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

[djswain1]

Yup, I am learning the diesel jargon. It seems like the 2 most common mechanical types that are applicable to the diesel model engines are the (1) unit injector :located in the head, driven by a cam and rocker arm, with the pump and injector as a single unit, and bypass for excess fuel back to the tank. Correct? (2) Separate, matched pump unit and injector unit, with the pump driven off the cam shaft, and only the injector mounted in the head. I think that is right.

At the earlier urging of Bruce (I think), I purchased the smallest and cheapest pump and injector pair that I could find, to take apart and see what makes it tick. It seems like the injector and pump are the major bug-a-boo for model diesels. And seeing this is my first build, I have no qualms about, if it is absolutely necessary, machining excess material off the purchased items to install on the model. I know it is a cop out, but I am not copying any particular design and am a pragmatist, not a purist. Hopefully I won't have to do that, LOL.

Here is a pic of the "type 186" parts I bought, which probably put out 10 times the volume I need. You can see the volume control lever on the pump. I imagine it is more precision, than complicated. Each item is about 3" long.
View attachment 128760

Yup, I am learning the diesel jargon. It seems like the 2 most common mechanical types that are applicable to the diesel model engines are the (1) unit injector :located in the head, driven by a cam and rocker arm, with the pump and injector as a single unit, and bypass for excess fuel back to the tank. Correct? (2) Separate, matched pump unit and injector unit, with the pump driven off the cam shaft, and only the injector mounted in the head. I think that is right.

At the earlier urging of Bruce (I think), I purchased the smallest and cheapest pump and injector pair that I could find, to take apart and see what makes it tick. It seems like the injector and pump are the major bug-a-boo for model diesels. And seeing this is my first build, I have no qualms about, if it is absolutely necessary, machining excess material off the purchased items to install on the model. I know it is a cop out, but I am not copying any particular design and am a pragmatist, not a purist. Hopefully I won't have to do that, LOL.

Here is a pic of the "type 186" parts I bought, which probably put out 10 times the volume I need. You can see the volume control lever on the pump. I imagine it is more precision, than complicated. Each item is about 3" long.
View attachment 128760

Yes essentially, but there are lots of different injection systems and variations. Plunger pumps can be driven from the main valve camshaft or their own seperate camshaft. Small engines especially single cylinder usually have a separate plunger (or jerk) type pump injection like the parts you have purchased. The type 186 are copies of the Yanmar L series which is one of the most common "modern" single cinder air cooled industrial engines. It is a direct injection (DI) engine with a multi-hole type injector nozzle. The pintle type nozzle is probably the easiest design to use they are usually on indirect injection engines (IDI). You should be able to download an L series service manual which may have details if the pump & injection.
IDI engine usually have flat top pistons and a pre-combustion or swirl chamber into which the injector injects. DI engines have shaped bowls in the piston crown with the injector, injectng directly nto the cylinder. Glow plugs can be used on DI & IDI.
Regards, Dave

 

[Peter Twissell]

Lloyd, the displacement of the blower is 6 lobe spaces per revolution.
Thus, at 3.2 to 1, the blower displacement is equal to the cylinder displacement, giving similar volumetric efficiency to a conventional crankcase induction 2 stroke.
Pete.

 

[Lloyd-ss]

Lloyd, the displacement of the blower is 6 lobe spaces per revolution.
Thus, at 3.2 to 1, the blower displacement is equal to the cylinder displacement, giving similar volumetric efficiency to a conventional crankcase induction 2 stroke.
Pete.

Pete, great, 6 lobe spaces per rev is more pleasing for the overdrive! Thx

 

[Lloyd-ss]

Hmmmm - - - I downloaded the pic and enlarged it using software but I can't read the gauges.
Would like to get more details on this setup as it would seem something that would be very very useful.
(the ratings on the pressure gauges is I think mainly what I'm looking for but if you have more notes (so far you seem to have such) they would also be
useful - - - - I'm trying to force myself to take more notes here to ease future stuff development - - - -memory is pretty good but all too often after 5 or especially 10 or more years there are details missing!!! - - - notes is what helps the memory - - - grin!! (thanks for the impetus!!!))
Dunno about board recommendations but maybe to make this info more easily 'find-able' a new thread may be quite useful - - up to you though!!

