The Navy not only needs more engine power, but also faces increasing pressure from environmental awareness.
In recent decades, the power and propulsion (P&P) systems of naval vessels have made great strides. This function aims to highlight the latest developments in the design and operation of prime movers in these P&P systems. The prime movers are gas turbines, diesel engines, and steam turbines, which convert the energy in the fuel into mechanical energy for propulsion or electrical systems. For modern naval ships, steam turbines have been largely replaced by gas turbine (GT) and diesel engine arrangements. Depending on the operation of the warship, it will require different types of prime movers to generate the necessary power and propulsion to perform its mission set. Since these systems are very important to the capabilities of ships and are essentially their defining characteristics, the design of new ships must first consider power and propulsion systems.
Most naval vessels will use diesel engines to provide standard levels of power for propulsion, sensors, weapons, and “hotel load” to maintain sailors’ living conditions, such as heating/cooling, lighting, charging, cooking, etc. Diesel engines can provide ships with speeds up to about 28 knots, although they are generally used to provide much lower patrol or transit propulsion speeds. However, frontline warships, especially surface warships such as frigates and destroyers, have special requirements for high-speed maneuvering, which requires the ability to suddenly increase power to achieve this. Adding GT to the ship’s power and propulsion devices can provide a surge in power to achieve top speeds from 28 knots to over 40 knots. Generally, marine GT will provide 18-30kts of propulsion power in most frigates and destroyers, and the propulsion power of less than 18kts will be powered by direct drive diesel engines or diesel generator sets driven by electric motors. In the past 20 years, the ship GT has made considerable progress and has become an extremely professional niche industrial capability. Today, the two main suppliers of Navy GT are Rolls-Royce and General Electric, which produce the most modern high-power GT, MT30 and LM2500, respectively. Ukraine’s Zorya-Mashproekt also manufactures marine GTs. Since the Crimea invasion stopped delivering products to Russia, Moscow has been developing new marine GT capabilities at its aviation GT company NPO Saturn.
Marine GT is developed from an aircraft gas turbine, and the MT30 is one of the most modern turbines on the market. The MT30 is derived from the Trent 800 aircraft engine, which has 80% versatility between them and is classified as the fourth-generation GT, which can generate 36MW to 43MW of power if required. The reason why MT30 can provide such a large amount of power is because the root of its development lies in the aviation GT contract arrangement in the 1980s and the computer power in the 1990s. During this period, Rolls-Royce signed more GT engine lease arrangements with commercial airlines. The company retained the ownership of the engines, while the airlines charged electricity consumption by the hour. This is one of the reasons why GT suppliers have been hit hard by the COVID-19 crisis because their engines have not been used. As this type of contract arrangement becomes more and more common, this means that the risk of engine reliability is transferred to the owner, which gives them great motivation to perform health and use monitoring analysis of engine components, and through comprehensive The maintenance package improves performance.
At the same time, by the early to mid-1990s, with the improvement of aerospace technology through computer processing and the use of computational fluid dynamics and finite element analysis, engines became more and more powerful. Trent 800 followed closely. As a large-diameter GT engine with greater air mass flow, it has become more powerful by improving the compressor, combustion system, and turbine, and providing a higher temperature margin. As a result, from this period onwards, Boeing 777 aircraft can operate with only two engines instead of the traditional four engines.
According to Richard Partridge, Chief Manager of Naval Systems at Rolls-Royce, the MT30 was developed because the naval market has demanded a 36MW GT with higher power density and higher reliability. Therefore, choose Trent 800 instead of Trent 700 or 500 for ship modification because it can provide better results. “For the Japan Maritime Self-Defense Force’s new FFM frigate program, we have actually been able to provide 43MW of power,” Partridge said.
The fact that the power density is so large means that the ship can use a single GT power and propulsion unit next to the diesel engine instead of two GTs, thereby providing more space and flexibility in design. This is also evident in South Korea, where the MT30 was modified to power smaller ships and was selected for use in the new Daegu-class (FFX-II) guided missile frigate of the Korean Navy. In addition, the reliability of the MT30 gives it an additional advantage in terms of maintenance, as it never needs to be disembarked for major repairs, thereby reducing the cost of ownership. “The overhaul life is very long, based on typical naval use of 300-600 hours per engine per year. Literally, it is a suitable and forgotten lifting capacity, which is for the operator in terms of reliability and overall life cycle cost. They are all great,” Partridge explained.
