Mini diesel engine.

[minh-thanh]

sition !
Thanks !
Hi All !
I will make the oil pump
I have a question: does the piston need an O-ring for sealing ?
If I make piston without O ring, will it be ok ?

 

[Willyb]

Enjoying your Diesel Engine build.

If you are talking about the piston in the cylinder, you are going to need metal piston rings as I don't really think O rings can stand up to the high compression pressures. For very long.
In regards to the Plunger and Barrel in conventional injection pumps, they do not use any type of seals. They seal using the diesel fuel in a very small clearance between these two parts. The Plunger is lapped to the Barrel to get this small clearance they require to make the seal. The fuel also lubricates these parts.

Cheers
Willy

 

[Steamchick]

Working at a car factory, and taking engines from a different manufacturer's factory, we had to guarantee the lubricity of first-fill fuel, in order to not ruin the fuel pumps and injectors when first started. Apparently, "any old fuel" would not do, as if the lubricity was too low, we could ruin the fuel pump in seconds at first starting.
Also, This is why the guarantee on the car is voided if you do not use proprietary fuels... (e.g. if you use a gallon of cooking oil with a coffee mug of white spirit in it!). While the engine will run with rubbish fuel, the wear on the high pressure fuelling components will be thousands of times higher than normal, and the components when worn cannot produce the fine spray pattern for cleanest combustion, so you'll get a smokey engine before it stops. You could have an expensive bill in just a few thousand miles, instead of a few hundred thousand miles.
I made a "ring-less" 1cc marine diesel for model aero-fuel... but the compression disappeared after the first few runs, as the bore and piston "ran-in". They had been lapped to the best fit I could achieve, but I guess the materials were no good for this due to the rapid wear I experienced.
After lapping, I suggest a very thorough clean to eliminate all lapping compound... Maybe my cleaning wasn't good enough?
K2

 

[minh-thanh]

Thanks for the comment !
A update :
The outlet pressure is quite good, but there is little oil coming out at the top
I use toothpaste for sealing the balls and valve seat
A project that I'm not sure will succeed

 

[minh-thanh]

Hi All !
I just tested :
the pressure is quite high, I can't seal the injector
It seems to be pretty good
I had to make new piston and lap cylinder , they weren't so good

 

[Alec Ryals]

Hi All !
I just tested :
the pressure is quite high, I can't seal the injector
It seems to be pretty good
I had to make new piston and lap cylinder , they weren't so good

If thats you hand its going to mess your tentendts up ! looks Great

 

[Steamchick]

Just NEVER put any flesh adjacent to the orifice of the injector. You WILL inject fuel through the skin, and possibly get brain damage or death as a result of the fuel passing around the body. It was the FIRST AND MOST IMPORTANT SAFETY RULE that I was taught when a teenage apprentice. Usually nowadays, the injection is into a plastic tube or bottle (clear) but we used large glass bottles (1 pint milk bottles) which we had to wash out afterwards. That way you can see the spray pattern, and collect the fuel for use later.
K2

 

[petertha]

That's really neat. So where to go from here? How to translate that amount of 'hand energy' to make the squirt in an engine? Mechanically activated? Solenoid activated? etc.

 

[minh-thanh]

Thanks for the comments !
petertha !
Oil pump controlled by cam lobe
You can see the last picture in post 76

 

[Willyb]

How are you planning to control the amount of fuel delivered per injection?
Your injector spray looks good but time will tell how it acts under the pressure of compression?
A very fine mist ignites well from the compression heat and has little smoke. Bigger droplets don't ignite as well and produce allot of smoke.
Keep up the good work.

Cheers
Willy

 

[Steamchick]

Don't quote me on this, but I have an idea Bosch and CAV mechanical pumps were up to 8 or 900 psi, before the move to common rail and piezo injectors... Now those have gone from 1200 to 1600 plus psi impulsive pressure. You can't measure those injection pressures on a gauge, as they are impulsive, I.E. A shock wave generated when the injector is fired.
Looking at M-t's injection, the pressure is too low, by hand. But a cam at speed is a different matter.
I remember injector testing with a CAV hand-pump in the 1960s. But I can't remember the pressures we had for valve opening, and to witness a "good spray cone". But the intrusions were on the label affixed to the device. I think they are still available on e&@y, etc...
K2

 

[Steamchick]

In practice the spray pattern is not allways conical, it is sometimes shaped using different sized holes and angles, more so laterly trying to satisfy emissions, again a reason for going to electronic control, however if you do manage to get a good spray of fuel at the right time and pressure with no drip you will have achieved something that many have not or would not attempt, me included, I had enough problems with all the right gear. I'm ashamed to say that if we did have some high smoke pumps and the destination didn't have tight emission control they would probably go depending upon how busy we were. Injection pipes also get very hot and are noisy, why I don't know.

