Author Topic: 20 cc Horizontal 2 Stroke Diesel  (Read 55917 times)

Offline AlexS

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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

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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 ....

Offline Roger B

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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

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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

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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' ?

Offline Roger B

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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

Offline Roger B

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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

Offline Roger B

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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