Heat development?

[alex]

Hi all!

I have a quick and simple question: How hot does a pulse jet become while running, static vs in air?

I understand these questions have been up before. Hope you want to help me still.

Thanks
Alex

[metiz]

900 degrees, maybe 1000 C static
unless you are moving at a considerable speed, the temperature is not realy going to drop - maybe a 100-ish degrees

[alex]

Thanks. Is that the temperature of the exhaust or inside the engine? What's the distance behind the tailpipe where you can put your hand without any injury?

I'm trying to make a picture of how much the tempreature of the exhaust decrease after leaving the tailpipe.

[metiz]

the outside of the combustion chamber and the exhaust.

You should probably just try to put your hand behind on and then start inching in - I'm guessing it differs a lot per engine. If you have any acces to some sort of thermal imaging equipment or maybe even just a infrared camera, you could try to get information on the heat pattern that way.

an easy mod to a cheap webcam would do the trick http://www.hoagieshouse.com/IR/

[larry cottrill]

unless you are moving at a considerable speed, the temperature is not realy going to drop - maybe a 100-ish degrees

metiz, I would respectfully challenge this statement.

I have static run the Dynajet scores of times, and flown it U/control a few times. In static running, the entire pipe is red hot in 15 seconds or less. This appears bright orange in shade or at dusk, with the highest intensity at the nozzle zone, right where the chamber necks down into the straight pipe. In flight (with the engine totally exposed to airflow), the heat of the engine is completely invisible in daylight, and at dusk the only visible reddening is at the nozzle point, with the whole remainder of the tube fore and aft remaining dark. That was at a speed of only about 90MPH (something like 150 km/hr, I think). Surely that must be a lot greater difference than 100 degC.

Moving air over a smooth surface is a very effective heat collector.

L Cottrill

[metiz]

Ok you got me there - but I was not realy talking about flight, 90Mph is a lot faster then say a gokart wich travels at 60 - 70km/ h also, when you double the speed of whatever you are traveling in, the air resistants quadruples. So when you are talking about 90 km/ h //Mph VS 45 km/ h//Mph the air cooling effect is much more than doubled.

Please correct me if I'm wrong.

[larry cottrill]

Ah ... well, I'm sure you're right in that case. (I guess it's all in what you think of as "considerable speed" ;-)

To me, 90 MPH seems like a pretty slow dog. That was my old 6 lb (3 kg) 4 ft wingspan (1200mm) "Buzz Bomb Trainer".

L Cottrill

[metiz]

Posted: Mon Apr 23, 2007 2:40 pm

Ah ... well, I'm sure you're right in that case. (I guess it's all in what you think of as "considerable speed" ;-)

L Cottrill

note to self: type faster :P

[marksteamnz]

Thanks. Is that the temperature of the exhaust or inside the engine? What's the distance behind the tailpipe where you can put your hand without any injury?

20 millimeters or 100 meters. Mind you the first on was a very small, very bad jam jar and the second one was a theoretical one using a road tunnel through the alps ;-)

I'm trying to make a picture of how much the temperature of the exhaust decrease after leaving the tailpipe.

Just trying to point out with out more definition of the problem the question can't be answered.

[El-Kablooey]

Well, with my chinese engine I have put my bare hand maybe 12" from the tailpipe opening. Not instant burn, but gets uncomfortable pretty quick.

With my FWE I have done the same and it gets alot more uncomfortable alot quicker.

[Mark]

My snorkeler does the same, about a foot above the snorkel, the invisible in daytime flame gets too hot to hold your hand over it in a few seconds.