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

[Lloyd-ss]

Hi Bruce,
"Haven't seen anything like that before," ha, ha, I know what that means. I actually have a video of that pressure test, and some others on youtube if you search on Airgun Lab.
I have to admit that the injector is quite a challenge. One step forward and 2 steps back.
I finally got the injector pintle to hold pressure and, testing with air, have been able to control the pressure where it pops from 500 to about 1000 psi by varying the preload on the closing spring. I will probably have to make a new spring and preload washers to get it pop at higher pressure for better atomization like you mentioned earlier.

And I am indeed making a test fixture with lever to test the injector. But I was drilling out the inside of the side-inlet adapter fitting on the injector to fit a check ball and all seemed good, but when I went to tighten it for testing, the ferrule is now too little for the hole and won't seal. I'll have to figure that out in the morning when I am fresh. Problem solving skills go downhill when I stay up too late, LOL.

 

[Lloyd-ss]

Bruce, I am glad you were so candid about the number of iterations it took to get a pump and injector you were happy with. That makes me feel better. I am now on to version number 3.

 

[weir-smith]

Lloyd

You are joining the club building this engine and there will be a few more versions to go so patience is required. The problem will be in creating enough pressure to atomise the fuel. We are talking about very small amounts of fuel which come into to the compressible range. If your problem is leakage past the high pressure piston then I could give you some suggestions. The other thing is, you don't appear to have a non return valve on the high pressure side. I think this could be a problem in that you are asking the the pump to go from zero to 2000 psi in one stroke with very little volume. How do you plan on adjusting the engine speed e.g. control the fuel? Your design is quite unique and I hope you are successful and you will learn much along the journey.

With my engine, I can inject from approx. 6mm to zero mm and I can adjust the stops for the range that I need. I do not concern myself with how much the pump is producing but rather measure the volume from the injector nozzle.

Also, I checked out your videos - interesting and clearly, you know a thing or two about pressure testing.

Bruce

 

[Lloyd-ss]

Hi Bruce, I appreciate your sticking with me and offering your voice of experience. And believe me, I do appreciate the advice. But I also often have to prove things to myself, and who knows, I might eventually end up right where you are pointing me. When I was actually being paid for being a manufacturing engineer, creative, cost effective solutions were my forte, and managers would often ask good naturedly in Monday meetings what solutions I had cooked up in my shop over the weekend. I loved the challenge, but of course the stakes were higher there, LOL.
But the challenge of this creative hobby is what makes it so special, isn't it? Enough rambling, ha, ha.

I did indeed install a spring loaded check ball on the input to the injector. I also managed to get the air out of the system and fill it for the first time with water and emulsified oil coolant. I didn't want to use diesel until I was close to happy. Didn't want the extra mess yet. I was also able to pressurize the system up to 1500 psi and bleed it and find the leaks, and also get it to inject. Kinda disappointing. The discharge was more like someone using the toilet than a nice mist from a perfume bottle.

This injector is supposed to (in my mind anyway) take an inlet pressure of maybe less than 1000 psi and boost its internal pressure with a cam driven piston, to a point high enough to make the injector pop open. I was not planning on a direct ecumenical connection from the cam to the injector pintle. But I know this is old territory for many people and I also am keenly aware that there are very few "new" solutions to these problems. Most of the new solutions are ones that somebody else already developed and that I am just not aware of.

I have to follow along the general theme that I have in mind for the injector, and when I have exhausted that, then I will take a different approach, and who knows, probably end up where you did, LOL.
Lloyd

 

[weir-smith]

Lloyd

You are right in that you are approaching the problem from a different perspective and you need to go where it takes you. The thing to remember is, that you learn so much usually what not to do. If we all did what everyone has done, then nothing new would be developed. I would like to follow your progress and see how it works out.

For your system, you could replace the rocker bearing with an eccentric bearing that you could rotate and thus vary the gap for operation and therefore the amount of fuel injected. However, note that this will also vary the injection timing. Unfortunately everything has a tradeoff.

I have been working on the new injector housing and have come to the most difficult task in that I need to drill a no 75 hole 25 mm or one inch deep. I usually break two or more drills using a high speed drill at about 15,000 rpm. It doesn't seem to matter how careful I am and using plenty of lubricant. It is not the drill breakage but the time to recover the broken drill if it is possible. This hole carries the fuel from the inlet connection down to the pintal and needs to be very precise.

