Simpl-Jector(TM) Fuel Tube Ready To Test

[larry cottrill]

Here is the fuel tube design that will be used in my Lady Guinevere engine, now under construction. This took about half an hour to make, and I could do another one in much less time, now that the method is proven.

All you need for materials is a flared 1/4-inch brake line and a coarse-threaded sheet rock screw. You've got to be good at pretty delicate welding, though ;-)

The construction process will be detailed in the photo descriptions.

L Cottrill

[larry cottrill]

Wow ... no one wants to comment. (Maybe everyone's waiting for me to see if they actually work ;-)

But, suppose they do. Would these be a good product offering? Say, a standard length of 24 inches (about 61cm), around $7 or $8 US, your choice of .003, .006, .009, .012, .015, .018 or .024 inch gap, color coded? There are actually stainless sheet rock screws, too - so, how about a premium line featuring Type 316 tubing, same selection, maybe $20 US?

What do you think?

L Cottrill

[Irvine.J]

Your a genius larry, what else can we say? Question though, this is going in your new "lady Guinevere" right? Are you going to test it first in a standard FWE that you can get running very quickly on your normal fuel lines? I think its great, can cant wait to see how you go, fingers crossed for you! Goodluck!

[El-Kablooey]

I like it. You've got a real knack for making things simple and easy.

[larry cottrill]

Have you tried it outside an engine? Then you can see how well centered it is. And if it's getting smooth separation

The only thing like this I did was blow through it while submerging it in water. Not a very adequate test for its intended purpose, but it did show very uniform distribution around the perimeter, which was what I wanted to observe. Obviously, a flame test would show a lot more - it would take some caution and guts, though ;-)

L Cottrill

[larry cottrill]

Since I don't have the benefit of planning the parts of the injector at some large scale and finely machining them to match, it is impossible to EXACTLY calculate the aperture area of the Simpl-Jector gap. However, it is still beneficial to calculate the APPROXIMATE area, so we'll have some idea of how to select a particular size. We can do this by making a reasonable assumption about where the effective perimeter lies in relation to the centerline. I decided it would be reasonable to assume a 0.125-inch radius, making the perimeter "length" of the aperture about 0.785 inches.

The area of the gap is considerably larger than I expected, due to that effective perimeter length. In fact, it is hard to imagine that the largest sizes will even be useful, or perhaps even work very well at low or moderate fuel pressure. Worse yet: It is doubtful, at the larger sizes, that the gap itself will be the "narrow point" in the flow - there can't possibly be that much clear area around the screw body within the tube, especially at the pinch point where it's welded in! This means that maximum theoretical flow (based on the aperture area) could never be reached, and that uniform flow around the aperture could not be guaranteed. I think that experimentation with the larger sizes will be needed to determine what the largest workable size for this design will be.

That being understood, here are the calculated aperture areas I get for the proposed gap spacings (increments of 0.003 inch) - the 'Equivalent Diameter' is just the diameter of a drilled hole of equal area:

Code: Select all

                           Equivalent            Equivalent
        Gap       Area        Diam.      Area       Diam.
        (in)      (in^2)      (in)      (cm^2)      (mm)
0.785 x 0.003  =  0.0024     0.0553     0.0155     1.4046
        0.006     0.0047     0.0774     0.0303     1.9660
        0.009     0.0071     0.0951     0.0458     2.4155
        0.012     0.0094     0.1094     0.0606     2.7788
        0.015     0.0118     0.1226     0.0761     3.1140
        0.018     0.0141     0.1340     0.0910     3.4036
        0.021     0.0165     0.1449     0.1065     3.6805
        0.024     0.0188     0.1547     0.1213     3.9290

All are welcome to make me aware of any errors in the above. And, all comments / criticisms are welcomed, of course.

L Cottrill

[Mr.B]

A good way to test the injectors/nozzles is by blowing smoke through them. My very large PJ didnt run, I took the freshly build injector out, blew some smoke through it and immeadiately the uneven flow was obvious.By adjusting it and testing it "dry"(with smoke) before inserting, I got the PJ to roar to life at the first try.

[larry cottrill]

I have started working on a sales page for these things. Now, here's my plan ...

I need a lot more testing with different sizes than I can do right now. So, when my sales page goes up, I will offer these FOR A SHORT TIME at $3.00 each, plus S&H. This is approximately my cost. I won't offer them for free, because if I do that, I'll have too many takers who will just set them aside to try out "someday". I need people that are into testing something right now and who are interested enough in these to try two or three sizes, at least for quick trials at starting and running. I'll ship them padded in mailing tubes, up to eight units per tube. Obviously, for anybody that really tries them and concludes that they're just junk, I'll give full refund including return shipping. Otherwise, just order what you really want to test.

S&H charges won't be super cheap, because I'll use the best shipping method I can afford - in the US, this will usually be USPS Priority Mail, with Confirmation and a Tracking Number. What I've tentatively come up with is the following:
$5.00 Shipping and Handling for 1-4 injectors, any selection
$6.00 Shipping and Handling for 5-8 injectors, any selection
$9.00 Shipping and Handling for 9-12 injectors, any selection
$10.00 Shipping and Handling for 13-16 injectors, any selection
$13.00 Shipping and Handling for 17 or more injectors, any selection


I will make them available in .003, .006, .009, .012 and .015 gaps. My gut feel is that they'll all be usable for vapor, and that the .003 and .006 gaps will probably be suitable for liquid fuels as well (though probably just for fairly good-size engines). I don't think any of these will work well for really tiny engines because the tubing cross section will take up too much of the intake (unless you re-design the intake for it). So, practically speaking, we're good for engines of about FWE size or larger.

