N2O/Ethanol bipropellant rocket engine

[Johansson]

Dec 4, 2010 12:02:01 GMT -5 ernie wrenn said:

Jonan

If you need one let me know and I will build you one. Mail cost could not be that much.

Ernie

Wow, thanks for the offer!

Since I have a full workshop at home it would probably be easier if I can ask for details on your ignitor and build it here instead, I will most likely shamelessly copy your design for a couple of other uses as well including a N2O/ethanol bipropellant rocket engine if that is ok with you.

[ernie wrenn]

That IS what this board is all about.

Anything I post is up for full use by anyone. I did notice that you need new wood on your work bench>>>>LOL.

I know it is cold over there but you should not burn the work table. If my table was like that I would NEVER get off my knees.

I am more than happy to help with any prototype work including what little brain power I have left.

A great assest to our team is Richard, his fresh eyes on problems provide some outstanding solutions. We have spent days brain storming about, what turned out to be a simple solution but some of the solutions were worst than the problem.

He is a damn good programmer also. He has taught me more about computers than I need to know...Now I am dangerous to my own computer... There is a whole pile of little screws in there that just fit in wiring harnesses on vehicles. Did you know that some of those cards will fall out if the screw is not put back?

Ernie

[ernie wrenn]

Jonan

Re: N2O/ethanol bipropellant rocket engine

Go to my web site: WWW.COMPUCARNITROUS.COM

I am CEO and started the company over 30 years ago. I can supply with any nitrous equipment to any spec including technical info.

Ernie

[Johansson]

Exactly my thought, the sharing of help and parts with "strangers" is the best thing about internet communities. For example a couple of years ago I sent an old digital video camera to a guy in the US that I "knew" from the pulse-jet.com forum, later he offered me one of his experimental engines for free.

Interesting company you´ve got, Ernie! I myself weld fibreoptic cables all day long which hasn´t exactly anything to do with my hobbies...

I really appreciate your offer of help, we are all relatively young guys (20-30 years) so there is much left to learn. Because of this we try to build everything inhouse and grasp the theory of everything we build, just building things after bought plans is never going to happen.

A rough plan is to design a bipropellant engine with 2000-2500N of thrust, the final thrust depends on how much oxidiser and fuel we can fit to the kick frame. The idea is to break the world record for motorised kicks, there are kicks with motorcycle engines that have run almost 280km/h so if we go faster than 300km/h we should be good.

The nitrous and ethanol tanks will be pressurised with nitrogen and have individual pressure regulators so the mix can be tuned without having to modify the engine, the ethanol will be used to cool the combustor walls before it is injected into the CC.

The ice raceway is 2000m so we plan to tow it at aprox.100km/h the first kilometer and then release the tow line and hit the engine, that initial speed should give the kick some stability when the engine ignites.

Oops, another sidestep from the gas turbine kick build thread. Lucky for me it is my thread, otherwise I would surely have been banned by now... ;D

[ernie wrenn]

Regulator with nitrous will NOT work. It causes the nitrous to flash for a liquid to gas. This cause a tremdous power loss.

The best way is using jets and using a constant fuel and 1000 psi nitrous pressure. The nitrous pressure is set using a bottle heater to raise the pressure and watching the pressure gauge. Install a jet holder on the outlet side of the nitrous bottle.

Using any on the ethenals for power is perfect. Remember you must use 2.5 time ethenol vs gas, due to btu content and viscosity. Use a 10 pond (content) bottle (25 ponds total weight). This will give you the volume and some control over the pressure drop.

Another idea is to use a nitrogen over nitrous cap to keep the pressure @ 1000 psi. A slight modification to the bottle valve will allow you to put the head pressure cushion on top of the nitrous (nitrous and nitrogen will NOT mix, so be sure to completely empty the bottle before refilling). This type system does not work well with internal combustion engines but should provide a tremdous push on the rocket engine.

