Type 076 Yulan LHA - Propulsion
This is the first time that the Chinese Navy has adopted all-electric propulsion and an integrated power management system for a ship. Some Chinese observers initially thought that the Type 076 would be able to reach a speed of 30 knots, because he thought it might use a more powerful gas turbine. The dock and vehicle deck might be removed, and in landing combat missions, it would mainly undertake helicopter assault missions like the "America" class. If needed, the ship can operate together with the Type 003 aircraft carrier, serving as the "extended flight deck" of the Type 003 aircraft carrier, forming a "small dual aircraft carrier formation."
There seem to be four diesel engine exhaust pipes on the top of this island module, and the top of the exhaust pipes are bent in the same direction. This may be the chimney of 054A. There is a relatively wide gap between the installation positions of the two islands on the starboard side of the 076 hull. This may be the location of the left outboard elevator. Openings for the power system intake and exhaust pipes can be seen on both sides of this position. In the yellow box in the figure below, there are multiple intake and exhaust pipe openings on both sides of the elevator gap, which can be used for the intake and exhaust pipes of diesel engines and gas turbines. According to previous public bidding documents, 076 uses 6 6MW diesel engines and two 21MW gas turbines. Therefore, multiple intake and exhaust pipes are required to lead to the chimney on the top of the island.
The power system of the Type 076 amphibious assault ship should be an all-electric propulsion system with a 21 MW gas turbine and a 6 MW diesel engine as the core. The so-called ship integrated power system refers to the integration of the two independent power systems of traditional ships, namely power and electricity, into one, which is used to supply power to propulsion loads, pulse loads, communications, navigation and daily equipment in the form of electric energy, thus realizing the comprehensive utilization of energy for the entire ship. Compared with traditional power systems, ship integrated power systems have the following significant advantages.
First, the integrated power system is conducive to the overall optimization design of ships, making the layout of the power system more flexible, and improving the maneuverability, controllability, endurance and economical use of ships. Because it breaks through the traditional mechanical propulsion mode of arranging the engine, propeller and transmission shaft system in a straight line, the mechanical connection is completely replaced by cables, making the layout of the entire ship system and equipment more flexible. The use of a ship integrated power system can shorten the shaft system, reduce the number of thermal engines and special power generation equipment, save space, and simplify the structure of the ship power platform. Its systematic, modular and integrated design concept is conducive to the overall optimization design of ships.
In addition, electric propulsion can quickly achieve reverse operation by converting the polarity or phase of the power supply, thereby improving the maneuverability of the ship. The ship's integrated power system can also adjust the number of prime movers according to the power load capacity, increase the prime mover load rate, reduce fuel consumption and maintenance costs, and improve endurance. According to calculations by the U.S. Navy's Advanced Surface Ship Mechanical Research Group, a ship using an integrated power system saves more than 20% of fuel annually compared to a mechanically propelled ship of the same tonnage.
Secondly, compared with the mechanical propulsion system, the integrated power system has no mechanical connection between the prime mover and the propulsion motor due to the elimination of the transmission shaft and gearbox, which shortens the shaft system and cuts off the main transmission path of mechanical vibration noise. In addition, the prime mover can be arranged above the waterline, which can greatly reduce the underwater radiation noise and make it quieter. Compared with mechanical propulsion, the noise can be reduced by 15-20 decibels in a wide frequency band and more in a narrow frequency band. Therefore, the comprehensive detection and combat capabilities of underwater targets (such as submarines) are improved, and the acoustic stealth performance of ships is enhanced.
Finally, the integrated electric ship reduces mechanical vibration and shock, and its hull structure is not easy to fatigue, which helps to increase the service life of the ship. The centralized power supply is adopted, and there is a certain redundancy in each link from the generator set to the propulsion motor. The failure of any prime mover, generator set and propulsion motor will not affect the operation of the propeller. Through reasonable layout and control distribution and other protection measures, the system has a strong fault resistance and improves the vitality of the ship. Due to the large reduction of complex closed pipeline systems and auxiliary equipment such as oil, liquid, and gas required by mechanical propulsion devices, they are replaced by small, light, and highly reliable motors, electronic and electrical components, integrated circuits, and various wires and cables, and the overall system complexity is greatly reduced. Therefore, its overhaul, transformation, and component replacement are also easier than mechanical transmission devices, and the security and convenience in use and combat are greatly improved.
