FirstTarget8418 t1_j6jegwt wrote on January 30, 2023 at 7:27 PM

Hasn't this been like a working theory since the 50's or something and never went anywhere?

cjameshuff t1_j6jof4l wrote on January 30, 2023 at 8:28 PM

The idea of using detonation to improve efficiency is quite old. The V1 "buzz bomb" used a pulsejet engine in 1944-1945, and experimental versions of pulsejets using detonations are about as old. The vibrations inherent in pulsejets of any sort have prevented them from being used much.

The basic concept of using continuous detonation waves in some form has probably been around for just as long, but has been more difficult to implement.

BackflipFromOrbit t1_j6l01s2 wrote on January 31, 2023 at 1:49 AM

Standing oblique detonation ram jets are also a thing. Instead of the detonation wave revolving around an annulus it occurs in a static position downstream of a really interesting series of C-D nozzles and fuel injectors. It uses the ram effect for oxygen intake and compression but undergoes a pre-burn through an upstream CD nozzle to accelerate the gas further to higher mach numbers. The gas then flows into another CD nozzle where more fuel is injected at the throat. This mixture then accelerates again and just downstream of the throat there's a ramp that causes a standing oblique shock wave. The rapid increase in heat and pressure crossing the boundary of the oblique shock causes the fuel rich hypersonic gas to detonate constantly.

cjameshuff t1_j6l0p7t wrote on January 31, 2023 at 1:54 AM

Oh, the shcramjet (not a typo). Yeah, I'd forgotten about those.

Shrike99 t1_j6k8b6k wrote on January 30, 2023 at 10:32 PM

Sometimes it takes quite a while for a theory to be practically implemented.

Work on Scramjets started in the 50s, with engines working in laboratory conditions in the 60s, but didn't operate in real flight conditions until the 90s and have only recently started to approach practical use - it's hard to say exactly where they are today since most such projects are classified.

I'm not sure when the theory for FFSC engines dates to, but the first example was built in the 60s. However it was unable to sustain stable combustion and the first stable engine wasn't tested until the early 2000s. The first test flight of an FFSC engine wasn't until 2019, and the first practical use will probably occur this year.

The basic theory for fusion dates back to the 1920s, with proposals for fusion power specifically dating to the 1950s, but it still hasn't gone anywhere, yet. We have been making steady progress, so it may still go somewhere given more time. The recent scientific breakeven at the NIF was a significant, if not directly applicable milestone.

Advances in computer control technology have been instrumental to a lot of the recent progress in the aforementioned applications. Having the theory is one thing, being able to control a complex and delicate process in practice is another.

Maintaining continuous rotating detonation has proven quite challenging in the past, typically breaking down due to instabilities in a matter of milliseconds. The fact that NASA were able to run this engine for what looks like about 8 seconds is very promising indeed.