Hi Alex, first, I am NOT a diesel expert, just had a bit of training 50-plus years ago, and a bit of modern train while I was the emissions Engineer at a car plant.
Pipes get hot because of the hot fuel oil within, heated by the pump. The noise is the shock wave from each firing pulse of pressure. I don't know sonic speed in oil at high pressure, but the speed of the shock wave is supersonic in air at atmospheric pressure, so it is effectively a series of Sonic booms - all be it very small ones - that you are hearing. That is why it is so loud. On a molecular level, the shock wave in the oil is a pulse of energy, that travels through various media at the sgonic speed for each medium. The steel pipework feels the internal pressure wave travelling along and flexes sympathetically (at a molecular level) to transmit the pressure wave from the oil to the air. But this wave is travelling along the pipe at speeds that are supersonic in air, and the molecules of air excited as the shock wave passes cause a sympathetic shock wave in the air that travels at a super-sonic speed in the air from one end to the other of the pipe. Hence the sonic booms. But that is only my imaginative explanation (guesswork!), not that of an expert.
Please can an Expert explain this and teach us all?
K2

 

[minh-thanh]

Hi All !
I just redid the new cylinder, it sprays a little better .

How are you planning to control the amount of fuel delivered per injection?
Your injector spray looks good but time will tell how it acts under the pressure of compression?
A very fine mist ignites well from the compression heat and has little smoke. Bigger droplets don't ignite as well and produce allot of smoke.
Keep up the good work.

Cheers
Willy

I plan to control the amount of oil entering the engine with the cam lobe height and the oil pressure adjustment bolt .
A project of which I do not know the outcome !

 

[Mechanicboy]

I plan to control the amount of oil entering the engine with the cam lobe height and the oil pressure adjustment bolt .
A project of which I do not know the outcome !

In fact not possible without centrifucal regulator.
Use centrifugal regulator, it's practical to control correct amount of fuel affected by engine via force of spring to regulate amount of fuel automatic by engine. To regulate required revolution: regulate the force of spring on the centrifugal regulator with the lever.

See at this movie why we need the centifugal regulator and the spring to regulate revolution and amount of fuel..

 

[Mechanicboy]

Minh-Thanh..

Take a study how the centrifugal regulator works as here, begin at the timeline 12:30 in this movie..

 

[Willyb]

Hi All !
I just redid the new cylinder, it sprays a little better .
View attachment 126716



I plan to control the amount of oil entering the engine with the cam lobe height and the oil pressure adjustment bolt .
A project of which I do not know the outcome !

The problem with both of these methods, is there is no feedback from the engines speed and they are not easily adjustable while the diesel engine is running. The cam lobe height is a fixed distance so your fuel oil delivery will be a fixed amount. The fuel pressure adjustment bolt has similar issues. Diesel engines speed is controlled by the amount of fuel injected into the cylinder. The amount of injected fuel needs to be controlled by the throttle and a governor with the governor having complete control.
As Mechanicboy has stated in post #94 and #95 you require some type of governor (centrifugal is the easiest and works well) to adjust the amount of fuel delivered depending on engine speed.
Find Hansen's diesel engine uses a movable wedge plate that moves in and out of the space between the cam lobe and the injection pump plunger. This plate is directly connected to the output of a centrifugal governor. When the thinnest part of the wedge is in the space between the cam and plunger, the amount of fuel injected will be small. As the thicker part of the wedge moves in, more fuel is injected because there is less space between the cam and the plunger. It is a simple method and works wonderfully at controlling fuel delivery. I have yet to come up with or see any better way of controlling ones fuel delivery on a model diesel engine.
Keep up the good work.
Cheers
Willy



I can't think of have

 

[minh-thanh]

Mechanicboy, Willyb !
Thanks !

If I just need the engine to run - I don't need adjust the speed , because I don't know if the pump and the injector are fine , so do I need that part ?

 

[Nerd1000]

Mechanicboy, Willyb !
Thanks !

If I just need the engine to run - I don't need adjust the speed , because I don't know if the pump and the injector are fine , so do I need that part ?

I think the danger is what happens if your engine works better (makes more power) than you expected. Without a governor it could accelerate to such high RPM that it throws a rod or suffers some other catastrophic failure.

 

[minh-thanh]

Nerd !
Although I'm not sure the engine will run.
But that's a good reason to think !
Thanks !

 

[Mechanicboy]

I think the danger is what happens if your engine works better (makes more power) than you expected. Without a governor it could accelerate to such high RPM that it throws a rod or suffers some other catastrophic failure.

Minh-Thanh..

I have experienced the vacuum regulator did not work (regulation takes place by vacuum which affects the piston when there is a high vacuum = less fuel and vice versa) in the Sabb semi-diesel engine. The engine ran so fast like a crazy horse that I had to stop the engine immediately by holding the lever down so the engine could not pump the fuel into the engine.
It is actually dangerous that the connecting rod can break in two and make holes in the crankcase / bottom frame. The reason was lack of vacuum due to leather packaging in the piston was hard and dry.