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Mini diesel engine.

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modelmotor

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Hallo Minh-Thanh,
You already know me from several model engine projects.My forumname is modelmotor we have had several times a short contact with each other.
I have been watching the building and running from your clean built horizontal one cilinder diesel engine.
What a beauty she is and what a nice running engine.It's finish is so beautifull you might be proud at your
beautifull Crafmanships work.I hope that you will enjoy your model engine work for many years from now on.


Many greetings from modelmotor-Gerard-The Nethelands-Europe.
 

minh-thanh

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Hi modelmotor !
Thank you for your compliment!
I hope that you will enjoy your model engine work for many years from now on.
Many greetings from modelmotor-Gerard-The Nethelands-Europe.
That is for sure !
There's one thing I don't like (from myself), when I watch the projects of the members of the forum, and I have a plan to do it someday (maybe I'm too greedy :D ).
About engines I have done, it is the result of the help of the members and useful information in this forum, I just try to do well what I have learned from all of you !
 

weir-smith

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Minh

I have been following your post and noting the various comments which I think you will find useful. I will add to the discussion with my own experiences re building a true model diesel.
Just over 2 years ago, I decided to attempt to build a true diesel e.g. one that runs on diesel and uses solid fuel injection. I did a lot of research on the net and determined that there were only a handful of engines built. There were several very fine models but I suspect that they were using fuel additive to kerosene or similar which means that getting the engine to run is that much easier because of the significantly lower compression required. Some of the mixes used 30% or more of ether which has a low compression ignition point.

Back to my journey. My engine is a horizontal type with a side shaft to operate the valves via cams. The bore is 45mm with a 80mm stroke and there were no problems with that part of the build.
When it came to building the fuel pump and the injector that was a completely different story. I ended up making 11 pumps and they all failed for different reasons. The main one was attaining the required pressure of 1800 plus psi. Up to 1200 was not a big problem however, after that strange things would happen. I spoke to all and sundry about the problem and came to the conclusion that I was not able to get the near zero clearances required in the pump bore and the two valves. I finally relented to purchasing a commercial pump which was quite small with the intent to remove all of the excess material to make it as small as possible. The pump worked fine and easily produced 4000 psi and at that point I couldn't turn the engine over. So that part of the problem was solved.

The next was to check the compression which I did using a temporary head fitted with a non return valve on both inlet and outlet ports and everything else blocked off. The piston was fitted with four rings and the best I could do was 300 psi approximately. Note, I had also ground the piston to fit using a cylindrical grinder. The piston was quite long and there was room to fit more rings which were 1.5mm wide. So I added three more rings and re did the test and this time, I reached in excess of 500 psi. That was problem two solved and then onto the injector.

The injector was a problem in itself because of its small size. I read up on all of the different designed types then developing my own and after twelve attempts I gave up. The problems involved clearances and sealing. I made an injection tester and the target was 1800 psi for pop off. At this pressure, the fuel was easily atomised however, all of my injectors dripped and now reside in the bin. In the end, I purchased a miniature pintal injector nozzle being the smallest that I could find at about $10. I then made a housing for it and went to the trouble of surface grinding the face of the compression plug. When I gave it a try, after putting in a stronger spring, the pop off range was from 2200 to 1400 psi. I set it to 1800 approximately.

After a lot of fiddling around, I managed to get the engine to run with a lot of smoke etc and noise. I clearly haven't got the timing right and the fuel control is too coarse. I believe I am now reasonably knowledgeable with respect to building these small engines and if I was to start again, I would have a good look at a long series injector nozzle and machine it down to be left with the barrel and needle which can be as long as 20 to 25mm. Then make a suitable housing. Note, the material that the pintals are made from is very hard e.g. better than 4140 but still machinable. The problem with building the pump, is the very small amount of fuel involved and its associated pressure. The fit between the piston and the bore must be absolute and you can't use conventional ball valves unless you have specialised experience or very good luck.

I would also suggest you purchase one of these cheap Chinese fuel pumps ($20) and have a good look as to how it works and use the non return valve from it. The pintal needle valve can be modified with a Dremel friction blade to give the fuel adjustment slot. Again refer to the commercial pump to see how it is done.

Building a true diesel is quite a difficult project and you join a special group if you do so. I have now diverted my attention to another project which is a Fairbanks-Morse R80 which is a three cylinder, igniter ignition engine. See attachment and note, it is entirely from bar stock e.g. no castings.

