Steve's ramjet revisited

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metiz
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Re: Steve's ramjet revisited

Post by metiz » Fri Jul 22, 2011 8:39 pm

What if the inlet was made with a big belmouth like on a augmenter? It would help with both the temperature and oxygen problems
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PyroJoe
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Re: Steve's ramjet revisited

Post by PyroJoe » Fri Jul 22, 2011 9:23 pm

Typically more fresh air entrainment causes overall lower velocity to inject into the ramjet.

Its trading high velocity narrow pj exhaust stream, for a wider slower velocity exhaust stream (with entrained air).

Don't take my word for it though give it a go, Eric achieved good results from his work, inspite of all the difficulties.

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Re: Steve's ramjet revisited

Post by metiz » Fri Jul 22, 2011 10:58 pm

PyroJoe wrote:Typically more fresh air entrainment causes overall lower velocity to inject into the ramjet.
Yes, but maybe the added mass will give a bit more "push" to compensate for the lower velocity. At any rate, do you still reccomend getting rid of the spike? I only put it in there because I thought it would help temper the pulsed air comming from the pj but if it is not realy necessairy then Ochams razor ftw. Btw, besides lower air speed, would the (a) belmouth mess with the ramjet's operation?

In the drawing in your previous post you corrected my dimensions to an engine with a mouth of about 60mm. I purposely made that intake 100mm because it's the same diameter of the M25 exhaust. I could just blow up the design until it's about 100 but I don't know if I can get away with that, can you shed some light? Also, by what measure did you get the new dimensions for the ramjet?
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PyroJoe
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Re: Steve's ramjet revisited

Post by PyroJoe » Sun Jul 24, 2011 3:34 am

The jet I posted below yours is a scaled up Decker subsonic, just for a comparison. There is a word document just above the drawing.

Only speculation on how the operation will affect the M25.

metiz
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Re: Steve's ramjet revisited

Post by metiz » Sun Jul 24, 2011 12:33 pm

Didn't see the word file. I think something went wrong with the upload though, it's only 162 bytes and it opens to like 4 lines of jibberish.

As for the engine, I'm not concerned about the M25, I'm worried about the ramjet. Can I just slap on a belmouth on the intake and still expect it to run just fine? (asuming ideal circomstances)
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PyroJoe
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Re: Steve's ramjet revisited

Post by PyroJoe » Sun Jul 24, 2011 10:19 pm

http://www.pulse-jets.com/ramjet/ramjet.htm

Can't say if it will run to any measure.

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Re: Steve's ramjet revisited

Post by ace_fedde » Sun Aug 14, 2011 9:46 am

Metiz,

Think about this set up:
PJ - augmentor - ramjet
The augmentor will produce a cooler, oxygen-richer and more constant flow to feed the ramjet.

Fedde
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Re: Steve's ramjet revisited

Post by metiz » Sun Aug 14, 2011 11:12 am

Hey Fedde,

Yes that is true, I've thought about it, but that also means that the air speed is reduced significantly. The orifice on the ramjet will also have to be a lot bigger.
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Re: Steve's ramjet revisited

Post by ace_fedde » Sun Aug 14, 2011 12:23 pm

metiz wrote:but that also means that the air speed is reduced significantly. The orifice on the ramjet will also have to be a lot bigger.
Ha! think so?
read this paper: Looks you can even make a oscilating augmentor (ejector), which is of course the opposite of what Rob Miller wanted to achieve, and follow that one with a second-stage-ejector :D

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Re: Steve's ramjet revisited

Post by metiz » Sun Aug 14, 2011 12:57 pm

I've read it about halfway through, but it's too complex for me to make any sense of.
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MARQUIS
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Re: Steve's ramjet revisited

Post by MARQUIS » Sun Aug 14, 2011 3:40 pm

metiz wrote:I've read it about halfway through, but it's too complex for me to make any sense of.
Hi metiz, I read too but Miller paper is out of ramjet concept. MARQUIS :mrgreen:

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Re: Steve's ramjet revisited

Post by makulit » Sun Aug 14, 2011 6:37 pm

If you had a thrust augmenter after the PJ, you would draw in cool air and oxygen, which would enhance the performance of a ramjet/afterburner following it, just like Fredde said. You could further enhance performance by cooling the ramjet inlet spike with the incoming fuel, which also makes the burn more efficient. If you're using propane, the expansion of the gas would give a nice refrigeration effect

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Re: Steve's ramjet revisited

Post by metiz » Sun Aug 14, 2011 8:01 pm

ok but, and I may be wrong about this because my unerstanding about this is limited, cooling the gas with an augmenter will also slow it down. and because of the augmenter, the ramjet will be further away from the exhaust effectively slowing down the gas more still. Will the cooling of the gas, and the cooling of the spike (good idea btw) compensate for this?

Any effective augmenter has a diameter bigger than the tailpipe. the end diameter is bigger still, this would mean I need a realy big ramjet which in turn would need a larger volume of fresh air. Can I reduce the diameter of the augmenter so I'll be able to use a smaller ramjet?

Actually, could I not make some sort of ejecter/ ramjet hybrid? The first stage forces in fresh air (ejector) and the second stage compresses, injects and ignites the fuel air mix (ramjet)
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Re: Steve's ramjet revisited

Post by ace_fedde » Sun Aug 14, 2011 9:35 pm

metiz wrote:I've read it about halfway through, but it's too complex for me to make any sense of.
Don’t try to understand the whole paper, just look at fig. 2, 5 and 7.
Fig. 2 names the different sizes of a choked ejector, fig. 5 and 7 show the effects of different ratio’s between the sizes. That’s all you have to figure out from this paper.
metiz wrote:ok but, and I may be wrong about this because my understanding about this is limited, cooling the gas with an augmenter will also slow it down.
metiz wrote:Any effective augmenter has a diameter bigger than the tailpipe. the end diameter is bigger still, this would mean I need a realy big ramjet which in turn would need a larger volume of fresh air. Can I reduce the diameter of the augmenter so I'll be able to use a smaller ramjet?
If you read the paper well you’ll see that the outlet of the choked ejector is smaller than the outlet of the PJ! So actually faster outstream!! :D
Gentlemen, stop wining, start experimenting!! :twisted:
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Re: Steve's ramjet revisited

Post by metiz » Sun Aug 14, 2011 9:48 pm

I'll give the pdf another look-through tomorrow. Shouldn't be to hard to whip something up. Fedde, has your situation cleared up to the point you can do "fun stuff" again?
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