Mini diesel engine.

[minh-thanh]

Hi All !
Yesterday, I watched some mini diesel engine on youtube, they are great.
a fleeting thought, it could be the next project when i finish V4 (my V4 is not done yet)
I have a few questions:
With mini diesel engine , compression ratio so it can run ?
How much should the oil pressure be?
What time should oil be sprayed on the compression stroke ?
Thanks !

 

[Peter Twissell]

Are you proposing a direct injection diesel?
I expect production of miniature injectors would be a challenge.
Oil pressure is similar to other IC engines, but the journals may need to be larger.
Compression will depend on the heat loss from the charge to the combustion chamber. In small sizes, this can be another challenge. Small 2 stroke diesels use ether or similar in the fuel to help with ignition.
Injection timing is similar to spark timing in a petrol engine.

 

[minh-thanh]

Thanks Peter Twissell !
Yes, a direct injection diesel
It looks like :

Regarding the challenges of making small diesel engines such as injectors, ..., I have read the discussion about it on this forum, it is really a challenge. I hope there are more comments, advice and information

 

[petertha]

Sure runs nice. Some details of the injector here on his website. I don't quite understand the plunger / ball valve interaction but maybe the pictures will be more meaningful to some of you.
http://findsminimodelhotbulbengines.dk/Aboutmymodelmaking.html

http://findsminimodelhotbulbengines.dk/truedieselengine/truehorizontaldieselmode.html

 

[minh-thanh]

petertha !
Thanks for the link , He has great diesel engines. I wish, someday, I could do it like he did.

 

[petertha]

He has a contact email address on his home page, maybe plans are available or he could elaborate on the injector for you.

 

[minh-thanh]

petertha !
Thanks for the suggestion!
I will send email him .

 

[Stefan-K]

You can try to email him, but i know that He won't give out any Kind of technical Information or Plans. He said this several Times in his Videos, which are very hard to understand, because his englisch speaking sounds very "danish ". So you have to watch his Videos a couple Times to understand them once.
But if you do, you will find some usefull information there.

 

[minh-thanh]

Stefan-K !
Thanks for the information, I will not waste any time waiting .
I have a question: if the air pressure in the cylinder reaches its maximum when the piston is at TDC (eg 1 bar), how much oil pressure must be achieved to be able to spray into the cylinder?
If you have not made small diesel engines, don't be afraid to give the answer. If you have experience with large diesel engines, can you tell me how much oil pressure should be greater than the cylinder air pressure?

 

[timar]

Stefan-K !
Thanks for the information, I will not waste any time waiting .
I have a question: if the air pressure in the cylinder reaches its maximum when the piston is at TDC (eg 1 bar), how much oil pressure must be achieved to be able to spray into the cylinder?
If you have not made small diesel engines, don't be afraid to give the answer. If you have experience with large diesel engines, can you tell me how much oil pressure should be greater than the cylinder air pressure?

6.25 bore caterpillars: cranking compression 350 psi. Fuel injection valve (nozzle) opening pressure spec (bench test) 400 - 750 psi. Hope this helps. These were pre combustion type engines

 

[Ironman2]

The pintle type injectors fire at 1323psi on a single cylinder Lister engine I have.
A cam actuated pump will give you all the pressure you need.
If you remember math figuring hydraulic piston forces. Think of the pintle as a piston, with a surface area of a few thousands, (the spray hole) so a spring can keep the injector shut against compression. The injector pressure is needed to open the pintle and to vaporize the oil.

 

[Peter Twissell]

Fuel pressure is more a function of the requirement to deliver sufficient fuel through the injector in the short time available.
This is, of course, nett fuel pressure, so the difference between gauge fuel pressure and cylinder pressure.

 

[minh-thanh]

timar !

6.25 bore caterpillars: cranking compression 350 psi. Fuel injection valve (nozzle) opening pressure spec (bench test) 400 - 750 psi. Hope this helps. These were pre combustion type engines

That's the information I desperately need, I don't have a big diesel engine to check, I just need to know how much oil pressure is greater than the pressure in the cylinder and then I'll calculate it proportionally on the small engine.

Ironman2 !

If you remember math figuring hydraulic piston forces. Think of the pintle as a piston, with a surface area of a few thousands, (the spray hole) so a spring can keep the injector shut against compression. The injector pressure is needed to open the pintle and to vaporize the oil.

Thank you for explaining how injectors work
I'm also learning about how injectors work ...


timar, Ironman2 , Peter Twissell !

Thank you for taking the time to reply and information!
I think I should try to make the pump and injectors to test ... before I can start with a mini diesel.

If anyone has any other information, please discuss it
It could be a mistake when you make a small diesel, or whatever

 

[timar]

Yanmar makes small diesels, L40 may be one to look at for ideas, or possibly adapt to the engine you are building. I have seen the injector and pump on the internet for under $50

 

[minh-thanh]

Yanmar makes small diesels, L40 may be one to look at for ideas, or possibly adapt to the engine you are building. I have seen the injector and pump on the internet for under $50

I think it is quite large with a cylinder about 20 mm

 

[timar]

Thought it might be a point of reference for injector & pump design

 

[minh-thanh]

Thought it might be a point of reference for injector & pump design

A good idea !
Thanks .

 

[timar]

Minh Thanh,
Google disa.it
On the top left you will find “ history of fuel injection”, click on chapter 1. There is a lot of information that you may find helpful

 

[minh-thanh]

Hi ALL !
After learning and thinking, I decided: the diesel mini engine will be my next project
It will be a project that sounds hard to succeed and takes a lot of time and there will be many parts that will be in the trash, so if anyone reads and is interested in this project please wish me : " good luck"
I will make injectors and pumps and hope it's okay and will post results in this thread !

 

[Cogsy]

Good luck Minh - I'll be watching with interest.