Experiments With
Hydraulic Injection Pump Ideas
The Eventual Design and Building of A True Diesel Engine.
31 July 2017:
Since building The Homebrew Hvid, I've decided that I really, really like engines that burn low grade fuels and don't have carburetors, spark plugs or need batteries or magnetos.

The "plan" is to come up with a simple and workable injection pump.  At first thought, Diesel pumps seem like simple variable volume high pressure hydraulic pumps.  The complication comes when you realize that the start of injection always needs to start at the same crankshaft position regardless of the amount of fuel the pump delivers.  Having said that, the complications start popping-up

I've designed a pump from scratch that I think will work although it seems to be a bit clunky and may take more force than a relatively small governor can produce.

It's kinda hard to read but here's my idea.
First of all, we have to remember that I don't have proper machines to make very small parts with high accuracy.  Keeping that in mind, I want to only have to do the really twiddly stuff to the pump itself.  Everything in the drawing is to scale and a reference is the pump plunger which will be 0.12600" in diameter.  I will drill, ream and lap the bore for an extremely close sliding fit to the plunger.  Today, I did a test piece to find out just how hard it would be to make this.

I have just guessed the approximate maximum amount of fuel that needs to be delivered to an engine with a one inch bore and two inch stroke (1.5708 cubic inches).  This is probably a lot more than enough but I have to account for pump leakage.

In the drawing, the top part is a simple hydraulic pump with a spill port to ensue that delivery occurs at the same point in the stroke.  The plunger, when it is at rest at the low part of the fuel cam below it, will uncover the 0.040" spill port that leads back to the fuel inlet.  As the piston rises and closes the port, delivery will immediately begin.  At the full fuel position, the cam is timed so that the spill port is covered at TDC on the compression stroke of the engine (this could be changed to suit the characteristics of the engine it is to be used on).  Fuel delivery stops when the apex of the cam lobe is reached, about 80 crankshaft degrees from TDC.

In order to keep the start of injection at the same point regardless of the amount of fuel pumped, I rotate the cam follower in opposition to the cam.  The total rotation allowed will be 40 degrees or less.  In other words, I advance the timing as I shorten the pump stroke but attempt to delay start of delivery to match the amount of timing advance.  

It may be a bit confusing, but I show the pump in the maximum fuel position.  Then, I show three more fueling positions.  At 20 degrees, or half fuel position, there is actually slightly more than half of the total delivery.  This is because I have no way of machining a complex curve on the follower shoe and am using a simple curve I can machine using the boring head on the mill.  Since the curve is simple, the timing is actually a bit advanced at this position so static spill timing will have to compensate for it.  If you think about it, as the engine speed increases, timing should be advanced a bit for optimum running.......  I think.

Oh, yes - Any leakage from the pump plunger will fall to the lower part of the housing where it will lubricate the cam, bearings, etc.  There will be a drain and overflow back to the fuel tank.

In the future, before I actually decide whether or not to build this pump for testing, I may fiddle with the curve of the follower shoe to see if I can get it closer.

Now for the test piece.

My test fit piece.
First off, I rooted around in my pin collection and found one that was 0.1245" as close as I could tell.  I checked sizes of other pins and found a box of pins that nominally measured between 0.125" and 0.126".  The body that the bore was made in is made of leadloy steel.  I drilled a 5/8" deep hole with a #31 drill (0.120").  Then I reamed it with a 0.125" reamer.  With the hole carefully reamed, the 0.1245 pin was a slightly tight fit but, using some very fine alumina made into a watery paste with Diesel fuel.  I got the pin to finish the bore for a relatively good fit.  After carefully washing out the bore and pin with Diesel I blew them clean with air.  

My test fixture was just a small digital 10lb scale. With a bore of approximately 0.125", pressing with a force of one pound on the plunger will produce about 86.4 pounds of pressure.  In testing by pumping air and using #2 Diesel fuel as a lubricant, I could only press with about 1.5 lbs of force (134.5 psi) before it leaked.  I think this step just removed the reaming marks left in the bore.

Since I have no way of measuring the bore size and can only get to within a ten thousandth of an inch (0.0001") with my micrometer, I had to rely on actual fit.  I tried some of the larger pins but they would only almost fit the bore.  I took the undersized pin and again applied alumina and turned it in the bore until I could get one of the selected pins to fit with only slight binding in the bore using Diesel as a lubricant.

I worked this and rinsed a few times until the fit was smooth.  This time, I had to press with about 4.5 pounds of force (403.4 psi) with Diesel fuel before it leaked.  This is about as good as it got and is not going to be good enough for a Diesel engine.  I think I will need between 1,000 and 1,500 psi so the injector will crack at a high enough pressure to overcome cylinder compression and atomize the fuel for combustion.

