Weird Fuel Grain Idea?

[larry cottrill]

All right, as I always say, "I know nothing about rocketry", and I haven't taken time to read through the whole forum, so if this is an "old hat" idea just tell me so and I'll shut up. This came to me when I first read the post yesterday about the wonderful rocket dragster that uses liquid NO2. So, here it is - probably dumb, but might spark further thinking or something.

I got to thinking about low-expansion insulating foam that comes in a pressurized can - it fills spaces perfectly and sticks like glue when it dries. Obviously, contractors don't use little "spray cans", they must have a machine that uses a compressed air or nitrogen tank or something. So, how about using pressurized nitrous oxide instead of air or nitrogen to create a blob (fuel grain) of this foam inside a chamber can? You would have to provide a cardboard or sheet balsa (or something) "wall" to form the "open" end (facing the inside of the nozzle). An ordinary electric igniter could be embedded in that surface.

Here's what (I think) would be good about it:
- It would fill the space perfectly
- It would provide a very uniform distribution of oxidizer within the fuel mass
- It would remain tough and slightly flexible, so the grain wouldn't crack from mishandling, etc.
- It would never separate from the chamber wall before or during the run
- It would be simple and quick to fabricate the grain
- The fuel grain would be ready to use almost immediately

Here's what (I think) would be bad about it:
- The grain would be pretty low density; I suppose that means the chamber would have to be "oversize" for the desired thrust
- Spillage would be hard to clean up off the ouside of the chamber or whatever
- The rig to produce the foam may be harder to get or to set up than I think it is (?)
- The material might produce toxic combustion products (?)
- There might be a lot of ash left in the chamber (?)

What do you think? To me, it seems like the low density of the grain is the only real killer in terms of actually making this work. On the other hand, I really don't know what I'm talking about ...

L Cottrill

[Tom]

SO are you saying that the motor would source it's oxygen from the Nitrous within the grain?

I've no idea what those compressed foam cans use for filler, though if you were designing this from scratch, I suppose you could use pretty much anything that fits the bill.

The main error I can see with this, aside from the light density that you mentioned, is that there simply won't be enough Nitrous in the grain, and as a result, not very much oxygen available for combustion.

Also, as a foam, I'd imagine it wouldn't stand up to the chamber pressure very well, so achieving any sort of reasonable ISP sounds difficult...

I like the sound of it though, if there were ways around those problems...

Tom

[larry cottrill]

Also, as a foam, I'd imagine it wouldn't stand up to the chamber pressure very well, so achieving any sort of reasonable ISP sounds difficult...

Yeah, I sort of didn't think of that ... a mere detail ;-)

L Cottrill

[Zippiot]

I have seen rockets with grains made from epoxy with oxygen bubbled up through it as it hardens, works btw!
Not very much fuel density is right

The biggest problem I see is the can of it I'm holding now says it doesn't burn and is fire retardant...

Though I have always wodnered what impregnating oxygen into styrofoam would do, especially under pressure (like a rockets CC).

[larry cottrill]

My scheme appears to be variously and seriously flawed. I will now slink away quietly back into Pulsejet Land, where I at least know the natives ;-)

L Cottrill

[Zippiot]

I still want you to build it!!
Or at least draw some shiny pictures to ebtter help [me] see your big scheme