Joe, I am going to combine a few responses into one and hopefully won't miss anything.

Flywheel-
Yes, for the inner band on the main wheel, I did the math and cut a section of the inner band and then squeezed with some bar clamps and forced it into the main outer wheel. It jammed in plenty tight. I am sure there are as many different ways to make a flywheel as there are hobbyists. For me it boils down to: what material do I have on hand, or what can I easily buy, what tools do I have, and what skills do I have, or think would be useful to learn. For me, the limits were poor welding skills, and a lathe that was barely big enough.

Lister drawings- I don't have clue about those.

Note taking-
wow, we all have our own methods, and it is a real pain when you forget what you did or how you did it. Spreadsheets, drawings, often partial drawings, but decent as-built drawings even if only I can understand them. A project notebook and a project folder on the computer. Plenty of pictures, with useful names, and the so-so pictures either deleted or put in an archive folder. Then maybe a few videos. I built high performance air rifles for a number of years and did a lot of material testing (airgun lab on you tube), so record keeping was pretty important so that if someone needed something fixed 5 years down the road, I had some info.

Pressure test fixture.
Here is a slightly better picture. The low pressure side gauge is a 10,000 psi gauge from McMaster. Maybe $15 or $20. The nice 30,000 psi high pressure gauge (30,000 psi full scale, 15,000 at 12 o'clock) is a deal I got on eBay. New it is ridiculous. PM me if you need other info about the test setup, but first check out my airgun lab youtube videos. I have lots of material test videos including tube burst failure tests, screw shear strength tests, and more.

 

[Lloyd-ss]

First Test of the Roots Blower.

The real setup will have a 29 tooth gear on each rotor shaft, meshed directly to each other. And, real bearings. This setup is made from gears salvaged from the planetary gearset from a battery powered drill. Even if there was only .001" backlash for each gear, plus, adding a little runout here and there, the needed .002" clearance between all the surfaces of the rotors, is totally hosed up. The rotors could be rotated manually, demonstrating proper clearances, but driving via the geartrain, there was clicking and clacking all the time.

Prior to testing, I operated the rotors within the housing and end plates with lapping compound and oil to remove any high spots. That process worked well and I took everything apart (again and again and again) to clean it all up and try rotating it, checking for clearance and smoothness. When I thought it was good, I attached the Rube Goldburg geartrain, and what a disappointment. If either rotor lobe is .001" too early or too late, they click. At .003" it makes a clack. At .005" everything locks up. Hopefully the larger 29 tooth gears will eliminate that problem.

I did test for pressure and only got a half psi from the outlet. I could feel suction on the inlet. I think, in the end, the blower itself will work properly. But this geartrain is garbage.

Lessons learned (actually, relearned for the umpteenth time):
Don't get greedy. You can see a 1/8" aluminum plug in the cover near a screw. I was using a 4-40 tap in the housing, and was at the point where I knew the tap needed to be backed out and cleaned and more oil added. But I only needed 1/8 more turn. You know what happened. There was 2 hours of crappy rework.
Be patient. I had my doubts about the improvised geartrain. The proper gears are still a week away. Should have waited.

Some habits are almost impossible to break.
Lloyd

 

[Lloyd-ss]

Yes essentially, but there are lots of different injection systems and variations. Plunger pumps can be driven from the main valve camshaft or their own seperate camshaft. Small engines especially single cylinder usually have a separate plunger (or jerk) type pump injection like the parts you have purchased. The type 186 are copies of the Yanmar L series which is one of the most common "modern" single cinder air cooled industrial engines. It is a direct injection (DI) engine with a multi-hole type injector nozzle. The pintle type nozzle is probably the easiest design to use they are usually on indirect injection engines (IDI). You should be able to download an L series service manual which may have details if the pump & injection.
IDI engine usually have flat top pistons and a pre-combustion or swirl chamber into which the injector injects. DI engines have shaped bowls in the piston crown with the injector, injectng directly nto the cylinder. Glow plugs can be used on DI & IDI.
Regards, Dave

