N2O/Ethanol bipropellant rocket engine

[Johansson]

Apr 20, 2012 7:32:04 GMT -5 turbochris said:

I've seen some people put model trains and villages in their gardens, Anders will have NASA

;D ;D ;D

[Johansson]

The book has arrived now, very interesting and informative reading indeed!

[britishrocket]

Hello Anders,

Thought you would enjoy it. You need to set aside at least a week. During that time the book will not leave your hands. You will wake up with it in your face....

There is not one single page of it that isn't essential and packed with information.

Enjoy yourself!

Carl.

[Johansson]

I have it with me in my lunch bag so I can spend at least half an hour each day reading, finding time at home to sit down and read for any lenght of time with two small kids and a ton of things to do around the house is very difficult.

Nowadays the 8 hours at work feels like getting some rest before the real work begins when I get home. =)

One thing that sucks is that NOX isn´t included in the list of propellant combinations, GOX, LOX and nitric acid seems like the only oxidisers worthy of mention no matter what book I read.

[Johansson]

The water cooling hoses are fitted, things are starting to look rather messy.



Cheers!

[rwatzlavick]

Hi guys - I stumbled across your site and noticed my name came up The pic of my injector that was posted was of the "v1" injector. It was a modified split triplet that was an attempt to keep the LOX from spraying onto the walls of the chamber. Unfortunately it didn't perform well, presumably due to poor mixing. Here is a picture is the water spray pattern for the revised injector which had much better performance:


I'm not sure I understand the comment about the injection pressure being low. The injection pressure for a liquid is typically the chamber pressure plus a nominal 20% pressure drop for good atomization. I chose 6 holes because that's about the smallest I felt comfortable drilling.

Regarding kerosene, I haven't had any problems with it breaking down in the cooling passages. I ran my 100 lbf motor for about 25 sec and the fuel temperature got up to about 480 degF without problems. After disassembly, there was no residue that I could see in the cooling passages. In fact, after I cleaned all the soot out of the chamber, I could still see some of the tooling marks on the inside walls.

Every so often, I consider switching to alcohol for the fuel since it's so easy to clean up but then I'm reminded that the soot deposited in the chamber from kerosene actually is a pretty good insulator which helps out with cooling.

Anyway, hope this helps.

-Bob Watzlavick

[Johansson]

Hi Bob,

Great to see you on the forum! I´ll start by congratulating you for some really inspiring work, very good craftmanship.

I'm not sure I understand the comment about the injection pressure being low. The injection pressure for a liquid is typically the chamber pressure plus a nominal 20% pressure drop for good atomization. I chose 6 holes because that's about the smallest I felt comfortable drilling.

So with 20 bar chamber pressure the injection pressure drop is only 4 bar? Then I understand how you can use so many injection holes without getting too high propellant flow, I have measured the liquid flow from a 1.5mm test injector to 3L/min@10bar so a single 1.5mm hole will flow enough methanol at 30 bar pressure drop for my 1000N engine (might be possible to reach 1500N if comparing the throat area with other engines at similar chamber pressures).

When using NOX that is self pressurising it is impossible to get the injection pressure down to the ~25bar an engine with 20bar chamber pressure needs, at least without keeping the NOX at -10C temps which would be somewhat of a gamble.

Are your aluminum chambers deteriorating during each run or do they stay just like new now that the R&D is finished? In other words, can I expect a working thrust chamber to keep working or will I have to rebuild it on regular basis even though the cooling system keeps it from melting?

Thanks a lot for your comments Bob!

Cheers!
/Anders

[britishrocket]

Hi Anders,

Glad to hear you are enjoying the book. I know what you mean, it is hard to fit hobbies into daily life.

Some of the later editions of Sutton include oxides of nitrogen as oxidisers. What I would advise is to download a piece if software called "Rocket Propulsion Analysis Lite" or "RPA Lite" as it is sometimes called. It is written by Alexander Ponomarenko. I reference it on my blog in the post "Shear Coaxial Injector - a Prototype for Practical Research".

This program is used to calculate engine parameters and is extremelly useful. It includes many fuel and oxidiser types including NOX.

You can get it at www.propulsion-analysis.com/

I think you will find it useful.

Best wishes,

Carl.

[britishrocket]

Hello Bob,

It is great to see you on this forum. As Anders has said, thank you for your inspiring work and for proving that it can be done...and should be done!

I must admit that it took me a long time to commit my project to the internet via my blog. I was also quite apprehensive about contributing to a forum like this. My concerns were unfounded. It is good to know that there are others out there working along similar lines to myself, and it spurs me on to see their progress.

Heres to the continuing enlargement of the collective pool of knowledge.

Carl.

[rwatzlavick]

Are your aluminum chambers deteriorating during each run or do they stay just like new now that the R&D is finished? In other words, can I expect a working thrust chamber to keep working or will I have to rebuild it on regular basis even though the cooling system keeps it from melting?

