However, this had been at the expense of improvements in lub oil quality and he believed that improvements were now desirable. Developing his argument, Mr Gros said that in many countries mere was a movement to produce more motor gasoline and less fuel oil from each barrel of crude oil. Mr Gros felt that this could concentrate ash, raise the aromaticity and consequently lower the ignition properties. High-ash fuels with a lot of vanadium and sodium contribute to deposit formation in exhaust and turbine systems and can lead to burned exhaust valves.
Wartsila, said Mr Gros had already introduced a number of improvements to permit the use of poor quality fuels. Indeed he believed that the slow movement towards higher ash content was not the operators main concern; more problematic was the occasional high ash content found in some bunker ports.
Mr Gros was concerned about the ability of lub oils to assist Wartsila Diesel meet its goals of improved engine reliability. In this respect he discussed the effect of emissions legislation.
Regarding moves to reduce the sulphur content of fuels, he felt that the international legion being considered within IMO was unlikely to affect sulphur content. However, the role of lubricants becomes more important and he said that the increased use of catalyst techniques, such as SCR for NOx reduction and oxidation catalysts for CO and hydrocarbon emission reductions, would require minimal fouling and poisoning by lub oil additives.
Mechanical developments highlighted by Mr Gros included the anti-polishing ring that Wartsila introduced in 1991. This had the effect of dramatically reducing lub oil consumption and led to increased cleanliness in the piston ring area. Wartsila’s first field application of its anti-polishing ring has now run for some 19 000 hrs without needing an engine overhaul, he noted.
But the anti-polishing ring has created new conditions for lub oil because the very low lub oil consumption combined with high-sulphur fuels causes a rapid depletion of the base number. Fast base number depletion can cause liner corrosion. A further drawback is that it leads to an increased need to change the lub oil - an expensive option.
Mr Gros hypothesised that the realistic options available were either to introduce lub oils with a higher base number, or to add very high alkalinity oil - such as crosshead cylinder oil - to the liner region. Of these two options he felt that working with two lub oils had a number of disadvantages. For this reason he believed that lub oils with base numbers of between 50 and 60 would be needed. Other properties needed by the lub oil included low volatility, and high thermal and oxidation stability. To achieve this he felt that hydrocracked base oils or poly-alpha-olefins would provide the protection required on future medium-speed engines.
Shortly after Mr Gros had presented Wartsila's views, the other part of MAN B&W - the medium-speed division - gave its perspective. Dietrich Friedel, operating media department manager, said the argument that two-stroke engines could be operated on more inferior fuels than four-stroke engines was false. He noted that the ability to change the injection timing on MAN B&W large-bore medium-speed engines overcame this problem.
The latest developments to the L32/40 engine is a separation of the controls for load-change and injection. By turning the camshaft the injection timing can be changed in relation to the driving gear wheel. Mr Friedel commented that the two adjustable camshafts are a further step towards the folly flexible engine able to adapt to both different operating conditions and fuel qualities.
Mr Friedel remarked that MAN B&W has frequently reported on the quality of medium alkaline lub oils for HFO operation. He particularly regretted that there are no international specifications for this class of lub oil. Because of this peculiar situation, general approval of an engine lub oil can only be given after extensive endurance test runs on a fully serviceable engine.
According to MAN B&W, even the use of today’s medium alkaline lub oils cannot prevent deposits. Expressing similar views to other engine builders, he noted the effect of high sulphur content and increased cylinder pressures. In Mr Friedel’s view the neutralisation capacity of the lub oil must be sufficiently high and matched to the sulphur content of current HFO grades.
To achieve this, MAN B&W recommends a 40 TBN lub oil for its 32/40, 40/54, 48/60, and 58/64 engines if the sulphur content is higher than 1.5 per cent. The exception tends to be Scandinavian ferries where the sulphur content is often less than 0-5 per cent. In the cases lub oils in the range of 24 to 30 TBN a acceptable.
Mr Friedel expected that the quality of h oil would continue to deteriorate which would require an increase in detergent capabilities. He also noted that increasing cot residues will affect deposits in the piston area.
For SEMT Pielsrick, Jean-Louis Magnet, general technical manager, underlined the development of the PC2.6B engine. Four 18 cylinder engines of this type will be used for the propulsion plant on SNCM’s latest car ferry newbuilding. Mr Magnet said that the development aims had included achieving a least 10 per cent power increase over the PC2.6 with SFOC unaltered. Other factors were that limited investment should be needed and a development period of about a year sought.
With a bore of 400mm the possibility of raising the engine power by increased BMEP was limited by turbo-charger pressure ratios and the peak combustion pressure limited to 150 bar, with a compression ratio set at 12.5 to permit the use of HFO.
Another method of increasing the power is to raise the mean piston speed. Mr Magnet noted that Pielsrick was conservative in this respect compared with its competitors. This led to two possibilities: either increase rotation speed or increase the stroke. After considering all the possibilities Pielsrick had opted to increase the stroke to 500mm. Experience has now been gained of the engine in industrial installations giving an output of 615 kW/cylinder and a 4 per cent increase in fuel over the original engine.
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