High-Mach Turbojets, Ramjets and Scramjets Question

[KJ_Lesnick]

I'm honestly curious about this. If we have turbojets that can do extremely high mach-numbers and have 25:1 or 30:1 or greater pressure ratios, and the fact that the inlet has to slow the airflow down to subsonic speeds (which produces a lot of pressure and heat in and of itself) how come there isn't problems with dissociation of O2 or ionization or heat or pressure problems like with ramjets?

I've been told that ramjets have problems at high mach numbers because of the extreme pressure produced and the need for an unusually heavy structure for the ramjet, heating issues, and dissociation of O2 to individual Oxygens, or ionization problems and such which is why scramjets become needed for high mach numbers.

But if you have turbojets and turbofans with high pressure ratios operating at high mach-numbers, wouldn't the pressure produced by ram-compression combined with the pressure produced by the compressor produce enough overall heat and pressure to get some of these these problems?


KJ Lesnick

 

[sferrin]

I'm honestly curious about this. If we have turbojets that can do extremely high mach-numbers and have 25:1 or 30:1 or greater pressure ratios,

The high-mach turbojets don't have high pressure ratios. And there's a big difference between Mach 3 and Mach 5. (Ramjets can hit at least Mach 5.4.) I think the engines that Allison (scuse me RR) and Williams are testing for the RATTLRS program are probably the closest to what you're referring to. If I had to guess, given the apparent complexity of the inlet on RATTLRS it is likely the engines are low-pressure designs with the inlet precompressing the air. In other words it may still be a high pressure engine, just that the inlet is precompressing the air rather than the compressor doing all or most of it if that makes any sense.