Diesel nozzles, EDM

[The Ignoble Troll]

Hi,

Professionally the jets in a diesel injector nozzle may be drilled by EDM. It creates tiny holes with extra hard edges.

I was wondering of forum diesel builders were only bit drilling jets or has anyone experimented with using a home brew EDM drill?

If so, would anyone share plans for their EDM set up?

 

[minh-thanh]

I used a small drill bit to drill the hole.

 

[The Ignoble Troll]

I used a small drill bit to drill the hole.

What material is your injector tip made from?

 

[petertha]

I read Ben Flemming's EDM book. I could sure envision the advantages of having one in the shop, but its above my pay grade at present. My friend is building his the next generation model & he has prior EDM industry experience. So hoping to see that in action one day soon.

But regarding the injector orifice, assuming there is some practical minimal drill diameter, could one drill a second hole at some defined offset & insert a matching plug so that the remining aperture is much smaller area? Hopefully sketch makes sense. Maybe the plug method is not an ideal flow channel though.

I also ran across this YouTube channel. Looks like interesting marriage of technologies (presuming I actually understand what's going on haha)

https://www.youtube.com/@MorlockEngineering/videos

 

[GreenTwin]

I noticed on my carbide mining lamps that there is a small hole in what looks like ceramic ? material for the tip, and that creates a long round symmetrical flame.

One particular carbide lamp I have has what looks like the orifice drilled in metal, and then the orifice is crushed slightly, to produce an almost slot shape, which produces a teardrop flame shape.

Most creative.

.

 

[Klrskies]

If one could make a 2-piece tip with a lapped, tapered center core, shallow machining or ground grooves could be cut on the core's face then the core inserted into the tapered seat?

 

[The Ignoble Troll]

If one could make a 2-piece tip with a lapped, tapered center core, shallow machining or ground grooves could be cut on the core's face then the core inserted into the tapered seat?

That's a design I've seen used on furnace nozzles. It works well for those.

 

[minh-thanh]

Hi,
It creates tiny holes with extra hard edges.

But at the same time it also creates a new challenge: sealing between the nozzle and the needle.

What material is your injector tip made from?

I use C45 and brass .

But regarding the injector orifice, assuming there is some practical minimal drill diameter, could one drill a second hole at some defined offset & insert a matching plug so that the remining aperture is much smaller area? Hopefully sketch makes sense. Maybe the plug method is not an ideal flow channel though.
View attachment 157827

That's one way too ,
As I said in my other thread :
The smaller the hole the better but it's not everything , What really needs is a completely sealed injector and enough pressure from the pump

 

[Roger B]

I have drilled nozzles down to 0.2mm in brass and stainless steel. Brass is easier .
A 0.2mm open backed by a one way valve did not produce sufficient atomisation for my 20cc diesel to run. It will run with a needle or poppet type injector so the fuel is being atomised by the gap between the needle and seat.
My usual tests of looking at the spray pattern on a piece of paper and trying to light the spray confirmed this.
I attempted to measure the needle lift with a dial gauge but nothing was detectable, it was probaly less than the flexing of the system.

 

[minh-thanh]

Hi Roger B .
When I watch your video...there is something...
When you press the pump at the same tempo - same time
but the vaporization of the fuel is completely different, the right picture is fine, but the left picture is completely different, it seems like something is wrong with the system

 

[Roger B]

Hello Minh,

I think that is due to the pump not always refilling. In engine use the stroke is a few tenths of a millimeter wheras the test pump has a stroke of over 2 mm. When the plunger returns there is a vacuum in the pump until the inlet port opens (not a problem with an inlet valve) and the pump may not fully refill through the 1mm inlet.
My petrol injection engines require a pressurised fuel feed of 0.8 - 1.0 bar to avoid the petrol vaporising. Full size petrol engines with mechanical fuel injection, old Mercedes, Peugeot, Porsche etc also require pressure pumps.

 

[The Ignoble Troll]

But at the same time it also creates a new challenge: sealing between the nozzle and the needle.

It wouldn't change the sealing, it would just replace the drilling technique for the nozzle holes. No change to the nozzle bore.

 

[minh-thanh]

It wouldn't change the sealing, it would just replace the drilling technique for the nozzle holes. No change to the nozzle bore.

Of course it doesn't change..but lapping it becomes more challenging

 

[The Ignoble Troll]

Of course it doesn't change..but lapping it becomes more challenging

I'm curious why lapping would be affected?

