providing adequate oil film and detergency properties.
In the present version of the Alpha Lubricator System the ship staff inputs the so-called 'HMI-setting' based on the sulphur percentage of the fuel used and a conversion table. An input is made at the appropriate system panel each time the fuel specification is changed.
Results from a 12K90MC engine powering a 6,800 TEU container ship illustrate (see diagram on page 3) the economic and environmental benefits of Alpha ACC, which was applied to the engine in December 2001.
The upper part of the diagram shows the load variation and the sulphur content variation in the fuel, both variations typical for this class of ship; the middle section shows the total amount of sulphur entering the cylinders with the fuel; and the lower part shows four curves for comparison.