Dave,
thanks for all the injection info. You know your diesel systems! I took your advice and downloaded a copy of the Yanmar service manual for the single cylinder L series diesels. I bought the 186 pump and injector 2-1/2 years ago and they seem applicable, design-wise. But golly, they are big and heavy, about 4" long. Made for years of service and abuse, I guess. The manual shows how to disassemble and what makes them tick. Trying to "skinny them down" looks like it would be a futile effort. A good learning tool, though.
Lloyd

 

[Lloyd-ss]

The Roots Blower is working

I had doubts at times, but the Roots blower is now working reasonably well. It has advanced from Proof of Concept, to Prototype.
The actual pressure and flow still need to be measured, but calibrated thumb pressure, LOL, shows significant output pressure and input suction at 2500 rpm. Flow appears to drop off with rpm but below 750 rpm, the flow is very anemic. The Detroit Diesel maintenance spec calls for about 4 psi at 2000 rpm and I think this blower is definitely there.

I ended up making a pair of 36 tooth gears, one being the drive, and the other the driven. The mill setup was kind of cheesy with a few hand-ground tooth profile cutters that approximated an involute. The spin fixture had an easy 36 spaces, so that is where the tooth choice came from. My 9 year old grand daughter was hanging around and wanted to "drill something" so she turned the table crank back and forth between the stops as I indexed the spin fixture. She was VERY proud of her work as she also did the final light sanding on the tooth tips and scrubbing them with soap and a brush in the sink.

There was a tedious amount of hand fitting and sanding and polishing of the rotors to get them to rotate with only a tolerable amount of noise. There is still quite a bit of work to do on the blower, mainly, real bearings.
A question comes to mind. With such little scavenging airflow from the blower at low RPM, will auxiliary air be needed during start-up? Possibly mini air tank and air motor for starting?
Lloyd

Drive and driven gears showing Inlet port

Outlet port
The black lube you see here and there is a little bit of moly. In the end, rotors will need to run w/o lube.

To do the testing, I am setting the blower gear-side-down on the drill press in a vise and driving it with a 5/32 hex bit in the left-side socket head "drive" screw.

Video and pressure test coming the next few days.

 

[djswain1]

Dave,
thanks for all the injection info. You know your diesel systems! I took your advice and downloaded a copy of the Yanmar service manual for the single cylinder L series diesels. I bought the 186 pump and injector 2-1/2 years ago and they seem applicable, design-wise. But golly, they are big and heavy, about 4" long. Made for years of service and abuse, I guess. The manual shows how to disassemble and what makes them tick. Trying to "skinny them down" looks like it would be a futile effort. A good learning tool, though.
Lloyd

No problem. Yes I think it is the difficulty of minuaturising the fuel injection system that is the main reason few diesel models are built. At least with a model there are not any strict performance or emissions criteria to adhere to. Often the main criteria (ignoring aesthetics) are that it starts and runs...
I can see by your approach to the blower you aren't one to throw in the towel at the first hurdle ;-)
Cheers, Dave

 

[Vietti]

Any chance some of the noise is gear noise? Really neat project!

John

 

[Lloyd-ss]

No problem. Yes I think it is the difficulty of minuaturising the fuel injection system that is the main reason few diesel models are built. At least with a model there are not any strict performance or emissions criteria to adhere to. Often the main criteria (ignoring aesthetics) are that it starts and runs...
I can see by your approach to the blower you aren't one to throw in the towel at the first hurdle ;-)
Cheers, Dave

Thanks Dave. You are correct, I have no delusions that this will be at all easy. It might be impossible for me. Who knows?
Looking at the level of perfection and skill and knowledge of the members on this forum, I am totally humbled and in awe. I am seeing that there are tips/tricks/techniques that will help, and in the end, if I get it to actually fire... by whatever means, I will be thrilled. And I will be 100% honest if I have to use "unapproved" techniques to get there the first time.
Lloyd

 

[Lloyd-ss]

Any chance some of the noise is gear noise? Really neat project!

