www.pulse-jets.com

I built a simple pulsejet using PyroJoe's second most basic design*, which currently runs on propane. What I would have to do to convert it to liquid fuel, preferably diesel because it's safer to work with. I would like to avoid mechanical parts, but I have a fuel pump if I absolutely need it.

the engine has a 2" exhaust pipe and the rest of the dimensions were scaled from the design, and very little thrust (A topic for a different thread)

*the one entirely made of straight tubes with a 20° cone transition from the CC to the exhaust pipe

It takes considerable knowledge to switch from propane to petrol liquids in valveless pulse jets.

PyroJoe wrote:It takes considerable knowledge to switch from propane to petrol liquids in valveless pulse jets.

I know liquid fueled engines are more difficult, but propane simply isn't practical, except for those who never expect to actually use their engines for anything. I know the GRIMjector I am using for propane will be useless for diesel in any case.

Try starting on propane and then switching to a liquid fuel. Use a Hago oil spray nozzle (the finer the mist the better). Use an automotive in-tank pump (12v, 3bar, 3L/min) to pump your fuel. Use either a flow bypass to controll your fuelflow or use a PWM (pulse width modulator) to controll the voltage through the pump. You can get the pump and the PWM on ebay for ~18$. Nozzles are about $5.

Take heed to what Pyrojoe said though, it's hard as balls.

What I really need at this point is a fuel delivery system that has no moving parts that is powered by the engine (I have a fuel pump, but that's a last resort), I can vaporize the fuel before it reaches the injectors by wrapping some tubing around or in the exhaust pipe, and use something else as a pilot light to get the engine hot enough to vaporize the fuel. Could the pressure generated in the engine be used to pressurize the fuel tank? The pressure in the engine swings, so would I need a flow diode to keep the tank pressure up? Are there any existing plans for a liquid fueled pulse jet that is not reliant on a fuel pump? I have some ideas about a low pressure injector design, but I require a way to pressurize the fuel tank a little for it to be effective.

I've only ever seen a gravity feed system on a valveless pulse-jet. It works but it's very crude. The problem is, a valveless pulse-jet is a finely tuned machine. Just taking some pressure from the combustion chamber is going to mess up the engine. If you want to harvest energy for your fuel delivery, do so outside of the engine, e.g., exhaust/ intakeflow or engine heat. You could maybe try a fueltank wrapped around the combustion chamber. The heat will vapourize the fuel and pressurise your tank, allowing gas to flow through an injector. There are some problems like overpressure to overcome. You don't want your tank to explode.

*edit*

You could add a buffertank to the fuel tank. A valve to the buffertank will open to keep the pressure in the fueltank within a certain range. as a safety, you could add a pressure gage in the buffertank that, when it detects the pressure getting as high as your fueltank, will send a signal to a valve on your injectors to stop fuelflow and kill the engine. One thing to keep in mind is that superhot flammable gas and air don't mix, so maybe use an empty acyteleen tank with kapok in it, or draw a vacuum in your buffertank first.

metiz wrote:I've only ever seen a gravity feed system on a valveless pulse-jet. It works but it's very crude. The problem is, a valveless pulse-jet is a finely tuned machine. Just taking some pressure from the combustion chamber is going to mess up the engine. If you want to harvest energy for your fuel delivery, do so outside of the engine, e.g., exhaust/ intakeflow or engine heat. You could maybe try a fueltank wrapped around the combustion chamber. The heat will vapourize the fuel and pressurise your tank, allowing gas to flow through an injector. There are some problems like overpressure to overcome. You don't want your tank to explode.

*edit*

You could add a buffertank to the fuel tank. A valve to the buffertank will open to keep the pressure in the fueltank within a certain range. as a safety, you could add a pressure gage in the buffertank that, when it detects the pressure getting as high as your fueltank, will send a signal to a valve on your injectors to stop fuelflow and kill the engine. One thing to keep in mind is that superhot flammable gas and air don't mix, so maybe use an empty acyteleen tank with kapok in it, or draw a vacuum in your buffertank first.

Interesting idea, it looks like I have some experimenting to do in order to find a satisfactory solution. the pressure harvesting would basically be a small port stuck in the engine that would allow a small amount of engine exhaust to flow into the fuel tank, basically it would act sort of like a pinhole in the engine at that location, and you are probably right about putting the port in the exhaust pipe instead of the combustion chamber, I think the exhaust pipe has the smallest pressure swings anyway.

Probably the first thing to do is to understand that valveless pulse jets are not like regular mechanical piston engines. There is no mechanical piston to crush the fuel air together. There is no intake valve that shields the intake from the positive pressure from the combustion cycle.

The factors I typically look at:
fuel air ratios
humidity
latent heat for phase change from liqued to vapor
vapor pressure of the fuel at different temperatures
ambient air temperature
fuel temperature
non linear reaction rates for varying fuel temperatures

Laminar jet breakup for simple built fuel nozzles
nozzle droplet size
nozzle placement

Hope that helps a little

OK, some tests have determined that vaporizing fuel is not a good idea, it seems to decompose by the time it's hot enough to vaporize, which would rapidly clog the fuel delivery system with carbon deposits, if I were using simple hydrocarbons or alcohol as fuel that wouldn't be a problem, but those are either too expensive or impractical. It appears I will need to inject any form of inexpensive petrol as a liquid, hopefully the pulsejets I will be working with will be able to deal with that. Now to figure out the pressure harvesting, and low pressure fuel injectors. I may use the heat from the engine to expand some air or water to pressurize the tank instead if pressure harvesting is a bust.

One possibility is a feeding of pressurized fuel towards a small inert gas cylinder as shown in the attachment. The nozzle must design it.

http://webserver.dmt.upm.es/zope/DMT/Me ... nables.pdf

daab wrote:One possibility is a feeding of pressurized fuel towards a small inert gas cylinder as shown in the attachment. The nozzle must design it.

http://webserver.dmt.upm.es/zope/DMT/Me ... nables.pdf

Pressure harvesting was a bust, and my next plan is similar to the one listed, except I would probably use a propane cylinder instead, or use engine heat to boil water and use an oxygen regulator I have to control the pressure fed into the fuel tank, seeing as I will almost certainly need to use a small homemade re-fill able propane cylinder to start the engine.

If you're going to have propane involved, why not use that to pressurise your fuel?

tufty wrote:If you're going to have propane involved, why not use that to pressurise your fuel?

Or you could use nitrogen, maybe a bit safer. Also higher pressure than propanetanks so you could get away with a smaller nitrogentank perhaps

As I see it, using an inert gas is to stop there being an explosive mixture in the fuel tank - but it doesn't need to be inert - as long as you're not using oxygen, acetylene, or nitrous to pressurise, your fuel tank shouldn't be a bomb waiting to happen.

There is danger involved, in that you have a pressurised tank filled with fuel, in close proximity (and the closer the better) to a machine that runs somewhere between red and white hot. If you burst or pierce your fuelling system, there's definitely going to be a major flame situation - but that's already the case with propane fuelling, adding liquid to the mix isn't making it any worse as long as there's no oxygen in the tank.

What works best for me is a duel fuel system. Start the engine on propane, then turn on the liquid fuel.