Why are gas turbines chosen as engines for large ships?

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Gas turbine engines are very fuel efficient compared to traditional piston engines, but why are they always chosen as the main engines for large warships.

A gas turbine engine is a type of rotor heat engine in which the work-expanding agent is air. The engine consists of three main parts, which are the rotor-shaped air compressor block (rotational movement); open type isostatic combustion chamber and rotor gas turbine block. The compressor block and the turbine block have a shaft connected so that the turbine rotates the compressor.

Compared with a typical piston engine, which is a Diesel engine, a gas turbine engine has more weaknesses: very high manufacturing technology, very expensive, and has lower thermodynamic efficiency (about two thirds compared to that of a diesel engine) that leads to poorer economy, rapidly degraded performance when running at low load.

But the outstanding advantage of the gas turbine engine is that it has compact volume and size but gives extremely strong power; The specific power index (hp/kg) of this engine is dozens of times larger than that of a diesel engine. However, gas turbine engines consume a lot of fuel compared to traditional piston engines.

So gas turbine engines consume so much fuel, but why are they always preferred to use them on warships rather than diesel engines; why is that so?

Currently, the best warships in the world use gas turbine engines as the main engine. For example, the British Navy’s “Queen Elizabeth” class aircraft carrier is equipped with MT-30 gas turbines, the US Navy’s Arleigh Burke class destroyers are equipped with LM-2500 gas turbines, and China’s Type 055 class destroyers are equipped with gas turbine GT-25000 engines.

Almost all the leading warships in the world today, use the best gas turbine engines as main engines; This is also the common choice of today’s naval powers.

Compared with steam turbines and diesel engines that appeared before, the advantages of gas turbines are obvious: high thermal efficiency, simple structure, convenient transmission, low noise, small volume.

Take the American LM-2500 gas turbine as an example, its box body has a volume of only 8×2.7×3.1 meters, and its overall weight is only 6 tons, but it can produce a large amount of powerful capacity, of about 28MW. Four LM-2500 turbines can propel the Japanese light aircraft carrier Izumo, which has a displacement of 27,000 tons, at a speed of more than 27 knots.

Moreover, due to the small size of the gas turbine engine LM-2500, it does not take up much space inside the hull; For example, on an Arleigh Burke-class destroyer, which has a displacement of more than 9,000 tons, it is actually possible to install four LM-2500 gas turbines at the same time.

As a result, replacement and maintenance are very convenient, and even the turbine housing can be lifted directly from the chimney. In contrast, the first steam turbine engines used on large warships were expensive to maintain because of their complex construction and enormous mass; they are not removable once fitted.

Of course, the power of a steam turbine engine can be very large, 4 steam turbines can take a 100,000 ton super carrier to run at a high speed of 30 knots.

One strong point of a steam turbine engine is that it is more stable and quieter than a gas turbine engine, which is why many large warships over 20,000 tons are equipped with steam turbines. However, compared to gas turbines, the advantages in volume, speed and ease of maintenance are obvious.

Compared with diesel engines, gas turbine engines have an overall advantage; Gas turbine engines are not only smaller and more versatile than diesel engines, they are also more powerful than diesel engines.

Currently, very few large warships use diesel as the main engine, because the power of the diesel engine cannot meet the requirements.

In the future, internal warships will popularly use electric propulsion technology, but in general, gas turbine engines are still used as generators and diesel engines are still auxiliary engines.

In modern warships, since destroyers have higher requirements for speed, maneuverability and variable speed, most destroyers use gas turbines and some smaller carriers also use gas turbine engines.

Diesel engines are mainly used on frigates, while steam turbine engines are used more on aircraft carriers. Therefore, even though the fuel consumption of gas turbine engines is very high, navies still appreciate its outstanding performance and the money spent on that fuel consumption is still affordable.

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