Let us know how you get on.

Bruce

 

[Lloyd-ss]

Seeing its been 2 and a half years since I last posted, I re-introduced myself in the Introductions forum. Hopefully things are stable enough (with me) that I won't disappear again. I just re-read the first post about forgetting the 2 stroke idea and going with a 4 stroke. But, without having read that post I re-started in the 2-stroke direction. Diesels on you tube and everywhere you look. Too much temptation. And I needed ANOTHER project to start.
Here's where it is now. more info coming. Someday I will get a DRO, sigh.
Lloyd

 

[Lloyd-ss]

Starting a Roots Blower

Trying for a 2 stroke diesel might not be a wise choice, but I'll see how it goes. It seems difficult to find dimensional data that is useful for design purposes, too. Looking at the tried and true Detroit Diesel 2-strokes with Roots blowers, each rotor appears to be approximately one and a half times the diameter of the cylinder bore. The scavenging boost, per the manual, can be up to 4psi. The length of the rotors is a bit hard to determine as each series of DD engines has a different length. The plan for the engine is 33mm bore and 66mm stroke and the 2 Roots rotors that I made are 43.7mm dia x 27.8mm long. I won't know how much air they will displace until I get the gears (29 tooth 1.0 mod) next week and build a housing.

Once I laid out the rotors in autocad and verified that they would roll without gaps opening up, or binding occurring, making the rotors was much easier than I was expecting. The cylindrical blanks started out as plain cylinders with a .375 +.001/-.000 hole thru the middle. Then, 6 more 3/8" holes on the mill (3 each on 2 different B.C.s). Manual mill without a DRO, yuck. Making a solid fixture plate with full diameter 3/8" cap screws seemed to be the trick to keeping everything accurate. The final size of the 3 valleys in the rotors was controlled by plunging them to size with a 5/8" endmill. The contoured tips of the rotor lobes are .303" radius and this was done by manually pivoting each lobe about its center with a lever/handle bolted to the top of the rotor. I turned the rpm up high, so that the 1/2" diameter contouring endmill would cut cleanly and not grab the part. Plenty of oil. Tedious, but the result is good.

Each rotor has about .002" taper per side so I just swapped ends on one of them so that the tapers offset each other. I put a pair of 3/8" pins (shanks from broken endmills) into the fixture plate to see how the rotors would mesh and turn. I machined the center distance about .002" larger than the gears are supposed to be and the rotors turn with only slight resistance in a few places. I will probably try lapping them together with autobody rubbing compound after I get the drive gears so that the center distance can be set correctly.

Here are some pictures of the process.

Rotor bolted to fixt plate, 7 holes drilled, plunging the lobe valleys to final size with a 5/8" endmill.

Handle bolted on to manually pivot the rotor about the lobe axis to achieve a .303" radius. The lobe must swing thru
a 195 degree arc to be properly contoured.

Rotor machined to size and ready for final finishing.

I know that I am avoiding the whole injector situation, ha ha.
Lloyd

 

[Peter Twissell]

Hi Lloyd,
Nicely made parts!
Looking at the way the rotors mesh together, you may need to alter the profiles to make them work when they are geared together.
In the picture of both rotors mounted on pins, it appears that the rotor on the right would need to rotate a lot more than the one on the left in that part of the rotation.
When you meshed them in autocad, did you do so by rotating both through the same angle?
From your cad model, you should be able to derive the areas of displacement between the rotors and calculate the theoretical flow rate.
I like your manual mill setups - I do a lot of that kind of rotary table work myself.

Pete.

 

[Lloyd-ss]

Hi Pete, Thanks for the comments. I see what you are saying about how the rotors mesh, but I spent quite a bit of time rotating them at a 1 to 1 ratio in autocad. The rotors won't drive each other. There are 3 points in the rotation where they will loose mesh, but because they are driven by mating gears to keep them in sync at a 1 to 1 ratio, they will still maintain a line to line fit thru their full rotation so that the air doesn't leak back thru the rotors. If you tried to drive just one gear instead of both of them, they would definitely lock up at 3 places in each rotation.

