Mini diesel engine.

[Steamchick]

No problem Tom. We all have moments when we have a little vacuum in the head...
And my wife could throttle me sometimes, when she wants a vacuum instead of my presence...
K2

 

[djswain1]

Post removed as it duplicated what others have said...

 

[djswain1]

The 6mm copper tube is only rated for 6bar - if regular "domestic" pipe - but will have a burst pressure well above that. However, it will be yielding if you attain anything like 50bar... But you want 200 bar pressure in the pipe... - all be it for small pulsations - otherwise you won't attain "atomisation" pressures at the injector. Solder won't hold that. The copper will flex and as it expands you won't get the pressure at the injector. Go to a scrap yard and get some old steel injector pipes from a diesel car or truck and use that material... cheap - easy to source - the right stuff!
Try and remember: You need 25 bar air pressure in the engine from the adiabatic compression stroke. Just to open the injector you need to exceed that. But to get atomisation you'll need to achieve 100bar plus in the pulsation from the injection pump. The volume is so small you need a very "stiff" pipework and connector system. I.E. THICK walled steel tubing with very small bore.
Have you checked the actual compression you are achieving in the cylinder? Have you checked the pressure you are achieving from the pump?
I think you need to know more so you can direct your efforts accordingly.
But enjoy it! - We are...
K2

Excellent post & advice K2

 

[Badhippie]

Omg I owe everyone an apology. Most of that content was for another site I belong to that was having issues with vacuum operated accessories on a truck. And got shall we say mixed in with this site. Lesson #1 don’t try replying to a chat when it’s 6hrs past your bed time and your belly is full of beer. Or you get what we have here a complete drunken failure.
Thanks
Tom

 

[Badhippie]

Minh
I think my original question was supposed to be more like this.
Are you sure you’re getting enough air flow through the intake system for the amount of fuel??? This is just an area that is often overlooked and mis-judged
Thanks
Tom

 

[minh-thanh]

Badhippie !
I do not know
How to know ?

 

[Badhippie]

Minh
Sorry for just getting back to you. It’s been a long time since I have worked on a flow bench. But if I am right on this. I think this is the equation you would use to figure the swept volume of a cylinder. The easiest way if I recall was the volume of air ingested in a cylinder for each rotation of the crank is close to half of the cylinder displacement. This is called the theoretical maximum volume. ( I think) So in other words it should be equal to what we used to call Sweep volume of a cylinder which if I remember 0.7854 x bore x bore x stroke so with that being said you have 1 intake stroke per 2 crank rotations. You have somewhere close to half the cylinder displacement or it’s running at 100% it’s displacement for every 2 rotations of the crank and this is called Volumetric efficiency. Now we both know there are a lot of variables in this intake passages exhaust passages chamber design lot of things can stop a cylinder from reaching 100% efficiency. But with them numbers you can now get the SCFM for the cylinder if it is at 100% efficiency and I think that was SCFM = displacement x rpm / 3456 god I hope that is right it’s been along time btw displacement is in ( ci ) so the 3456 is the product of 1728 that how many cubic inches is in a cubic foot.
Who said we would never use that math in real life. Lol lol I am sure you can check me on the old interweb. But this is what I have in my old ass notes from a long time ago. When it used to be fun building 2,000 - 3,000 h/p hemi engines hope this helps this can be used with out a flow bench to get some base figures this just should show what the cylinder is capable off. Taking in now with all that **** being said all of the variables would come into play to limit the 100% efficiency as some I mentioned earlier but there is also cam lift, valve over lap, valve size, cam duration. There are so many things that can impact air flow into and out of a cylinder it’s about stupid. But now you should know what your cylinder is capable of ingesting
I know this sounds like a hell of thing to figure out and you would be correct. But its how you figure it. Btw you can convert the SCFM to CFM if that’s easier to understand
Sorry if this is confusing it’s supposed to be and please by all means check this over because this is from memory and my notes from years past
Thanks
Tom

 

[weir-smith]

Minh

I have been following this discussion with some interest and there have been some useful comments so I will add my ten cents worth.

