Author Topic: 20 cc Horizontal 2 Stroke Diesel  (Read 48402 times)

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #240 on: December 22, 2018, 04:13:55 PM »
Some success :)  :) The weather was not so bad so I had another try. I was getting some combustion without ether and was able to optimise the timing, which was quite sensitive. I then played with the injector spring pressure. Interestingly the results improved as I lowered the pressure  :headscratch: Finally with  the adjusting screw on it's last threads I got a run  :D


If you look closely as it stops you can see the injector adjuster, spring and needle shooting out  ::)
Luckily all the parts could be found but I did not get much success when I put it back together, problem, the injection pump roller had failed again  :( A redesign is needed.
« Last Edit: December 22, 2018, 04:50:20 PM by Roger B »
Best regards

Roger

Offline Ye-Ole Steam Dude

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #241 on: December 22, 2018, 04:20:12 PM »
Hello Roger,

That is great news, boy that is an angry little thing when it does fire up. Just a matter of time now and it will be running as expected. Great job on your part  :praise2:

Have a great day,
Thomas

Offline fumopuc

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #242 on: December 22, 2018, 07:29:59 PM »
Hi Roger, really impressive. I admire your patience.
Kind Regards
Achim

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #243 on: December 22, 2018, 10:33:18 PM »
Even if only for a very short run - I would consider it a great success  :whoohoo:  as it shows that you are on the right track :praise2:

Yes it is a bit of a pain to have to remake some parts, but you do know for sure that some worked exactly as planed => improved confidence - and that goes from the rest of us following too  :cheers:   :popcorn:

Offline Dave Otto

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #244 on: December 22, 2018, 10:34:32 PM »
That's really cool Roger, congrats!

Dave

Offline Art K

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #245 on: December 22, 2018, 11:27:12 PM »
Roger,
This is great, even for  short run. One more revision should about do it. :cartwheel: happy dance time :)
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Graham Meek

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #246 on: December 23, 2018, 01:08:19 PM »
Hi Roger,

It has been a long journey, you are a whisker away from a reliable miniature true diesel. I bet old Rudolf had his set backs too. I too have often wondered about the injector spring pressure.

I am in awe of your achievement.

My best regards
Gray,   

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #247 on: December 24, 2018, 08:36:12 AM »
Thank you all for your support and optimism  :ThumbsUp:  :ThumbsUp:  :wine1: 

I have started modifying/repairing the various bits that failed. When the injector tappet roller pin fell out the end of the fork scored the cam. Luckily this is outside the normal working surface so I polished it and then case hardened the lobe. Next up was a locknut for the injector spring adjuster from a piece of 10mm hex brass followed by milling some 6mm spanner flats on the end of the adjuster. I made a new silver steel pin for the roller which is held in place with M2 nuts rather than E clips. Due to a momentary lack of concentration the head has four flats instead of six  :facepalm: but it will work. This was then hardened.

I will measure the compression/load on the injector spring in the 'running' condition and see if I have a spring that can give this mid range rather than at the limit. I think further trials with the different nozzle sizes will be useful as well as a further increase in compression ratio. The amount of unburnt diesel that comes out of the exhaust suggests that the spray is hitting the walls or piston  :headscratch:
Best regards

Roger

Offline cnr6400

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #248 on: December 24, 2018, 04:23:25 PM »
The new parts look great Roger! Hope this results in a great runner. Couple of questions re the design of the plunger:

1. Is the small slot in the plunger a keyway to control rotation of the plunger, and keep the bearing square to the cam? If so how close a fit is the key or pin in the slot?

2. How far is the plunger engaged in the block it runs in when the engine is assembled? Could play in the plunger to block fit allow the plunger to move too far sideways?

I'm asking about these things in view of what caused the mark on the cam in the last run. It almost looks like either the roller got angled to the cam and dived off sideways, or roller was still square to it but plunger and roller wandered off cam centre to the side, and jammed.

Great effort so far on this engine!  :ThumbsUp:

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #249 on: December 25, 2018, 08:11:17 AM »
Thank you for your interest  :ThumbsUp:

1. That is correct. The clearance is less than 0.1mm.

2. The plunger passes through a 10mm long block and is a close fit.

The score on the cam was caused when the pivot pin for the roller came out followed by the roller. One side of the fork on the plunger then dug into the cam. Due to the width of the cam the other side just missed. The pivot pin was retained by a couple of E clips which have failed before but just at cranking speed so there was no real damage. I am guessing that there is a slight difference in angle between the cam and the roller which is causing a side force on the pivot, but both times both E clips came off  :headscratch: Just one would be understandable.
This pin was another item copied from my petrol injection version where the forces are much less (same as the starting dog  :facepalm: )

I checked the compression of the injector spring in the final run which was about 1.5mm giving a theoretical opening pressure of ~15 Bar. This is the top end for the petrol injection spring so I can use that in the next trials. I imagine that with the short injection period, ~10-15░, and the 0.2mm hole the actual pressures are somewhat higher.
Best regards

Roger

Offline cnr6400

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #250 on: December 25, 2018, 04:07:44 PM »
Merry Christmas Roger!

