Thread by @FToddDavidson

Do you want to learn about gas turbine performance? It’s kind of a big deal.
/THREAD

Gas turbines are used for two primary things:

1) Electricity Generation (The most efficient gas turbine in the world is made by GE. The 9HA: ge.com/power/gas/gas-…), &

2) Propulsion (e.g. jet engines on airplanes: animagraffs.com/inside-a-jet-e…).

Between electricity generation & jet propulsion, high temperature gas turbines convert over 12% of all the energy consumed in the United States, and turn it into useful products like air travel and electric lights

Consider: A 1% incr in gas turbine efficiency (e.g. incr to 33% from 32%) for the existing US power generation fleet would produce enough additional electricity to power nearly 2.4M average US homes and save ~$800 million per year in natural gas costs.

Said another way, the added elec. production due to increasing avg GT efficiency by 1% to 33% would be enough to satisfy nearly 20% of all electricity needs for the greater Los Angeles and San Diego metro areas, COMBINED
(an area with more than 22 million people).

Further: A 1% incr in jet engine efficiency (e.g. incr to 38% from 37%) could result in additional fuel savings of nearly $900 million per year for aircraft.

For clarity: When I say “jet engine efficiency” I’m really talking about improvements to overall efficiency, including thermal and propulsive efficiency.
If you want the details, check out equations 2.22, 2.31 & 2.42 here: web.stanford.edu/~cantwell/AA28…
And: ocw.mit.edu/ans7870/16/16.…

But, increasing efficiency is no small feat. According to GE, it has taken 10 years to improve efficiency by 1% for the highest performance combined cycle power generation systems. ge.com/power/about/in…

Gas turbines have 3 primary components: 1) Compressor, 2) Combustor, & 3) Turbine

Thermodynamics shows us that the efficiency of a GT is proportional to:
1 – (Exhaust Temperature / Turbine Inlet Temperature).

For details see here: web.stanford.edu/~cantwell/AA28…
Or here: web.mit.edu/16.unified/www…

From the Brayton Cycle, we know that turbine efficiency will increase if we increase the turbine inlet temperature. i.makeagif.com/media/8-25-201…

But it’s not that simple. As the temperature increases, we begin to reach material limitations. The engine will destroy itself if the combustor temperature is too hot.

My PhD dissertation developed empirical methods to model the extreme heat transfer conditions in a gas turbine, while implementing strategies to improve the thermal protection of the engine components. repositories.lib.utexas.edu/handle/2152/ET…

There are three primary ways to thermally protect turbine components: 1) Improve the durability of the metal itself, 2) Actively cool the metal with relatively cool air, and 3) Passively cool the metal by coating it with low thermal conductivity materials
i.pinimg.com/originals/27/d…

Inlet temperatures can approach 2,700 F for power generation & exceed 3,500 F for military aircraft. Consider: the nickel based superalloy used in many engines will melt at around 2,400 F….these engines are operating beyond the limits of most materials.

Furthermore, an increase in metal temperature of just 50 degree F above its design point can result in a two-fold (2x) reduction in airfoil durability. We better get our cooling strategies correct to uniformly protect the components and avoid hotspots
link.springer.com/article/10.136…

This is what a single turbine vane in the first stage of an engine looks like (this component is exposed to some of the highest temperatures in the engine) Notice all of the holes. Those holes are meant to provide “film cooling”.

Film cooling works by routing relatively cool air through internal cavities of the vane and then bleeding the air out on to the surface. This cools the component from the inside and creates a gaseous film to protect the external wall of the component from the hot combustor gas

But, using too much film cooling can decrease the power output of the combustor and reduce the aero qualities of the turbine. It’s a challenge to provide just enough cooling to endure high engine temperatures while also maximizing engine efficiency.
researchgate.net/figure/Variati…

To combat the extreme environments, Pratt & Whitney developed single crystal turbine components in the 1960’s to improve durability…literally casting components into a single-directional crystal! americanscientist.org/article/each-b…

Modern engines also employ thermal barrier coatings, such as yttria-stabilized zirconia (YSZ). YSZ is used to coat the metal structure of the turbine components, and protect them from the extremely harsh, high temperature environment science.sciencemag.org/content/296/55…

The purpose of all of these thermal protection techniques is to drive up the combustor temperature and improve the efficiency and performance of the gas turbine.

An aside: Notice the “J58” data point in one of the previous images. J58 is the legendary engine that powered the SR-71 Blackbird, an incredible leap forward in gas turbine engineering and propulsion.

For power generation, the increases in inlet temperature has helped move us from D class engines to the modern H class (from GE and Siemens) and J class (from Mitsubishi) with corresponding improvements in thermal efficiency
mhi.co.jp/technology/rev…