In theory, a motor designed for steady state operation will not see any significant erosion. I never achieved steady state operation on my tests (tanks were too small) so I can't prove yet that my 100 lbf design has sufficient cooling. All I can say is that it ran for 25 sec without any visible erosion and it almost reached steady state. The temperatures in this plot have started to level off so another 5-10 seconds may have been enough:
www.watzlavick.com/robert/rocket/regenChamber/tests/20071006-run1-regen2-data.png

After the last series of runs, I measured the throat and it was a few thousands of an inch larger than when I built it. I attribute that to the chamber being made from aluminum and the throat radius not being large enough. Some folks have anodized their aluminum chambers to try and reduce erosion. Put it this way, I ran that motor 8 times so far and I'm sure it's good for a few more.

Back on pressurization, with a pressure-fed rocket, you want the tank pressures to be as low as possible to minimize structural weight and the amount of high pressure gas you have to carry. That's why I try to go with a minimal 20% drop across the injector. In general, the "discharge coefficient" equations in Sutton for pressure drop through an orifice work for cold water testing. NASA SP-125 has the same set of equations but the update to SP-125, Modern Engineering for Design of Liquid -Propellant Rocket Engines (AIAA) has an alternate form of the injector orifice equation that may give better results. That same book says that ideally, cold flow injector tests needs to be done with raised back pressure. With ambient pressure, you can only really get reliable results up to the cavitation point which they says is up to 30 psid. Also see SP-8089.

There were a lot of discussions about self-pressurizing propellants on the aRocket forum a while back. For some reason, the list archives on the web only go back a couple of years, not sure why.

-Bob

[Johansson]

"In theory, a motor designed for steady state operation will not see any significant erosion."

"Put it this way, I ran that motor 8 times so far and I'm sure it's good for a few more."

That sounds promising indeed, I won´t have propellants for more than 15 or so seconds of running so hopefully the circulating coolant won´t have time to heat up overly much.

Anodizing the inside of the thrust chamber would be much easier than applying cheramic coating like I have done, it would probably stay in place better as well.

Since my engine is designed to be fitted on a land based vehicle propellant tank weight and the size of the pressurising tank is of no concern at all, the entire system up to the throttle valves will be filled with water and tested with 200bar to make sure that the tanks and lines will hold in case the nitrogen regulator fails and lets full bottle pressure through.

Cheers!
/Anders

[ckikilwai]

Interesting project Carl! What's the status now, were you able to do a test fire?

We are a student team in Holland working on a N2O/ethane engine, we hope to do a test fire this summer. We want to use ethane since it is also self pressurizing like nitrous oxide. (35 bar at 20 C)

Currently we only built an actuator for our ball valves, next step is building the tanks and the injector to do injector tests.

We don't have a blog, but I am thinking of starting one this summer.

[britishrocket]

Hello,

Hi, I think you have become confused. This is Anders' project, not mine. He is much further on than I am. If you are a student team in Holland you must know all about DEIMOS and the stuff at TU Delft, under Steven Engelen.

Once more, this isn't my project it is Anders Johanssons'. Mine is under "GOX/Ethanol bipropellant rocket" and britishreactionresearch.blogspot.com, and is far less interesting.

Best Wishes,

Carl.

[Johansson]

You are being very modest Carl, you are way ahead of me in terms of research and most likely the one who will come up with an engine that doesen´t need a couple of rebuilds before it works correctly.

A quick update on my "progress" of late: there hasn´t been any.

Ok, I might make it a bit longer than that. I have been asking around for a suitable nitrogen regulator and so far the one I found makes a hole as large as a mining truck in the project budget.

I have 30 years of neglect to sort out on our new house during this summer and the turbine bike project has reached the turboshaft development stage so I am a bit short on both cash and time for the rocket engine build right now.

If I don´t find a cheap enough regulator I will run the engine without external pressurisation of the nitrous oxide and use CO2 to pressurise the methanol tank. It will be far less "interesting" but hopefully still produce enough thrust to propel the gocart at decent speed down the ice track.

[ckikilwai]

Indeed, I mixed you two up

Carl, I hope to find some time to through your blog as well, because reading about other amateur rocket engine builders is always very interesting
And I do know Steven Engelen, we actually took over his project about a few years ago, but we lost a lot of time with our valves (we bought a pair of valves, but they leaked, had to wait months before they were repaired, and then they still didn't work) and weren't able to book any real progress.

Anders, too bad about the expensive pressure regulators, I guess we are lucky we can borrow them for free at our university. Heating up the N2O is also an option to increase the pressure in the tank. The team working on a hybrid engine at our university do it all the time.

Anyway, as long as you can pressurize the methanol to decent pressure, the thrust shouldn't suffer from it that much. The mass flow is related to the square root of the pressure difference, so if you would only have half the pressure difference between tank and chamber of what you initially wanted, you will still have 70% of your mass flow and thrust. (sqrt(0.5)=0.7)