Author Topic: 20 cc Horizontal 2 Stroke Diesel  (Read 82389 times)

Offline AlexS

  • Full Member
  • ****
  • Posts: 269
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #315 on: November 17, 2020, 07:19:19 PM »
I admire your patience. Just have read some of the previous building post of this engine (So many small parts that you have made and modified).

Have you ever tried to preheat the cylinder with a gas burner?

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3752
  • Søften - Denmark
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #316 on: November 17, 2020, 07:54:46 PM »
Quote
I think you are saying that greater oxygen content will cause more issues? If that were the case, you would expect supercharged and turbocharged diesels to run rough due to the excess air. If you were not, please ignore this post :)

No I was more thinking about how much air would flow into the crankcase (as in not enough). This usually requires a certain speed to do well enough and Roger might even get a better idle with a kind of open throttle Carb ala a troathy funnel (velocity stack) ....
But as my only diesel experience has all to do with not supplying the injector pump with enough fuel - problematic filters and lines on tractors and cars ....
I'm not really qualified - I just compare to my Two-stroke racing youth ....

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #317 on: November 20, 2020, 11:45:13 AM »
Thank you all for your interest  :ThumbsUp:

When I made the trials on this engine last year it would start after a long cranking period and accelerate to around 4000rpm. Changing the injection quantity at this point didn't seem to make a diference. I think that at this time it was running on fuel that was atomised by blowing past the piston and the speed was limited by the size of the air intake.

This time the response is rather different. I start cranking with the drill and then increase the fuel quantity until it fires. If I leave the fuel rack in this position and crank again I get a short burst of firing,often enough to kick the drill out and then it stops  :headscratch: I am thinking in two different areas:

Is it lacking induction air due to something? This would reduce the compression pressure so it will no longer fire (hence my thoughts about the air intake).

As the new injection pump has the fuel intake from the side rather than the top am I getting some form of cavitation when the helix reopens the inlet port to stop injection which is causing fuel starvation? I should be able to resolve this by pressurising the feed as I had to with the petrol injection.
Best regards

Roger

Offline john mills

  • Full Member
  • ****
  • Posts: 417
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #318 on: November 20, 2020, 12:35:37 PM »
just looking have been following  amazing  how you are making such a small fuel injection system
i would be wondering if the inrush of cold air as the engine starts lower the temperature so it no longer firers
is the cylinder warming up at all with the cranking and it starts firing.
john   

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3752
  • Søften - Denmark
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #319 on: November 20, 2020, 08:08:32 PM »
I know it can't be easy to start your engine with the force it requires to bring over the compression or the kick it gives when it fires .... but I can't help thinking / compare to how I usually start full size engines before FI - similar to what you describe Roger. Crank the it while slowly opening the throttle. You mention that this also start this one - but leaving it at the 'Starting Position' doesn't quite cut it ....

How about continue to open up while cranking or is this a bit of a handful on this one ?

If this is the case - how about a truely one way clutch / bearing and the starter fixed into position, so you only have to 'Press the Button' and have at least one hand free to 'manipulate the controls' ?

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #320 on: November 22, 2020, 08:13:18 AM »
Thank you for following along  :)

John, in last years tests it took a long time to start, partially due to heat build up and as I suspect the need to vaporise fuel past the piston.  This time it seems to fire after a couple of turns so I guess I am getting sufficient heat from compression. The engine heats up with the compression and firing but does not seem to run significantly longer when hot, maybe just a few seconds.

Per, I know that the injection system can deliver significantly more fuel than the engine requires at lowish speeds (550 rpm with the battery drill. I will have to make some tests at higher speeds to see if the output is linear) so I am cautious about overfueling and washing the oil off the cylinder walls. In some of the early trials the engine tightened up but as it is all cast iron luckily nothing seized. For the last video I just left the fuel rack in a position I knew would give a start but in other trials I have increased the fuel delivery without success other than blowing more unburnt fuel from the exhaust.

My next planned steps are:

-Make the injection timing more easily adjustable by moving the pump vertically. As the fuel volume is set by rotating the plunger this will stay fairly constant.

-Fit an air bleed screw at the injection pump inlet.

