Author Topic: 20 cc Horizontal 2 Stroke Diesel  (Read 48435 times)

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #270 on: February 02, 2019, 03:15:57 PM »
The temperatures eased a little today so I had a play  :)

In the first video I slowly raised the fuel rack until it started and then gradually lowered it until the engine stopped. In the second clip I tried the same but the fuel didn't shut off and I had to choke it. I also did a quick speed check and it seems to settle down around 4 000rpm  ::)



So it will have to sit in quarantine in the garage for the next week before I can investigate the fuel pump again  :headscratch:
Best regards

Roger

Offline Kim

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #271 on: February 02, 2019, 08:43:56 PM »
So, what's the quarantine for?  Is your shop inside, and the engines smell too bad after they've been run?

Just curious,
Kim

Offline yogi

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #272 on: February 02, 2019, 09:50:39 PM »
Progress!!! It's fun to watch how that project came along.  :popcorn: :popcorn: :popcorn:
Looking forward to the next step... Thanks for sharing Roger.  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #273 on: February 03, 2019, 10:19:44 AM »
Thank you both  :ThumbsUp:

Kim, my workshop is in a communal cellar so I have to be very careful not to upset the neighbours, checking my shoes for swarf before going out etc. The diesel does smell quite strongly at the moment after running but hopefully that will improve as I improve the combustion.

Looking back at yesterdays runs I think I will make another cylinder head with a further reduction in volume. The theoretical compression ratio is already high, around 28-1, but being a two stroke the cylinder filling is probably not that good  :headscratch: I will also go back a try the larger injector nozzles again. It seems that the original lack of combustion was due to insufficient compression temperature rather than poor atomisation  :thinking: I may also need to think about limiting the lift of the injector needle as the needle opening increases the fuel volume in the injector.

However after a couple of Fohn days the snow has come back so the R+D department is closed again.
« Last Edit: February 03, 2019, 11:59:05 AM by Roger B »
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #274 on: February 10, 2019, 07:38:21 AM »
I bought the engine into the cellar and dismantled the injection system. The cam follower bearing had failed, possibly as I had continuous contact for the last trials  :headscratch: The helix plunger was still ok  :thinking: I then removed the cylinder head, everything was black and oily but otherwise ok. I turned it over a couple of times and got a fine mass of black gunge that can only have come from the transfer port. That's probably why it wouldn't stop the last time  :facepalm:

Next steps:

Make an oil return line from the crankcase.

Skim another 1 - 1.5mm from the cylinder head.

Check the 0.5mm nozzle and make a new 0.35mm nozzle
Best regards

Roger

Offline bent

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #275 on: February 11, 2019, 06:12:27 PM »
Roger - did the bearing fail by losing a couple of balls, or did it gall/seize?

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #276 on: February 11, 2019, 07:06:34 PM »
It looks like it failed due to side pressure, I think one ball is missing and the cage looks distorted. Needs more investigation  :thinking:

I drained most of the gunge out of the crankcase and the started on the drain fixing. I could have completely dismantled the engine and clamped the crankcase to an angle plate or used a slightly risky setup  ::) With the engine held in my largest vise I started off, planning to minimise the amount of swarf in the crankcase. First a flat with my largest center cutting end mill, than center drill and drill 4mm, but not right through. Next a counterbore as it is guided/supported and finally right through with a 4.5mm drill.
« Last Edit: February 12, 2019, 07:23:41 AM by Roger B »
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #277 on: February 11, 2019, 08:16:47 PM »
The last step was to tap M5x0.5 for a union, followed by carefully cleaning any bits of swarf from the crankcase. I made up short connecting pipe and started re assembling. It's interesting that a 2mm hole is sufficient to destroy the crankcase compression at low speeds in the same way that a 0.35mm hole in the injector was enough to destroy the compression in the cylinder  :thinking:
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #278 on: February 16, 2019, 08:09:15 AM »
The non return valve was made from 6mm hex rod with a 2mm bore and 3mm ball. The cage was a cross cut in the union with a junior hacksaw. I put a length of clear tube on the outlet and spun the engine will the drill for a few minutes and was rewarded with some gunge  :) There also seemed to be a lot of air so I may need to add some restriction after the valve :thinking:
Best regards

Roger

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #279 on: February 16, 2019, 04:50:21 PM »
So what we see in the last picture is from the bottom of the crankcase then .... if so, quite a bit more than I would have expected .... but it certainly explains the extra smoke when you run it + to some extent its unwillingness to stop when you cut the fuel.

