Constant development refines designs
The Motor Ship, January 2005
Diesel engine developments discussed by designers at a recent forum
included improved wear rate, steps to cope with low grade fuels and demands
placed on lub oils.
Occasionally - the previous meeting was in 2005 - the French lub oil company Elf Lub has a gathering of international representatives to discuss recent and forthcoming diesel engine developments. The latest conference was held in Paris in late November and the presentations covered a number of areas affecting the marine industry.
One of the speakers at this Elf Lub Conference was Ole Grone, MAN B&WA vice-president for marketing and sales. In his presentation Mr Grone discussed the potential growth container ships and considered how low-speed engines might be developed to meet these demands.
Noting that demand for the current maximum outputs of about 55 000kW
(75 000 bhp) was high, he disclosed that his company would be introducing engines with higher outputs. These would be needed for container ships of between 5 000 and 6 000 TEU with service speeds of about 25 knots.
Mr Grone said that there were a number of options which MAN B&W could explore to meet these objectives. The most obvious possibility would be to increase the ratings of the K90MGC and K9QMC engines. This could be done by raising the BMEP and would only need a few design modifications.
A more likely possibility is to introduce larger-bore engines. He noted that the company had launched its K98FF and K98GF j engines in the late 1960s. The majority of j these engines are still in service and some have even recently been upgraded. This underlined the owners' belief that they would I continue to meet their needs for much longer.
The difficulty with these engines, by modern standards, is that they only develop moderate power. The 12-cylinder version only developed 36 800kW(50 000 bhp); modern techniques could make outputs of more than 66 000kW(90 000 bhp) achievable. However, there are other possibilities.
One with potential is an MC engine with the cylinders arranged in a narrow V-form rather than the traditional in-line format. Although MAN B&W has not published details on this engine it has investigated the possibility in detail and the company holds patents on a numbers of innovations.
By using a narrow V-form the width of the engine would remain virtually unchanged but its length could be markedly reduced, Mr Grone noted. In the case of a K90MC-C engine a saving of over 10m for the largest engines could be achieved, he said.
The final possibility would be to develop the existing range of K90 engines to include 13 and 14-cylinder units. While this solution was technically feasible it suffered from an operational disadvantage: the length would be increased and cargo space effectively reduced.
Another aspect of MAN B&W engines was also covered in Mr Grone’s presentation. This was the company's search for an optimal vibration pattern. This had become especially relevant to operators of 10, 11 and 12-cylinder engines. Mr Grane noted that MAN B&W had investigated so-called uneven firing orders. These have now been implemented on marine engines and Mr Grone displayed a chart that showed that the result was a marked drop in first order external free moments - both horizontally and vertically. There is an increase in some of the other free moments but the overall vibration profile is now much flatter.
To further minimise vibration, the company has introduced a simplified type of hydraulic top bracing. According to Mr Grone this is a more attractive solution to vibration control.
In his concluding remarks, Mr Grone noted that the building of large diesels is not
as vulnerable a business as suggested by MAN B&W competitors in the prevailing market conditions.
Improved wear rate
Of the other low-speed designers, Mitsubishi (MHI) also gave a presentation which summarised the development of its UECLSH series engines. Yuji Wakatusuki, acting manager of the power systems engineering department; told the conference that the UEC60LSII, the latest in the series, is shortly to be installed in a bulk carrier being built in Japan.
In respect of the performance of the UECLSH engines, Mr Wakatusuki noted that the earlier engines had experienced large-scale wear of the piston rings. Because the engine durability itself did not meet MHI’s expectations its investigations covered a number of different aspects. One of the aspects considered was the effect of bunker fuel with a 4 per cent sulphur content. To overcome this MHI suggested a change of lub oil from 70 TBN to 80 TBN.
As durability and design enhancements were incorporated the wear rate improved rapidly. These improvements were particularly noticeable on the second ship to be fitted with a UEC75LSH unit where a lower sulphur content fuel was used. MHI has concluded that the sulphur content in the fuel used during running-in was the most important factor. Mr Wakatusuki said that all piston ring problems found on the UEC75LSH have now been solved.
Mr Wakatusuki commented that most ships initially fitted with the UEG75USH consumed a great deal of lub oil. Four years after I the first engine was delivered, modifications to the cylinder oil feed rate were made and the UEC75LSII is currently consuming about 1.05 g/bhp.
Demands on tab oils
Wartsila’s representative at the conference was Stefan Gros, diesel technology laboratory manager. Mr Gros concentrated on the tub and fuel aspects of marine diesel operation.
Mr Gros started by summarising the complex functions of lub oil in a diesel engine. These include such considerations as the prevention of metal-to-metal contact, the sealing of engine components, the cooling of engine parts, and the prevention of corrosion. New engines launched in the past few years feature a substantial reduction in the lub oil consumption, he observed, and he felt that lower prices for trunk piston engine oil had been the trend over the past five years.
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