Solenoid diesel injection pumps

[The Ignoble Troll]

Darn, I carefully drilled a tiny hole for the spill port, and as I was afraid of, it now spills everywhere, all the time. I'll probably have to make one or 2 replacement pieces to fix whatever I messed up. Not sure what that is yet.

Can you thread the hole and block it with a screw, to give yourself the chance of redrilling the spill in a different way - before you remake all the affected parts?

Or use the erroneous spill hole to run a mini accumulator?

 

[JimSvarv]

"As for my dream of 5 cylinders, that would mean that there would always be a cylinder in each stage of the engine cycle and if there is enough mass in the webs, the flywheel would not need to be very big."

Wouldn't the same be true for a 3 cylinder engine?
A 5 cylinder is cooler sure but a three would also always be in a power stroke I guess.

Anyway if you can make your 1 cylinder working well you could make another with how many cylinders as you wish for!

 

[The Ignoble Troll]

"As for my dream of 5 cylinders, that would mean that there would always be a cylinder in each stage of the engine cycle and if there is enough mass in the webs, the flywheel would not need to be very big."

Wouldn't the same be true for a 3 cylinder engine?
A 5 cylinder is cooler sure but a three would also always be in a power stroke I guess.

Anyway if you can make your 1 cylinder working well you could make another with how many cylinders as you wish for!

I want to base it on the MAN B&W 5S50MC. Part of the reason for 5 cylinders is to try and get in enough air flow for the engine to be able to run a small turbo to provide scavenging.

 

[Roger B]

There is quite a lot already in this thread however I have picked a few points from the OP to comment on:

To get good diesel combustion a rapid start and end of injection is required as well as good atomization. Using an inlet port in the side of the pump cylinder allows the plunger to get up some speed before injection starts. A separate ball inlet valve like Minh uses should close almost as soon as the pump piston starts rising. As his pumps are cam driven this works. I am not sure how rapidly your solenoid system will accelerate.

The volume of fuel to be injected is small and the pressures are high so any flexible item or trapped air will cause poor or no injection. With a plunger type pump may be difficult to get the air out of the clearance between the plunger and the barrel. An elastomer O ring may also deflect sufficiently to cause problems. PTFE of HDPE may be better.

You are looking at a ~50cc cylinder which is more than double the size of mine. I am using a 2mm pump plunger with a working stroke under 1mm (difficult to measure with a helix controlled pump so you could increase the bore to 3mm. A 1mm plunger will have quite a long stoke and may suffer from Euler buckling, a risk at an L/d of more than 5.

I would suggest that you start with a simple hand operated injection pump to develop the injector design before you move onto your rather interesting solenoid design.

There is a lot of information, which I am sure you are aware of, in this thread:

https://www.homemodelenginemachinist.com/threads/request-injector-designs.36273/

I am not doing and further fuel injection development at the moment as I am building a 20cc Junkers style opposed piston two stroke diesel.



When it is ready to run I will need to do some more work on improving the atomization.

 

[The Ignoble Troll]

There is quite a lot already in this thread however I have picked a few points from the OP to comment on:

To get good diesel combustion a rapid start and end of injection is required as well as good atomization. Using an inlet port in the side of the pump cylinder allows the plunger to get up some speed before injection starts. A separate ball inlet valve like Minh uses should close almost as soon as the pump piston starts rising. As his pumps are cam driven this works. I am not sure how rapidly your solenoid system will accelerate.

The volume of fuel to be injected is small and the pressures are high so any flexible item or trapped air will cause poor or no injection. With a plunger type pump may be difficult to get the air out of the clearance between the plunger and the barrel. An elastomer O ring may also deflect sufficiently to cause problems. PTFE of HDPE may be better.

You are looking at a ~50cc cylinder which is more than double the size of mine. I am using a 2mm pump plunger with a working stroke under 1mm (difficult to measure with a helix controlled pump so you could increase the bore to 3mm. A 1mm plunger will have quite a long stoke and may suffer from Euler buckling, a risk at an L/d of more than 5.

I would suggest that you start with a simple hand operated injection pump to develop the injector design before you move onto your rather interesting solenoid design.

