My new project ...Small diesel engine .

[Steamchick]

Tony M. I agree he didn't really purge the fuel lines and injector of old fuel before proving the road fuel was an OK starter....
But the engine is still a fantastic model.
K2

 

[minh-thanh]

I'm not convinced by the video. I imagine that when he restarted there was a fair bit of original fuel in the pipework and even some in the bottom of the tank despite the ''bleeding''. That takes nothing away from his fine engines even if they are normally running on higher grade fuel.

Yes, there are many problems with his information
For those looking to build a diesel engine: check out his videos as a reference for designing your own engine. But if you use his information as a standard to build your engine - then I'm sorry, you will go down a dead end path.
I confidently tell you that because:
Here is my pump cylinder, I use a tool rod as a plunger - I do not use o-rings for plunger - and my fuel pump creates enough pressure to pump fuel into the cylinder at about 23 to 25 before TDC

He can't, he uses an o-ring for the plunger and has to set the fuel pump timing at 45, 50 degrees before TDC
You don't need to believe what I say, but you must believe in the principles of a diesel engine and no one can change that principle. At least the auto-ignition temperature of the fuel you want to use
Designing and building a diesel engine is an extremely difficult task and don't make it complicated and impossible for everyone and that's something I really hate

 

[petertha]

There is an interesting YouTube video by 'Smarter Every Day' called Why Fuel Injectors are Awesome (28,000 fps Slow Mo).... Seeing those teeny, tiny injector holes spray mist/droplets over millisecond pulse duration at 2-3 Kpsi is very interesting. Spoiler alert, he breaks out the torch for some exciting flames! I can see where miniaturization would be very challenging scaling that by 1/4 or whatever. Yet progress is being made. Never discount a dedicated model engineer on a mission! LOL. I have a gut feel that fuel type must play some significant role. When I look down the venturi of my methanol or gasoline engine, its a liquid firehose stream by comparison, yet atomization/vaporization occurs within inches to a combustible mix & the engine runs. Real diesel is even more viscous & less volatile by comparison.

 

[peterl95124]

I'm not convinced by the video. I imagine that when he restarted there was a fair bit of original fuel in the pipework and even some in the bottom of the tank despite the ''bleeding''. That takes nothing away from his fine engines even if they are normally running on higher grade fuel.

I've built a working gasoline + spark ignition version of a Hansen Vertical, after I got the carburetor venturi correctly sized I can start it by hand, and at the recent Golden Gate Live Steamers show even some enthusiastic kids were able to start it by hand,

but I'm now working on a true diesel version, and with 20:1 compression its very hard to turn over by hand, its on the back burner so to speak (so many engines and so little time ! ), but I'll be very surprised if I end up being able to start it by hand.

 

[minh-thanh]

but I'm now working on a true diesel version, and with 20:1 compression its very hard to turn over by hand,

I've noticed that since I started watching his videos. With engines with compression ratios of 18-1, 20-1: it is very difficult to turn the flywheel by hand.

), but I'll be very surprised if I end up being able to start it by hand.

And the compressed air in the cylinder will reach the auto-ignition temperature of the fuel you will use???? (210 degrees Celsius with kerosene) . What temperature will you achieve?? 70, 90 or 100 degrees Celsius ???

A lot of information is "strange " to me
On the internet, I don't care what someone will think of me, I wouldn't share if I wanted to, But when I say it has to be exactly what I did with my engines
Building a diesel engine is not easy
You have the right not to share,That is your right ,BUT you should not give information that confuses new people !!!!!!!!!

 

[minh-thanh]

There is an interesting YouTube video by 'Smarter Every Day' called Why Fuel Injectors are Awesome (28,000 fps Slow Mo).... Seeing those teeny, tiny injector holes spray mist/droplets over millisecond pulse duration at 2-3 Kpsi is very interesting. Spoiler alert, he breaks out the torch for some exciting flames! I can see where miniaturization would be very challenging scaling that by 1/4 or whatever. Yet progress is being made. Never discount a dedicated model engineer on a mission! LOL. I have a gut feel that fuel type must play some significant role. When I look down the venturi of my methanol or gasoline engine, its a liquid firehose stream by comparison, yet atomization/vaporization occurs within inches to a combustible mix & the engine runs. Real diesel is even more viscous & less volatile by comparison.

Don't expect fuel atomization with the 10cc diesel
Take the hole in the injector of a 100 cc engine and you reduce its size by a factor of 10. If you can do that with what you have on hand then you can achieve fuel atomization.
Mist spraying is ok .

 

[Roger B]

Small diesels are interesting. There are many different possibilities starting with the model aircraft type using compression ignition of a carburetted mixture of kerosene (paraffin), oil and ether. There was the Lohmann commercial moped engine that used an 18 cc carburetted compression ignition engine with variable compression running on diesel fuel.

