Pressure Regulators and Pulsejets

[ferret]

Hi guys, first post here. I'll try to keep this short.

Today I bought a 0-60 PSI propane regulator, with the intention of using it to run my 2 pound thrust "pipewood" pulsejet. 

There's two problems with my plan. Number one is that the pressure regulator may shut off the gas flow entirely due to backflow pressure from the pulsejet running. (I have heard someone say this is possible on the pulse-jets.com forum) Second is that 60 PSI max may be too low to run the engine. 

I have already run the engine on unregulated propane, straight from the tank. This works, but I would like more control over the flow if possible. I also have built the Metiz M40, and I would like some way to control fuel flow for when I run that engine.

So I guess I have 4 questions;

1.) Can an engine be run with a propane regulator?
2.) Will 60 PSI be enough for a 2 lb thrust PJ?
3.) Will 60 PSI be enough for a 40 lb thrust PJ?

and, if "No" to number one;

4.) How can one regulate/control fuel flow to a pulsejet?

On a side note, I have seen 0-100 PSI regulators on ebay for 60 bucks, which could be an option for greater pressures, but this 0-60 PSI regulator only cost me a cool 5 dollars. (So It's okay if it won't work) 

Thanks for any help, great forum you got going here guys! 

[ferret]

All right, it appears regulators are not an option for fuel control.

from : www.pulse-jets.com/phpbb3/viewtopic.php?f=7&t=290

"You can not use a gas pressure regulator in the supply line to a pulse jet! we have spoken about this before but it was on the old forum, so to reiterate.

The problem is nothing to do with the maximum flow rate of the pressure regulator as is normally assumed, the regulator mechanism maintains a constant pressure drop at varying flow rates using the outlet pressure as the reference pressure.

If the regulator is connected to your engine by a pipe that goes directly in to the combustion chamber when the engine fires a pressure pulse will be transmitted back along the pipe to the pressure regulator, that pulse will alter the reference pressure for the regulator mechanism, the mechanism has a certain amount of inertia so the small pulses add up to a steady high pressure, and that will fool it in to shutting the flow down to lower the pressure.

So your engine fires and shuts down its fuel supply! now I know there are cases were it is the shear flow rate that is the problem but they have different injector locations.

Resonance in the fuel system can be a real problem, changing from soft to hard gas hose changed the way a test engine ran due to the hard hose transmitting the pressure pulses from the combustion chamber better, in the end we had to fit check valves behind the injectors to stop this.

Remember! when the fuel valve on top of the gas bottle is open, you have effectively added it as another component to the resonant system that is your engine!

Viv"


So, maybe a ball valve? needle valve? I don't know, i'm just trying to find some reliable way to control fuel flow.

[racket]

Hi Ferret

I used both a needle valve and a ball valve on my "Turboprop Pulse Jet " www.youtube.com/watch?v=uqMn0A2aUdo ( theres a build thread on the PJ Site ) ...............the needle valve gave irregular fuel delivery due to the play in the needle valve stem thread , whereas the ball valve , which was originally only installed as a quick shutoff valve , gave more consistent flow, I also used the gas cylinder valve as a throttle in the early days of development before I switched over to petrol as the fuel .

Cheers
John

[metiz]

Hello Ferret,

Question number three is null and void now I guess but if you run the M40 of off a regular propane bottle, the valve on the tank itself will give you more than enough controll over the throttle, considering the fuel consumption and the relatively high idle rate.

Do you have a picture of your M40?

[ferret]

Hi metiz, my name is actually "username" on the pulse jet forums, and I'm the same guy who was asking questions about building the 2 lb pipewood a week or so earlier. So I think you saw my rusty M40 in one of my build videos.

The tank doesn't have much control over fuel flow itself, otherwise I would simply rely on that. Almost as soon as you crack the valve on the tank it is full on, which doesn't offer much control over fuel flow. Anyway, thanks for the help, I guess i'll take a trip to the hardware store to get a ball valve.

[metiz]

Sept 2, 2013 17:47:17 GMT -5 ferret said:

Hi metiz, my name is actually "username" on the pulse jet forums, and I'm the same guy who was asking questions about building the 2 lb pipewood a week or so earlier. So I think you saw my rusty M40 in one of my build videos.

The tank doesn't have much control over fuel flow itself, otherwise I would simply rely on that. Almost as soon as you crack the valve on the tank it is full on, which doesn't offer much control over fuel flow. Anyway, thanks for the help, I guess i'll take a trip to the hardware store to get a ball valve.

Ah ok, I thought it sounded familiar but I couldn't find a user by the name of ferret on the pj forum, guess that clears it up