small lockwood - propane injection problems?

[mk]

hello.

i have a problem with my small lockwood engine.

when i try to start it with a hot-air pistol it just pops one time and then just burns inside the combustion chamber at the propane outtake like a torch. i tried placing it on and next to the intake-cc-cone (entering the cc or the intake), but nothing changed. when turning the gasflow with a needle-valve, the "torch" justs gets bigger or smaller.

i use a 2.5bar regulator and a transistorized ignition with a normal motorcycle coil (average sparkling).

besides i haven't added a kind of injector noozle (is it necessary?), but tried different hole diameters (1.5mm, 3mm, 6.5mm). no result.

then i tried to tune the intake and tailpipe length a little bit, but it just got worse.

-> so i think that s.th. is wrong with my propane injection! <-

hope that somebody can help me.

mk

note: -dimensions (in mm): nl - 140 nm - 41 cl - 145 cm - 75
tl - 915 ti - 28 to - 65
(i can't show a pic, because i haven't got a digi-cam, sorry!)
-tailpipe with U-bent
-all parts conical

[Dave]

MK
I believe your problem is the regulator restricting the necessary flow of fuel. A pulse jet engine consumes much more fuel than any torch. Pulse jets of any size appear to run on unregulated gaseous or liquid propane. Carefully review the information on this forum regarding fuel delivery before going any further.
Dave

[Viv]

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

[Dave]

Viv
I can see that back pressure and resonance in the fuel system can be real problems, but can they also be harnessed. One of the issues with Pulse Jets appears to be high fuel consumption. Some have suggested this is partially because the fuel flow of something like propane is constant and not timed to the pulse rate of the engine. Has work been done to try to use, rather than suppress back pressure pulses and resonance and if so what was the outcome?
Dave

[Bruno Ogorelec]

One of the issues with Pulse Jets appears to be high fuel consumption. Some have suggested this is partially because the fuel flow of something like propane is constant and not timed to the pulse rate of the engine. Has work been done to try to use, rather than suppress back pressure pulses and resonance and if so what was the outcome?
Dave

Fuel flow is not constant. Its input pressure is constant, but the pressure variations (pulses) inside the engine effectively impose pulsation on the fuel flow. Whatever you do in a pulsejet, it will resonate. So, you must tune the resonance to suit your purposes or make the component non-resonant. (You can do the latter by making the natural frequency of the component very far off the natural frequency of engine parts or by introducing damping.)

[Viv]

Viv
I can see that back pressure and resonance in the fuel system can be real problems, but can they also be harnessed. One of the issues with Pulse Jets appears to be high fuel consumption. Some have suggested this is partially because the fuel flow of something like propane is constant and not timed to the pulse rate of the engine. Has work been done to try to use, rather than suppress back pressure pulses and resonance and if so what was the outcome?
Dave

Its a bit Tricky Dave, the fuel systems allready work with a bit of resonance pulsation in them, its one of the varibles that is so hard to tie down when fault finding some ones elses engine.

Resonance could be harnesed to improve fuel delivery and timing or it could be cut out so as not to interfere, a simple check valve will do that but it must be quick enough to respond to the engine.

Back pressure from the combustion chamber and a springy hose will give a certain amount of fuel delivery pulsation but on a high pressure engine like the BCVP it stops the fuel flow when it fires completly.

electronic injection systems would be better for liquid fuels from a high pressure pump, but the pressure must be high! have a look at this posting from Bill.

http://panther.msrootserve.com/~admin11 ... .php?t=206

Viv

[Lawrence]

MK,

My first lockwood had the same problems you mentioned, only producing a flame (a nice blue cone flame at the exhaust). I first thought that the propane injector nozzle wasn't good, so I made a few, tried them all, but it still didn't run..

I decided to build a new lockwood, constructed according to the dimensions mentioned in the patent as an example. It started immediatly, and runs better without a nozzle on the injector at all... (the injector is in fact just a steel pipe with a 4mm ID)

This engine doesn't use too much gas, when the valve is opened too much, the gas won't mix up well enough with the air because of the speed the propane enters the CC (With small diameter nozzles this would occur much earlier), or the engine will get overfueled, and drops dead.

My propane tank doesn't have any kind of restrictor (as far as I know), but I'm not sure your regulator is the cause. My lockwood needs only a very small twist on the valve to start, and keep idling.

Looking back at my first lockwood, these might be the reasons why it didn't run

-CC diameter was too small compared to the intake diameter, causing far too less turbulence at the CC inlet, so the propane wouldn't mix good enough with the air to produce good bangs. Complete combustion only started in the tailpipe, as it turned red hot, while the CC was frozen because of the propane.. after a lot of time experimenting with airgun positions, the combustion zone moved in the CC, showing that mixing improved. On that moment the engine came in some sort of resonance, but it was a weak humming noice. This could mean that the CC volume was too small, producing far too weak explosions, to create a vacuum large enough for sucking fresh air in.

-The tailpipe was too short, and maybe a little too large in diameter too get the engine in resonance, igniting the next air/fuel charge

-The tailpipe was made of 6 straight cones, welded together. The welds weren't very smooth in the inside (first time on the TIG machine for me, on 0,75mm :P), The corners and the welds might obstruct airflow.. This wouldn't occur in my second engine, as it has a straight tailpipe.