I hope this helps you back on track with the next run  :cheers:

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #280 on: February 17, 2019, 05:02:48 PM »
Thank you Per  :ThumbsUp: As ever more to learn  :headscratch:

When I drew the thinned down version of the current head the combustion  chamber was looking rather pancake like so I decided on a 8mm bore 8mm deep version. The bumping clearance was a little large, I have been aiming for ~0.5mm, so I had to skim 0.2 mm off the face. I then stared thinking about the clearance volume between the piston and the head  :thinking: 0.5 mm is not much but it is a reasonable area. A quick calculation gave a volume of 0.25cc, a significant amount compared to the combustion chamber  :facepalm:
Recalculating gave the (using the swept volume after the exhaust port closes, 15cc) original compression ratio as 16-1, the next step as 20-1 and the new head as 24-1. This is more in line with the measured compression pressures. With the new head and cranking at around 2000rpm I was getting nearly 40 bar  :)
I now need to make a new 0.35mm nozzle and wait for the R+D department to be open for the next trials.
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #281 on: April 07, 2019, 09:07:46 AM »
A quick catch up on the trials and tribulations of this engine. I made a new 0.35mm nozzle using the floating reamer holder for the D bit and waited for better weather.

The initial trials with the new cylinder head were not so good. It would fire but not sustain running. I also tried with the 0.35 nozzle again without success. There was a definite optimum timing point but I need to develop a way to accurately measure this  :headscratch:

This set of trials came to a stop when the repair sleeve under the starting dog failed  :( There was no significant damage to the crankshaft so I suppose it served it's purpose as a mechanical fuse  ::) I made and fitted a new sleeve.

The 8mm bore combustion chamber did not seem to be successful so maybe a thinner 10mm chamber will be better. I didn't want to modify the existing one that had given the best results and so started on another new head.
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #282 on: April 07, 2019, 09:13:14 AM »
The head was machined much as before. When I removed the 8mm chamber from the engine to check the bumping clearance of the new one there was an interesting soot free band at the start of the cone  :thinking: Does this mean that the injection spray was mostly hitting the sides of the combustion chamber and this are was in a shadow? Was this area being washed off by the fuel spray?
Best regards

Roger

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #283 on: April 07, 2019, 09:13:26 PM »
Guesswork on my side, but .... for some reason a region where you do not have combustion.
Racing engines often use shapes that provide (thin) layers of air that don't have any combustion in order to keep those areas cool - so perhaps you created such an area by accident  :thinking:

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #284 on: April 14, 2019, 09:06:16 AM »
I fitted the new cylinder head and checked the compression pressure which was around 30 Bar. This seemed a little lower than with the 8x8 chamber which theoretically had the same volume. I wondered if the cone angles were incorrect and made a pair of templates from some offcuts. All seemed to check out OK so I remeasured the compression pressure with all the existing heads.
The original cast iron head gave around 20 Bar.
The first reduced volume ali head gave ~25 Bar.
Both next stage heads gave around 30 Bar.
The higher initial reading I got with the 8x8 chamber may have been due to excessive oil in  the system  :headscratch:

Yesterday had some moderate weather ~11C (it's snowing again today) so I gave it a try. I couldn't get any runs with the 0.35mm nozzle and changed back to the 0.2mm one. This gave similar runs to before including the tendency to keep running after the fuel rack was moved to zero delivery position  :thinking: I wonder if the fuel is getting past the piston into the crankcase and is then being 'carburated' before coming back into the cylinder and firing  ::)

I made a couple of trials with less fuel delivery and think there may have been signs of 'real' operation but not really sustained.




Best regards

Roger