Author Topic: 20cc Four Stroke Diesel  (Read 14783 times)

Online Kim

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Re: 20cc Four Stroke Diesel
« Reply #75 on: September 10, 2022, 04:54:16 PM »
Nice work on the tensioner arm, Roger!  :popcorn:
And I like the gas tank bracket - very functional. And from your spare parts!  All the better  :ThumbsUp:
Kim

Offline RReid

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Re: 20cc Four Stroke Diesel
« Reply #76 on: September 10, 2022, 05:17:33 PM »
Looking forward to the last bits and the first start, Roger. :ThumbsUp:
The highest compression I've ever turned over by hand is 9:1. Can't quite imagine what 20:1 must feel like! Do you still have to make up a starter, or do you already have something suitable?
Regards,
Ron

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #77 on: September 12, 2022, 07:22:39 AM »
Thank you both  :)

Ron, I have a mains powered electric drill I use as a starter.

The next piece was a flange for the exhaust pipe. I made four as this size is also used on the horizontal engine and I have a couple more experiments planned for that.

The blanks were cut from 3mm thick brass bar with the Proxxon table saw. The fixing holes were drilled with a simple jig and two blanks were clamped together with 6mm and 12mm filing buttons. A little bit of filing and ready for use.

I am waiting for some 8mm elbows to complete the exhaust so next up is a few studs.
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #78 on: September 24, 2022, 09:47:54 AM »
The studs for the injector and exhaust flanges were turned from 3mm stainless steel and the nuts from 5mm brass hex. A quick trial with the compression tester showed a clearance problem so a redesign is needed. To fit the injector and the valves in the head I reduced the stud spacing from 16mm to 14mm so there is no clearance for a spanner for the 8mm body of the tester. The 6mm body of the injector is no problem.

The exhaust elbow was silver soldered to the flange and installed pointing down to avoid the 'clag fountain' of the two stroke version.

Next I primmed the oil system. By removing two of the pump fixing screws it can be tilted out of engagement with the worm and spun with the cordless drill. By blocking the pipes in sequence it is possible to force oil through the crankshaft and the feed pipes to remove any air.

The starter dog showed some signs of abuse so I skimmed most of the damage off.

The final step was to check the injection system and confirm that the zero fuel position was really no fuel and that there was good atomisation.

<a href="https://www.youtube.com/watch?v=YBNC1RCqSJQ" target="_blank">http://www.youtube.com/watch?v=YBNC1RCqSJQ</a>

<a href="https://www.youtube.com/watch?v=YBNC1RCqSJQ" target="_blank">http://www.youtube.com/watch?v=YBNC1RCqSJQ</a>

« Last Edit: December 04, 2022, 04:48:41 PM by Roger B »
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #79 on: September 24, 2022, 10:24:03 AM »
Yes - that is a very tight squeeze ...!

The rest looks very functional now - getting close to first Pop  :ThumbsUp:

 :cheers:   :popcorn:

Per

Offline Brendon M

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Re: 20cc Four Stroke Diesel
« Reply #80 on: September 24, 2022, 12:51:50 PM »
Yes getting very close :D
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Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #81 on: October 08, 2022, 03:51:36 PM »
I modified the design of the compression tester. It's not perfect but can be assembled. When I was dismantling the old set up I found a crack in one of the fittings which have been part of the cause of the leak off. The compression was over 30 bar when cranked with the electric drill so I packed it all up and took it to the welding bay at work for a trial.

After various injection timing adjustments it started to fire but still blows unburnt fuel and oil out  :( Then it caught and ran for a short while and would respond to the fuel rack  :) The next attempt after the short video clip produced no results at all, the fuel injection cam had fallen off  ::) I am happy with that run as it confirms my thoughts that the two stroke was running on fuel that had blown past the piston into the crankcase. Now I think I need to work on better atomisation from the injector. You can see the fine puddle of fuel and oil under the exhaust.

<a href="https://www.youtube.com/watch?v=8NKiJ2hAi3c" target="_blank">http://www.youtube.com/watch?v=8NKiJ2hAi3c</a>

<a href="https://www.youtube.com/watch?v=8NKiJ2hAi3c" target="_blank">http://www.youtube.com/watch?v=8NKiJ2hAi3c</a>
« Last Edit: December 04, 2022, 04:49:22 PM by Roger B »
Best regards

Roger

Online Kim

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Re: 20cc Four Stroke Diesel
« Reply #82 on: October 09, 2022, 05:40:56 AM »
That looks like a very successful test run, Roger!  :popcorn:

Kim

Offline Brendon M

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Re: 20cc Four Stroke Diesel
« Reply #83 on: October 09, 2022, 07:32:23 AM »
Fantastic! The moment we have been waiting for :D

It sounds like it will run great once you get the cam issues sorted
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Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #84 on: October 09, 2022, 12:29:09 PM »
You are still in a very small group of people that has mannaged to construct, build and run a true model Diesel Engine  :praise2:  So I would consider this another succesful test if I was you  :cheers:

I agree with Brendon - that the Cam issue should be manageble   :cheers:

Per

Offline RReid

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Re: 20cc Four Stroke Diesel
« Reply #85 on: October 09, 2022, 02:56:04 PM »
Congratulations Roger!  :ThumbsUp: :cheers:
Regards,
Ron

Offline MJM460

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Re: 20cc Four Stroke Diesel
« Reply #86 on: October 10, 2022, 09:56:38 AM »
Great result Roger, it proves you have all the primary elements together..

Minor component failures show the importance of these parts which possibly experience greater forces than we might imagine, but I am sure you will overcome those issues with your persistent and thorough approach.

Your thread is an inspiration to read, I always read each new update.

MJM460

The more I learn, the more I find that I still have to learn!

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #87 on: October 15, 2022, 12:17:44 PM »
Thank you all for your interest and support  :)

I refitted the cam and checked the timing by removing the delivery valve and turning the engine until the fuel flow stopped. This was around 20° BTDC which is more than I was expecting.

The spray pattern from the injector looks good but I think that it could be smaller so I will make a couple more injectors with a smaller cone angle. This will be documented on the fuel injection thread:

https://www.modelenginemaker.com/index.php/topic,10603.0.html

The camshaft I am using is not the best, there is about 15 degrees of negative overlap and the inlet valve closes around 40° ABDC which does not help the compression pressure at cranking speed. It was a reject from the 25cc horizontal engine but was enough to prove the principal. I have started make a new one with a reduced angle between the lobes. It can't have too much overlap due to the limited clearance between the piston and the valves.

I will also need some cooling for longer runs. I think that thermosyphon with a computer cooling matrix will be enough initially. I can always add a pump if needed.
Best regards

Roger

Offline Don1966

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Re: 20cc Four Stroke Diese
« Reply #88 on: October 15, 2022, 08:37:12 PM »
Some great work Roger you are persistent. I Can everyone you that…… :Love:


 :cheers:
Don

Offline cnr6400

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Re: 20cc Four Stroke Diesel
« Reply #89 on: October 15, 2022, 09:01:01 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
"I've cut that stock three times, and it's still too short!"

 

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