Now I can supply you with parts needed to mfg the nitrous system. All I will need is some of the flow needed.

A lot of the rocketters state side just use a 1/4 turn valve and start the burn. They also use PVC for the engine fuel and nitrous for the oxider.

Keep me up with this project, I would like to involved with the Word Record Attempt.

Ernie

[Johansson]

Regulator with nitrous will NOT work. It causes the nitrous to flash for a liquid to gas. This cause a tremdous power loss.

I think that you misunderstood me, I meant that the nitrogen line would be regulated so the pressure in the nitrous tank could be adjusted. No restrictions at all between the nitrous tank and engine except for a servo controlled ball valve.

Because of this we won´t need any bottle heating either since the nitrous oxide won´t have to pressurize itself.

We haven´t done any calcs at all regarding fuel consumtion, but since we aim to travel 1000m accelerating from 100 to 300+ km/h we will need all the fuel/nitrous we can fit to the kick. I don´t think that any standard nitrous parts can be used because of the huge flows involved.

Great that you are interested in our project, you are hereby named our official Rocket Oxidizer Expert Consultant!

A lot of the rocketters state side just use a 1/4 turn valve and start the burn. They also use PVC for the engine fuel and nitrous for the oxider.

Yup, a hybrid engine. The problem with those is that they need much more tuning with the fuel grain castings to work acceptable, a bipropellant liquid is trickier to build but much easier to tune.

We should probably continue this discussion via email since it has nothing to do with turbine engines, we won´t have time to do much before this years race is over since there is much work to do on the jet kick.

[ernie wrenn]

I will ask Richard to add a "rocket and Hybrid power" header to the board. There are a LOT of guys wanting to do turbine, jet, DIY and rocket .

Richard and I have been talking about a rocket powered go-cart. I think it would be a informative addition.

Rich can move the rocket thread to the new header..

Ernie

[Johansson]

Sounds like a good plan! Just make sure the posts about the jet kick stays, perhaps it is easier if we keep this thread as it is and I can start a new rocket kick thread later?

[ernie wrenn]

10-4 That is what we are going to do. I will just move the rocket section, if that is ok with you.

Ernie

[Johansson]

Perfectly ok.

[Johansson]

We have talked this over and decided to start our project by building a smaller engine first to try out injector designs and find the right CD nozzle proportions without ruining ourselves on nitrous oxide.

I have bought a book on the subject but unfortunately it doesen´t cover the basics very well, I have yet to find out the relation between thrust, chamber pressure and throat area.



The experimental engine will be regeneratively cooled by the fuel and the chamber and nozzle will be built out of a single piece of aluminum with a stainless tube as cover. I was not sure if aluminum could be used since most engine internals seem to be build either out of copper or unobtainium, but I found some clips of an all-aluminum engine so I guess that it will work for us too. Much easier to build from aluminum since I have a lenght of aluminum stock at home.



The expansion angle of the nozzle will be 15 degrees from axial, that much is decided at this moment. We need to find out what a suitable chamber pressure is and a rough estimation on the nozzle proportions (throat vs. exit diameter), since this is a test engine we don´t need to design towards a specified thrust but it would be interesting to have a theoretical thrust figure for a certain chamber pressure and throat area so we can see how close to that number the engine performs in real life.

[racket]

Hi Anders

Further to our PM on the subject , my Zucrow Vol 2 p468 gives a list of various rocket propellants , combustion pressures and jet velocities , .............the lowest combustion pressures are ~300psi, gas velocities ~7,000 ft/sec and temps ~5,000 deg F .

With a pressure ratio of ~20:1 you'll be needing an outlet to throat area ratio for the nozzle of between ~2.9 - 3.2 :1 , actual ratio will depend on the exhaust gas composition .

