How To Build A Jet Engine (and Natural Gas Power Plant Turbines)

A good friend, who also happens to be an engineer, recently sent me an intriguing article titled “Why it's so hard to build a jet engine.” It is rather lengthy but full of fascinating details. It’s not for everyone, but I was drawn to it because I once did work for a small energy company in the north country of New York State that ran a little power plant using a turbine from a jet engine. Not being an engineer, I had no idea at the time that such a thing was even possible, but it is, as Grok notes:

Yes, a jet engine can be used as a turbine in a natural gas-fueled power plant, and this is often done in certain types of power generation systems. Specifically, jet engines are used in aeroderivative gas turbines, which are adapted from aviation jet engines for stationary power generation. Here’s how it works:

• Aeroderivative Gas Turbines: These are essentially jet engines modified for industrial use. They burn natural gas (or other fuels like diesel) to produce hot exhaust gases, which drive a turbine to generate electricity. The core technology is similar to that of jet engines used in aircraft, but they are optimized for continuous operation and power output rather than thrust for flight.

• Advantages: Aeroderivative turbines are lightweight, compact, and highly efficient, with quick start-up times (often 5-10 minutes). They are ideal for peaking power plants, which provide electricity during high-demand periods, or for combined-cycle plants, where waste heat is used to generate additional power via a steam turbine.

• Examples: Common aeroderivative turbines include models like the General Electric LM2500, LM6000, and Pratt & Whitney FT8, which are derived from jet engines used in aircraft like the Boeing 747 or military jets. These are widely used in natural gas power plants globally.

• Operation: In a natural gas power plant, the jet engine’s compressor draws in air, mixes it with natural gas, and combusts it. The high-pressure exhaust spins the turbine, which is connected to a generator to produce electricity. In simple-cycle mode, the exhaust is released; in combined-cycle mode, it’s used to produce steam for additional power.

While not every natural gas power plant uses aeroderivative turbines (many use larger, heavier industrial gas turbines), jet engine-derived turbines are a well-established technology in the industry due to their efficiency and flexibility.

And, believe me, building a jet engine is no easy task, although there are multiplee companies today that do it, which says a lot about human ingenuity. Here are a few excerpts from this very well-illustrated post at Construction Physics:

The jet engine is a type of heat engine: it converts heat into useful work. Like a steam turbine or an internal combustion engine, the jet engine works by taking some working fluid (in this case air), compressing it, heating it, and then expanding it, extracting work from the heated fluid in the process.

More specifically, a jet engine operates on the Brayton cycle. Air is taken into the front of the engine, then run through a compressor, increasing the air’s pressure. This compressed air flows into a combustion chamber, where it’s mixed with fuel and ignited, producing a stream of hot exhaust gas. This exhaust gas then drives a turbine, which extracts energy from the hot exhaust as it expands, converting it into mechanical energy in the form of the rotating turbine. This mechanical energy is then used to drive the compressor at the front of the turbine.

In a gas turbine power plant, all the useful work is done by the mechanical energy of the rotating turbine. Some mechanical energy drives the compressor, while the remaining energy drives an electric generator. In a jet engine, the energy is used differently: some energy drives the compressor via the turbine, but instead of using the remaining energy to generate electricity, a jet engine uses it to create thrust through hot exhaust gases, pushing the aircraft forward the same way an inflated balloon propels when air rushes out of it.

Diagram of a twin-spool turbojet, via Gas Turbine Aero Engines.

…[A] key development for jet engine commercial use was the turbofan. In a conventional jet engine, all the air flows through the compressor, into the combustion chamber, through the turbine, and out the rear. This arrangement is known as a turbojet. But if you mounted a fan to the engine spool that was larger than the rest of the engine, some air would flow around the sides of the engine, rather than through it.

Turbojet vs turbofan, via StackExchange

Adding this fan offers several advantages. On a turbojet, the hot exhaust exits the engine at a high speed, but jet engines are at their most efficient when the exhaust stream is as slow as possible. Air moved by the fan around the sides of the engine will be much slower than the hot exhaust from the combustion chamber, improving engine fuel efficiency. This slower air also makes much less noise — an important factor, since people were getting fed up with the noise from jets. A large fan also makes it easier to increase engine thrust, making it possible to power larger, heavier aircraft…

The difficulty is building an engine that meets its various performance targets — thrust, fuel consumption, maintenance costs, and so on. There’s no point in designing a new engine if it doesn’t significantly improve on the state of the art, and that means engine development projects are constantly pushing technological boundaries: higher compression ratios, hotter temperatures, lighter weight, larger fans, and so on. An engine that isn’t an improvement over what’s already on the market won’t be competitive, and engine performance targets will often be contractual obligations with the aircraft manufacturers buying them…

A commercial jet engine must operate for thousands of hours a year, year after year, before needing an overhaul, demanding high durability and high fatigue resistance. It must burn fuel at temperatures in the neighborhood of 3000°F or more, nearly double the melting point of the turbine materials used within them. Turbines and compressors must spin at more than 10,000 revolutions per minute, while simultaneously minimizing air leakage between stages to maximize performance and efficiency.

A commercial jet engine must operate across a huge range of atmospheric conditions – high temperatures, low temperatures, both sea level and high-altitude air pressures, different wind conditions, and so on.¹¹ It must withstand rain, ice, hail, and bird strikes. It must be able to successfully contain a fan or turbine blade breaking off.

There is so much more. Read the whole thing for more insights, the history of the jet engine and thoughts about the future. Bear in mind, though, how most of what’s said about the jet engine is also applicable to natural gas power plant operation today. The turbines involved are amazing pieces of work. simply

#JetEngine #NaturalGas #Turbines #PowerPlants