When building a model diesel say 6th scale or less, there are some aspects of the combustion cycle that are difficult to replicate in terms of the real thing. Firstly, the pipe work from the injector pump to the injector must have a very small diameter typically 0.5mm or less. In theory you can't compress diesel fuel however in this case you are talking about significantly less than half of a single drop of fuel. If the internal diameter of the tube is large say 6mm the tube simply expands with each pulse of fuel. I used 1.5mm OD (0.25mm ID) stainless steel capillary tube via ebay and tig welded the joints. This worked out well. The other problem you have is, that you can't get the cylinder and cylinder head hot enough to ignite the fuel air mix using just standard diesel. One of the reasons some diesels need glow plugs to get started. The information is on the net re the compression pressure for different types of liquid fuels.

You will find kerosene is significantly less than diesel and further, ether is significantly less again. For a miniature diesel, a mix of kero 70% and ether 30% makes it quite easy to start. If you want, after the engine is hot, you can switch to straight kero.

As for injection pressure, my testing showed that 1800 to 2000 psi was sufficient to atomise the fuel. You can't see it as such but put some paper in front of the injector. If you can see the spray, it not atomized as such.

I used parts from a cheap commercial pump eg the barrel and plunger for my pump and it would pump up to 3000 psi with out any trouble. For the injector, I used a small commercial pintal type nozzle fitted into a steel body. The best I could ever achieve making my own was about 1200 psi for the pump and a dripping injector at about the same pressure. I tried many variations and they ranged from a total failure to just not good enough.

Just my thoughts from building a miniature diesel.

Bruce

 

[minh-thanh]

Hello Everyone
An update
Because it is not possible to buy small tubes, gauges...
I made one more injector style,

 

[Lloyd-ss]

Minh, That injector looks so nice that it doesn't have to work, LOL. But I hope it does!

 

[Thommo]

I have to agree with Lloyd, that’s a beautiful looking injector. I also hope it works well mate.

 

[reichpaul630]

Hello Everyone
An update
Because it is not possible to buy small tubes, gauges...
I made one more injector style,

here's a place that might be able to help. not a recommendation/endorsement, whatever. there is
a size shown here HERE that is .005" ID and a .06" OD, rated to about 27000 PSI. the search term
was "stainless steel capillary tube".
LC Stainless Steel Capillary Tubing

i think these will work better for you as another poster said earlier.

ALSO, here's some Bosch stuff i found on my 'puter. i intended to send these earlier.
https://www.youtube.com/watch?v=SqBlqdeP3uE
describes the operation of the Bosch VE11 diesel injection pump, a common distributor type pump.
(18 min.)

this youtube shows the internals of the Bosch VE11, and describes all of the parts (16 mins):
https://www.youtube.com/watch?v=QwVTm2-W-JE

paulr

 

[minh-thanh]

Thanks for the comments and " Like" !
I tested it with compressed air, it's completely sealed,
Again ...Due to the epidemic situation and travel restrictions ... I am not able to buy small tubes and pressure gauges to adjust.
I really hate it but I can't do anything else

 

[Thommo]

Hello Everyone
An update
Because it is not possible to buy small tubes, gauges...
I made one more injector style,
View attachment 128740View attachment 128741

Hi Than, I was thinking, if you need some small and specific sized tubing. If it’s available in Australia I could get some pieces and mail them to you. If it will help you get the job done and it’s not too expensive I’d be happy to just buy and send it you you for free

 

[minh-thanh]

Hi Thomas !
Thanks mate !
The problem is that the disease in my area is quite complicated, so the transportation of non-essential goods has stopped.
I can buy small tubes in Vietnam , but the problem is travel and transportation is not possible

 

[Thommo]

Hi Than! I’m sorry to hear about the situation over there mate. I’ll make sure you are in my prayers. Take care of yourself and please let me know if I can assist in any way!

 

[djswain1]

Hi Minh-Thanh
I see you have commented on a new thread regarding a model diesel engine, I have replied with some basic info that may be of use to you.

https://www.homemodelenginemachinis...c-4-stroke-injector-details.31110/post-364837
Cheers, Dave.

 

[minh-thanh]

Hello Everyone !
An update :
I bought small diameter pipe
I made a new injector body, and changed it a little
and test
This is probably the type of injector and the way it sprays that I am most satisfied with so far .

 

[Mechanicboy]

This is probably the type of injector and the way it sprays that I am most satisfied with so far .

Much better atomized fuel. The important is the amount of the injected fuel into the engine.

 

[Thommo]

Hey Than, as an old diesel mechanic I must say that spray pattern looks excellent. The only question I have is have you been able to measure the volume of fuel that you are spraying per cycle? I might be wrong but it looks like a lot of fuel based on the engine size?