Due to many factors, engine markets are in a state of continual evolution, and the influx of high speed diesel engines into the low end of what were traditionally medium-speed engine markets is just one example. This change is evident in marine engine markets, but can also be found in rail traction, as well as some electric power generation and oil and gas applications.
One example of a high-speed engine in the
MTU product line is its 20V4000 series,
which MTU reports with a maximum output
of 4300 kW.
“There has been an influx of high speed diesel engines into the low power end of the medium-speed engine markets for several years now and there are many reasons for the change,” said Geoff Conrad, general manager of Cummins’ marine engine business. “The activity has really picked up within the last three years and seems as if it will continue into the foreseeable future.”
Some drivers of this trend are the improved performance of the latest generation of high speed engines with increased output and durability in a more compact,lighter package; exhaust emissions legislation; initial capital costs; and, simply,
“In the last 10 years, the high speed engines have made tremendous progress,” said Conrad. Fifteen to 20 years ago, the highest output you could get from a highspeed diesel was maybe 1500 horsepower (1119 kW). Now manufacturers can get 3500 horsepower (2610 kW) and the engines are more accepted in the market.”
High-speed engines continue to break output barriers, with reported output figures in excess of 2000 kW. Examples include the Caterpillar 3500C series (2525 kW), Cummins QSK 60 (2125 kW) and the MTU 4000 Series (4300 kW). If 1000 r/min is considered the division point, the MTU 8000 series, with a rating of 9100 kW at 1150 r/min, or the Caterpillar C280 (right on the line) at 1000 r/min with a rating to 5650 kW, pushes the figure higher.
These engines have also been developed for durability with extended service and rebuild intervals, enabling them to withstand the duty cycles of applications that in the past would have been the domain of medium-speed engines.
“The technology advances have enabled significant improvements in reliability and durability on the high-speed engines,” said Dennis Heathfield, general manager of Cummins’ oil and gas business. “A high-speed engine will always wear faster; physics dictate that an engine running at 800 rpm will live longer than one running at 1200 to 1800 rpm. However, the gap has closed sufficiently over the years, and the high speed engine is at least an option now in what was traditionally a medium-speed-only application.”
“In terms of life-cycle costs, highspeed engines have made a drastic step just in the past three to four years,” said Jaime Tetrault, division manager, Americas for Caterpillar Marine Power Systems. “The benchmark of this for Caterpillar is that the overall intervals are more or less identical to medium speed on our traditional 3500 series product.”
The reported average time to rebuild a high-speed engine is now up to 30 000 hours. Basic service check intervals for high speed diesels are in the 8000 to 10 000 hour range and may be higher. Of course, application duty cycle and operating environment can affect these intervals so they may be higher or lower. With this in mind, manufacturers find using fuel consumed, as a guide, is more accurate than operating hours.
For some marine applications, those with higher and longer duty cycles remain the domain of medium-speed engines and that will likely continue. These include long-distance tow tugs and push boats. However, ship assist tugs and small coastal tugs where maximum power is only needed for short periods of time, with good dynamic behavior of the propulsion system in a smaller package and where the operating hours are fewer are more suitable to high speed engines.
The development of propulsion system technology has also helped the case for high speed engines in some applications. The adoption of dieselelectric propulsion systems on vessels allows the high-speed engines to be used in many vessels that in the past would have been medium speed specific applications.
alt=”Cummins QSK60″ width=”400″ height=”400″>
The Cummins QSK60, although not the highest output model available
from the company, has an output of 2125KW.
The systems allow vessel designers to package them in a configuration more beneficial to the vessel and cargo volume optimization, as fewer concessions need to be made for the propulsion system.
“Nowadays, the trend to deliver more power using a smaller package is very important,” said Stefan Müller, director of Application Center Marine at MTU. “For mobile applications, reducing weight, reducing space, means increasing the possibility of smaller engine rooms and the ability to haul additional freight. With regard to the oil and gas business, this could be beneficial because the offshore platforms are being transferred to deeper waters further offshore.
In deep seas, weight issues become more and more critical.”
Diesel electric propulsion systems also allow the use of multiple, smaller engines to provide a vessel with the desired overall power output. This creates the ability to turn on and off different combinations and numbers of engines, thus varying vessel power output to suit conditions adding flexibility. A side benefit of this is increased fuel efficiency and built-in redundancy, traditionally an issue for high-speed engines of these applications.
In regions where emissions regulations come into play or the mandated use of low sulfur or even ultra low sulfur diesel exists, the fuel cost advantage held by medium-speed engines traditionally burning lower cost marine diesel oil or heavy fuel oil has eroded. However, in those areas where fuel is not a concern, medium-speed still has an edge.
“Today, the main disadvantage that remains for high speed engines in some applications is their inability to burn heavy fuels,” said Tetrault. “If you look at an application and heavy fuel is an absolute requirement, chances are, it is going to be a slow or mediumspeed engine. These engines have distinct burn properties which make them better suited to burning heavy fuel of different qualities.”
Another factor now under consideration is the initial capital cost of equipment. “Historically, customers looked at the useful life of equipment and expected it to last longer,” said Conrad. “Now, it is viewed more and more as a tool with a defined lifespan that will be replaced when the time comes. So, front end capital costs are more of a consideration, and depending on the objectives of a project, the lower initial costs of a highspeed engine are very attractive.”
This can be seen in oil and gas markets where a project may have a defined lifespan of three to five years at a compressor station. This is an application where the light weight and low initial cost of a highspeed engine can be realized as the portability of the equipment allows it to be moved. Capital costs also need to be considered for the whole package and not just the engine, which in some cases can be as much as 50% less than the cost of a medium-speed engine.
alt=”Caterpillar C280 engine” width=”400″ height=”400″>
The Caterpillar C280 engine, considered medium-speed, has
a maximum rated output of 5420 kW.
“If you think about the installed cost differences, the 2000 horsepower (1491 kW) medium-speed engine would be significantly more weight than the 2000 horsepower (1491 kW) high-speed engine,” said Conrad. “So if you think about the vessel structure to support the weight the steel work, the stringers, the sub hull, support frames it is usually different. This equates to less material involved and a lower cost of installation for the vessel as a whole.”
Not to be forgotten, a simple, but very important factor is engine availability. With the state of the engine markets today, manufacturers of medium and low-speed engines are reporting full order books into 2010 and beyond in some cases. This has allowed high speed manufacturers whose products are typically built in higher volumes on a shorter production schedule, to fill the market gap. Manufacturers are reporting availability in many cases as early as 2008.