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Mike's question to K-PT engine series fuel injector types

Posted: Fri Jan 07, 2005 5:48 pm
by mk
jmhdx wrote:Your cumbersome looking fuel injector is actually rather good, could you describe it again?
It could even be made less cumbersome by using brake line of smaller OD, but at the date I built this engine only 12mm OD V2A pipe (because of the need of welding I had to take some small steel pipe) was available...so it was rather a fact of circumstances. Now the market also sells 10mm OD and 8mm OD V2A pipes.

There is nothing really special about the injector. It is a derivate of Bruce's "fuel rail" (other names: "swizzle stick", "internal pipe fuel injector" or something like that).
For the K-PT 04c (60mm comb. chamber ID) the 12mm pipe was flattend a bit for reduction of drag and blast reflection.
I drilled holes of 1.8mm to 2.2mm diameter (don't know exactly, but I used a drill about 2mm in diameter, but there was no special scheme of [e.g. widening to the diameter to the centerline] used) into every of the two more or less flat sides, so that propane spilles out about 90degrees to the virtual center line.
The distance between the middle of two holes is about 9mm to 11mm.
Because of the fact the injector lies in cross-section plane and crosses the virtual center line of the comb. chamber, the holes were put from one side to the other, leaving a distance from a hole middle to the wall of about 6mm to 8mm (5 to 6 holes per side; about 10 to 12 all in all).
Having a pipe size of 12mm OD I welded a M12 connector nut onto the top of the piece of pipe looming out of the comb. chamber.
To the connector nut a steel pipe heat protection transition is attached, which then is connected to the propane hose via a homebuild thread transition (propane hose special thread - M12).
The other end of the injctor had been squeezed together and then been welded.

The main problems of this injector are the restriction at smaller engines, the prevention of starting without additional air - short: prevention of an air-induction effect - and addition of an internal Helmholtz resonator to the engine, what might cause disadvantages (but perhaps advantages when well opimized for a special engine) through frequenzy interferenzes.
The last problem could then become a real devil in the detail.

But as you can see I've been lucky by not getting real trouble with these injector type. But at following engines I'll rather use a mixture of SNECMA/Bill Hinote/Mike Everman/(assumption here:)Milisavljevic style injectors.

Under the "Small Lockwood - propane injection problems?" (much earlyer, about Jan./Feb. 2004) you'll find (a) drawing(s).

Good Luck!


P.S.: Thanks for the flowers.

Re: Mike's question to K-PT engine series fuel injector type

Posted: Sat Jan 08, 2005 5:02 pm
by jmhdx
Thanks for the detailed reply, I think you might have stumbled upon a cheap, simple albeit crude way of preheating a good volume of gas. Can you lean the motor out well?

Re: Mike's question to K-PT engine series fuel injector type

Posted: Sun Jan 09, 2005 10:24 am
by mk
If the engines are leaning out well is hard to say, but every self-sustaining engine of mine are throttleable using the main valve of the propane bottle.

The K-PT 05b (~48mm comb. chamber ID) about a 1/4 turn range, but it's very difficult at such a small engine. An additional ball valve or so would be better here I think.

The K-PT 04a/b/c(l-v) (~60mm comb. chamber ID) are also throttleable. About 1/2 to 3/4 turn I think. At lowest idle only the beginning of the tailpipe and the comb. chamber back cone are glowing slightly. At maximum throttle the half of the tailpipe and the combustion chamber are glowing brightly. The flames out of the intake are nearly disappearing at minimal throttle. At maximum throttle blue flames are comming out of the tailpipe and the intake (less at the 04c[l-v]).

The K-PT 04c(s-v) is not throttleable as good as the other 04 types. It is rather optimized for high frequency operation what seems to work in some ways, but might also be negative therefore. Perhaps therefore starting is a real problem. Blue flames are only slightly visible at the intake mouth when running on maximum throttle. The engine is glowing brightest of all I think from the comb. chamber front cone up to a point ~30mm away from the tailpipe outlet. More experimentation needed.

The K-PT 04d has another injector type, the "two port comb. chamber fuel injection". It seems to work fine. The engine was throttleable at about the same range as the first mentioned 04 types, but was less weak at lower throttle. Glowing distribution also was the same as for the first mentioned 04 types. Here is surely more experimentation needed, too.

The K-PT 01c (~72mm comb. chamber ID) is throttleable in a wide range over a whole turn. At minimal throttle there is no flame output visibl. Also the comb. chamber back and the beginning of the tailpipe are only glowing slightly. At maximum throttle blue flames are comming out of the intake and the exhaust again. Then the engine is glowing brightly from the comb. chamber front cone to a point about 50mm away from the tailpipe outlet.

The K-PT 02a (~80mm comb. chamber ID) is still under developement. I made some errors and the whole design was unable to work.

The K-PT 03a (~102mm comb. chamber ID) was also throttleable, but I don't think in a wide range for its size, but it has rather been optimized for relatively high frequenzy operation, too, but seems to fail somehow - could be disadvantegeous. I haven't test it often enough for getting all the necessary conclusions. Blue flames are visible at the intake outlet at low throttle and the comb. chamber back and the tailpipe beginning are glowing (brighter as in the smaller engines). At maximum throttle bright blue flames are comming out of the intake and the tailpipe and are relatively long, what seems disadvantegeous. More optimization needed.


All in all, all engines are throttleable not too bad. If they are leaning out well enough I can't tell exactly, but my assumption is "yes, they do". Perhaps it is more a question of exact fuel flow adjustment, especially for my relatively small engines I got some useful experiences with and learned about nice behaviour.