John

Hi John. I was thinking about that when I first got it rotating, too. I worked on smoothing the gears up some and then spun them in the housing with the shafts and end plates installed but the rotors removed. Eventually I got them to be almost silent. (my hearing isn't that great, ha ha) But after putting the rotors on the shafts, I could feel the interference points as I rotated the assembly with a hex bit and slow speed drill. I would take the rotors out and work on the problem areas, and put it back together (with index marks) and try again. Eventually, they ran kinda smoothly, but the noise was definitely coming from the rotors clicking together here and there. I don't want to remove any more material until I get some proper bearings in place and get the runout under control. Each effort results in an incremental improvement. It DOES test one's patience, and I am sure I hear some chuckling from members, LOL. Trial by fire.
Lloyd

 

[Ghosty]

Lloyd-ss, Invest in a set of gear cutters, then you can cut the gears to mesh with almost no backlash, and would be able to get it to spin over very easy.
Cheers
Andrew

 

[Lloyd-ss]

Andrew, yup, I know you are right. I can buy gears relatively inexpensively, but being able to dial in the center distance and backlash when necessary would be very nice. I worked at a gear shop in Detroit in the '80's and know how beautiful nicely made gears can be. And the Roots blower needs zero backlash, for sure.
Thanks for planting that bug in my ear about a few cutters. I've just never needed the capability before; but maybe now.
Lloyd

 

[Ghosty]

Lloyd, I have bought 3 sets at the moment(Mod 1, 0.5, and 0.4) still looking at getting a 1.5 and mod 2 sets, also looking at DP24 and was looking at the DP64, but the Mod 0.4 is exact copy. I'm working on a step up counter rotating gear box for RC boat at the moment.
Cheers
Andrew

 

[Lloyd-ss]

Lloyd, I have bought 3 sets at the moment(Mod 1, 0.5, and 0.4) still looking at getting a 1.5 and mod 2 sets, also looking at DP24 and was looking at the DP64, but the Mod 0.4 is exact copy. I'm working on a step up counter rotating gear box for RC boat at the moment.
Cheers
Andrew

Andrew,
thanks for sharing those pictures of your gear train work. Can I call them inspirational? I had planned on the inevitable need to re-make few of the parts for the roots blower. Surprisingly, I think the rotors themselves are ok. The housing and end-plates are ok, too. But new shafts, gears, and bearings are necessary if this thing is going to work. The end plates are thick enough that they can be counterbored for the shaft bearings.
It looks like you are using fully sealed ball bearings at both ends of each shaft, is that correct?
Progress is slow, but the learning process is really amped up.
Lloyd

 

[Ghosty]

Lloyd,
They are fully sealed but they still leak, Oil leaks out, not very quickly, but it does leak, may be to do with pressure, or speed, input is almost 19,000rpm, but when there is only 3ml of oil to start with you have to keep on top of it.
The gear box shown is the one I am replacing, it has a ratio of 1-1.07 , new one is 1-1.15.
And the boat that it goes in.
It is all trial and some error when designing from scratch, just have to keep at it, took three goes to get the gear box design right.
Cheers
Andrew

 

[Lloyd-ss]

Lloyd,
They are fully sealed but they still leak, Oil leaks out, not very quickly, but it does leak, may be to do with pressure, or speed, input is almost 19,000rpm, but when there is only 3ml of oil to start with you have to keep on top of it.
The gear box shown is the one I am replacing, it has a ratio of 1-1.07 , new one is 1-1.15.
And the boat that it goes in.
It is all trial and some error when designing from scratch, just have to keep at it, took three goes to get the gear box design right.
Cheers
Andrew

That yellow thing looks like it is going 100mph while still on the bench! 19,000 on those fast pitch props sounds crazy.
I like the collet/flarenut arrangement for quick disconnect from the props. A serious hobby.
Thanks! Lloyd

 

[ajoeiam]

snip
And the Roots blower needs zero backlash, for sure.
snip

Hmmmmmm - - - - I would have thought that of all places a machining type forum would NOT promulgate the idea that ZERO error could ever be achieved.

(It is possible to get backlash very low - - - - but its NEVER zero!!!!)

 

[Lloyd-ss]

Hmmmmmm - - - - I would have thought that of all places a machining type forum would NOT promulgate the idea that ZERO error could ever be achieved.

(It is possible to get backlash very low - - - - but its NEVER zero!!!!)

