Injected Diesel 56cc 2 Stroke, Will it ever work?"

[Roger B]

Ok, if I understand correctly injection starts when the piston closes the inlet/spill port and ends when the wedge cutout exposes the port. By my experience the piston should only return far enough to fully open the port and the working stroke should only displace the maximum amount of fuel required plus a bit for leakage. This reduces the amount of 'churn' in the port.

 

[Lloyd-ss]

Ok, if I understand correctly injection starts when the piston closes the inlet/spill port and ends when the wedge cutout exposes the port. By my experience the piston should only return far enough to fully open the port and the working stroke should only displace the maximum amount of fuel required plus a bit for leakage. This reduces the amount of 'churn' in the port.

Roger, You have described the operation perfectly, and I agree with your suggestions. The inlet/spill port is round and I have considered using a carbide burr to make the bottom edge of it flat ("D-shaped") to give a more crisp closing cut-off and pressure build-up. What do you think? When the pump is driven by the electric motor in the test set-up you can definitely sense/feel when the pressure is building and the pump is really "working."

I agree that there probably is excess piston stroke. At this stage, modifying the cam lobe is the only option to correct that. Luckily, the cam is keyed onto the shaft and my index head and arbor are still set up on the mill so modifying the profile is just an annoyance, not really a problem. It is only a problem if I go to far and remove too much height. LOL.

A gentle nudge from someone else is often the impetus needed to make such changes.
Thanks,
Lloyd

 

[Nerd1000]

Another bit of funny business I encountered when testing my injector was that certain liquids (such as the lanolin spray I tried to pump through for corrosion prevention between uses) can have lots of dissolved gases, these gases will come out of solution in the pump and 'de-prime' it on the suction stroke.

 

[minh-thanh]

I have avoided pressurizing the fuel supply, but in the end, it might be necessary. I don't know. The entire set-up is very touchy with so many variables during the optimization process. Things like stroke length, starting point and ending point of the stroke, check valve design and cracking force, excess volume, the outlet pressure check valve to the injectors, and more. Changing and testing the variables is time consuming and they are all inter-related, and it is difficult to tell what change is causing what result.



The design is super touchy and I am not sure I made the correct choice in using this design, but when it works, it works well. But each stage in the engine building process seems to change something and a tweak is needed to get it working properly again. Unfortunately, "which tweak?" is often a mystery. It definitely tries my patience and is more of a psychological challenge than anything else. Probably a little unhealthy, LOL.

I quite agree with you
With a 4 cylinder engine I have 4 fuel pumps, I changed the pump system...to find out (I did a total of 20 ball valves including changing the ball diameter...). With a lot of testing, I don't really understand the fuel pump system for small engines yet
It was too small to control...so I went back to the original design the same way I used it in a single cylinder engine.
As you say : " It definitely tries my patience and is more of a psychological challenge than anything else " , yes it is
But I really like the way you deal with it : "ha ha., LOL "

 

[Lloyd-ss]

UP AND RUNNING AGAIN..... AT LEAST FOR A WHILE June 19,2023

I totally rebuilt the inlet/spillage check valve assy, with improvements. The learning never ends, which is a good thing. Once you stop learning, its all over.

I cleaned the injector all up and put it back together, and GD it! A lot of pumping activity, but no fuel coming out of the injector. More frustration. I decided to lower the fuel level in the fuel tank (pic in reply #176 ) so that it was below the 1/8" return line. I tried it again and I could see proper return spurts of fuel coming back into the tank. So at least some type of pumping was occurring. Light bulb moment: How about a dirty injector tip? I had previously made a little pressure fixture where the injector tip could be loaded into it with forward flow or backward flow. Pressure was from a high pressure hand air pump. I loaded the tip in in the standard direction, and pumped it up to 700 psi and stopped. Yup plugged. I took the tip out and reversed it and it cleared out with less than 100 psi. Rinsed it all out nicely with alcohol. Reassembled it and bled it. With the spill port above the fuel level in the tank it was easy to see the air coming out of the spill port. The fuel actually got cloudy with air, but then nice and solid with just the fuel. A minor preload adjustment at the rocker arm to adjust the stroke starting point, and there it went. Just like it is supposed to. Time to quit for the night on a high note.

 

[Roger B]

Your combined pump and injector is based on the GM version I believe:

The central bore for the spill port is similar to the Simms Uniflow pump. This was supposed to reduce the side forces on the plunger:

The more normal Bosch CAV design has a spill groove leading to the helix. This gives a positive stop position when the groove is over the inlet port. There are also separate inlet and spill ports to try and reduce turbulance although they both lead to the same fuel gallery:

The Benes pump tries to further separate the inlet and spill ports:

The source of the information is this book:

 

[Lloyd-ss]

Roger, you are correct, the "unit injector" is "loosely based on", or "similar to", the Detroit Diesel unit injector for their iconic x-71 series of 2-stroke diesel engines.

Your reference manual is excellent. I notice that it is a Chiltons publication. I can remember the Chilton's, and Motors, and Audels, manuals in the garage at home when I was growing up. All the greasy fingerprints on the pages. Great memories. I remember overhauling a Ford C-6 automatic transmission when I was 17, and it actually worked fine when I completed the project. Successes like that just make you want to do more.