Thanks for explaining re the questions. Your experience with e clips is similar to mine with them in industry. They were very much in fashion at one firm I worked for but eventually they were placed on the "restricted use" list in design reviews. In applications where the side loads are small and evenly distributed on the clip they work great, but where side loads are higher or unevenly distributed, not so much. We had a lot of spring loaded mechanisms with e clips jumping off and causing major product malfunctions. We did a lengthy investigation and found that variations in clip heat treatment, and in groove geometry (top and bottom rads and side wall angles), could seriously reduce the side load the clips could handle, and where mechanisms were spring loaded, there were unforeseen side loads from spring buckling during compression. Everyone had the mind set that springs exert their force straight along the axis of the spring- not so in real life at all, there can be forces in many axes at the spring end! If these uneven or angled forces act on an e clip its' side load carrying capability drops dramatically and it is only a matter of time til it jumps out. One rough fix which was effective in some cases was to use the next OD size down clip for a given shaft diameter, and an extra deep groove. This gave more side wall to clip engagement. The clip manufacturers used to publish a fair bit of info on groove geometry and permissible loads. Not sure if they still do. The loads are not so easy to estimate or measure in model engine work though.  I think your bolt and nut approach for roller holding on the engine plunger is a good one since it will carry lots more side load than e clips.

Regarding control of the roller angle to cam - not sure exactly what dia your plunger is, but if the plunger is say 6 mm dia / 3 mm radius and the keyway to pin has 0.1 mm clearance, doing the trig, the roller could be angled at 1.91 degrees to the cam by the slot to pin clearance alone. (inv tan (0.1/3)) I think this may be a significant angle. An idea that occurred to me for a way to control it better would be to add a dowel pin at 90 degrees to the plunger just behind the roller, if there is room. This dowel could extend up or down to fit in a slot in the base or the cylinder assy to keep the roller as close to 90 deg to the cam as possible. The longer the pin is, the smaller the angle of rotation. For example if the pin was 10 mm from end to plunger centre the angle goes to 0.57 degrees with same 0.1 mm clearance pin to slot.

Good luck with the next run!

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #251 on: December 27, 2018, 04:02:16 PM »
Thank you  :) I think the problem with the E clips may have been that they were being pushed by a cylinder rather than a flat surface  :headscratch: I have used them as valve retainers without problems but there they are supported by a flat surface.

I had another try Today. I did run but adjusting the fuel rack had no noticeable effect  :headscratch:  :headscratch: As planned it stopped when I put my finger over the (very accessible) air intake which was the back up in case of a runaway. May be I have got the phasing of the helix with the rack incorrect  ::) It is definitely firing on the injected fuel as when the tappet started stick again it would stop instantly ( I did wonder at one point if it was running on the lubricating oil).


Apologies for the poor handheld video.

Next step: a weeks quarantine in the garage and then into the cellar to dismantle the injection pump and see what is happening.
Best regards

Roger

Offline cnr6400

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #252 on: December 27, 2018, 08:48:47 PM »
Hi Roger, the latest run was great!  :ThumbsUp: :ThumbsUp: I think you are very close to having a reliable runner now. Standing by with the  :popcorn: for the next run!

The attached picture is of a Goold, Shapley and Muir 22 hp twin engine built around 1910 in Brantford Ontario Canada. They used a unique guide fork to keep the cam follower and end of pushrod lined up to the intake cam.  A fork on either side of the cam rode on a wheel with a close fit. This kept the follower on the straight and narrow. Simple but elegant solution. Just a thought in case it turns out the plunger is cocking and jamming in its' bore. Maybe you could do something like the GSM fork on the diameters beside the cam lobe? It would a) keep the plunger square and guide its' back end, b) would keep the roller dead square to the cam. Only food for thought.
« Last Edit: December 27, 2018, 08:59:30 PM by cnr6400 »

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #253 on: December 29, 2018, 08:48:48 AM »
Thank you Jeff  :ThumbsUp:

I think that I have a clue to the cause of the problem. When the engine is turned by hand there is clearance between the locknut on the roller pivot and the aluminium mounting plate. Having made the last test runs there is a definite impact mark between the two so the follower must be rising above the cam. This unbalanced force could then slightly distort the fork  ::)

Thinking about it the lack of response to the fuel rack was probably due to moving from 'too much fuel' to 'even more fuel' which was just being sprayed everywhere from the exhaust. Although I tried to maintain the relationship between the helix and the rack after the first sticking plunger problem it must have moved  :facepalm: The engine revs are being limited by the porting, which I noticed when it rans as a petrol engine.

When I can bring it back into the cellar I need to make some measurements of the output of the fuel injection and lubricating pumps. I have ordered some 10ml measuring cylinders and have a smaller Veeder counter I can attach to the end of the crankshaft to allow me to measure output per 100 revolutions (or more?).
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #254 on: January 03, 2019, 07:20:44 PM »
The diesel that came in from the cold.

I bought it back into the cellar and was able to take some measurements. The Veeder counter could not keep up with my battery drill at 550 rpm and died so I just worked on time. Zero fuel was certainly not zero fuel and max fuel was definitely more than I needed  ::)

As I dismantled the system there were obvious overshoot and impact marks in several areas. The actual cause of the jamming was impact from the end of the injector plunger on the tappet body. A quick twist with a 5mm reamer got everything moving properly again but I need to sort out the various strokes and clearances as well as rephasing the helix.
« Last Edit: January 03, 2019, 07:30:08 PM by Roger B »
Best regards

Roger