General Ramjet Info Please

[ZVWOLF]

Hi people,

I need some basic information on the ramjet, I have looked everywhere for this information but nothing is really helpful. Anyway is my questions:

What type of fuel is best used for a ramjet about the same size as the Maggie Mugs Ramjet?

What is they approximate fuel consumption rate of the Maggie Mugs Ramjet (or something of that size)?

Is there a forumla for working out the fuel consumption rate?

Is there a forumla that you can work out thrust relative to airspeed and Ramjet dimensions?

Also, are guys/girls finding the ramjet fuel hungry and inefficient in fuel consumption relative to the amount of thrust you are getting?

Thats about all, thanks in advance for any replies.

ZVWolf

[ZVWOLF]

I have been doing some more research and by the looks of it the best way to understand a ramjet is to build one.

I am actual studing the efficiency of a ramjet and how to improve it for a senior physics assignment.

Mainly, what liquid fuels do you find to be most effective or efficient in running you ramjet?

Also, ramjets don't have the capability of throttling do they?

Thanks

ZVWOLF

[Irvine.J]

Well, where to begin...
First, look at this page to get a basic understanding of the Ramjet. All the links that follow are contained on this site, so go for a bit of a looksee.
http://www.pulse-jets.com/ramjet/ramjet.htm

If your doing senior physics, this is a document which will help you with the hardcore maths in relation to airspeed/fuel consumption/efficency/thrust etc.
http://www.pulse-jets.com/count/pulse.php?ID=32

Larry, the builder /inventor of the maggiemugs, has detailed how he made and the technicals of the maggie mugs on his website
http://www.cottrillcyclodyne.com/#Engines
(scroll down a bit)

Is there a forumla that you can work out thrust relative to airspeed and Ramjet dimensions? Yes, the PDF above will help you calculate this.

Also, are guys/girls finding the ramjet fuel hungry and inefficient in fuel consumption relative to the amount of thrust you are getting?
Yes, it requires alot of fuel, and are practically useless at anything under 200mph. At high speed however, they really push well.

A ramjet can be throttled yes... fuels are generally kerosene, or a mixture of kerosene and other highly flamable liquids introduced under pressure. As far as I know there aren't alot of "Experts" on ramjets on this site, we keep making bodge ones... that is unless Thecheat or Amwar can show us how its done, we are waiting with excitement for those for sure. I believe that propane is the best place to start, as its already under pressure in your tank and the pressure at which the fuel is introduced has a major influence on thrust (If my understanding of the PDF is right, but I'm still reading it over and over).
If you go to this posting from Amwar's ramjet, you will see larry giving some good equations on how to calculate airspeeds/pressure for your engine....
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=3434

I hope i've been able to point you in the right direction for some of the equations you are after, some of them are very complex, and hopefully someone will be able to give you some more specifics on the calculus later, goodluck with your assignment wolf.
#47

P.S: I like ya hat Larry, suits you like the ramjet your holding next to your barn there :D

[Glenn Olson]

I suggest you also look at http://www.alt-accel.com/ramjet2.htm then read http://www.alt-accel.com/arla/3m-arla.htm, including the references and Back Pages. Some of the material is a bit dated but still has some useful information on ramjets. The other folks have more recent experience as well as ongoing projects.

Good luck.

Glenn

[ZVWOLF]

Thanks for the information 47 and Glenn Oslon, it is proving helpful. I have been looking into building a nice small ramjet... for experiments.

I don't have any experience with machining my own parts... I am contemplating making the Maggie Muggs Ram jet though wouldn't mind making something of a smaller size, About the size of an aerosol can.

Has this been done before? Also what are peoples experiences with different metal types? What doesn't work?

Thanks again,

ZVWolf

[Mike Everman]

I like this quote from the first link:

Zoom: In 1951 NACA launched a ramjet powered missile which reached an apogee of 159,000 ft. This missile was launched at a 75 degree angle and ran out of fuel at 67,200 ft and Mach 2.92. This missile could have reached astronaut-wings altitude with almost any combination of a) steeper launch angle (it was still doing over 1,000 fps at apogee), b) more fuel (it started with only 25 lbs or 11% of its mass), and/or c) bigger engines (it had two 6.6 inch diameter engines).

It coasted up another 91,800 ft after running out of fuel! I've always wanted to try a ramjet second stage to go on a buddy's rocket. That's just good, clean fun!

No, I'm not going to crunch the numbers to see if that scenario makes sense!

[milisavljevic]

No, I'm not going to crunch the numbers to see if that scenario makes sense!

Hello Mike --

Well, I did crunch the numbers... and yes, the scenario does hold together! =)

Cheers,
M.

[milisavljevic]

Hello Again --

Here is an example of a "back of the envelope calculation", often known as a second-order approximation:

Code: Select all

[1] absolute airspeed ... M2.92 * 968.08 fps           = 2830 fps;
[2] vertical airspeed ... 2830 fps * sin 75°           = 2730 fps;
[3] time to climb ....... 2730 fps / 32.2 fps2         = 84.8 sec;
[4] distance ............ 1/2 * 32.2 fps2 * (84.8 s)^2 =  116 kft;

[5] compare altitudes ... 116,000 ft > 91,800 ft.

note (1) : to keep Mike Everman happy, this example makes use of the fugly system of units
note (2) : to keep me happy, this example holds a proper accounting of significant figures
note (3) : to keep me happy, this example assumes a constant gravitational acceleration
note (4) : to keep me happy, this example assumes zero winds at altitude

The difference of altitudes (approx. 24,000 ft) is accounted for by (a) atmospheric drag,
and (b) the fact that the missile's angle of climb slowly decreased, from its intial value
to zero, after engine shutdown. We only need to show that the *calculated* altitude
exceeds the observed change in altitude, which it does. Happy now, Mike?

