Mini diesel engine.

[minh-thanh]

Hi my friend !

The only question I have is have you been able to measure the volume of fuel that you are spraying per cycle? I might be wrong but it looks like a lot of fuel based on the engine size?

I haven't measured the fuel yet
when i try , i also see too much fuel injection ,
Even though I reduce the stroke of the piston pump, it seems that the amount of fuel is only reduced to about 2/3 per cycle
Right now, i think i will make a new pump cylinder 1/2 . smaller
The new cylinder with diameter is about 2 mm diameter
Current cylinder diameter is 4mm

There is 1 problem: i plan to keep the whole 4mm pump, for testing
and make a new pump with a diameter of 2mm
But there's so much to do .

 

[Thommo]

That sounds like the way to go mate. Keep all your test results mate. I’m sure that there will be guys in the future that would be very grateful. You’ll save them a great deal of work. I’m looking forward to hearing the beast run. It will be an awesome achievement

 

[minh-thanh]

Hello Everyone !
An update :
When I was thinking about ways to reduce fuel , I realized that I could reduce the lobe lift
so I sharpened the lobe, currently the cam lobe only lift about 1.8mm
And :

 

[Thommo]

Hey Than, the volume looks better but now the spray pattern looks a bit uneven (could be the video). Assuming that the spray pattern is ok, I would work on getting a finer mist. Once again it could be ok but I can’t really tell with the video.

 

[Mechanicboy]

Find Hansen diesel engine has a pump stroke at 0,03 mm under idling. It means that you can have a smaller injection nozzle.

 

[minh-thanh]

Find Hansen diesel engine has a pump stroke at 0,03 mm under idling. It means that you can have a smaller injection nozzle.

Are you sure ???
With my little experience and ability...., I cannot make the injector open in the cylinder with a pressure that produces at 0.03 mm stroke. .,and can't even open the needle with the pressure of the spring in atmospheric pressure

 

[Mechanicboy]

Are you sure ???
With my little experience and ability...., I cannot make the injector open in the cylinder with a pressure that produces at 0.03 mm stroke. .,and can't even open the needle with the pressure of the spring in atmospheric pressure

How big are the bore and stroke in your engine? Find Hansen engine has bore 20 mm and stroke 36 mm. Small cylinder volume = small amount of fuel to be injected and vice versa. The small engine need small injector to atomize the fuel better with small amount of fuel than the large injector. Too much fuel or too coarse fuel drops of atomized fuel from the large injector can't work well in the small engine (too wet and difficult to start up the engine).

 

[Peter Twissell]

0.03mm or 30 microns, does sound unlikely.
Remember the oil has a bulk modulus of around 1500 MPa. To generate any significant pressure with 30 microns of piston travel, the volume of oil to be compressed would have to be very small indeed.

 

[Mechanicboy]

0.03mm or 30 microns, does sound unlikely.
Remember the oil has a bulk modulus of around 1500 MPa. To generate any significant pressure with 30 microns of piston travel, the volume of oil to be compressed would have to be very small indeed.

From Find Hansen homepage

 

[minh-thanh]

I really don't understand with only 0.03 mm of stroke.....
So I'll try my way.

 

[Mechanicboy]

I really don't understand with only 0.03 mm of stroke.....

Minh-Tanh..
You wrote in post #76:

"I just finished designing the engine
Bore : 19 mm , stroke : 38 mm"

Also near same dimension as a Find Hansen engine who has 20 mm bore and 36 or 44 mm stroke.
Also you need small diameter pump and small injector nozzle + regulator.

The amount determined by the regulator that the engine runs at a certain speed should have a certain amount of fuel. A certain cylinder volume that goes at a certain speed must have a certain amount of fuel. We can not control this manually without a regulator, not even if we try with a specific pump stroke or the amount to turn on. The regulator is what helps the engine to run smoothly on a certain amount of fuel. As I wrote that Find Hansen used 20 mm bore and 36mm stroke for hot bulb engine and 44 mm stroke for diesel engine due to the compression ratio is not the same in hot bulb engine and diesel engine. Both motors have a 2 mm diameter pump and the stroke length is determined by the regulator to a desired speed range.

The injection nozzle is so small that it atomizes so nicely on small amounts of the fuel pumped in from such a small injection pump. The injector has a spring loaded injector valve, with a valve head angle of 14 degrees and a valve stem 0.90mm thick. The valve stem is treaded so that the spring can be adjusted to the right fuel pressure with one nut, and locked with another nut. Compare that to matches at Find Hansen's injection nozzle, a real masterpiece!

The best one can make an injection nozzle is a watchmaker lathe if the large lathe is too rough and difficult to make such fine and small parts.
Maybe you can ask the watchmaker to make a small and fine injection nozzle?

 

[minh-thanh]

You should try with pump with 2mm and 4mm diameter and with 0.03mm . stroke
I don't know how to generate oil pressure?? and that pressure is enough to pump into the cylinder??
How to produce a pressure of about 50 bar , 80 bar with a stroke of 0.03 mm??
Can you explain it ?

 

[Mechanicboy]

You should try with pump with 2mm and 4mm diameter and with 0.03mm . stroke
I don't know how to generate oil pressure?? and that pressure is enough to pump into the cylinder??
How to produce a pressure of about 50 bar , 80 bar with a stroke of 0.03 mm??
Can you explain it ?

To generate the pressure is determined by the spring in the injector and not from the pump. Strong spring generate better atomized fuel and vice versa. Also adjust the spring to generate the oil pressure and get fuel atomized. The oil is not compressible and the nozzle will open at high pressure.

 

[Vietti]

does anyone remember the DUX? It was a small diesel described in one of the last few issues of MEB. Probably some really relevant info. If I remember correctly the injector was made by scratching.

John

 

[Vietti]

Should say the last PRINTED issues. I believe the builder was dutch. John

 

[Vietti]

Well my memory isn't so good. The construction series for the Dux was in SIC not MEB.

The Author is Martin Alewijn, his 20 year old email is [email protected]

The series was in SIC starting in Vol 13 No. 78 and was in Vol 14 No 78, Vol 14 No 80, Vol 14 No 81 and concluded in Vol 14 No 82, five parts.

Someone will hopefully suggest how to get back issues.

I personally would not attempt a small diesel without reading this series. The engine described was about the same size as being discussed. Of particular interest is his design for a simple injector and pump. He used a glow plug to aid starting just like some big engines.

I hope this is of some help. John

 

[minh-thanh]

Mechanicboy !

We will not argue about stroke 0.03 mm
Maybe I'm wrong
So I'll try my way.

 

[Mechanicboy]

Mechanicboy !

We will not argue about stroke 0.03 mm
Maybe I'm wrong
So I'll try my way.

Read again this: Both motors have a 2 mm diameter pump and the stroke length is determined by the regulator to a desired speed range.

 

[minh-thanh]

For you .
That's all I need !!

 

[Mechanicboy]

For you .
That's all I need !!

Minh-Thanh,...

It is allowed to dream, but be realistic and listen to us who can provide the answers to what you need to know based on our knowledge and experience. Here in the forum, it is nice to be guided to solve the problem and make the engine work with good results of patience and focused on the small important details that must not be overlooked. For a beginner, there are many pitfalls and expensive to try and fail without a good result. Do not forget that you made it work with the help of us who guided you to make glow plug engine, model diesel engine with compression screw and the 4 cylinder 4 stroke engine with good results and these model engines ran so well. In other words, do not give up when you can really make your engine work with injection equipment which is a big challenge and not so easy for others to make and make it work properly in small dimensions.