OK Joe, let me start by saying that I do have a smile on my face right now although the text of this message might not sound that way. My last 25 years of work were as a manufacturing engineer, where setting people up for success was the goal, and esoteric discussions were neither understood nor appreciated. But I also worked with the hardcore design theorists/research engineers where a joke about someone not knowing that the cosecant and cotangent of extremely small angles are "essentially" identical, would bring a hearty round of laughter. They understood the esoteric discussions, when time permitted.
I used the qualifier "essentially" and I guess I could have said that the backlash should be "essentially" zero, but I didn't. Didn't think it was necessary given the context of the conversation.
But I will give you 2 examples where the backlash can be zero. If you roll a newly ground steel gear against a master gear to inspect center distance variation and find that the max is 10 millionths of an inch, I would say that that test fixture operates at zero backlash. The other is when I was making the aluminum gears to try on the blower in this thread. As I was creeping up on the proper tooth thickness/backlash, I installed the gears on the assy and got it where I could barely rotate by hand. I could feel the bump-bump from tooth to tooth as the clearances were all used up and the soft aluminum of the teeth yielded enough to rotate while maintaining point to point (line to line) contact.

Whether we call it zero backlash, or almost zero backlash, doesn't matter to me. I want it to feel, with my fingertips, like there is no backlash, and, if you checked with a dial test indicator, (one .0001" per graduation), you probably couldn't say for sure if there was or was not any backlash. I am still smiling!

Different subject. Just wondering, did the additional picture of the high pressure hyd test fixt show you what you were curious about?
Enjoy your weekend!
Lloyd

 

[Lloyd-ss]

Roots Blower Pressure and Volume Tests - Video and pictures

The Roots Blower is working well enough for testing, but not well enough to used in a working model engine. Proper bearings and gears are required, but the rest of it should be serviceable. After much reading about positive displacement blowers, like the Roots, I became quite curious about the actual performance. It seems like using the Roots as a supercharger, to get several pounds of boost was not part of the original design goal, but it certainly has been adapted well, using better sealing and very high overdrive speeds.

The old Detroit Diesel Roots blowers ran at 1 to 1 to about 1.3 to 1. Pressures were up to 4 psi at 2,000 rpm, but I am not sure how that was measured. The blower that I made is about a 1/5 th scale version of a DD 1-71 blower. But even though the blower is 1/5 th scale, the clearances between the rotors themselves, and the housing are still at a 1 to 1 scale, so the leakage (slippage) in the blower might be proportionally 5 times greater in my model than in a real DD Roots. And, that shows up during the testing.

I set the Roots up on an old drill press and am driving by a hex bit via a piece of rubber hose to serve as a flex joint. For the test setup, the output goes into a PVC plenum that is 67cc in volume. There is a pressure tap off the side of the plenum that is hooked to a manometer that reads in inches of water column. The pressures are very low and I didn't have a gauge that would read that low, accurately. The end of the 67cc plenum has a 3/8" hole (9.5mm) drilled in the end of it. When the blower is in operation for testing, the air can be monitored 3 ways. First, it can just exhaust out the 3/8" hole and the back pressure in the plenum is recorded. This pressure is very low. The next reading is with the 3/8" hole bushed down to .182" (4.6mm). This increases the back pressure some more. Using the back pressure readings, and the exit orifice size the approximate volume of that that is being pumped can be calculated.
https://www.tlv.com/global/US/calculator/air-flow-rate-through-orifice.html?advanced=on
Lastly, tif the exit port is plugged, the manometer will give the maximum pressure that the Roots will make at that particular rpm. I guess pump curves could be graphed from all the various readings.

Vacuum. Because the Roots is symmetrical inside, by driving the rotors from the hex head screw on the other rotor, the rotors turned backwards and the pressure plenum became a vacuum plenum when the orifice was plugged. I was pleasantly surprised to find that the max vacuum was almost the same as the max pressure at same rpm.

Here is the test set-up.


Here is the internal dimensions for the Roots


Here is the outlet port, which is the same as the inlet port. Are they big enough?


Here is the video of some of the actual testing.
I will tabulate the actual test results in the next post.
Lloyd