[Dave]

Viv, Bruno and others:
The first valveless engine I fell in love with was E. G.'s Pressue Jet. While it was an interesting piece of technology, few appear to live up to the advertised thrust levels. All that said, has anyone tried to apply the fuel delivery concepts used in the pressure jet to a pulse jet? For example: Could high velocity fuel delivery start a pulse jet without the need for compressed air? Could that same high velocity help to improve compression on the intake cycle...
Dave

[Bruno Ogorelec]

The first valveless engine I fell in love with was E. G.'s Pressue Jet. (snip!) has anyone tried to apply the fuel delivery concepts used in the pressure jet to a pulse jet? For example: Could high velocity fuel delivery start a pulse jet without the need for compressed air? Could that same high velocity help to improve compression on the intake cycle...

Dave, the short answer is 'probably yes'. It has been tried. John A. Melenric, whose Thermo-Jet Standard Inc. of Kerrville, Texas, manufactured an orginal kind of pulsejet in the 1960s, patented and tested a pulsejet that reportedly achieved Mach 0.85 powering a flying drone in the early 1970s. It used a similar kind of fuel delivery.

[mk]

thanks for your support, ideas, opinions...(call it whatever you want)!
i think it will help me very much.

i try do get a digi-cam from a friend to post some pictures then.

mk

[mk]

BAD NEWS!

I don't have a pressure regulator anymore, but my lockwoods just don't want to start running alone!

I'm using a 5kg propane bottle with a 3m long 3/8 hose. I fitted a needle valve between the hose and the ~9in long injector pipe (0.25in inner dia.).
After switching on the ignition and turning on the propane, I'm blowing air into the intake with a hot air gun. Usually I'm getting a loud "pop", what differs from the valve opening. I would say engine gets enough propane, because I'm getting the loudest "pops" around a half opened valve. But after the first the engine doesn't start running, but a continousflame burns inside the cc (which is then slowly getting aut of it through the intake). But when I hold the hot-air gun to the intake again, the engine pops again or a little pulsating burning starts taking place in the cc (airflow from the hot-air gun is still needed). When I then adjust the needle valve the I can figure out the best propane flow rate (again around a half opened needle valve).
This process works best when injecting propane in the middle of the intake, 90 degrees to the symmetrical line. Injection in the combustion chamber doesn't work as good as injection in the the intake. I'm then usually only getting one single "pop" and the burning powered by the hot-air gun isn't as good, too. I don't use any fuel injector nozzles.

My smaller, straight testing engine gives relatively good "pops" and forced burning. Injection points are: intake, first cone, cc beginning.
My bigger engine with a U-bend just gives one single "pop" or rather "breath". Injection point: between cc beginning and first cone.


MEASUREMENTS (inch):

straight engine: Nl=5.25 Nm=1.21 Cl=5.40 Cm=3.04 Tl=36.58 Ti=0.82 To=2.03

U-bend engine: Nl=6.24 Nm=1.59 Cl=6.22 Cm=3.85 Tl=45.13 Ti=1.07 To=2.53

I just don't really know what to do. I would only try to experiment with the tail pipe and intake length a bit.

Maybe someone can give me one or more hints. But I know that a diagnosis only within this forum is nearly impossible.

mk

[resosys]

I don't know your exact setup, but here is what I would try:

I would use the valve on the propane tank to adjust the fuel. Take the needle valve out of the line. If it's not a true needle valve and is just a 3/8" valve, it should work fine and can be left in.

Lengthen the tailpipe by slipping a piece of pipe over it. It doesn't have to be exactly the same size as the opening, as long as it is within an inch or so. Make it so it can be adjusted.

The hair dryer may not be enough to start your engines. You may be able to fashion some sort of augmentor tube to the hair dryer to help.

Chris

[Graham C. Williams]

You have got your fuel injection point in the right place, have you?
Graham

[mk]

The attachement shows the propane injector positions. Position I "works" best at the moment. My U-bend engine is only assembled with position III.

I have already tried to lengthen the exhaust a bit, without getting any better result. But trying some more lenghts could be useful, couldn't it?
I'll try the injector version without this "true" needle valve (thanks for this hint!) soon.

Can I leave the hose connector/injector with its inner diameter of 0.25in like it is? I think it best like it is, because the propane doesn't flow too fast into the cc, but fast enough for making a good air/fuel mixture. Has somebody any experiences?
Could it also be that temperatures around -2°C are too low (->propane over-pressure)?

[resosys]

It would seem position 3 would be the best for getting the propane stream to intersect the incoming fresh air at 90 degrees, but it may be too far back for things to mix correctly before they hit the returning hot gasses. My inlets are placed where your #2 inlet is, but mounted so the gas flows in at 90 degrees to the intake flow. Inlet 1 should get you a good mixture by the time it hits the ignition point, but it may be too early. There are too many factors and fuel inlet placement seems to be one of the toughest.

I run my propane tanks directly to the pulsejet via 0.375" hose and the inlet on the engine is 0.25".

Propane doesn't like to move when it's cold. We built a propane vaporizer so that we wouldn't freeze our tanks. Keeping the tank in a safe but warmer than outside place will help. Wrapping it in a blanket will also help.

Last year we did some testing out on a desert and we had problems with the tanks becoming too cold to run the engines.

I haven't tried it, but I've seen others wrap some copper tubing around the combustion chamber to pre heat the propane.


Chris