My final test to just see if it would work any better, I switched to 30 weight motor oil.  This time, I coudn't make it leak air past the fuel lubricant no matter how hard I pushed on the plunger.  Since the scale only goes to 10 pounds, all I can tell is that the fixture makes more than 900 psi.

After doing this test, I think I can be confident that a serviceable injection pump can be made in my shop.  I know I can do the rest of it.  
I will order a one eighth inch cylindrical lap, a couple of extra replacement barrels and one or two 0.126" precision steel perforator pins if I decide to go ahead with this design

There are other pumps I can make.  The simplest is one that has a manual timing adjustment.  Since, without changing the timing adjustment, only mediocre performance can be achieved at varying loads.

I've also studied the fuel pump used in a large, old Diesel engine that always starts delivery at the same time with a fixed stroke but uses lever, eccentric and pushrod arrangement tied to the pump rod to raise the inlet valve to the pump and stop fuel delivery.  My guess is that it will take a substantial amount of force from the governor to counteract the force of the inlet valve lifting pushrod when under injection pressure.

I'll think on it for a while.
1 & 2  August 2017:
Looking in one of my old technical books, I found what I think is a very simple and buildable pump that has constant start of delivery and varies end of delivery to control volume.  This one came out of a 1925 book and is simply titled "Typical Arrangements of Mechanical Injection Pump".
"Typical Arangements of Mechanical Injection Pump" from 1925 book.
                                                  This side shows my take on the design .      
I like the method of timing the end of delivery although, at over 1,000 psi, it may take a bit of force to crack the inlet valve.  If the load eccentric is designed right, the load on the governor will only be significant when the pump is making pressure.

I think the design I'm working on (above right) will work.  I've still got to dimension the drawing and add some refinements.  I will try for the main fuel tank to be mounted directly to the injection pump housing and feed fuel by gravity.  If there is too much leakage in the pump, I may have to go with a small overflow day tank for the injeciton pump with a lift pump to raise fuel from the main tank.
3 August 2017:
I woke up this morning and had a "DOH!" moment.  As is my usual practice, I made too much of a simple concept.  After watching Find Hanson's YouTube channel and thinking about it for a while, his simple and effective method of controlling injection really makes sense to me.  I've seen the system before in books about larger engines and just didn't think it would work with something small.  

What Find does is to insert a governor controlled "floating" wedge between the cam follower and the pump plunger.  Because the wedge floats, as it is moved in and out between the follower and the plunger, varying the stroke of the plunger.  In ooperation, it tiltsto take-up any space (there is never any clearance between the cam follower and the plunger, so that the pump always starts delivery at the same time but stops delivery when the cam finishes rising.  Of course, the pump is simply a precision built pump with check valves.

There may be a pause in this narrative while I await another book on Diesel principles and think this whole thing over.  In the meantime, I may modify ENG12-2.DWG, making it ENG12-3.DWG which uses the floating wedge for control.

Since this whole precision pump thing is new to me, I will make the pump as a separate, self contained mechanism so it can be modified in the future without having to partially disassemble the engine.    
7 August 2017:
While awaiting delivery of another Diesel fuel injection book to study, I made a major revision to ENG12-2.DWG.  This design should be easier to build and I have fleshed it out with some fittings, a day tank, etc.

This should be buildable.
I've substituted a flat bottomed wedge for the swivel and eccentric arrangement.  I've added a fuel lift pump and a day tank.  There will be an inline filter between the outlet of the lift pump and the day tank inlet.  Note that the overflow from the day tank flows to the cam/tappet/wedge housing and from there it overflows back to the fuel tank.  Any leakage past the injector plunger naturally goes back to the tank.  There will be a trough inside the housing to direct the overflow from the day tank to the middle of the assembly to make sure fuel flows over all of the moving parts.

It is assumed that #2 Diesel will have enough lubricating properties to take care of the moving parts of the fuel injection pump assembly.  The cam bearings and cam followers are unsealed ball types.

The entire day tank and the facing cover of the bottom mechanicals are to be made of 1/4" plexiglass so I can see what'e going on.

