Mini diesel engine.

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Chaffe

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Hi Chaffe !
One question I can only answer: I don't have any pressure readings at the moment
Sorry !!
I will buy a pressure gauge and will check
When I made this diesel engine, the Covid epidemic situation increased, so my place was completely lockdown, I could only test the injectors and pump with the engine., I could only trial and error and do everything the best thing possible.
Until the epidemic situation showed signs of abating, I could only buy back a small copper pipe from a friend that he had left over, but I still couldn't buy a pressure gauge., again I can only test the injectors and pump with the my engine and based on my experience and judgment
Trial and error, adjust...... until the engine feels like it can "run"., and trial and error, adjust..... until the engine run
I can't watch your video
 

Chaffe

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I have done some maths and I think 40 bar injection pressure will work with 45 degrees injection timing. Cylinder pressure at that point will not be high. The injector should withstand 650bar cylinder pressure with that spring too, assume 8kg spring and the size nozzle I am running.
 

minh-thanh

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Your pump produces pretty good pressure !
Do you have oil leaks between the cylinder and piston or in the joints ?
I plan to buy a pressure gauge to measure the pressure in the cylinder and also the pump
Do you have any suggestions for pressure gauges ?
 
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Chaffe

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Your pump produces pretty good pressure !
I plan to buy a pressure gauge to measure the pressure in the cylinder and also the pump
Do you have any suggestions for pressure gauges ?
Thanks, I think it will be adequate, I will now continue work on my engine and try complete the project in 2022….
As for gauges this was surplus’s from a job at work, but something off eBay would do? I don’t think you will need one above 100 bar… but you never know!
 

minh-thanh

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Thank you !
Do you have oil leaks between the cylinder and piston or in the joints ?
 

Chaffe

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Thank you !
Do you have oil leaks between the cylinder and piston or in the joints ?
No leaks at all so far, the screwed connections were surprisingly easy to make successfully. It will hold 40 bar (500psi) for several seconds too, which is promising.
I will focus my efforts on a 40 bar injector and then the engine itself now.
 

minh-thanh

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Looks like you're one step closer to building an diesel engine of your own
Please update when there's something new !
 

Chaffe

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Looks like you're one step closer to building an diesel engine of your own
Please update when there's something new !
I will do, I don’t have the time or inclination for a full thread, but will certainly highlight any new breakthroughs.
 

Bentwings

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You may have to get automotive gages I’ve been looking for model steam gages for some time too. I might just be too picky in what I want and need. Automotive gage prices have gone up dramatically in price just in the last year. I don’t know what small engines might require . I know my one ton dusky Cummins has pretty high around 2500 psi. The lift pump I only about 10-15 but that is just supply to the high pressure pump. . I have not dealt with model diese excep early model airplane ones Davis diesels they did not use high pressure pump just enter based fuel they had adjustable compression so they did operate as “real” diesel or compression ignition.
byron
 

Chaffe

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A gauge is a gauge, as long as the range is correct it will work fine.
 

Gedeon Spilett

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Looking at the plan of your diesel engine, I wonder why the ratio stroke/bore reaches 2, is it for simple geometric reason to get high compression ratio or a thermal explanation underlies this choice? I know that many very old diesel had also a similar ratio, and other early engine too !
I'm not yet ready to the challenge of building one, i'm afraid to loose motivation during the test of the injector and pump, I'not a young man.
 

minh-thanh

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Hi Gedeon !
Looking at the plan of your diesel engine, I wonder why the ratio stroke/bore reaches 2, is it for simple geometric reason to get high compression ratio or a thermal explanation underlies this choice? I know that many very old diesel had also a similar ratio, and other early engine too !
Simply: High compression ratio and including heat
The higher the compression ratio, the higher the air is compressed and more heat is generated due to the compression
And....I plan to make some engines that I like in that ratio

I'm not yet ready to the challenge of building one, i'm afraid to loose motivation during the test of the injector and pump, I'not a young man.
Young or old doesn't matter !!
Do think of making a diesel engine as a "game" and you are playing with it
Don't try to think it's too complicated or too difficult....
Although I succeeded, but if I make the new injector and pump: I will definitely have to redo a few times to get the injector or pump good enough.
Please be patient !!!
 

gg89220

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I'm not yet ready to the challenge of building one, i'm afraid to loose motivation during the test of the injector and pump, I'not a young man.
vas y Gedeon,lance toi !!:D
 

Gedeon Spilett

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Thanks Minh-Thanh for the answer, I 've got it.
It also has to do with the low rpm that diesel engines have.


hi gégé, I don't want to break your priority, buddy ! go head
actually I think I'm chickening out...
 

krakkah

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Well - - - in reading your attached url - - - it does say - - - - 'no relationship
with actual diesel engines' .

