Black Powder Ignition - Altitude Question

[bguff]

At what altitude does black powder become difficult to ignite?

Bob

 

[runandgun13]

As far as I know, it will ignite fine at any altitude. The composition of the black powder is fuel and an oxidizer. The little fire triangle shows that fire needs 3 things. Fuel, oxegyn and heat. Black poweder fires guns under water, and lack of oxegyn should not be an issue.

 

[SteelyEyed]

I don't know the answer to your question, but if you use the RouseTech CD3 deployment system it doesn't matter. It's clean and cold, doesn't fry your parachutes or shock cords, and doesn't cover the insides of your rockets with "schmootz." In all my HPR rockets other than those smaller ones that use motor ejection, I use the CD3. Try it, you'll like it.

 

[constevens]

As the Cd3 is a cool deal I'm waiting Patiently for a specific manufacture that I know to release a product similar BUT superior as well as more functional for more in variety of sizes as well.

But for now I still use BP and yes it does have a problem working at higher altitudes. In fact altitudes as low as 10,000 to 15,000 ft can have a effect on the effectiveness of a BP charge the higher you go the worse it gets. Confinement is a definite aide in this Like using a finger of a rubber glove. Or even having to add more BP as a charge that may have worked at 8.000 ft will not have enough at 28,000 ft. Pressure is an issue here.


Ejection systems based on FFFF black powder have to burn long enough to ensure that all the powder is consumed before pressure drops. The biggest problem is that at higher altitudes unless Contained very tightly sealed the BP will not all burn or burn fast enough

 

[MarkM]

Originally posted by runandgun13
As far as I know, it will ignite fine at any altitude.

Untrue. The burn rate of BP is dependent upon pressure. Pressure decreases with altitude. The lower the pressure, the slower the burn. At altitudes higher than ~20,000 ft (above sea level) there is a dropoff in BP's burn rate so as not as much gas is generated, resulting in a less forceful ejection. Further, in addition to slower burn rates, incomplete burning of BP can also result at higher altitudes.

I'd say if you're approaching 20,000 ft above sea level (not AGL..keep in mind where you're flying), you might want to employ the CD3 ejection system SteelyEyed suggested. Under this altitude you should be just fine. I've seen plenty of rockets deploy perfectly at ~15,000 ft AGL (in Florida, AGL and above sea level are basically identical altitudes) using standard BP ejection systems.

 

[snowman2]

Originally posted by bguff
At what altitude does black powder become difficult to ignite?

Around 20,000'. The problem is not the lack of oxygen, but the lack of a medium (air) to transfer heat to sustain combustion.

Dean

 

[constevens]

Here is a great site that id testing with the BP and the CD3 system for high altitude deployment. Their conclusion was that properly confined BP at even 100K will still outperform the CD3.

https://spacewarptechnology.com/SWT/High Altitude Tests/TABLE_CONTNETS.htm#conclusions

Pretty cool read on the subject I thought.

 

[runandgun13]

Originally posted by MarkM
Untrue. The burn rate of BP is dependent upon pressure. Pressure decreases with altitude. The lower the pressure, the slower the burn. At altitudes higher than ~20,000 ft (above sea level) there is a dropoff in BP's burn rate so as not as much gas is generated, resulting in a less forceful ejection. Further, in addition to slower burn rates, incomplete burning of BP can also result at higher altitudes.

I'd say if you're approaching 20,000 ft above sea level (not AGL..keep in mind where you're flying), you might want to employ the CD3 ejection system SteelyEyed suggested. Under this altitude you should be just fine. I've seen plenty of rockets deploy perfectly at ~15,000 ft AGL (in Florida, AGL and above sea level are basically identical altitudes) using standard BP ejection systems.

Sorry about that. I guess I learned something new today.

 

[tfish]

Not sure of the scientific reasons this works. But I've used it to 29K in a 54mm min dia rocket https://hometown.aol.com/tfish38/page16.html I'm also using it in a 5" min dia rocket this summer.

Tony

 

[cjl]

Originally posted by constevens
Here is a great site that id testing with the BP and the CD3 system for high altitude deployment. Their conclusion was that properly confined BP at even 100K will still outperform the CD3.

https://spacewarptechnology.com/SWT/High Altitude Tests/TABLE_CONTNETS.htm#conclusions

Pretty cool read on the subject I thought.

I have to disagree with their conclusions though.

The only caveat I would give is that of the somewhat anemic separation when using only one CD3 when the compartment to be pressurized is not airtight.

My experience contradicts this - I sent a 3+lb nosecone more than 30 feet across my backyard while ground testing my CD3. It easily performs as well as bp with less mess.

 

[constevens]

Originally posted by cjl
I have to disagree with their conclusions though.



My experience contradicts this - I sent a 3+lb nosecone more than 30 feet across my backyard while ground testing my CD3. It easily performs as well as bp with less mess.

