Diesel Injectors

[canonicalman]

Has anyone built their own fuel injectors for a diesel engine? I understand that building injectors is a high precision operation, and that most engine builders farm out the pump/injector work to a specialty company. What techniques are involved in building an injector? Any links to references?

[solek]

"Strictly I C" had the building of a 9.5cc Diesel engine, starting about 12 / 2000.
The building of an injector nozzle, for the engine, was covered. You could buy back issues from them, on their web site.

[DIX]

I make my own injectors and all it requires is careful work. Tolerances are fine so there is a lot of lapping of parts. You can go with a pump and an injector or use the GM type injector that combines the high pressure pump with the injector itself. You can find design details for injector systems in any library. I prefer the separate pump deal because it simplifies the building process by allowing me to split the job between two devices. If you botch one it's not as big a deal as with the GM injector. BTW, you will need the injector nozzle made from tool steel or the fuel squirting through at 1,700 psi with soon destroy the fine tip required to make the fine spray. I use a little piece of drill rod hardened after threading and drilling.

I think the hardest part is calculating the amount of fuel to inject per power stroke. The accepted figure is 14 to 15 parts air BY WEIGHT to one part fuel by weight. In my little 4 HP engine this comes out to be about 3 milliliters. About one "fat" drop!

Dick

[Harold_V]

Very interesting, Dick. Do you have any pictures you'd like to share with us?

Harold

[DIX]

Harold,
I looked around today but cannot find pictures of the injector or the pump. The engine itself is at my son's house 35 miles from here powering a small AC generator for standby power. Next time I'm out there I'll get a picture or two. Just never thought anyone would be interested in one of my toys.

Dick

[Harold_V]

Well, Dick, you were wrong! [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]

I've been interested in a miniature diesel for some time now. I've even given consideration to building a scale 3 cylinder like the one in my Kubota tractor. It would be a fun project that could actually be useful. To be perfectly honest, one of the things I have wondered about was the injector system, something I've never explored. I figured it would be possible to build one in miniature, but had no idea how to go about it.

I'd be pleased to see some pictures of the little generator, at your convenience. I thank you for your kind offer. If you take more than you'd care to post, feel free to send them to my email address. Each and every one will be appreciated.

Harold

[DIX]

Harold,
I don't have the pictures anywhere around here. They are in the house but I can't remember where. I can take the picture of the engine next time I'm out to my son's place, that's no problem.
In the meantime I can sketch out the drawings for the pump with the variable stroke which is how you control the throttle on a diesel. I can also sketch the injector itself.
If you are building a 3 cylinder engine you just make three of each and gang the pumps together like the big boys do.

Dick

[Harold_V]

Hey Dick,
No hurry, I'm still in the throes of building our house, a seemingly endless project----although I can finally see some light at the end of the tunnel. I won't be doing any work on the fun stuff until we've moved out of the shop, but I enjoy dreaming!

I think the thing that intrigues me most is the variable pump. I've never explored how injectors work, so all of it will be news to me. If you aren't too busy and don't mind doing a sketch or two, at your leisure, I'd certainly enjoy seeing what you have to offer.

I was just reviewing my email of old and still have several of those I received from you in '03. I get the idea I may have abandoned you, noticing the last one was in August, when we were likely pushing like crazy to get the house closed in. If so, I apologize. The fall I experienced sort of messed up our schedule and lots of things were forgotten. Nothing personal!

Best regards,

Harold

[canonicalman]

Dick,

Thanks for your reply. I would also be interested in any pictures or drawings that you may have of the injector setups that you have worked on.

I have done some lapping for a sterling engine project where the pistons had to fit the cylinders to a close tolerance because of the lack of piston rings. The lapping was easier to do than I had imagined.

I read another article that mentioned that the tolerance on injectors is typically about 90-160 millionth of an inch. (About 1/10 thousands) Does this correspond with the accuracy to which you have been building?

[DIX]

Right now I'm stuck making some custom parts for customers and also shoveling that #$%! snow and ice we keep getting every few days! So personal projects are on hold. I just finished the crankshaft for the engine. I'll get to the fuel system later. Pictures will be available but for my convinence I prefer to send them via e-mail. But hold off on requests right now.
Answering the question on accuracy to the millionth of an inch. Gee!!! I have no idea. I lap the parts together and that always works. There is very little leakage or blow by on the injection parts so it must be ok. Remember the fuel IS also the lubricant so you do need some leakage to assure lubrication.
I have a suggestion on simplifying your diesel projects. Why not go to compression ignition mode instead of direct fuel injection? You induct a fuel air mixture into the engine and the heat of compression will fire the mixture and make the engine run. You can fine tune the ignition by using a contra piston which changes the compression ratio even while the engine runs. Like a BIG model airplane engine.
I have such an engine fairly well advanced in construction. It is 1 1/8"bore with a 1 1/2" stroke. The cylinder is horizontal and the exhaust port faces down. The reason for that is to prevent the cylinder from flooding and to recoup the lube oil since this is a two cycle engine. You can reuse the lubricating oil since it does not burn. Intake is valved by a reed operated by differential pressure. The fuel mixture is diesel #1 75% and two cycle lube oil 25%. This will be my second engine after the prototype did so well I wore it out playing with it.
I think you can tell I have a love for diesels of any kind. Maybe because I've been around the "real" thing for years. I also have another engine on the drawing board.

Dick

[Doug_C]

This will be my second engine after the prototype did so well I wore it out playing with it.

I can't seem to find time making one complete let alone wear one out and start another. I'm certainly envious with gratitude for you sharing your work here! [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]

DC