rocketbob

rocketbob

Well Known Member
I have to make a decision in the next couple of days on what kind of smoke pump I will be using in my rocket, which has led me to question why smoke systems are pieced together the way they are. I'm leaning on putting in a Facet 40185 I have a couple of on the shelf. (32gph, 9-11 psi.) I have a couple of other high pressure pumps I can use as well. Most guys are running a marine-type water pump at 50psi, with a needle vale turned way down, with an injector aft of the heat muff (typically). This seems to be ill-conceived. Size of the pump is overkill and putting the injectors so far aft in the coldest areas of the pipe would promote incomplete combustion. I'm thinking the best place for injectors would be way up high on the pipe for better combustion, like just downstream of the EGT probes. Solenoid valves seem to be completely unnecessary, as I can machine an injector with a ball/spring check valve.

I'm going to try doing the above and if it fails to work well, so what. I'll fix it later. Unless someone can disprove my ideas.
 
Pooooner,
I have found the location of the injector to make no perceivable difference. In my R/C days, we had to preheat the oil and get it as hot as possible before injecting in the not very hot exhaust.

In the full scales however, these seems un-necessary and makes for additional plumbing to get it from the FW to near the cyl head. While it seems obvious that the hotter the location, the better, it has not proven to be the case.

When inspecting certified installs, at least on the half a dozen different ones from the factory I have looked at, they all just dump it near the end of the pipe, not the beginning. A head scratcher yes, but my guess would be this has been thuroughly tested and vetted across the planes and it made no difference. Cause if it did, you can bet on these purpose built, smoke matters planes, they would put the injectors in the best location given other factors.

As for the pump, not sure.

As for the injector, if you machine some up with a check ball built in, make a bunch!
 
Another point is that with your below EGT probe placement, you will need a minimum of three injectors on a six cylinder engine (opinion) and maybe six.
 
pump choice/injector location

Hey Bob:

If you gonna use a firewall solenoid to control the flow, the marine pump is designed to run up to pressure & shut off. This higher pressure atomizes the oil better, or so it would seem. I can say this marine type of pump works fine in this sort of application, but I can't say that about the fuel pump (never used one that way).
As for injector placement, follow the norm: near the exit. If there was a better place, we would have some knowledge about it. Might research WW2 smoke generators - I'm sure they were optimized at gov't expense. Let us know what you find!

Carry on!
Mark
 
I think it has something to do with the expansion rate of the combusted oil. It can not expand in the exhaust. Only on exit. So you could put it anywhere you wanted, but it wont be able to gas until pipe exit.
 
pumps and stuff

Pooner,

Don't bother with a vane type pump.I tested one early on when working on a system for my -3. A Holley blue if I remember correctly. The viscosity of the oil is enough to lift the vanes. I know some are using Shurflo water pumps which are designed to cycle off when pressure builds and cycle on when it drops. Crank the regulator up high enough and it never shuts off. My guess is that seals designed for water and run at a constant 60 psi will eventually lead to failure. Better to use a bypass-type Shurflo with proper seals. It runs at a constant 35 psi. My setup uses injectors with a 1/16" hole and no needle valve. And McMaster-Carr check valves. Except for the pump being on top of the oil tank, I pretty much copied everything for the -4.

Tony
 
Ok thanks guys. It makes sense to me now that the middle of the pipe might be better. Dumping the smoke oil in a hotter part of the pipe may make less smoke due to more complete combustion.

I have aux tanks in the wings (I call them 'Kahuna tanks', since I borrowed the idea from some guy I know) and the right one doubles as a smoke/aux fuel tank. So I need to have a pump in place that's compatible with fuel. A selector valve that's going beneath a door in the floor will allow switching between the two. The facet pumps aren't vane pumps they're diaphragm pumps and are used in diesel applications so it should work fine.
 
rocketbob said:
Ok thanks guys. It makes sense to me now that the middle of the pipe might be better. Dumping the smoke oil in a hotter part of the pipe may make less smoke due to more complete combustion.

I have aux tanks in the wings (I call them 'Kahuna tanks', since I borrowed the idea from some guy I know) and the right one doubles as a smoke/aux fuel tank. So I need to have a pump in place that's compatible with fuel. A selector valve that's going beneath a door in the floor will allow switching between the two. The facet pumps aren't vane pumps they're diaphragm pumps and are used in diesel applications so it should work fine.
Click to expand...

One point that's purely academic. The smoke oil isn't combusting, it's vaporizing. There's (hopefully) no oxygen in the exhaust stream to support combustion. That's why forcing the oil though a nozzle into the exhaust at some significant pressure will help atomize the oil and aid in the vaporizing process.

Always listening up for good smoke system improvement ideas...

Thx
 
4 injectors

My home built system has 1 injector nozzle installed in each pipe (4) located about 4 inches downstream of the cylinder head.( 4 pipe system) I ran small stainless tubing from a "flow divider" to the injectors. No check valves and no solenoid. Using the shurflo pump with viton diaphram and the pressure cutout removed. The nozzle openings are .100".

I wonder... if the check valve is located in the nozzle if carbon and oil residue would foul the check valve?

CM
 
Pumps

Keep in mind that pressure, flow, and nozzle size are all working together. I know with the smoking airplanes system I installed, the pressure in the hose after the flow valve is only around 1 psi. A smaller nozzle and higher pressure can result in the same flow volume but it will atomize the oil into smaller droplets. If the droplets are made to small, will they produce the same amount of smoke as a larger droplet? It's a trade off, but I would prefer to have a lower working pressure in any type of hose.
 
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