Request - Injector designs

[The Ignoble Troll]

Hello,

I was curious and hopeful that those folk who have successfully built their own diesel injectors, might share their designs and words of wisdom in this thread.

There is a bunch of fantastic work spread across the site and for those of us dreaming of compression ignition, it would be great if the successfully completed injectors were shared in one place.

Any and all info would be immensely helpful.

Thanks,

From under a bridge.

 

[minh-thanh]

Any and all info

Here for you,

 

[The Ignoble Troll]

Thank you @minh-thanh, that's awesome of you!

 

[Roger B]

I am very much an experimenter and don't produce real drawings like Minh. There is a lot of technique and feel in producing miniature injectors without a full toolroom and metrology lab available. I will share the drawings the I have however all the manufacturing detains are on:

https://www.modelenginemaker.com/index.php

You need to sign up to see the pictures (same user name and Avatar)

 

[The Ignoble Troll]

Thank you!

 

[Roger B]

Here are a few that I have made. The poppet injector works and is the basis of Minh's design. The open injector with a 0.2 mm nozzle wouldn't run and the latest needle injector runs quite well.

There are significant detail points.
The angle of the cone on the poppet injector is critical but difficult to measure. If the angle is too acute it just jams up. My first attempt was with a floating needle but this was not consistent so the current version has the needle guided with 4 small slots milled in the guide section to allow the fuel to flow through.
The open injector was an experiment after the needle in an injector jammed and I wondered if a 0.2mm nozzle would work
open. It didn't, the atomisation is evidently happening in the very small lift of the needle.
The current needle injector tries to reduce the critical machining operations but the concentricity is ensured by the accuracy of the lands on the end of the body and the nozzle and the bore of the fixing nut. It works well but the long 1mm drilling thorough the body and the attachment of the inlet union are not easy.

 

[The Ignoble Troll]

That's fantastic Roger, thank you!

 

[ninefinger]

Many thanks to both minh-thanh and Roger B. for contributing to the public knowledge base.

I'd like to ask a question about springs for injectors.
It would seem that the main objective of the spring is to prevent opening of the injector until sufficiently higher pressure is achieved in the fuel, and closing the injector once the fuel pressure has subsided.

Has anyone experimented or considered using Bellville washers (disc springs) instead of coil springs? They have a very high spring constant for a short length, and seem like they would be suited for the purposes of miniaturizing the injectors. Also from my reading it looks like there is almost no travel of the pintle or needle on these injectors - the pressure probably goes down very fast as soon as the injector begins to lift off its seat.
What are the possible downsides to using bellville washers in this application that I'm not seeing?

 

[Nerd1000]

Many thanks to both minh-thanh and Roger B. for contributing to the public knowledge base.

I'd like to ask a question about springs for injectors.
It would seem that the main objective of the spring is to prevent opening of the injector until sufficiently higher pressure is achieved in the fuel, and closing the injector once the fuel pressure has subsided.

Has anyone experimented or considered using Bellville washers (disc springs) instead of coil springs? They have a very high spring constant for a short length, and seem like they would be suited for the purposes of miniaturizing the injectors. Also from my reading it looks like there is almost no travel of the pintle or needle on these injectors - the pressure probably goes down very fast as soon as the injector begins to lift off its seat.
What are the possible downsides to using bellville washers in this application that I'm not seeing?

I think they would work. And of course you can have whatever spring constant you like by stacking them. However I suspect many of us know how to wind coil springs on the lathe, so making custom ones is fairly straightforward vs buying bellville washers.

 

[GreenTwin]

I have studied the injector that Find Hansen built, and he describes the construction at 21:50 in this video.

As I understand it, his injector is built just like a standard gasoline engine 4-cycle valve, but very tiny.

I think he said that in order to get a good seal, and prevent pressure from forcing fuel backwards in the injector line, he uses this approach.
The pressure from his pump forces the valve up off its seat, and then the cylinder pressure closes the injector.

And I think he has a check valve in his fuel line somewhere.

His injector seems to work well, and he also seems to have good speed control with his variable throw injector fuel pump.

Has anyone else duplicated/verified Find's injector build method ?

 

[minh-thanh]

Thank you @minh-thanh, that's awesome of you!

Many thanks to both minh-thanh and Roger B. for contributing to the public knowledge base.

Just a plan and hope it gives you some ideas...
Designing an injector is not too difficult, the real thing is making it sealed.
In the attached picture - The design on the right I used in my 4 cylinder engine, it is quite compact - maybe I will use that design in all future diesel engines

 

[Roger B]

I have studied the injector that Find Hansen built, and he describes the construction at 21:50 in this video.

As I understand it, his injector is built just like a standard gasoline engine 4-cycle valve, but very tiny.