-Check if the fuel delivery is linear with speed or does it starve in some way.
Best regards

Roger

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #321 on: November 23, 2020, 06:51:56 PM »
Starting the timing adjuster. There will be a guide bar mounted just behind the cylinder that the pump body will slide up and down and an M3 screw at the tappet end to allow adjustment. Total range will be 3 or 4 mm coarser adjustment can be made with the existing system on the crankshaft. The fixings for the guide bar were drilled 1.5mm with the battery drill and freehand tapped M2 which was a little bit worrying.
Best regards

Roger

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #322 on: November 26, 2020, 08:04:04 PM »
A bit more on the adjuster. The pump was dismantled and the body drilled for the guide block, bleed screw and adjuster screw. The two supports for the adjuster screw were drilled and the set up was assembled with a 2mm rod to see how far out of position everything was.
Best regards

Roger

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #323 on: November 29, 2020, 07:59:48 PM »
When I tried tightening the fixing screws it was obviously not in alignment. The lower countersunk screw was proud so a few turns with the cordless drill fixed that  :) I also needed to make some clearance for the tappet guidance pin. The next step was to turn down the ends of some M3 all thread to make the adjusting screw. So far it all seems to fit  :) Next step is to make a new smaller guide for the control rack.
Best regards

Roger

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #324 on: December 01, 2020, 07:45:27 PM »
The next bits were a new support for the fuel rack and an adjusting knob for the timing. I need to look for a smaller knurling tool. After this a clean up in the ultrasonic bath, reassembly, and start the next trials.
Best regards

Roger

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #325 on: December 05, 2020, 03:36:33 PM »
It all went into the ultrasonic bath for a clean up and the pump was reassembled. I tried to determine the start of injection by judging the point when the intake port closed, using a vice to maintain the position whilst I ground a mark in the cam follower as a reference. I fitted the pump back onto the engine for some output trials but the cooking alcohol I use leaked out everywhere  :(
I dismantled the pump again and found a small nick out of one of the O rings where it had passed the inlet port. I tried to remove the sharp edges and also increased the lead in using an oversize centre drill that came in a set many years ago. The O rings didn't feel very elastic so I checked on the material spec. I had chosen Viton as it is very good with diesel, but closed study showed it is no good with alcohol :facepalm2: Nitrile would have been a better choice. I replaced both O rings and put it all back together for the trials which worked this time  :)
I measured the output at half rack and full rack position for 1 minute driven by the battery drill at 500rpm and for 15 seconds at 3600rpm with the mains drill. The speeds were measured off load. The results, converted to strokes were:
1/2 rack slow 500 strokes 0.5ml
1/2 rack fast 900 strokes 2.5ml
Full rack slow 500 strokes 1.8ml
Full rack fast 900 strokes 3.7ml

At full rack the output looks fairly linear with speed and is more than required. At slow speed it is 3.6mm3 per stroke. The calculated requirement is 2mm3 per stroke maximum.

At 1/2 rack things are not so linear but even at slow speed there is still 1mm3 per stroke.




Best regards

Roger

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #326 on: December 07, 2020, 05:15:32 PM »
Following some thoughts from Per I decided to make a trumpet (velocity stack, ram pipe, etc.) to smooth the inlet air flow. This was a fairly simply turning job from some 25mm aluminium bar. The final radius was cut with an edge rounding milling cutter clamped in the tool post on the grub screw flat. I had to mill some clearance for the fixing screw heads as the fixing screw centres are for a flange. I don't know if it will make any difference but it looks quite good  :)
Best regards

Roger

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3752
  • Søften - Denmark
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #327 on: December 07, 2020, 09:15:50 PM »
Looks good - let's hope it also has a positive influence on the running.

Offline cnr6400

  • Full Member
  • *****
  • Posts: 2728
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #328 on: December 07, 2020, 10:12:13 PM »
Sporty lookin' ! It may smooth out the intake air and increase the V a bit too.  :cheers:
"I've cut that stock three times, and it's still too short!"

Offline Zephyrin

  • Full Member
  • ****
  • Posts: 766
  • near Paris, France
Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #329 on: December 08, 2020, 09:42:13 AM »
I have great admiration for your perseverance on this project, the developments are exciting.

I remember an article published in "Maschinen im Modelbau", issue 3, 2006, about a functional 7cm3 true diesel engine, amongst a lot of jibber-jabber, I read that the fuel was injected at more than 100 bar in the cylinder, and few other technical details.
I can send a copy of the paper if you wish.

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal