Solenoid diesel injection pumps

[The Ignoble Troll]

I just finished moving and am months away from getting my shop to be functional. That being said I am picking away at the issues I will need to solve to build a small two stroke diesel.

Currently my thoughts are a 1" bore with a 4" stroke.

My initial plan is to build a single cylinder proof of concept unit and supply it with shop air at 15psi.

From there I want to build a 5 cylinder version that will use a bought roots blower as the air supply.


I want to start with the fuel system and perfect that before building the engine.

To that end, I plan on designing a small injector that will use minimal lapped parts and a separate fuel pump to generate the flow to run the injector. They will be connected with some sort of schedual 80 small bore stainless pipe.

For the fuel pump I am thinking that the easiest solution is to do away with mechanically driven pumps and to use a series of solenoids with a common plunger. One coil would extend a 1mm diameter plunger into a true plunger pump, the other coil would take the place of a return spring and withdraw the plunger.

With off the shelf solenoids, a 1mm plunger pump should easily generate 10,000psi.

The stroke length and timing would be arduino controlled. The dual coil solenoid pump would only need a single double pole relay to control it.

I have a few quadrat sensors somewhere that could be used to adjust timing, injection duration and injection volume.


The plunger pump will have a positive pressure feed pump, which will also allow for a fuel filter to be used.

Can anyone see any foreseeable problems with this set up?

 

[JimSvarv]

Sounds like a very interesting build in my opinion.

Some of my thoughts.
You may need a crosshead with that big stroke to bore ratio.

At 1000rpm and a injection cycle of 40 degrees you will have about 6.6 milliseconds of injection time.
40 degrees may be a bit long especially for low rpm?

So you need enough speed in your solenoids.
And at 10000 psi you will need about 12 pounds of force for a 1mm plunger.
I wonder if a servo motor could drive a injector pump?

Your 50cc cylinder will also consume 100 liter of atmospheric shop air a minute at 1000 rpm and 2 to 1 pressure ratio (15psi).

You could also use your solenoid system to operate the injector as a common rail with a constant fuel pressure. if it will give you any advantage I don't know.

If you succeed I would like yo try it for myself, model diesel is something I have been wanting to do some time in the future and this could simplify the injection if it works well.

Best of luck to you!

 

[Lloyd-ss]

Some interesting concepts. (BTW, I work on and off on mine in the background. It is still moving forward.)
I agree that a cross head would be needed with the long stroke to bore ratio, but that would be very cool.

The electronic injection intrigues me. If you can indeed get the 1mm plunger to "mechanically" produce the proper pressure, duration, and volume, then I think you can drive it with solenoids but you might be surprised at how large the solenoids need to be to provide the "hammer hit" on the plunger.

I have used solenoids to directly open valves in airguns. If you van envision trying to push (knock) a tiny engine exhaust valve open against 2,000 psi of air pressure, that is similar to what you are trying to accomplish. The valve might have more than 50 pounds of force holding it closed and the solenoid will have to generate energy (velocity) in the solenoid armature to knock the valve open.

Often, a high current, high voltage LiPo battery charging a capacitor, and then dumping the cap into the solenoid will work. But in yours, some empirical data on how the 1mm plunger will work, basically, finding the losses that you must surpass before you can actually produce any hydraulic pressure will need to be determined.

Here are a few pics that might pique the interest. The first is a 2 pound pendulum setup that the solenoid armature strikes, and the height that it raises the pendulum is indicative of the energy. Impact distance, armature mass, and and other factors determine how much useful energy you can extract from the armature. The relative force that a solenoid can produce is proportional to the square of the product of the amps x turns in the coil. The coil resistance and the available volts determine the amps and the turns is a constant. You might need 40 volts of LiPo batteries charging a 10,000 uF cap to get sufficient power. The 2nd pic is of a scope trace of dumping a cap charged to 40 volts into the solenoid. You can see the instantaneous voltage rise in the coil. The second trace is the same setup, but with the batteries remaining connected and cutting off (mosfet circuit) after 25msec. The voltage spikes to 40v and then drops to about 25v for the duration. A robust circuit is needed control the watts of power. An SCR will dump the cap, but you will need something controllable to adjust the dwell in the pump, probably some mosfets. If you can get the plunger to work mechanically, I think the electronics can be handled also.
I hope this helps. Lloyd

 

[The Ignoble Troll]

Sounds like a very interesting build in my opinion.

Some of my thoughts.
You may need a crosshead with that big stroke to bore ratio.

At 1000rpm and a injection cycle of 40 degrees you will have about 6.6 milliseconds of injection time.
40 degrees may be a bit long especially for low rpm?

