Mini diesel engine.

[Mechanicboy]

Hi Chaffe !

With me : drill - reamer - lapping
Small hole lapping tool : you can buy it or make it yourself - I made it myself

https://www.mcmaster.com/lapping-tools/
Lapping pump cylinders is challenging and very patient

Tolerance : I think it's about 0.01 -> 0.02 mm - I'm not sure - Because it's too small
I used o - ring - just for testing . They fail quickly with high pressure.

The tolerance must be tight to prevent leakage in the fuel pump and still move free. Tolerance is 0.001 mm. Steel piston in cast iron cylinder. First lap the cylinder to final blank as mirror and lap the piston blank as mirror. Then adapt the piston into the cylinder carefully with oil and test the piston is moving free without leakage into the cylinder.

 

[minh-thanh]

It is possible, if you are able to make 0.001 mm tolerance, as well as cylinder and piston should be 100% straight
it's impossible for me

" Mirror surface " : I'm not sure
The surface that looks like the picture is fine:

 

[minh-thanh]

Here in action with 100% kerosene, injection pressure is very low at 8 bar, this is something I am working on

Your injector are pretty good !!

 

[Mechanicboy]

It is possible, if you are able to make 0.001 mm tolerance, as well as cylinder and piston should be 100% straight
it's impossible for me

" Mirror surface " : I'm not sure
The surface that looks like the picture is fine:View attachment 132676

Surface in cylinder is good.

In fact not impossible to make straight cylinder and piston. I did with the Wakefield lubricator for steam engine without O-ring.

To keep tight without gasket or O-ring: make piston long as possible in relation to diameter so that there are smaller leaks past the piston and cylinder. Round off the end of the piston so that it fits more easily into the cylinder during installation and avoid accidental scratches. Use finer abrasive, eg polishing paste, to fit the piston into the cylinder with the utmost care. If the piston has entered the cylinder, clean properly and lubricate and take a leak test that it is without leakage of fuel.

 

[Chaffe]

Thanks guys, I have finished my steam engine project, now I have spent some time on my new injector pump. Cast iron body with steel piston, still need to refine the piston as it has some leakage, but looking promising.
I have a question, my delivery check valve doesn’t seal (ball and spring type) how are we all making successful check valves? This one is flat sealing face with seat hole size 75% of ball diameter. My next design was going to be with a 30 taper (60 degree inclusive, ie centre drill) I feel the ball is not being driven in hard enough or on centre currently.
interested to hear how others have succeeded

 

[Richard Hed]

Thanks guys, I have finished my steam engine project, now I have spent some time on my new injector pump. Cast iron body with steel piston, still need to refine the piston as it has some leakage, but looking promising.
I have a question, my delivery check valve doesn’t seal (ball and spring type) how are we all making successful check valves? This one is flat sealing face with seat hole size 75% of ball diameter. My next design was going to be with a 30 taper (60 degree inclusive, ie centre drill) I feel the ball is not being driven in hard enough or on centre currently.
interested to hear how others have succeeded

Do you have any photos of your engine? Have you polished the check valve? I would certainly thimpfk an angled valve would be better.

 

[Chaffe]

Do you have any photos of your engine? Have you polished the check valve? I would certainly thimpfk an angled valve would be better.

Only the photos I posted a few posts ago.
I am treating the engine and injection system as two separate things. I think the engine it’s self will be an easy task.

 

[Chaffe]

 

[Chaffe]

The brass fitting above is in fact my delivery check valve, it’s m5/m6 so you can appreciate the size. The ball is 2mm and is some 11mm deep to the seat, there is also a spring and retaining collar inside. I am not sure how you would polish such a seat so deep?

 

[ajoeiam]

The brass fitting above is in fact my delivery check valve, it’s m5/m6 so you can appreciate the size. The ball is 2mm and is some 11mm deep to the seat, there is also a spring and retaining collar inside. I am not sure how you would polish such a seat so deep?

My first response was going to be - - - carefully - - - but then that's being a turkey!
Some emery on a stick - - - - some scotchbrite (there are ever so many grades of this stuff!) on a stick.

I've never seen it but molds for CDs/DVDs etc are polished to an incredibly high level so a high polish 'is' possible.