 

[minh-thanh]

Hello Minh,

I think that is due to the pump not always refilling. In engine use the stroke is a few tenths of a millimeter wheras the test pump has a stroke of over 2 mm. When the plunger returns there is a vacuum in the pump until the inlet port opens (not a problem with an inlet valve) and the pump may not fully refill through the 1mm inlet.

I use the same pump type and adjust the plunger stroke within the pumping range of engine from 0.3 to 1 mm, which allows me to learn...and of course my pump type is different from yours.

https://www.homemodelenginemachinis...e-kromhout-gardner-4lw-1940.33617/post-398028

 

[minh-thanh]

I'm curious why lapping would be affected?

Hi,
It creates tiny holes with extra hard edges.

Trust me, sealing the needle and nozzle is really difficult, I wouldn't try to make it too hard.

 

[The Ignoble Troll]

Ah gotcha, I understand now thank you. I had pintle style injectors in mind, so the seal would be higher up. That's where my confusion came from.

Looking around the web, the power supply for a home brew EDM is pretty basic. The tricky part is the hollow electrodes but hypodermic needles come *very* small.

https://www.hamiltoncompany.com/laboratory-products/needles-knowledge/needle-gauge-chart

Also, because the liquid fuel is heated by leaving an orifice, the smaller the holes the more physics should bend to keep little engines running, as the more vapour should be produced; even ignoring the shearing atomization that is increased by smaller holes.

I can't find a graph to prove or disprove myself, but I have this nagging recollection that the smaller the high pressure orifice, the greater the heat.

Can anyone confirm that?


If so, a lot of micro holes might get the fuel to heat up to or beyond it's boiling point?

 

[ajoeiam]

Ah gotcha, I understand now thank you. I had pintle style injectors in mind, so the seal would be higher up. That's where my confusion came from.

Looking around the web, the power supply for a home brew EDM is pretty basic. The tricky part is the hollow electrodes but hypodermic needles come *very* small.

https://www.hamiltoncompany.com/laboratory-products/needles-knowledge/needle-gauge-chart

Also, because the liquid fuel is heated by leaving an orifice, the smaller the holes the more physics should bend to keep little engines running, as the more vapour should be produced; even ignoring the shearing atomization that is increased by smaller holes.

I can't find a graph to prove or disprove myself, but I have this nagging recollection that the smaller the high pressure orifice, the greater the heat.

Can anyone confirm that?


If so, a lot of micro holes might get the fuel to heat up to or beyond it's boiling point?

Hmmmmmm - - - you know - - - before you spend more than a few $$$$ building your EDM and finding that right sized hollow stock (the needle sizes I saw were all still far too large imo) why don't you find who in your somewhat general area represents Mikron tools. IIRC they have drills (Crazy drill is again IIRC) down to 0.04 mm if not even less. They won't be cheap -- - - but far cheaper buying a couple expense drill bits than doing all this other stuff.

 

[Lloyd-ss]

A couple of thoughts.

1. 3d printer nozzles are cheap and available to 0.2mm, maybe smaller.

2. The 2 piece nozzle already mentioned with a hole and then a partial tapered plug is promising.

3. When I was a kid I made a little EDM, probably from something in Popular Science or Popular Mechanics and it actually worked. Considering I didn't know squat about electronics back then it must have been cheap, simple, and probably dangerous. But again, it worked.

4. If a hole is accidentally (or purposely) made too big in a non-hardened nozzle, might it be possible to lightly hammer the nozzle to distort and partially close the hole up, AND, form crisper edges?

5. If the design of the nozzle is simple enough where a handful of blanks can be made easily such that failures in the hole making process won't be heart breaking, that makes experimentation more enjoyable.

Lloyd

 

[Steamchick]

Best I can drill is 0.25mm in brass. - So WELL DONE those of you who drill smaller!
My Uncle was on a Government project just after "WW2"....
The story went....
The Americans sent a glass tube to the UK with a hole so fine they thought it would surprise the Brits.... But it was returned with another smaller glass tube, a sliding fit, up the bore.
As a kid I believed everything my Uncle told me though. (Still do!).
On creating small holes for shearing fuel to droplets.
The simple solution to me is a hole - sensibly small - with a smaller wire up the bore...Then the fluid passes through the annulus and the gap is incredibly small compared to the hole diameter... Will is work? - The "wire core" could be a part of the valve... perhaps? - I am sure I have seen this used commercially on something so it isn't anything original... (I don't do "clever").
K2