Now that the unit injector seems to be working reliably (I still need to measure output volume, though), there is a 2.5mm length of dead volume in the pump cylinder left over when the plunger is at the bottom of its stroke. There seem to be other areas of dead volume in the various injector designs, so I am wondering if it would be worth the effort of making a stationary plug to fill up that dead volume? The volume is equivalent to about 30 injections from the injector.

On thing that is interesting is the relative sizes of the return springs that are required in a model compared to the full size component. If the model is 1/3 scale, running at a specific rpm, the velocity of the part is 1/3 of the original and the mass might be as small as 1/9 the original. Therefore the inertia of the component could be as low as
Inertia = mV^2, or (1/9)x((1/3)^2) = 1/81. In reality the springs can't really be that small and still function properly because of practical constraints, but I believe that calculation is correct.

I now need to get a good video of the entire valve train including the injector pumping fuel.
Lloyd

 

[Roger B]

Dead volume does not seem to be a great problem as long as it can be purged of air. An air bubble of similar size to the injection volume will mess up the injection completely. The maximum fuel volume you will need for 56cc is less than 5mm3 unless you have a significant boost pressure from the blower.

 

[Lloyd-ss]

Dead volume does not seem to be a great problem as long as it can be purged of air. An air bubble of similar size to the injection volume will mess up the injection completely. The maximum fuel volume you will need for 56cc is less than 5mm3 unless you have a significant boost pressure from the blower.

Yes, that is what I was thinking/hoping about the dead volume.
Our fuel calcs agree, so that is a good thing. My testing seems to indicate that the roots blower will fully scavenge the cylinder, but not not add any boost. In the Detroit Diesel the 1-71 blower runs at twice crankshaft speed.

 

[minh-thanh]

Dead volume does not seem to be a great problem as long as it can be purged of air. An air bubble of similar size to the injection volume will mess up the injection completely.

.

 

[ajoeiam]

Your combined pump and injector is based on the GM version I believe:



The central bore for the spill port is similar to the Simms Uniflow pump. This was supposed to reduce the side forces on the plunger:



The more normal Bosch CAV design has a spill groove leading to the helix. This gives a positive stop position when the groove is over the inlet port. There are also separate inlet and spill ports to try and reduce turbulance although they both lead to the same fuel gallery:



The Benes pump tries to further separate the inlet and spill ports:



The source of the information is this book:

View attachment 148117

Hmmmm - - - - - where did you get your copy of the book - - - please?

 

[Roger B]

I purchased it online from someone like this:

https://www.abebooks.co.uk/Modern-Diesel-Automotive-Oil-Engines-Transport/30902675577/bd
There are several versions available. I have a pre WW11 version and a post WW11 version. These were taken from the later version.

 

[Lloyd-ss]

Choices, Changes, Learning, the Journey, and a Thank You

This thread, this build, is now in it's 4th year. It's not that I am exceptionally slow, but it is amazing how many life changing events continue to occur in our later years. I am now 72, but certainly don't feel old, except for maybe when doing some outdoor labor in the hot summer. The thought of retirement being a time of leisure and with all the time you want to do those things that YOU want to do is just a myth. But that is life for each of us, and it all enriches us with new experiences and opportunities to learn. It all keeps us young, and worn out, LOL. Maybe too much of a good thing, but I love it!

There are a lot of threads in this forum about choosing a first engine to build: find plans for a proven design that looks like fun, and build it and learn from it. But I am too hard headed, or maybe I just prefer certain types of intellectual and mechanical challenges. So here I am 4 years later, still working on a 2 stroke diesel, with roots blower, and a unit fuel injector. Sometimes I look in the mirror and think, "What a fool." Other times I think, "I can't believe how fun, and how fulfilling this is." I am loving it, and overall, have almost no regrets. And a lot of that positive attitude comes from the members of this forum. My sincere thanks to all of you!

Lloyd-ss

 

[Roger B]

I started playing with fuel injection and diesels 8 years ago. I'm getting there

 

[minh-thanh]

Hi @Lloyd-ss !
""Injected Diesel 56cc 2 Stroke, Will it ever work?""

To me, it doesn't really matter whether the engine runs or not
Finding something new , strange .. difficult .. building it and sharing it with everyone that is really important . Trust me, I have learned a few things from your project and I plan to apply it in my engine building later.
And thank you for sharing this project !
Edit
And I actually like the way you deal with mistakes / failure more than the way you build engine

 

[minh-thanh]

The rockers are roughed in and now need roller tips.

View attachment 146893

Hi !

I am designing a cylinder head similar to yours,
I have a question, do you think the high temperature will affect the fuel pump or the fuel ? because the pump is too close to the cylinder head

 

[Nerd1000]

Hi !

I am designing a cylinder head similar to yours,
I have a question, do you think the high temperature will affect the fuel pump or the fuel ? because the pump is too close to the cylinder head

The heat will reduce fuel viscosity, but maybe that is a good thing?

 

[minh-thanh]

Yes, that's possible., but if he uses volatile fuel it could be a problem, just my speculation.

 

[Roger B]

Pump diesel will not be a problem, many common rail engines circulate the fuel through the injectors. Plant oil based fuels can be a problem as they break down at high temperatures. Using cooking oil as a fuel for a conventional jerk pump system is ok, for common rail expect problems.

 

[Lloyd-ss]

Hi !

I am designing a cylinder head similar to yours,
I have a question, do you think the high temperature will affect the fuel pump or the fuel ? because the pump is too close to the cylinder head

I don't know if it will be a problem. The pump is located there just for testing. I am not sure where it will be in the final version.
Lloyd