So you need enough speed in your solenoids.
And at 10000 psi you will need about 12 pounds of force for a 1mm plunger.
I wonder if a servo motor could drive a injector pump?

Your 50cc cylinder will also consume 100 liter of atmospheric shop air a minute at 1000 rpm and 2 to 1 pressure ratio (15psi).

You could also use your solenoid system to operate the injector as a common rail with a constant fuel pressure. if it will give you any advantage I don't know.

If you succeed I would like yo try it for myself, model diesel is something I have been wanting to do some time in the future and this could simplify the injection if it works well.

Best of luck to you!

Yes, absolutely cross heads. I am taking a lot from the design of the slow running mega diesel ship engines.

70N solenoids are readily available and looking at a force chart 15 pounds of force is not unreasonable. The packing on the plunger pump will consume some of the force, so I am de-rating the possible peak psi down to 10,000psi which will also let me use a Harbour Freight style hand pump to test the injector pop, which might be much lower then 10,000 psi in practice.

I think a servo motor arranged like a Klaxon horn could work?

Engine RPM - I haven't really started on the engine design beyond knowing I want to copy the large two stroke ship engines. So I don't have a definitive rpm in mind. It will end up being based around the speed required for good ignition. 1000 rpm would definitely be the highest I could see going. I have a large gast vaned air motor that I could convert into a blower if I find exceeding the shop supply is problematic.

I want to stay away from common rail systems, because that adds complications to the injectors.


Thank you for your inputs.

 

[The Ignoble Troll]

Some interesting concepts. (BTW, I work on and off on mine in the background. It is still moving forward.)
I agree that a cross head would be needed with the long stroke to bore ratio, but that would be very cool.

The electronic injection intrigues me. If you can indeed get the 1mm plunger to "mechanically" produce the proper pressure, duration, and volume, then I think you can drive it with solenoids but you might be surprised at how large the solenoids need to be to provide the "hammer hit" on the plunger.

I have used solenoids to directly open valves in airguns. If you van envision trying to push (knock) a tiny engine exhaust valve open against 2,000 psi of air pressure, that is similar to what you are trying to accomplish. The valve might have more than 50 pounds of force holding it closed and the solenoid will have to generate energy (velocity) in the solenoid armature to knock the valve open.

Often, a high current, high voltage LiPo battery charging a capacitor, and then dumping the cap into the solenoid will work. But in yours, some empirical data on how the 1mm plunger will work, basically, finding the losses that you must surpass before you can actually produce any hydraulic pressure will need to be determined.

Here are a few pics that might pique the interest. The first is a 2 pound pendulum setup that the solenoid armature strikes, and the height that it raises the pendulum is indicative of the energy. Impact distance, armature mass, and and other factors determine how much useful energy you can extract from the armature. The relative force that a solenoid can produce is proportional to the square of the product of the amps x turns in the coil. The coil resistance and the available volts determine the amps and the turns is a constant. You might need 40 volts of LiPo batteries charging a 10,000 uF cap to get sufficient power. The 2nd pic is of a scope trace of dumping a cap charged to 40 volts into the solenoid. You can see the instantaneous voltage rise in the coil. The second trace is the same setup, but with the batteries remaining connected and cutting off (mosfet circuit) after 25msec. The voltage spikes to 40v and then drops to about 25v for the duration. A robust circuit is needed control the watts of power. An SCR will dump the cap, but you will need something controllable to adjust the dwell in the pump, probably some mosfets. If you can get the plunger to work mechanically, I think the electronics can be handled also.
I hope this helps. Lloyd

View attachment 163962View attachment 163963View attachment 163964

Thank you Lloyd. That's a fair bit of info and I'm still digesting it.

A bit more on the proposed solenoid pump. I want to use a pair of 70N 12v continous duty solenoids. By using a customized common plunger in them I will size the length of the plunger so that it only has a few mm to travel before it deadheads in either direction. The goal being that the solenoids are each able to operate at close to their maximum force, rather then having to pull in the plunger from partially outside of the coil. The force required to pull in the solenoid is roughly exponential, as I understand it... so by having the solenoid plunger only moving out of position by a slight amount, the power required to generate full force should be subsequently reduced?

I'm not great on electrical, you know far more then I do, so your inputs are most welcome.

Ideally I want to avoid caps and mosfets and have the pump firing off a single relay. It will make it far easier to program the arduino as well as far easier to control the pump output.

 

[Lloyd-ss]

Thank you Lloyd. That's a fair bit of info and I'm still digesting it.