There is a lot of information, which I am sure you are aware of, in this thread:

https://www.homemodelenginemachinist.com/threads/request-injector-designs.36273/

I am not doing and further fuel injection development at the moment as I am building a 20cc Junkers style opposed piston two stroke diesel.



When it is ready to run I will need to do some more work on improving the atomization.

Thank you Roger. Yes, definitely no O-rings. I plan on using Teflon glands held inplace/compressed by nuts.

If the Teflon is not suitable - HDPE.

That does make sense, to start the injector build first.

I don't think the plunger will buckle as it's only going to have around 15 psi pushing it, but if it does, I will switch to tool steel (already purchased as a "just in case")

Your feedback is very welcome

-Troll

 

[Roger B]

I am happy to see someone else working on fuel injection systems and diesels, it’s a lonely world.







This is my test pump. It is a 2mm lapped bore and piston with an 1mm inlet port in the side of the cylinder. The discharge valve is a 3mm ball on a lapped seating.

https://www.precisionballs.com/ball_valve.php

If you blank off the discharge port you can check the sealing quality of the piston by how rapidly the piston moves with a defined load (it is fun getting the air out first).

The operating lever on mine gives a 2-1 advantage so my 2.5 kg spring balance will give 5 kg (50N) on the piston.

There seems to be a big difference between the static and dynamic loads on the system. This pump will inject and produce good atomization with 50N on the pump piston.







On the first engine I used a miniature ball race as the cam follower for the injection pump, this was rated 50N static load, 178 N dynamic load. After a few trials the ball race shattered, as did it’s replacements. I then replaced it with a roller made from bearing bronze, this started to spread and I am now using a hardened steel roller on a hardened steel cam.

 

[The Ignoble Troll]

Have you tried a hand held brake bleeding kit for priming. That's what I had in mind... obviously untested at this point.

If check balls keep breaking, maybe I should look at small spring loaded poppet valves..?

I like your set up. It gave me some ideas on component placement, thank you.

 

[The Ignoble Troll]

Have you tried a hand held brake bleeding kit for priming. That's what I had in mind... obviously untested at this point.

If check balls keep breaking, maybe I should look at small spring loaded poppet valves..?

I like your set up. It gave me some ideas on component placement, thank you.

Oh wait, morning brain the FOLLOWER shattered. Gotcha.

 

[The Ignoble Troll]

Your flame test looks very positive, a nice clean flame.

 

[The Ignoble Troll]

I think I figured out a way to control displacement without fiddling with pwm controls on the solenoid.

In the side of the pump body I will drill a cavity and add a spring loaded plunger. The spring tension will be controlled by a fine threaded rod that will be connected to a servo.

This way, if the threaded rod is all the way in, the plunger will be stationary for full injection.

As the servo winds the plunger retaining rod out, it will let the spring retain the plunger in position until the power stroke, when that happens the plunger will be moved back, increasing the pump body volume and decreasing the injected fuel volume.

As the pump plunger is withdrawn, the spring will force the displaced fuel back into the pump body.

The spring only needs to be stiff enough to resist the positive pressure created by the charging pump.

Thoughts?

 

[JimSvarv]

I think it's a very clever way of fuel metering you have come up with!
How well it would work I can't tell but it sounds good in theory.

I was wondering how much fuel a 50cc needs.
So I did mess with the calculator and did get something like 0.005 milliliters.
Could this be right or have I thought wrong?

minh-thanh 10cc must have tiny amounts injected at idle...

 

[The Ignoble Troll]

I think it's a very clever way of fuel metering you have come up with!
How well it would work I can't tell but it sounds good in theory.

I was wondering how much fuel a 50cc needs.
So I did mess with the calculator and did get something like 0.005 milliliters.
Could this be right or have I thought wrong?

minh-thanh 10cc must have tiny amounts injected at idle...

That's where I ended up too on idle.

minh-thanh is quite the artist. It must be running on the hint of fuel fumes!

 

[ninefinger]

Heres a plunger pump design I've been working on, the next iteration from what I showed previously. I've drawn it with a cam and rocker but those could be replaced by a solenoid (to keep this somewhat on topic).

The idea is similar to a helix controlled spill port, but the helix is effectively moved outside and is now a wedge.