In addition, the emergence of integrated ship power systems has also laid the foundation for the deployment of new concept high-energy weapons such as electromagnetic guns, electrothermal chemical guns, laser weapons, and microwaves.
From the current global perspective, integrated power systems have become an inevitable trend and trend in the development of ships, and the configuration of gas turbines plus integrated power systems is the best choice for large ships and aircraft carriers. The 076 amphibious assault ship will use electromagnetic catapult technology, and its tonnage should be larger than that of the 075. Ordinary diesel power is too small to meet the consumption and power requirements of electromagnetic catapults. Taking the 075 amphibious assault ship as an example, it uses four large diesel engines with a total power of 48 megawatts, which is almost impossible to bear the electromagnetic catapult; in contrast, the all-electric propulsion system with steam turbines, gas turbines, etc. as the main power can meet the needs of the 076 amphibious assault ship.
The most notable example is the British Queen Elizabeth-class aircraft carrier, which uses an integrated power system. Its main power system is two 36MW MT-30 gas turbines and its cruising power is two Wartsila 12V38B diesel generator sets with a single power of 9MW. The maximum output power of the main power system is 108MW, of which 80MW is used to drive four advanced induction motors of the French Corfud Electromechanical Company with a single power of 20MW. The total propulsion power is 108,000 horsepower, which can enable the 65,000-ton aircraft carrier to reach a maximum speed of 26 knots. The combination of gas turbines and integrated power systems can achieve satisfactory power performance even for super-large warships such as aircraft carriers, not to mention amphibious assault ships with relatively small tonnage. Therefore, if the Chinese 076 amphibious assault ship is equipped with four 21MW gas turbines at the same time, its power level will exceed that of the "Queen Elizabeth-class" aircraft carrier, which is enough to support the power consumption of the electromagnetic catapult system and other systems of the entire ship.
The use of an integrated electric propulsion system helps optimize the design of ships and greatly improves their maneuverability, controllability, endurance and economic efficiency. As for why gas turbines are used instead of steam turbines, it is because gas turbines have incomparable starting and acceleration properties. For example, if a steam turbine aircraft carrier wants to leave the port, it must first check the boiler. It takes at least ten hours to start a fire, while a gas turbine aircraft carrier can do it in 8 hours; in terms of acceleration, gas turbines are also better than steam turbines. For example, it takes 2 hours for a steam-powered aircraft carrier to accelerate from a cruising speed to a maximum speed of about 30 knots, while a gas-powered aircraft carrier only takes 20 minutes. Such a huge gap is fatal in actual combat. Compared with steam turbines, the only disadvantage of gas turbines may be the huge fuel consumption. However, with the advancement of technology, today's high-performance gas turbines can achieve lower fuel consumption. The full-power fuel consumption of the Queen Elizabeth-class MT-30 gas turbine is 207 grams/kilowatt-hour, which is equivalent to the full-power fuel consumption of 210 grams/kilowatt-hour of a medium- and high-speed diesel engine.
In addition, another major advantage of gas turbines is their reliability and maintainability. Ship-based gas turbines are generally evolved from mature aircraft engines. The classic LM-2500 is developed from the TF-39 turbofan engine on the C5 transport aircraft. More than 2,000 units have been sold so far, and the total operating hours have exceeded an astonishing 50 million hours. The MT-30 gas turbine of the Queen Elizabeth class is derived from the Trent 800 aircraft engine, which is used in Boeing 757 and Boeing 777. The total number of installed units has reached 250, with a cumulative use of more than 5 million hours and a reliability of up to 99.9%.
The British Queen Elizabeth-class aircraft carrier uses a combination of gas turbines and integrated power systems. China's 076 amphibious assault ship will also use this power system. In summary, the combination of 076 gas turbine plus integrated power system is in line with the development direction of future ship power systems and is also a major trend in the development of ships in various countries around the world. Of course, in the long run, nuclear power plus all-electric power is undoubtedly the best choice for large ship power systems, but the development cycle of ship-based nuclear reactors is long, the cost is high, and the technical difficulty is great. For the current Chinese Navy, the gas turbine plus integrated power solution is more suitable for future development needs.
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