Here's a drawing I'll put at the top of the sales page (probably in reduced size).

All comments welcome!

L Cottrill

[Al Belli]

Hi Larry,

The EIA -RS-279 color coding is an excellent idea !

Black Birds Ruin Our Yellow Grain Butchering Very Good Wheat

Al Belli

[Eric]

$3 a piece! Mind if I outsource to you instead of china?

Eric

[larry cottrill]

$3 a piece! Mind if I outsource to you instead of china?

Eric ... you'll remember I said, "FOR A SHORT TIME" !!! That will be like, two days, and then when the clock strikes midnight after Day Two it turns into a pumpkin and all the mice run away and you're left with (probably) $8.00US each from that point on. Shipping will stay the same, of course. The three bucks will just be my "Introductory" price (meaning that my material expenses are covered, but my time is worth nothing).

The sales page will be PayPal based - remember, though, that you don't need a PayPal account to purchase using the PayPal shopping cart; any of the big name credit cards will work just fine.

I'll let the forums know as soon as my sales page is online and the clock starts ticking. Stay tuned ...

L Cottrill

[larry cottrill]

Well, sure enough - as suggested by Eric, my first few Simpl-Jectors do NOT show perfectly uniform flow. But, I think I know why, and what to do about it.

As shown in the accompanying drawing, the flow pattern comprises an almost semicircular cone of uniform flow on the side of the tube nozzle that aligns with the plug weld, with a pair of high-speed regions at the ends of the crescent pattern. The other side of the nozzle shows no perceptible flow at all!

My hypothesis on the cause (also shown on the drawing) is simple: The plug weld, as it cools and shrinks, bends the tube slightly inward, i.e. rotating the end of the tube toward the welded side. The screw is not affected as much by the weld shrinkage, so the flare closes against the screw head on the non-welded side and the gap opens on the welded side, i.e. the gap becomes wider than the aluminum spacer. The gap has the desired spacing only at two points between the welded and non-welded sides, and those points are where the high speed flow regions develop.

In my first tries, the spacer actually seized up and was impossible to remove without leaving small bits captured between the screw edges and the tube flare. Since this left an irregular "blob" of the spacer torn off in the gap, the pattern was very rough. On my next attempt, I was careful to avoid overtightening the screw and I used a different layout of spacers, and this resulted in the pattern shown.

It is doubtful that a second plug weld on the opposite side from the first would correct the problem, because of the reinforcement inherent in the initial weld. Welding experience has shown me that a one-sided distortion like this is EXTREMELY difficult to correct by welding on the opposite side of a piece. Rather, the best thing to change is probably the most obvious: Abandon the drilled hole and plug weld, and use a resistance weld (i.e. done with an ordinary pedal-driven "spot welder") that will drive a uniform current through the entire pinched zone & screw body. I can try this, because my artist friend Jim Russell has a small spot welder available. So, I think that will be my next iteration. Note that if this works well, it would also be a good technique for making stainless Simpl-Jectors, since SS tubing and SS sheet rock screws are both easily obtainable.

Note that the defective pattern would not make these unusable - the pattern is reasonably uniform over almost half the circumference. They would certainly out-perform a simple cutoff tube, and for some uses might even be ideal (say, a situation where for some reason it is impossible to center the injector in the intake cross-section). So, I have no fear of using these in experimental fueling, I just have to be conscious of the injector orientation.

L Cottrill

[Dave_G]

Larry,

Did you check the heads of your fasteners for runout?

In my industry it is common to sometimes encounter a batch of Flat-head socket screws that have a runout of up to 0.020" in the #10-32 size.

The heads are similar in profile to your drywall screws, and are made using similar technology.

Generally, we do not count on the heads of the fasteners to be concentric with the threaded body. When we DO need good concentricity, we machine it in.

The best way to check your fasteners would be to chuck them in a lathe collet and measure the runout with an indicator. If you don't have the means to do this, an alternative method is as follows:

Use two flat plates to create a step that leaves a small amount of clearance for the screw head, when the screw is laying on it's side (on the threads). Roll the screw along the top plate and measure the clearance between the head and the bottom plate with a feeler gage, to determine the head run-out (lack of concentricity) as the srew is rolled along on its' threads. This is how much your gap will vary when assembled in your injector.

It's possible that your first hypothesis is correct, but it's likely to be a COMBINATION of both of these factors that are causing your problem.

Just a thought...

[Dave_G]

Larry,

One other thought...you don't have to weld these in at all. You can swage them in place using a number of different methods.

If you have a lathe chuck (3, 4 or 6 jaw), you can easily make some swaging tools using soft-jaws with some threaded-in ball-nose or dog-point setscrews. If your chuck can't accept softjaws, you could make a simple 'spider' attachment to do the same thing with the hard jaws.

If you don't have a lathe you could do something as simple as modifying a cheap pair of vise grips by drilling an undersize hole _longitudinally_ (not cross-wise) through the jaws and using this modified tool to make your crimp.