. It was about pure effectiveness of a deployment charge when done in the correct manner with BP being contained and not while being on the ground but at high altitude. I'm sure the experience of the people conducting the test as well as several flyer's i know that still use BP contained correctly prefer it even with high altitude flights. Its all in how you use it. The CD3 showed to not be nearly as energetic as the BP was even when done under altitude pressure. The experience of testing your nosecone and rocket on the ground are far from being one in the same. The experience you speak of is no where near anywhere what they are talking about. That experience is a whole other story vs actually flying higher altitudes and having that experience in dealing with that. Unless you push well close to the 20K above MSL and over range you may not experience this issue, so ground testing as you put is not showing any real data vs Altitude. .

My best flight Starting at 5500 ft above MSL was a flight to roughly 16K and i can tell you it was different as I had to add more BP at that altitude as well as prep it to be sealed under pressure and confined. Worked very well. By no means am I bashing what the CD3 does but its just not the same. As far as the mess... Its no biggie to me as in a composite rocket I can just hose it all down. Now here is a question for you. What does a rocket person or team do when they fly something as big as the Pheonix @ 18" around and 550lbs on a Q motor to over 20K and the launch site is 5K above MSL. I cant see a CD3 working here or MANY of them having to do the job. Or how about one large charge confined correctly.

 

[DynaSoar]

Originally posted by MarkM
Untrue. The burn rate of BP is dependent upon pressure. Pressure decreases with altitude. The lower the pressure, the slower the burn. At altitudes higher than ~20,000 ft (above sea level) there is a dropoff in BP's burn rate so as not as much gas is generated, resulting in a less forceful ejection. Further, in addition to slower burn rates, incomplete burning of BP can also result at higher altitudes.

That's not right. The burn rate is independent of pressure.

Under low or no pressure, the outgassing from the BP will be much more powerful as the burn products try to fill the emptier space. Enough so that what's burning can blow itself away from the remainder, thus incomplete combustion. Even with complete combustion, without air pressure already in the chamber, the BP has to generate that first 14.7 lbs/in^2 just to come up to sea level pressure, and then top that with enough to work the ejection system. The larger the chamber, the worse this effect, so the smaller the chamber the better.

The wording in the Space Warp Technologies research paper's first conclusion is misleading in this respect. It's correct, but it ("burns long enough") leads one to assume that there's a difference in the rate of burning. It's the "so that all the powder is consumed before the pressure drops" that's the point of the sentence. The BP has to burn, build up pressure, and do its job, before the vacuum sucks the pressure away. Hence the "smaller chamber is better" conclusion.

 

[cjl]

Originally posted by constevens
. It was about pure effectiveness of a deployment charge when done in the correct manner with BP being contained and not while being on the ground but at high altitude. I'm sure the experience of the people conducting the test as well as several flyer's i know that still use BP contained correctly prefer it even with high altitude flights. Its all in how you use it. The CD3 showed to not be nearly as energetic as the BP was even when done under altitude pressure. The experience of testing your nosecone and rocket on the ground are far from being one in the same. The experience you speak of is no where near anywhere what they are talking about. That experience is a whole other story vs actually flying higher altitudes and having that experience in dealing with that. Unless you push well close to the 20K above MSL and over range you may not experience this issue, so ground testing as you put is not showing any real data vs Altitude. .

My best flight Starting at 5500 ft above MSL was a flight to roughly 16K and i can tell you it was different as I had to add more BP at that altitude as well as prep it to be sealed under pressure and confined. Worked very well. By no means am I bashing what the CD3 does but its just not the same. As far as the mess... Its no biggie to me as in a composite rocket I can just hose it all down. Now here is a question for you. What does a rocket person or team do when they fly something as big as the Pheonix @ 18" around and 550lbs on a Q motor to over 20K and the launch site is 5K above MSL. I cant see a CD3 working here or MANY of them having to do the job. Or how about one large charge confined correctly.

For that I agree with you, as the CD3 is inadequate for a rocket of that size. However, for a smaller rocket, the CD3 can be equally energetic when done properly. The CD3 works much better with shear pins rather than a simple friction fit. If the nose is held on long enough for pressure to build up, then it has a much more violent ejection. As for the altitude, I can't see that having much of an effect on the CD3's performance (though it absolutely can impact BP). Honestly, either one works fine for getting out a parachute, so use what you're most comfortable with

 

[Chicagonative17]

Around 20,000'. The problem is not the lack of oxygen, but the lack of a medium (air) to transfer heat to sustain combustion.

BINGO!

My uncle is a physicist and chemist and he has explained this proccess to me.

As long as the BP stays under reasonable air pressure (such as under 20,000 ft.) it will ignite no matter what. That is why it is possible to ignite it in a space ship orbiting earth where the BP is in a pressure container.

It is the same reason you die when your in space without a suit. It is not because lack of oxygen, you die much sooner than you suffocate. It is because your blood boils due to zero pressure in and around your body to help regulate your blood temp.

So a long winded responses summarized: As long as you keep the BP fairly sealed (air tight, not just enclosed) it will have no problem igniting.

Ian