A bit more on the proposed solenoid pump. I want to use a pair of 70N 12v continous duty solenoids. By using a customized common plunger in them I will size the length of the plunger so that it only has a few mm to travel before it deadheads in either direction. The goal being that the solenoids are each able to operate at close to their maximum force, rather then having to pull in the plunger from partially outside of the coil. The force required to pull in the solenoid is roughly exponential, as I understand it... so by having the solenoid plunger only moving out of position by a slight amount, the power required to generate full force should be subsequently reduced?

I'm not great on electrical, you know far more then I do, so your inputs are most welcome.

Ideally I want to avoid caps and mosfets and have the pump firing off a single relay. It will make it far easier to program the arduino as well as far easier to control the pump output.

The solenoids will take some experimentation to find out how best to extract the power you need, in the form that you need it to be in. Sometimes you can start the solenoid farther out of the coil and let it pass thru to gain velocity for an impact, using the laws of conservation of energy and conservation of momentum to your advantage. Just a slight change in starting point or impact point can make a noticeable difference. Because your solenoids are rated at 70N @12v@100% duty, you will have some room to play around with the electrical power applied to the solenoid. Because you will be operating at less than 100% duty cycle, you can (for example) double the voltage and get approx 4 times the impact power from the solenoid. But the speed of actuation is where the biggest gain will probably be. A sharp hit, rather than a slow thump might better suit your needs. Despite wanting to keep the control circuitry simple, you will still need a solenoid driver (controlled by the Arduino) to actually fire the relay, that will in turn, transfer the required amps to the injector solenoid. It might sound complicated, but once you get into it, it will start to make sense, and the design will evolve.

 

[ninefinger]

I started down the thought experiment path of a small 2 stroke diesel as a proof of concept before embarking on a much more ambitious mutli-cylinder model, and I've conclude (obvious to many) that the biggest difference between it and a normal IC or steam engine is primarily the fuel pump & injector combination. My next observation was that I didn't think it was really a design issue, but rather a fabrication issue that is preventing small model diesels being built, i.e. micron level fits on 1 or 1.5mm plungers to have good control and reliable performance requires a degree of precision few modelers want to try to (or can) achieve.

To that end, I plan on designing a small injector that will use minimal lapped parts and a separate fuel pump to generate the flow to run the injector

I agree the injector can use minimally lapped parts - but what about the pump? Are you just planning on designing a pump that can tolerate leakage, i.e. make it capable of way more volume than required and map its performance so even if it is only 80% efficient it can still work, and that is the reason for solenoids?

 

[Lloyd-ss]

I started down the thought experiment path of a small 2 stroke diesel as a proof of concept before embarking on a much more ambitious mutli-cylinder model, and I've conclude (obvious to many) that the biggest difference between it and a normal IC or steam engine is primarily the fuel pump & injector combination. My next observation was that I didn't think it was really a design issue, but rather a fabrication issue that is preventing small model diesels being built, i.e. micron level fits on 1 or 1.5mm plungers to have good control and reliable performance requires a degree of precision few modelers want to try to (or can) achieve.


I agree the injector can use minimally lapped parts - but what about the pump? Are you just planning on designing a pump that can tolerate leakage, i.e. make it capable of way more volume than required and map its performance so even if it is only 80% efficient it can still work, and that is the reason for solenoids?

@ninefinger I agree with Everything you said. The fuel injection is the evil devil in model diesels. The injection system, whether it is a pump-line-injector, or pump-line-solenoid injector, or a unit injector of pump and injector in a single unit, that is the real bugaboo. A few on this forum have successfully gotten past that hurdle, and have moved on. My mental battle with the unit injector on my 2 stroke project is probably not healthy, but I continue working on it in the background. I will post when there is success.
Ignoble's project can work and his ideas are solid, but, as stated, the actual build of the injection system is a killer. Ignoble is presenting some unusual concepts that hopefully will lead to success, and I am anxious to see.
Lloyd
Edited the last sentence to improve the tone a bit. I was half asleep when I first wrote it, LOL.

 

[The Ignoble Troll]

I started down the thought experiment path of a small 2 stroke diesel as a proof of concept before embarking on a much more ambitious mutli-cylinder model, and I've conclude (obvious to many) that the biggest difference between it and a normal IC or steam engine is primarily the fuel pump & injector combination. My next observation was that I didn't think it was really a design issue, but rather a fabrication issue that is preventing small model diesels being built, i.e. micron level fits on 1 or 1.5mm plungers to have good control and reliable performance requires a degree of precision few modelers want to try to (or can) achieve.


