Lopsided spraybar

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Lopsided spraybar

Post by tritile » Thu Nov 21, 2013 1:10 am


I built a valved engine with lopsided fuel spraybar. It means that the spraybar is perpendicularly inserted in the throat section of air intake. In my case, for convenience, the spraybar is directly connected to a needle valve responsible for controlling the mixture ratio.
The best point of this configuration is that it is pretty easy to build. However, by other hand, it shows not good homogeneity of spray. It means that the spray of fuel does not meet all holes in the same amount. This causes problems of local overheating in petals, once there is no fuel to evaporate and drop the temperature or intake air, only dry air.

This next picture shows one petal as example of this non homogeneity of petals cooling. As it is not cooled the tip of petal overheats and fails prematurely.
I experienced dozens of petal with the same systematic behavior.
I tried changing the spraybar length beginning from the center of throat, until only 5 millimeters long (next picture… really short!!).
What I noticed was a better petals cooling, however the engine was substantially unstable and harder to start (maybe because it was too close to wall).

I made one picture showing what looks like the overheating profile of petal based on the damage found after some tests.
Sem título.jpg
It looks like that the spray bar causes a “shadow of fuel” on intake. As the fuel comes out of spraybar and insist to go straight and do not come back to the back of spray bar.

What is a fact is that I have never seen a popular engine using the configuration of spray bar. The closest I could find are the plans of the German “Pulso 1” witch uses a similar concept.
Sem título.png
The feeling says that it may fix the problem, once there is an obstacle (the needle itself) that organizes the fuel spray, and so it is easily spread to each hole.

Has anyone here who has worked with this type of fuelling and could share results? I would be very glad.

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Re: Lopsided spraybar

Post by IRONMAN » Tue Mar 11, 2014 8:09 pm

The mini pulsejet I made to a 1956 "Mechanics " magazine design uses a spray bar with two cross holes across the centre line of the venturi, originally the needle was set in the spraybar but it got broken off so I blanked off the broken end and used a remote mounted needle valve from an old Kavan carb. this seems to work just as well but is very sensitive. The reed is a single 0.006" spring steel leaf 0.5" wide covering a single hole in the valve face which is cut to a slant to increase the effective area, it is retained with a single screw and a brass plate. had one reed failure where the reed indented itself into the valve port slightly and the free ends curled up. Guess that with only one petal it is bound to get all the fuel/air mix! This motor was designed to run on petrol but I only got it to go on 80% methanol 20% nitromethane.
The overall spraybar effect looks similar to the Dyna-jet Flojector with its two cross holes
There appears to be a modern version of this motor flying a small foamie on U-Tube under the "foamie Pulse jet " title

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