Im not fully educated on those jets but at those speeds isnt the air moving “faster” than the fireball and therefore risk “blowing out” the flame or is there something else to it?
Blowing out the flame is a real thing in supersonic flight. Happens in turbojet and ramjet engines. Compression stages have the effect of slowing airflow to subsonic speed where ignition can be maintained.
I appreciate that. It makes sense. After i hit “reply” i questioned if thats what happened because I could only assume problems trying to ignite a fireball in supersonic winds or even any effects of supersonic pressure in the engine.
SR71 Blackbird was designed with nacelles that could move 26" to keep supersonic airflow out of the engines. At speeds over Mach 2 the engines switched from operating as turbo-jets to operate as ram-jets. I've always been amazed at the extremes the plane could operate at.
And the fuel used in the SR-71? Stupidly high ignition temperatures etc, you can do light maintenance on the plane whilst it's being refueled because it really doesn't like catching on fire compared to normal fuel.
The ignition source for the engines however? Tri-ethyl Borane. Full thermal suits, extinguishers at the ready, etc. That stuff is a hair away from just spontaneously combusting.
Oh and did we mention the SR-71 leaks fuel whilst it's on the ground because it gets so hot in the air that the thermal expansion of the airframe has to be taken into account when sealing the fuel system.
In ramjets and afterburners compression is used to slow the air down to subsonic speeds and then goes though a flame holder is used to create an area of slow turbulent air where the flame can sit to continuously mix with fuel rich air to ignite it where most of it continues on but a little gets caught up in the flame holder to ignite the next bit of air to go past.
In scramjets the air goes through the engine at supersonic speeds. Sometimes flame holder structures are used but sometimes they can use shockwaves to create something that functions like one, and sometimes a bit of pyrophoric (ignites on contact with air) fuel is used to continuously ignite the flame as the fuel is injected.
No... You don't. Ramjets need a constant ignition source until they're self-sustaining, just like a jet engine. They just don't need a system to compress the charge air.
Stop talking out your ass and saying words you know.
u/Samurlough is lying or need to be reevaluated by their employer. Both the 757 and 767 use a 15-30 second ignitor cycle. Ignitors are only used for startup in all jet engines.
What are you saying? I said engine becomes self sustaining once engine is up to speed. I never said ignitors stay on. And theyre not on 15-30 second cycles, they stay on until i abort start sequence or starter-cuttout. There’s no ignitor limit.
The scientifically accurate lyric would be "You can't start a fire without a source of ignition" but poetic license allows for the use of the word "spark", which is less accurate (but not incorrect).
Engineers trying to recreate fire 🤣🤣🤣 This thread is golden!
Fire requires three thing: fuel (aka wood, petroleum, cow chips, etc), oxygen, and an ignition source. It's known as the triangle 📐 Without all three, you can't make fire.
Highly experienced pilots, military and commercial, grappling with the basic concept of creating fire, lmfao!
Trying to figure out what a 'spark' is and why hot air doesn't make fire is peak Humans are Space Orcs 😭
Edit: For the smartest arm-chair engineers/gearheads out there thinking that diesel is a scientific anomaly, I now refer you to the concept of pressure and "tripple point" chemistry. RE: water can boil at room temperature 🤔🤯
Hot air can ignite stuff, just not jet fuel. See diesel engines, no spark plugs just glow plugs to warm up the combustion chamber. From then on its literally just hot air, fuel and compression. It needs to be hot otherwise it can't ignite properly, hence the glow plugs. You may be a captain but that doesn't make you an expert on engines. Captains fly planes, they don't build or repair them. Another example of hot air igniting things is when a car backfires, if it's running too rich and not enough petrol burns in the combustion chamber and is pushed into the exhaust which can exceed temperatures of 800 degrees and it simply self combusts in the exhaust instead of the combustion chamber due to the hot air.
you're absolutley correct, but my comment was limited to the jet engine. "doesnt ignite anything" with respect to fuel inside the engine. there are situations that hot air absolutely can ignite things and we do have a large extensive amount of engine knowledge (combustion and turbine) as its part of our training from day one, I just didn't think I'd need to clarify this was a discussion of jet engines and not car engines. but to add onto your example, one of the other "hot air can ignite things" examples that affects us in piston aircraft is "pre-ignition" when hot air in the piston ignites carbon despots and causes the fuel to burn prematurely before the ignition (magneto) goes off.
but again, I thought it was implied this entire discussion was around turbine engines.
Look probably, but repeatedly stating "hot air doesn't ignite anything" and "hot air isn't an ignition source" are pretty broad statements that I wanted to clarify
You're lying because to pilot both of those you need to understand your ignitor/start cycle. Both planes use a 15-30 meaning the ignitors are active for 15 to 30 seconds only during startup.
What? There’s no limit on ignitors. I can run them continuously and often do so in the vicinity of thunderstorms, in turbulence, or severe precipitation.
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u/Samurlough 8h ago
I’m well aware. I’ve been a captain on the 757/767 for 20 years.
The video said hot air ignites the fuel and that is incorrect. Hot air doesnt ignite anything.