With the wedge fully out (minimal engagement) the plunger will perform the maximum stroke before the spill port is opened.
With the wedge fully in it forces the spill port to be exposed very early and minimal pumping is performed.

The start of the pumping (and therefore injection) is consistent and its the cutoff that is controlled.

A few advantages I see for this over a helix on the plunger and rack control:
The plunger is a simple cylinder and just needs a circumferential relief for the spill port simplifying manufacture. (relief is exaggerated for visibility - really only needs a small clearance to relieve pressure).
No need for a miniature rack.

Like my previous iteration, this plunger pump is intended to be closely coupled to an injector that will be screwed on to the end of it (not shown here).

Thoughts on this arrangement? (solenoid actuated or cam driven)

 

[Roger B]

I think I figured out a way to control displacement without fiddling with pwm controls on the solenoid.

In the side of the pump body I will drill a cavity and add a spring loaded plunger. The spring tension will be controlled by a fine threaded rod that will be connected to a servo.

This way, if the threaded rod is all the way in, the plunger will be stationary for full injection.

As the servo winds the plunger retaining rod out, it will let the spring retain the plunger in position until the power stroke, when that happens the plunger will be moved back, increasing the pump body volume and decreasing the injected fuel volume.

As the pump plunger is withdrawn, the spring will force the displaced fuel back into the pump body.

The spring only needs to be stiff enough to resist the positive pressure created by the charging pump.

Thoughts?

Some thoughts:

Moving the plunger will alter the start of injection point. This could be compensated for by adjusting the timing of the solenoid but is an added complication.

The plunger needs to be sealed against full injection pressure yet able to move freely. This suggests lapped components. A polymer seal would probably bring too much friction.

The inertia of the plunger needs to be considered. If it does not move rapidly to the threaded rod the rate of pressure rise at the start of injection will be reduced. This will tend to cause dribbling rather than atomisation.

 

[Roger B]

I think it's a very clever way of fuel metering you have come up with!
How well it would work I can't tell but it sounds good in theory.

I was wondering how much fuel a 50cc needs.
So I did mess with the calculator and did get something like 0.005 milliliters.
Could this be right or have I thought wrong?

minh-thanh 10cc must have tiny amounts injected at idle...

This is my calculation for a 20cc engine.

The density of air is around 1.2kg/m3 so 20 cc of air is around 0.024g. Taking a fuel air ration of 14-1 this would require 0.0017g of diesel fuel. The density of diesel fuel is around 0.8kg /dm3 so at full output around 2mm3 of fuel would be required. This could be achieved with a plunger of 2mm diameter and a stroke of 1.5mm (plus a bit to allow for leakage).

The working stroke of the pump when it is running appears to be around 0.5mm.

This matches my output test results:

 

[The Ignoble Troll]

Heres a plunger pump design I've been working on, the next iteration from what I showed previously. I've drawn it with a cam and rocker but those could be replaced by a solenoid (to keep this somewhat on topic).

The idea is similar to a helix controlled spill port, but the helix is effectively moved outside and is now a wedge.

With the wedge fully out (minimal engagement) the plunger will perform the maximum stroke before the spill port is opened.
With the wedge fully in it forces the spill port to be exposed very early and minimal pumping is performed.

The start of the pumping (and therefore injection) is consistent and its the cutoff that is controlled.

A few advantages I see for this over a helix on the plunger and rack control:
The plunger is a simple cylinder and just needs a circumferential relief for the spill port simplifying manufacture. (relief is exaggerated for visibility - really only needs a small clearance to relieve pressure).
No need for a miniature rack.

Like my previous iteration, this plunger pump is intended to be closely coupled to an injector that will be screwed on to the end of it (not shown here).

Thoughts on this arrangement? (solenoid actuated or cam driven)

View attachment 164587

Your idea makes sense to me for a cam driven pumps. It look like it would take a lot of lapping.



For a solenoid driven pump I was playing with the idea of a split wedge (shaped like a snakes tongue) that would go where your return spring is. It would act to shorten the solenoids stroke and would be servo actuated. This obviously wouldn't work in fixed stroke cam driven pumps.

My thoughts were along the lines of limiting the stroke of the solenoid.

I do like the idea of adding a lever, because it could make up for minor misalignments.