I've run into a lot of different kinds of engines but never a high compression
otto cycle engine with hot bulbs.

Wonder why they would even want to make an engine like that chain saw
with the hot bulb. Maybe so that kerosene could be used.

Know that in extreme cold temperatures the 'gasoline' formulation is modified
so that everything works well.

I will - - - still - - - maintain that a real compression ignition engine does NOT use a carburetor.
(Notwithstanding certain anomalous variants!!)
If you know any history behind how typical diesel injection came about, youll know Rudolph Diesel himself almost killed himself using a carburettor style fuel supply. Which is why he invented the injector. But for small stuff a carby works.
 

minh-thanh

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Hi All !

Sharing some of my diesel discoveries:
1/ Injection time: More precisely the time the lobe begins to contact the pump piston: 22 to 45 degrees before TDC
2/ Engine runaway : Should be worried?
If your design calculates lobe timing, intake and exhaust ports....exactly like a full size diesel engine then you should worry. But with a small engine you can easily stop the engine.
With many tests, my engine can not runaway
3/ Injection : Fuel vaporization-Atomized fuel . How to inject fuel
3A/ Fuel vaporization-Atomized fuel : It is necessary but not all.
Fuel vaporization-Atomized fuel will give you an objective view of the efficiency of the pump and injectors: the pressure generated by the pump, the tightness of the injectors....and when the engine is running it will have very little smoke.
" Not all " because when i make some test with my engine the injectors just "inject " fuel - as in the picture (Some cases are even worse)- -and the engine is still run

1.jpg

. This leads to 2 cases: a/ the engine runs but a lot of smoke and some unburnt fuel (it looks like mud) comes out the exhaust pipe and b/ the engine a lot of smoke . Solve this problem: simply increase the compression force of the needle spring
3B/ How to inject fuel :
fuel injection : radiates from the center - good
Fuel injection is left or right: it doesn't matter
With a full size diesel engine, the fuel vaporization-Atomized fuel, the fuel injection, ... needs to be really good because it concerns the performance ... of the engine, and that's what is really needed.
But with a homemade diesel engine, you can stick to that rule if you want, and that's how I do it with my engine.
If you only need one engine running then it shouldn't be too important. And the engine has running, you can easily adjust the injectors...to make the engine run better

One important thing is : the injector must be completely sealed .
If the injector is not completely sealed it will affect the pressure in the cylinder and the oil pressure in the oil pipe
Hope this gives those who are or intend to build diesel a little more confident
 

Badhippie

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One thing that has not been mentioned that I have seen in this thread. The normal diesel exhaust should I say all diesel exhaust has a very nasty chemical it produces. You can’t get rid of it but you sure in the hell can make it worse by incorrect injector timing, a dripping injector, incorrect pump to engine timing etc.
The chemical a Diesel engine exhaust produces is sulfur this is a by-product you of combustion process. Then you add another by-product that every engine in the world produces is moisture. Then you add moisture to sulfur and what do you have?? A great little product called sulfuric acid. This is just something for everyone to think about when building a Diesel engine. With proper maintenance of the engine it’s should never be a problem. But without proper maintenance it becomes a huge problem. I have actually seen rod caps,rod studs and other items either eroded or eaten all the way thru and cause catastrophic engine failure. Just wanted to throw that out there and let you all soak that up
Thanks
Tom
 

Steamchick

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Hi Tom. I went to a presentation by Caterpillar (they make big engines and big tractors and earth moving plant that use the engines). The guy presented a talk on use of their engines for NON- earthy applications. Eg. Generators using industrial waste as fuel. One of the worst was sewage plant gas. It was so full of sulphur that the engines were corroded (exhaust valves ports, etc.) in 1/10th of the "normal" plant useage with diesel fuel. But they also had generators burning chaff from granaries, sawdust and other dust of particulate organic hydrocarbons. Some of those were particularly toxic to engines, and needed huge exhaust gas treatment plants. He reckoned he had the highest order book for spares of any engineer! So we should be thankful that DERV is such a clean (cleverly engineered) fuel.
And did you realise the nitrous oxides made in diesels form nitric and nitrous acids? As bad as the sulphuric and sulphurous acids! Yet the planet will be destroyed (So we are taught) by Carbon dioxide, which when dissolved in water makes Carbonic acid! We are on a hiding to nothing!
Enjoy modelling!
K2
 
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