 

[Chaffe]

You’ll not get emery or scotchbrite in a 2mm hole, 11mm deep….
ideally I would want to polish it with a ball soldered onto a brass rod, with compound. I believe the new design with a 30 degree seat and slightly larger ball will be better.

 

[minh-thanh]

You’ll not get emery or scotchbrite in a 2mm hole, 11mm deep….
ideally I would want to polish it with a ball soldered onto a brass rod, with compound. I believe the new design with a 30 degree seat and slightly larger ball will be better.

Make a lapping tool by aluminum with diameter 2mm , first with grit 400 , 600 after : 1800 , 2000
then use a small hammer to lightly tap the ball to make a valve seat

 

[Chaffe]

Make a lapping tool by aluminum with diameter 2mm , first with grit 400 , 600 after : 1800 , 2000
then use a small hammer to lightly tap the ball to make a valve seat

Hi, I have what I consider to be quite a good bore (size and finish) in my cast iron pump, the piston was in fact not machined and I tried to use ground stainless bar, it is too small… I’ll make a piston when time permits.
The check valves seem to be the real test for me I will try a tapered seat instead of the usual flat bottom seat, I think the spring is pushing the ball off centre slightly

 

[minh-thanh]

The check valves seem to be the real test for me I will try a tapered seat instead of the usual flat bottom seat, I think the spring is pushing the ball off centre slightly

Hi !
Flat seat or tapered seat : they are the same when in contact with the sphere - balls
Make the valve seat surface like polishing, and the way i do it will be fine .

 

[minh-thanh]

Chaffe !

Hi, I have what I consider to be quite a good bore (size and finish) in my cast iron pump, the piston was in fact not machined and I tried to use ground stainless bar, it is too small… I’ll make a piston when time permits.
The check valves seem to be the real test for me I will try a tapered seat instead of the usual flat bottom seat, I think the spring is pushing the ball off centre slightly

Real test : Including me, I had to redo it at least a few times before it was really tight
I have tried both the flat seat and the taper seat, and they are ok. Important is the valve seat surface, it must be Perfect. Use a magnifying glass when you look at the valve seat surface
Cylinder - piston : Make the piston until it can only slide into the cylinder with a little oil w20
Remember: We are working with a very small amount of fuel and must have high pressure

 

[Thommo]

Hey Than, it seems that you are rapidly becoming the miniature Diesel engine guru!! Good on ya.

 

[minh-thanh]

Hi mate !
"guru" or "expert" : I'm not
I'm not sure if what I said is true
Just hope it provides some information ...

 

[Gedeon Spilett]

Hi Minh Thanh
great achievement with your engine, thanks for the plan...
as a good compression ignition engine may have volumetric ratio near 1:19 and above, how come we need to add ether to get combustion ? any clue ?
I'm a novice in the theory of the diesel cycle may I add...

 

[Chaffe]

Hi Minh Thanh
great achievement with your engine, thanks for the plan...
as a good compression ignition engine may have volumetric ratio near 1:19 and above, how come we need to add ether to get combustion ? any clue ?
I'm a novice in the theory of the diesel cycle may I add...

Simple answer is heat, heat is lost to the cylinder walls, piston, head and the fuel. The smaller the cylinder the less heat energy you will get from the air charge. Physics don’t scale very well, especially when it comes to thermal dynamics.

 

[minh-thanh]

Hi Gedeon Spilett !
Thank you very much !

as a good compression ignition engine may have volumetric ratio near 1:19 and above, how come we need to add ether to get combustion ? any clue ?
I'm a novice in the theory of the diesel cycle may I add...

With high compression ratio can be from 18 -1 or higher without adding ether to the fuel.
The theory of the diesel cycle: when I made this engine I didn't pay much attention to that theory. I just need an engine with a high compression ratio - somewhere around 16 -1 , If the engine can run with an ether mixture I would increase the compression ratio to 18 - 1 or higher
When I was a student, I could spend hours thinking and solving a difficult problem of physics, math... Now I'm very lazy.


Chaffe !

Simple answer is heat, heat is lost to the cylinder walls, piston, head and the fuel. The smaller the cylinder the less heat energy you will get from the air charge. Physics don’t scale very well, especially when it comes to thermal dynamics.

Thank you !!