The forecast is that the MT30 will require more than 25,000 hours of operation to be fully overhauled, and the main engine produced has not yet reached this level of use. The large-diameter core of the MT30 increases the air mass flow, then compresses to generate high temperature, and then injects fuel and ignites in the combustor with the correct air-gas ratio to produce an appropriate amount of high-pressure exhaust gas to turn the turbine. Partridge said: “You can imagine that heat will increase the centrifugal force that tries to separate the engine rotation, but this makes the turbine more efficient than it has ever been.” But it is not only metering (measurement and calibration) that is a factor, but also Additional niche technologies were implemented to help the system withstand these pressures. Although the turbine blades have a thermal barrier coating to withstand the heat generated, one of the biggest differences that enable the GT to operate in the high temperature range is the cooling system. “The high-pressure turbine immediately downstream of the combustion chamber has a series of very complex cooling channels in each rotating blade. It needs those that remove heat from the metal and allow the blades to really survive under these conditions and spin at very high speeds,” Pa Trichy said.
The design details and technical level required to build a functional, reliable and efficient gas turbine are considerable. The knowledge level of GT manufacturing company has been established for more than 70 years, which makes it a high barrier for new companies to enter the market. Due to the cost of design and development, unless there is a large demand and there are gaps or weaknesses in existing products, a new GT is usually not produced for the navy market. It is possible to create a more powerful GT, but this requires increased complexity and cost. Therefore, products must meet market requirements while remaining competitive.
At the same time, although diesel engines cannot match the power density provided by GT, improvements have been made to provide warships with greater power and propulsion capabilities to maintain higher speeds and greater electrical loads, and to meet more stringent requirements. Environmental regulations. This means that if the Navy questions the value of buying GT, diesel engines will become more attractive as an option. The appeal of diesel engines is due to the development of electricity and propulsion in the past 20 years that began in the UK in the 1990s. Due to the inclusion of an electric motor, the diesel engine can be removed from the shafting, allowing greater flexibility to meet certain mission requirements.
Simon Riddle, general manager of Wärtsilä Marine Solutions’ Naval and Research Ships Division, explains that another benefit is redundancy: “You may have four generator sets and you can still operate the ship on three, but you can still make reservations. This is also It means that when the ship’s power demand is low, you can increase the engine load because you can transfer the load from one generator set to another,” he explained, “and you have a power management system that can Keeping the load on the engine is more controlled than running the diesel engine into a traditional gearbox.”
Although the Navy does not prioritize fuel efficiency as the commercial market does, it is still an important attribute of diesel engine performance. Riddle stated that it has been the “biggest driving force” behind the development of the new Wärtsilä 31 marine engine launched in 2018, which has achieved a lifetime cost reduction.
“The first thing we do with all engines is to ask us how to design them with fewer components. The reduction in the number of components means that there are fewer chances of actual failure. Then we designed it to reduce the large number of service operations on the engine. ,” Riddle explained.
Ultimately, engines become more environmentally friendly by becoming more efficient and using less fuel. Much depends on the speed of the engine—stroke—but the fuel injection system and turbocharging method are also important factors. “When considering efficiency, we are trying to reduce losses,” Riddle said. “We are focusing on Wärtsilä 31: combustion shaping, injection combustion and the use of high maximum cylinder pressure-so we are always looking to improve fuel injection technology.”
Wärtsilä also provided CSS with a selective catalytic reduction (SCR) device, which will reduce nitrogen oxides [nitric oxide] Ship emissions comply with International Maritime Organization (IMO) Tier III regulations. The company provides its own SCR device without using third-party suppliers, thereby reducing the need to complete on-board certification during ship construction. Marine engine development is a professional capability, and competition is fierce because there are few suppliers of gas turbines and diesel engines. Driven by improvements in the commercial sector, the company is able to provide its navy customers with more efficient and capable prime movers, and provide warships with appropriate power and propulsion equipment to suit the mission. In the past ten years, Rolls-Royce MT30 has been challenging GE LM2500 in the GT market with its power density and lifetime maintenance cost reduction competitiveness. Improved maintenance is also a key driving factor for Wärtsilä, as it has improved efficiency through the latest 31 engine products.
By Tim Fish