I agree the injector can use minimally lapped parts - but what about the pump? Are you just planning on designing a pump that can tolerate leakage, i.e. make it capable of way more volume than required and map its performance so even if it is only 80% efficient it can still work, and that is the reason for solenoids?

I agree with you but was inspired by the relatively rough finish on a commercial pintle injector I bought to examine.

The only honed surfaces where where they absolutely had to seal.

By using a plunger pump, not a piston pump, to generate the needed pressure means I only need a smooth shaft and the seals in the plunger pump body, to get the pressure I need. This way the only precision sealing surfaces will be in the separate injector. It should be leak proof when done.


I think plunger fuel pumps will offer modelers the same advantages that they offer modelers in make up pumps for steam engines.

 

[The Ignoble Troll]

The solenoids will take some experimentation to find out how best to extract the power you need, in the form that you need it to be in. Sometimes you can start the solenoid farther out of the coil and let it pass thru to gain velocity for an impact, using the laws of conservation of energy and conservation of momentum to your advantage. Just a slight change in starting point or impact point can make a noticeable difference. Because your solenoids are rated at 70N @12v@100% duty, you will have some room to play around with the electrical power applied to the solenoid. Because you will be operating at less than 100% duty cycle, you can (for example) double the voltage and get approx 4 times the impact power from the solenoid. But the speed of actuation is where the biggest gain will probably be. A sharp hit, rather than a slow thump might better suit your needs. Despite wanting to keep the control circuitry simple, you will still need a solenoid driver (controlled by the Arduino) to actually fire the relay, that will in turn, transfer the required amps to the injector solenoid. It might sound complicated, but once you get into it, it will start to make sense, and the design will evolve.

All great insights, thank you. Your work is part of the hobby work that led me to my current design work.

Ah... the listing for the solenoids I wanted has vanished... and I can't locate listing's for full duty 70n solenoids now. Bigger ones are available though, which is fine. I might go the route of using stronger ones.

 

[The Ignoble Troll]

@ninefinger I agree with Everything you said. The fuel injection is the evil devil in model diesels. The injection system, whether it is a pump-line-injector, or pump-line-solenoid injector, or a unit injector of pump and injector in a single unit, that is the real bugaboo. A few on this forum have successfully gotten past that hurdle, and have moved on. My mental battle with the unit injector on my 2 stroke project is probably not healthy, but I continue working on it in the background. I will post when there is success.
Ignoble's project can work and his ideas are solid, but, as stated, the actual build of the injection system is a killer. Ignoble is presenting so unusual concepts that might lead to success, and I am anxious to see.
Lloyd

Thanks,

I am really hoping to only fight my battles on the injector hill, and that the pump will fall into line.

-Troll

 

[JimSvarv]

As you are not using a helix cut off type of pump you don't need a plunger to cylinder sealed finish.
A o ring in the cylinder as some steam boiler feed pumps should be good enough.
Making the pump itself a easy build.
Controlling the stroke and timing for fuel metering will be done with the solenoids.

So it's only the injector that may present a different machining challenge compared to other ic engines as I see it.

Did just look back at the thread and saw that Troll wrote pretty much the same conclusion...

Anyway a different way for you to control the metering with solenoids is to have them acting on a bleed valve.
So after your plunger have travelled say 40% the solenoid push a ball or poppet open.
The timing you can adjust with this system is a bit limited but you can fully adjust the amount.
Many full size diesels are running at fixed timing anyway.

 

[JimSvarv]

https://www.disa.it/wp-content/uploads/2020/07/01HystoryOfDieselFuelInj.pdf
On page 3 fig 5 is a system I wrote about.
But instead of a wedge you use a programmable solenoid.

 

[ninefinger]

Unfortunately a plunger pump still requires a tight tolerance on its shaft, otherwise the leakage is significant relative to the size we are dealing with, and leakage = pressure loss and uncontrolled volume displaced. In larger sizes (say 3/8" or 10mm), a good fit maybe measured in a difference of thousands of an inch (~25microns), but on a 1.5mm plunger the fit needs to be much better, measured in ten thousandths of an inch (~2.5 microns). Maybe I'll start a new thread with my pipe dreams for a model diesel (as I'm so far behind on other projects mine may never get going properly).

Anyways, that is why I asked if leakage doesn't matter, you can overcome leakage with more displacement and more force for pressure (solenoid) and electronic control for timing. However, that solution doesn't play well with making a scale model that at least looks similar to a full size prototype, unless all the pumping and electronics bits are concealed in a base cabinet (similar to how many display IC engines are done).