Also note that the main bearing mounts are independent from the front and back covers.  Pipe fittings are approximately scaled to 1/8NPT.  Virtually all of the screws shown are 6-32, except for the day tank which are 2-56.
10 August 2017:
While awaiting "The Book", I went ahead and made the parts for the day tank.  As it is, I have to go to Fastenal to get the 2-56 X 1/2 screws before I can put it together.  Here are the plexiglas parts.  There was one change made becaause when I started looking at the scale of things, I substituted some 1/8" steel tube for the 1/8 NPT fittings which looks a lot nicer.  This tubing can be partially threaded with a 10-32 die and the female parts threaded with a matching plug tap and they fit really nice.
14 August 2017:
Day tank parts
I got "The Book" yesterday and am studying it to see how my idea for a pump compares with what the "professionals" do.  So far, I have seen some really good designs that are proven by time to work well on modern engines but they are too complicated for my shop.  Later today and before I do any more, I will finish the book to make sure I don't make too many stupid mistakes on this project.  
12 August 2017:
"The Book" is read, the decision made.  I will use my design, above.  It is the simplest and has the greatest possibility of being built successfully.  Having said that, here is the day tank.  The back cover is loose because it has to be off to be able to tighten the drilled bolt to the injector pump.
14 August 2017:
The mostly finished day tank.
13 August 2017:
Okay, I've finished the injection pump itself (not the rest of the system).
Here I am at the start of the day.                                                       Ready to be assembled.                                                                  Looks nice but doesn't pump.
I've made the pump body out a piece of ductile iron left over from another project.  On the left in the left hand image above, you can see the cylindrical lap.  Then, there's the extractor pin that I will use for the plunger.  They are ground and polished and very accurate.  This one has a diameter of 0.126".  I drilled the piston bore with a 0.120" drill then reamed it with a 0.125" reamer.  The bore actually was about 0.1255" due to the cheap reamer set I have.

The lap is a rod with a split brass end piece.  There is a tapered plug in the end that can be screwed in to increase the size of the lap.  Since this is the first really close lapping job I've done, I used some very fine alumina powder made into a thin paste using Jet-A (kerosene, parrafin).  I chucked the lap in the lathe and took my time and slowly increased the bore by the approximately 0.0005" until the pin just fit with a slight interference.  I hope that's good enough for this engine because I don't know how I can get the fit any closer.

Then, after lapping the ball valve seats, I put it all together and filled the day tank with Number 2 Diesel.  The first thing I noticed when I worked the plunger was bubbles coming out of the intake port.  Not good!  At that point, I quit for the day.  Tomorrow, I will take it apart and see if I can improve the valves.
14 August 2017:
Spent the day fiddling with the injection pump valves.  Both leaked under pressure.  I ended-up making a lap for the outlet valve seat.
    The 45 degree lap.                                                                           Lapping the inlet seat.
The lap was made from a piece of drill rod, turned to fit into the 1/4-28 threads of the outlet valve cavity.  The outlet valve ball seated well enough to not leak gasoline with just gravity holding it to the seat.

I also lapped the inlet valve seat.  No matter how much I tried, I could not get it to hold any kind of pressure.  There is an issue with there not being enough space for the spring and it continually cocked to the side, making the ball unseat.  I got frustrated with it and ended up making a poppet valve out of a flat head 4-40 machine screw. Because the little poppet valve stuck out from the inlet bolt seat much less than the ball did and had a larger head, there was room for a larger diameter spring.  I used the lap to widen the seat in the bolt then lapped the 4-40 valve to th
14 August 2017:e seat.  It also holds well enough for the pump to prime and move Diesel fuel..

The pump undergoing initial tests.
The pump slowly leaks down to the fuel cup but, when I put my finger over the outlet hole and press the plunger, it still squirts no matter how hard I press the outlet.  Tomorrow, I will again thrash with the pump valves.
15 August 2017:
I got an email from David Jones in Texas and he sent a couple of images of a McCormick Deering WD-40 injection pump.  Looking at them, they are very similar to the ones in the 1&2 August post.
McCormick Deering WD-40 injection pump, courtesy of David Jones.
Then, David very politely set me straight on my faulty design.  The way I have the latest edition, as the fuel delivery is decreases, the start of injection is later and later.  NOT GOOD!

The bad news is that I've got to go back to CAD and re-design the whole outfit so the governor controls the inlet valve of the pump.  That way, the pump stroke is constant and injection always starts when the plunger starts moving.  Injection is terminated when the eccentric causes the inlet valve to open earlier and earlier in the pump stroke.  That's why I try to get all the input I can on these brainstorms.  My best work has always been when I'm getting input, criticism, kibbitzing and argument from other technical types.  This working in isolation causes me to do a lot of back tracking.  Thanks, David.

I also got an email from Chris in Illinois with suggestions on how to make ball valve seats seal by "coining" the seat with a ball that is disposed of after banging it into the seat with a punch.  I didn't think it would work in cast iron and steel.  I have done it in aluminum and brass with success.  If I make the next pump with ball valves, I'll give it a shot.

Aside from all of that, I did get the gauge and made up some plumbing to hook it to the pump.

Pump test fixture.
As you can see, it will hold about 150psi for a quite a while after pumping.  That's the good news.  The other good news is that the pump will make at least 1000psi when pushing the plunger with my thumb (that's about as hard as I can push it without it getting painful.  Because of the leaks, the pressure drops down within a second or two.  The bad news is that I'm gonna have to re-think the whole thing and start over.  At least all i've gotten done is the pump itself and that was good practice for the real thing.

Well, I guess if it was easy, everybody would be doing it.
Boy!  This is fun!

In case you see me about to do something really stupid and want to warn me, here's my email address
[email protected]

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