Cheers,
M.

[thecheat]

ZVWOLF, unfortunately, there are nothing but guys on this forum, and, apparently there isn't anyone over the rank of "a bit o experience". They make up for it with their pretty welds....

also, for fuel consumption, these things I assume will suck a propane tank dry. All you need to do is watch a vid and check out the flame! (I'll post Steve Bukowsky's vid) If you look at the flame, it's not hard to see how much fuel is being poured into that thing!

47, hehe, I'm waiting to get this thing welded! I hope to have that part done soon, but, I'm going to wait a couple days and see if that TIG stays down. (the one posted in my thread) If it does, I'll get it, then, I'll need to get an argon tank... and that's about it. Since my budget is so low, I think I'll probably end up borrowing a welding mask from a friend. The final step is to figure out how to mount it... which should be easy.

PS: Then I've got to make some plans for it, I'll call it the two tank ramjet. (that's all I've used, two empty 20oz propane tanks!)

[larry cottrill]

Cheat, unfortunately for me, that's Steve Bukowsky's video, not mine! And it IS a beautiful example of what can be done with a really small engine. You can see the whole story of Steve's little ramjet here:
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1881

Yes, they are real hogs - not just in terms of fuel, but in terms of air supply, as well. Steve's jet was welded up out of ordinary mild steel. The fuel is fed in a forward-flowing direction from a point just behind the center of the asterisk-shaped flameholder.

L Cottrill

[thecheat]

Thanks for clarifying that, oops... (I edited it) (gee, don't you just hate it when that happens?)

PS: I'll just close my mouth for a little bit... ;)

[Zippiot]

Kerosine is a fine fuel...unless there is a flameout...

I noticed the best fuel to be a mix of white gas and bacon grease. Equal performance came from a mix of diesel and WVO (waste veggie oil).

Seems the more power a fuel makes the harder it is to keep lit...and the hotter it burns. I have actually melted Stainless with my bacon grease formula, and I expect to see the same from any oil/fuel mix.

Stoich burning with air
Stoich burning of WVO can be 3k degrees F, well past the fail point of steel and into the melting range of some types! Stoich burning of propane is considerably cooler but these things suck gas at an insane rate...
Stoich burning of gasoline can be from 2200 F to 2800 F, kerosine is upwards of 2800 and so is diesel.
Generally the more heat made the more power locked inside of the fuel, but after about 2200 the metals start to fail. Adequite cooling is required to use liquid fuels or risk losing you rammy!

Also
Gasoline makes a fine fuel. Its cheap easy and commonly available. The fuel throttles well and can be easly extinguished if not contained in the jet (the air source works fine in most cases) but dont try to put out an oil fire!!!!!!!!!!!!
Gasoline CAN EXPLODE IN THE CORRECT CIRCUMSTANCES!!!



BE CAREFUL!!

[ZVWOLF]

Thanks for all the info guys... it is very helpful.

Zippiot, what about propane? what sort of temperatures are we looking at there?

I have decided to build the maggie mugs ramjet to start experimenting.

I will keep you guys posted.

Thanks again.

ZVWolf

[ZVWOLF]

I have put together an idea for a more efficient ramjet. This idea is still very much work in progress so feel free to critize it and throw your two cents in. My idea doesn't consist of any new major ramjet breakthrough ideas, it is merely a collection of other peoples findings put together to create an efficient ramjet.

Now before I go on I think it is important that you know what the purpose of this ramjet is and without further ado, its primpary purpose is to power UAV's (Unmaned Aerial Vechiles) efficently. By efficently, i mean light weigh, low velocity, high thrust and efficently fueled. All these things are most likely what every ramjet engineer dreams of achieving.

As we all already know, the ramjet is a lightweight engine in comparison to the other options of turbojets and so forth so there is no real problem there but operating at a low velocity is a problem. There is one thing that caught my attention when looking at low velocity ramjets, motorjets. I believe by designing a ramjet to incorperate a fan is a great way to reduce the required velocity.

Efficent fueling. This is something i have to look into a bit deeper but as I understand it (thanks to zippiot) the fuel/oil mix is powerful and by using WVO, the ramjet can recycling waste products as well as giving some nice powerful thrust. Also there is the fact of overheating. When the ramjet is moving through the air, overheating should be provented, my only problem is while it not moving.

So now a few questions, How exactly is a ramjet throttled? Is it velocity or Air/Fuel mix. Againt there is still the question of propane and also the fuel inlet, does it have to be a pin valve or anything special or can it just be a peice of coper tube.

Thanks,

ZVWOLF

[Jim Berquist]

So in the Ram Jet world! How do you measure the thrust on a test bed with the intake air blowing at some 200mph.????

Do you just measure the static trust deducting the thrust of the air source? It so fare seems to me there is little to gain with the amount of fuel required to produce the little thrust from said engine. Yet it does seems to work!

Could a ram jet augment the output of a valveless P.J. and provide more thrust then the unit weighs? Including fuel to Carrie???

Every thing I've seen so far looks like a After burner set up!

How much thrust can a Ram Jet Produce??

Jim