Page 120. 1953 Lohmann Diesel 18cc engine. SOLD

There have been many attempts at a model ‘true diesel’ which I define as the fuel being injected into air heated to sufficient temperature to cause ignition with the fuel sufficiently atomised for almost instantaneous ignition.

If the fuel is injected during the induction or compression stroke it can become sufficiently vaporised to be ignited by the heat of compression. I think some of the models work like this.

To achieve ignition of straight diesel oil the air needs to be compressed to around 30 bar (450 psi). The compression ratio required to achieve this is somewhat complex. The simplistic combustion chamber volume divided by the swept volume + the combustion chamber volume formula is inadequate. The compression starts when the inlet valve closes, which depending on the valve timing, can significantly reduce the effective swept volume. Heat losses will also reduce the effective compression. A simple almost spherical combustion chamber is best, a complex pre-chamber is the worst (but has other advantages).

Once you have the temperature for ignition you then have to atomise the fuel into the high temperature and pressure air. This was one of Rudolf Diesels biggest problems and is why he went for air blast injection. I have experimented with several injector designs, the current one being a fairly prototypical needle type with a removable nozzle. Keeping everything concentric is a problem. The fuel pump has a 2mm plunger with metering by a helix. The injection pressure is around 100 bar (1500 psi) measured using a test pump with a 2mm bore and a spring balance to determine the force. The injector nozzle has a 0.2mm (8 thou) orifice.

This is a video of my 25 cc four stroke diesel cold starting. I gradually move the fuel rack to increase the fuel delivery until it starts. Atomisation is still not very good as you can see by the amount of unburnt fuel coming out of the exhaust.



This is a test of the atomisation using my hand operated test pump.

 

[minh-thanh]

Hi All !
I just tried making a cylinder with a diameter of 1.8mm : Failure

Sometimes: knowing enough is good! !
I will do the diameter that I had success with : 2 or 2.2mm

 

[minh-thanh]

Hi All !
An update :
With the purchase of small drill bits for a project and with helpful informations from @Roger B , I decided to change the injector design.
Thank you @Roger B .

Old: left ------ New: right

 

[minh-thanh]

Hi All !
I bought round toolbar 2.2mm HSS on AliExpress to make a plunger for the fuel pump
Today I checked...and the result: All of them are bent.
I reported it to AliExpress, hopefully I get my money back
Making an engine is difficult and finding a place to buy a good enough product is much more difficult

 

[timo_gross]

Hi All !
I bought round toolbar 2.2mm HSS on AliExpress to make a plunger for the fuel pump
Today I checked...and the result: All of them are bent.
I reported it to AliExpress, hopefully I get my money back
Making an engine is difficult and finding a place to buy a good enough product is much more difficult

View attachment 155589

That is odd. The HSS blanks I bought from SUS were always straight (as far as I could measure or see)
How long do they need to be? The ones I have are 57 mm long. A pack of 10 costs about 10 USD. Can buy them one by one.
https://www.suspt.com.tw/drill-blanks-b-102.html

p.s. maybe they got wet during storage or transport

Or they are "angle drill blanks".
https://etel-tuning.eu/produkt/90-bohrer/

 

[minh-thanh]

I don't know why, but it's really bad, far beyond my imagination
I will buy according to your suggestion...Just hope they can ship to where I live
Thank you .

 

[minh-thanh]

p.s. maybe they got wet during storage or transport

Or they are "angle drill blanks".
https://etel-tuning.eu/produkt/90-bohrer/

Maybe .....

 

[Steamchick]

Or maybe they were cut from coil stock, not straight stock? I had that recently.
But I also have had ceramic plaques and bar stock that were "bent" during transit. (The ceramic was like a jig-saw puzzle where it had been "folded". The supplier thought it was my fault for receiving the goods, but Ebay insisted he refund me. Yet he still requested a 5 star rating from me, because he thought the ceramic was OK just in a flimsy package, because it felt strong!).
"Sic transit gloria"?
K2

 

[Roger B]

I have not had a problem with bent silver steel (drill rod) but I did have a piece that was not round, trilobar, which measures correctly with a micrometer but won't fit through a hole of the specified diameter.
After that I moved to using pin gauges to make my injection pump plungers from. They cost a bit more but are already hardened and lapped.

 

[minh-thanh]

but I did have a piece that was not round, trilobar, which measures correctly with a micrometer but won't fit through a hole of the specified diameter.

It's an issue worth thinking about...
Or should I choose the my old solution: buy a Nachi ( Japan )2.1 or 2.15 drill bit
or 2.2 mm and cut to get the handle
Compared to price and shipping costs, they are much cheaper
I chose 2.2 mm ( max ) because that is the diameter that I can machine the cylinder "most perfectly"

 

[minh-thanh]

Hi All !
A little free time...

 

[Nerd1000]

What component is this?

 

[ruben]

Hi All !
An update: I designed more parts, assembled them and see how they look

View attachment 149788

Hello, where can I find the plans for that engine?