Now comes the bit you might need to think about , propulsive efficiency ................with an exhaust velocity of 7,000 ft/sec but at a vehicle velocity of ~250 ft/sec the rocket isn't very efficient , ideally we need both velocities to be closer together , rocket engines are great for rockets going at Mach 3 where theres only a 2:1 ratio between velocities , but a "slow" land vehicle has a 28 :1 ratio .......................you need a "slower" jet velocity , more like a fan equiped gas turbine vs an afterburning one .....................the fan will win every time at modest velocities below Mach 1

Lets think about a normal GT jet exhaust for a second , you need ~500 lbs of thrust , this would require a mass flow of ~10 lbs/sec at ~1,500 ft/sec .

A pressure ratio of ~1.4:1 across the jetnozzle will give us 1,500 ft/sec , a 1.4 PR requires ~22 hp/lb/sec so ~220 hp required to power the 10 lbs/sec "fan" , not much .

Now , 500 lbs force at 250 ft/sec is 227 hp , but the rocket engine has 500 lbs force at 7,000 ft/sec is 6,363 hp .

Anyway back to our rocket nozzle ........ with 500 lbs of thrust at 7,000 ft/sec you'd need ~2.3 lbs/sec flow , at 5000 deg F ........lets say 3,000 deg K gas density of the gases might be ~140 cu ft /lb so ~320 cu ft/sec , so exhaust area ~0.046 sq ft or 6.6 sq ins or 2.9 inch dia , now our ratio between exhaust and throat is ~3:1 so the throat needs to have an area of ~2.2 sq ins 1.67 inch dia .

I think I need to do a bit more reading :-)

Cheers
John

[Johansson]

lets say 3,000 deg K gas density of the gases might be ~140 cu ft /lb so ~320 cu ft/sec , so exhaust area ~0.046 sq ft or 6.6 sq ins or 2.9 inch dia

Can you explain a bit further what the relation between flow and exhaust area is? I followed your calculations up to there.

So what you are saying is that I can design the engine for lower exhaust velocities and get higher mass flow? Wouldn´t the CC volume have to be larger then with lower pressures and lower combustion intensity?

We are in fact going to use this experimental engine for a rocket project later when we are done testing it, it might never see Mach 2 but I still want to design the engine to be flight worthy. At least I want to see some mach diamonds in the high speed camera clip from the tests.

[racket]

Hi Anders

LOL, these a fairly rough numbers , but lets take thrust first , thats mass times velocity , so 500 lbs of thrust = 7,000ft/sec times mass divided by 32.2 (gravity) , or mass = 500 X 32.2 div by 7,000 = 2.3 lbs/sec .

Density , using "normal" GT sort of equations , 3,000 degrees K times a constant of 96 , div by 14.7 div by 144 = 136.05...., I rounded it up to 140 cubic feet per pound just to be on the safe side

Therefore our total volume will be 140 cu ft/lb X 2.3 lbs/sec = 322 cu ft/sec , I like nice round numbers so made it 320 :-)

Now 320 cu ft/sec going at 7,000 ft/sec needs a hole area of 320 divided by 7,000 = 0.0457 square feet , multiply by 144 = 6.582 sq inches or a hole 2.895 inches in diameter , again rounded up to 2.9" to be on the safe side .

Because of the throat to exhaust ratio of ~3:1 we need to divide the exhaust area by that 3 to get a throat area of ~2.2 sq inches or a hole of ~1.6736 ............lets go 1.68 inch dia .

Now as I said initially , these are rough figures , you'd need to know the gas characteristics of your exhaust to get accurate figures , but these will give you some idea of where to go .

I'd certainly be trying for lower gas velocities , the "problem" with high gas velocities is theres a need for greater and greater energy required for less and less velocity gain , same as with our gas turbine jet exhaust , unfortunately thrust is mass times velocity , whereas the kinetic energy has a "squared" component in it that can't be used in the thrust calculation .

Lots more calculations required :-(

Cheers
John

[Richard OConnell]

John, you sure do know how to take the fun out of building something that looks "kinda right-ish" then taking cover behind a plexigalss shield in case you were wrong :/