Bruce W-S
Western Australia







Screen Shot 2020-03-22 at 4.07.44 PM.png
 

minh-thanh

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Hi weir-smith !
About of fuel: I do not plan to use diesel, diesel is too concentrated , with a small engine to create the necessary pressure to vaporize diesel oil is a challenge of endurance of metals (injectors, valve . , pump ..) I just need an engine that runs on the principle of a diesel engine.
I have 2 ideas to make injectors and one idea to process ball valves - I am trying to make
Thank you very much, especially for the cylinder pressure and oil pressure data, as well as the tips for injectors and pumps and all the difficulties you have encountered
 

minh-thanh

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Hi Petertha !
I just post on this forum.
I know that forum for a long time, in the past, I tried to register but was not accepted, 2 times
So I don't watch on that forum
And I can't find it if I'm not a member
Maybe that forum is not for me ;):D
 

Mechanicboy

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Hi Minh-Thanh..

Spring force in the injection nozzle determines the opening pressure and atomization of the fuel. Weak spring force creates poor atomization of the fuel and too high spring force can damage the injection nozzle and the pump system. A correct adjusted spring force in the nozzle should make a snoring sound during atomization of the fuel when pumping the injection pump. "Snoring" in injection valve who are vibrating to make fuel is atomized.

In a small model diesel engine with the injection equipment, there should be paraffin with 2% oil for lubrication of the pump / nozzle so that it is easier to atomize, better than with ordinary diesel oil from a petrol station. The compression ratio should be 20: 1 which Find Hansen used in his engines. To regulate the speed, there are only springs to regulate the centrifugal regulator with a wedge to regulate the pump volume, ie: tight springs give higher speeds and vice versa.

I recommend you take the same measurements as Find Hansen in cylinder diameter 20 mm and stroke 40 mm (long stroke generate more hot in air before ignite the atomized fuel). Injection pump piston is 2 mm in these engines by Fin Hansen. The length of the pump piston must be longer than the diameter to get less leakage and less side forces in the pump piston/pump house. 2 alternatives to make injection pump leak free: Seal the pump with gasket or pump piston lapped and adapted into the pump housing that has lapped bore (difficult to get sealed in gasket free injection pump). Stroke of pump is determined by regulator who are affacted by spring in a determined revolution.
 
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minh-thanh

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Hi everybody !
I just tested the injector (I don't know if it is a injector 😅 )
It does not open at a pressure of 4 bar, and opens at a pressure of 7.5 bar of compressed air
Sometimes, the nozzles and the needle are not really airtight
20210114_184604.jpg
20210114_184633.jpg
 

bigjy

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Hi Minh

How far did you get with the injectors, I am also very interested in small injectors
 

minh-thanh

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Hi bigjy !
The problem is: the needle and nozzles are not completely sealed, i am trying to figure out how to sharpen the needle and make the nozzle
 

Mechanicboy

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The solution : Lap the needle and nozzle togheter to keep sealed.
 

minh-thanh

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The solution : Lap the needle and nozzle togheter to keep sealed.
I did everything, like making valve of engine and ball valve , and include both at the same time ..... but it was too small
I looked at the tip of the needle with a magnifying glass. trying everything but the surface was still not good,
I still don't have a way to finish the surface
 

johnmcc69

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Good luck Minh!
I don't know much about diesels so I'm interested in how you go about it.

John
 

minh-thanh

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Peter Twissell !
What materials are you using for the needle and nozzle?
Needle : steel and stainless steel
Nozzle : brass
johnmcc69 !
Good luck Minh!
I don't know much about diesels so I'm interested in how you go about it.

John
Thanks !
I also don't know much about diesel 😆 .

HI All !
I made another injector body, The old one looks like I drilled not alignment
Re-sharpen the needle and make a new spray nozzle: the situation is improving
My small compressor cannot adjust high pressure (above 8 bar), maybe I will have to go to my friend to test
The hole of the nozzle I drilled is large 1 mm, so it does not spray into "oil mist"
I will buy a 0.5mm drill bit and make a new nozzle

As Mechanicboy said " "Snoring" in injection valve who are vibrating to make fuel is atomized."
I hear a "snoring" and feel a vibrate slightly in injector
 
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