Tough market for medium-speed

The market for medium speed diesel engines has been particular tough and, if forecasts are to be believed, things are going to get a lot more difficult. This is likely to force engine manufacturers into cooperation agreements or partnerships to reduce development costs.

Rolls Royce has already stated that it is looking for a partner to further its interest in offering a complete propulsion solution and has stated that it is looking at some of the major players in an effort to increase its 3 per cent market share of the diesel engine market.

Medium speed engines have come a long way in the past few decades with engines producing far higher power to weight ratios and increasing the average brake mean effective pressures by as much as 50 per cent. However, improved engineering skills and new alloys have allowed engine designers to extend service intervals.

Engines may be simpler to maintain but their advanced complex designs leave little margin for error, which places huge demands on their lubricants. Fuel, lube and water testing specialist Kittiwake says that it is well known that modern medium speed engines stress the lubricant more than in the past. Indeed some designs are such that the specific lubricant consumption is low and the sump charge is small. The stresses on the lubricant is a factor that becomes more dominant as engine designs operate at higher and higher mean effective pressures with smaller sumps.

The company says that medium speed diesel engines operating on residual fuel are also prone to the formation of deposits within the engine, often called black paint or black sludge. This sludge may also affect auxiliary engine equipment including the lubricating oil centrifuge, filters and fuel pumps.

Kittiwake says that the deposits can be seen in the rocker box and generally in the sump and can affect the piston ring pack to such an extent that they interfere with the correct lubrication of the ring/ liner interface.

The company explains that there are various theories why black paint exists. One theory is that it is caused by the increase in brake mean effective pressure and fuel injection pressure that causes the fuel to leak into the engine crankcase. Once there, the asphaltenes in the residual fuel come out of solution and form the characteristic deposits. Another theory is that it is a fuel related problem because fuels have become more viscous and closer to the specification limit. Yet another theory is that the black paint problem is a fuel combustion problem and can be overcome by the use of a fuel additive, thus providing an economical solution when better fuel quality is not an option.

However, research has shown that while fuel may be a contributing factor it is not necessarily the dominant one, suggesting that the solution lies with the lubricants.

A number of new lubricants specially formulated for the more demanding modern medium speed engines have been launched by oil companies recently. These include ExxonMobil?s Mobilgard M range, Shell?s anti-lacquer Gadinia AL and more recently Lubmarine?s Aurelia XL, which was launched this month.

While oil companies get valuable information from lub analysis programmes operated in the field, most have their own engines in which new products can be tested and ExxonMobil says that its new Mobilgard M range is the result of three years of bench and field testing. It has since been accepted by major four-stroke engine manufacturers, including Wärtsilä, MAN B&W, Pielstick and MaK. ExxonMobil says it launched the new M series ? M330, M430, M340, M440 and M50 ? to deal with stresses caused by today?s increased use of lower-quality residual fuels, higher fuel injection pressures, and lower specific lub-oil consumption rates. The oil company says: “These factors typically result in piston undercrown and ring-belt deposits, fuel contamination of the lub oil, and sludge build-up in the crankcase.”

“The Mobilgard M Series was engineered to address each of these problem areas, and its unique additive system provides world-class piston undercrown control, unmatched lub-fuel compatibility and excellent overall cleanliness,” says Mark Andreotta, vice president, ExxonMobil Marine and Aviation Lubricants. “We are introducing the best overall performing marine lubricant for medium-speed diesel engines. For ship owners and operators interested in reducing downtime and saving money on maintenance, Mobilgard M Series is today?s answer.”

Shell?s Gadinia AL is specifically designed to target the serious problems associated with lacquer formation in medium speed diesel engines. The company says that after three years and more than 30,000 hours of field tests in Deutz and MAN B&W engines, the oil has been proven to reduce operating costs significantly and increase engine reliability.

Shell says that the resulting mix of low-sulphur fuel and increasing cylinder pressures has led to problems of engine oil consumption. In heavy-duty operating conditions, a highly rated engine can form a lacquer on the cylinder liner surfaces, destroying the performance characteristics of the engine, resulting in a dramatic increase in lubricant consumption, along with potential over-lubrication scuff damage.

While the problem has been more common in highly rated engines operating at variable load conditions such as on fishing boats, supply vessels and container ships, the problem has become more common in recent years and is likely to increase as sulphur levels in fuel continue to fall.

Lubmarine?s Aurelia XL has been specially formulated using the latest additive technology to cope with the increasingly demanding environment in modern medium-speed engines and high stress applications. The company says that it offers compatibility with residual fuel of different qualities leading to excellent engine cleanliness in both the hot and cold areas of the engine, while giving good high temperature thermal and oxidation stability. The oil also has low volatility, high load carrying capacity and, according to Lubmarine, excellent corrosion protection.

This should mean that engines will remain cleaner and the piston ring belt, cylinder liners and piston undercrown deposits will be reduced, leading to greater engine reliability, especially in high stress or engine overload conditions.