Unfortunately, while the reddit post seems authoritative, it contains a multitude of errors and ends up somewhat misleading. The most significant error is:
"What the front half of a jet engine (the intake/diffuser, and the compressor blades, i.e. all the stuff that happens before fuel is burned) does is; it heats up the air until it's hot enough for fuel to ignite" ...etc.
The heating up of air in the gas turbine cycle (Brayton cycle) is an UNDESIRABLE, but difficult to avoid consequence of the ideal gas law. A higher efficiency and power output would be possible if this heating did not occur, hence measures such as water injection or intercooling on large stationary gas turbines.
There are a number of other more subtle errors in the post.
If you have any interest in manufacturing, IMO the turbine blades in a jet engine are incredible.
Without going into loads of detail, 2 points that blow my mind:
1) Due to compression in the intake (and as per the ideal gas law D_Alex mentions above), the temperature of the air when it reaches the turbine is higher than the melting point of the turbine blades. The workaround for this is the blades are made with hollow channels through which cold air is blown, keeping them just cool enough.
2) You may be familiar with 'creep' - where materials under stress gradually relax to relieve that stress, even when the stress is lower than the yield stress of the material. Creep is made worse by (i) repeated stress cycles and (ii) high temperatures. In a typical jet turbine engine, you have blades spinning at 10000 rpm, at high tempratures, with a few microns clearance to the edge of the turbine housing. If they were to elongate and rake the edge of the housing at that speed ...
I worked as an IT intern for Pratt and Whitney in the Middletown, CT plant in the mid 90's. I got to see samples of the blades straight from the factory floor, and indeed they had those cool-looking grooves and channels in the them.
My occasional trips to the shop floor for some PC maintenance or another was really the coolest part of that job.
Point #2 is also pretty cool. In order to prevent overcome problems of creep, the turbine blades can be made in a single crystal [1] [2]. This prevents much/all of the creep, as creep is associated with grain boundaries. It's pretty phenomenal that these single crystals can be manufactured into jet turbine blades.
On modern jet engines: yes. There's a documentary / video about the manufacture of the Rolls-Royce Trent engine that mentions this fact and shows a CAD drawing / part of the manufacture process of the blades right after the combustion stage.
It also dances around the key innovation used to divert the flow from the turbojet core to the ramjet component: the movable (fore and aft) inlet cone. It doesn't happen automatically.
"What the front half of a jet engine (the intake/diffuser, and the compressor blades, i.e. all the stuff that happens before fuel is burned) does is; it heats up the air until it's hot enough for fuel to ignite" ...etc.
The heating up of air in the gas turbine cycle (Brayton cycle) is an UNDESIRABLE, but difficult to avoid consequence of the ideal gas law. A higher efficiency and power output would be possible if this heating did not occur, hence measures such as water injection or intercooling on large stationary gas turbines.
There are a number of other more subtle errors in the post.