I think he said that in order to get a good seal, and prevent pressure from forcing fuel backwards in the injector line, he uses this approach.
The pressure from his pump forces the valve up off its seat, and then the cylinder pressure closes the injector.

And I think he has a check valve in his fuel line somewhere.

His injector seems to work well, and he also seems to have good speed control with his variable throw injector fuel pump.

Has anyone else duplicated/verified Find's injector build method ?

Find Hansen’s design is similar to that used in the GM 5.7 Litre diesel engine. It has the benefit of only one critical sealing point and no requirement for a fuel leak off. The problem is accurately controlling the angle of the cone. If it is too acute it jams and too obtuse will bring a spray that won’t suit the combustion chamber. Both Minh and I used this style as our first successful (as in the engine ran) small injector design. As I said above I got more consistent results by guiding the needle as in the GM version rather than letting it float like Find Hansen.

 

[Roger B]

Many thanks to both minh-thanh and Roger B. for contributing to the public knowledge base.

I'd like to ask a question about springs for injectors.
It would seem that the main objective of the spring is to prevent opening of the injector until sufficiently higher pressure is achieved in the fuel, and closing the injector once the fuel pressure has subsided.

Has anyone experimented or considered using Bellville washers (disc springs) instead of coil springs? They have a very high spring constant for a short length, and seem like they would be suited for the purposes of miniaturizing the injectors. Also from my reading it looks like there is almost no travel of the pintle or needle on these injectors - the pressure probably goes down very fast as soon as the injector begins to lift off its seat.
What are the possible downsides to using bellville washers in this application that I'm not seeing?

Depending on the details of the design Bellville washers may block the fuel flow wheras it will flow through a coil spring. They will also require a fine adjustment of the closed length to set the load correctly.
Do you have a source of small Bellville washers ~1.5mm bore, 3mm OD?

 

[The Ignoble Troll]

Find Hansen’s design is similar to that used in the GM 5.7 Litre diesel engine. It has the benefit of only one critical sealing point and no requirement for a fuel leak off. The problem is accurately controlling the angle of the cone. If it is too acute it jams and too obtuse will bring a spray that won’t suit the combustion chamber. Both Minh and I used this style as our first successful (as in the engine ran) small injector design. As I said above I got more consistent results by guiding the needle as in the GM version rather than letting it float like Find Hansen.

View attachment 157965View attachment 157966

It's the tiny size of Mr. Hansen's injectors that gets me.

 

[Roger B]

Maybe it's a big match

 

[minh-thanh]

Maybe it's a big match

It's not too difficult, just reduce the diameter of the spring wire - but that comes with a trade-off: it will inject fuel sooner.

 

[The Ignoble Troll]

It's not too difficult, just reduce the diameter of the spring wire - but that comes with a trade-off: it will inject fuel sooner.

The springs he uses look very light. Like the springs from a mechanical pencil.

 

[HMEL]

It's the tiny size of Mr. Hansen's injectors that gets me.

I have looked at Mr Hansen's design very closely. Its not the injector but the fuel delivery system and how the fuel is controlled by the injector pump with the throttle. He showed how he tested the spray pattern and the amount. However, I am of the opinion that controlling the flow is more important then the injector because I dont believe that the pattern has that big of an impact in such a small cylinder volume.

 

[The Ignoble Troll]

I have looked at Mr Hansen's design very closely. Its not the injector but the fuel delivery system and how the fuel is controlled by the injector pump with the throttle. He showed how he tested the spray pattern and the amount. However, I am of the opinion that controlling the flow is more important then the injector because I dont believe that the pattern has that big of an impact in such a small cylinder volume.

He has a combustion chamber, his spray pattern looks wide enough that it might mostly hit the walls of his burn chamber?

Maybe you are on to something and it's the precise way he can adjust timing and spray volume more then magic at the nozzle end...

...buuuut that tiny simple injector is wonderfully sized and functional.


minh-thanh constantly states that timing and volume control are critical.

 

[GreenTwin]

I have played around with oil burner nozzles, and they come is a variety of spray pattern widths, and even in solid and hollow cone sprays.

My foundry furnace does not seem to be that sensitive to spray angle, but the interior of the furnace remains red hot, and that is basically acting like a glowplug.

Foundry oil burners can be sensitive to droplet size, and a white paper says that a finer droplet does not necessarily burner hotter/better than a very fine mist. It is a matter of finding the droplet size that produces the largest amount of the hottest flame temperature possible.

I would think that the simpler an injector/pump system is, the better chance of it working reliably/consistently.

I think the Detroit Diesel 671 injectors are cam actuated, but I don't know how they vary the amount injected if they are cam actuated.

The Find-style injector has the advantage of being very small, and allows the larger parts (the pump mechanism) to be located remotely.

Minh's statement about spring tension controlling the release timing is most interesting, and not something that was readily obvious to me.
This is a critical point though for timing of a diesel engine.

.