I think the leak-back between the rotors is called slippage which is not exactly the correct term for what is happening. I am really anxious to get this housed and spinning to see how much air it outputs. If I drive it with a toothed belt, the overdrive ratio could be changed to possibly make up for the "slippage". Because there is clearance on all surfaces of the rotors, some amount of slippage is normal.

I am not trying to make a model of any particular engine, there is a fair amount of poetic license in my "interpretation", LOL. I change it as I go and just keep the as-built drawings up to date.
Lloyd

 

[Lloyd-ss]

Here is some more work completed on the Roots blower rotors and housing. This is just to check the fit, and next will be work on the gear train, machining the air inlet and outlet ports, and then actual testing of the blower function.
There is a temporary Lexan cover on the front to allow observation of the gears during operation. Two idler gears will be needed to get the rotors to rotate into each other (one CW, and one CCW) for proper airflow and meshing. Using 2 idlers will also make it easier to sync the rotors together. The final version probably will not have idlers. Lots more to do.

Lloyd

 

[ajoeiam]

Lloyd I was interested to read this thread and see your photographs of the progress on your Diesel engine. About six years ago I followed the same path and for the same reasons. I had drawings for the 6/1 Lister Diesel engine and used these to make a scale model. The engine is 20cc and uses direct infection into a pre combustion chamber. I used a modified gass jet as the injection nozzle and the injection pump had a bore of 4mm and a stroke of 1mm. A manual bypass was used to pass the excess fuel. The injector fuel line had check valves to prevent fuel coming back down the line. I am very much a " a try it and see if it works" type of model engineer and don't get bogged down with too much theory, but there was some discussion relating to it not being a "real" diesel. In my book if there was no spark plug to ignite the mixture so it was a Diesel engine. I have included some photographs of this engine and should you want to see it working it is on U tube - just type in model lister Diesel engine. Good luck with your project and I will continue to follow your progress.
George.

Hmmmmmmm - - - - very curious - - - - your source for the drawings please?

 

[ajoeiam]

Lloyd

Just noted your diesel build and its good to see someone else giving it a go as there are very few around. Approximately two years ago, I commenced to build a true diesel of no particular type. It was made from material that I had on hand and to my own design based on a horizontal type engine with a 40 mm bore and a stroke of 80 mm using an auxiliary shaft to drive the fuel pump and valve cams. The valves were mounted on the side of the cylinder head e.g. top and bottom. The purpose of the build was to see if I could make it work using diesel as the fuel. I have learn much during the build - mostly what not to do however, I have learnt a lot about diesel engines.

Initially, all the components were made and the first test to start the engine was a complete failure. The problem was where to start to work out what was wrong. The first thing was the compression, as the design required 500 psi or better if it was to work. I removed the head and replaced it with a temporary head with an inlet valve and the exhaust valve which had a pressure gauge fitted. The valves were inline types that were good for 2000 psi. After cranking the engine, the best I could do was just over 200 psi. The piston was remade to allow for four more rings and retested and I now had better than 500 psi. Next was to test the valves and both failed at approx. 300 psi, so more grinding and heavier springs. I now had the basis of an engine that should work however, no such luck.

I put a pressure gauge on the fuel pump and the best I could do was about 600 psi. Eight more attempts were made to build a pump and the best I could do was just over 1200 psi. Putting that to one side as I was fed up with it, I tested the injector using an injector tester. The results were not very good or consistent so I tried several designs and they all failed in some way. A friend gave me a pintal injector nozzle and out of desperation I used this as the basis of a new injector. The results were very good in that at 2000 psi it produced a atomised cloud of fuel. At lower pressures, it produced a very fine cone spray however it had a tendency to drip. Probably why it was replaced in the first instance. A new one was ordered but it is not quite the same and I will need to modify the injector body.

I still had the problem of the fuel pump. I was given a CAV pump which I dismantled to see how it was made and while doing so, someone else advised that there were cheap small injector pumps available on Ebay. So for $25 one was ordered and while is was well out of scale, I could see how I could machine parts down to bring it closer to what I needed. However, before doing so I wanted to test it as is. On the bench, it easily produced 3500 psi which was the limit of my pressure gauge. The pump was fitted however at the required pressure 2000 psi, the auxiliary shaft was deflecting so a new mounting bracket for the injector pump cam was made. I was now in the position to give it a try and on the first test I had large clouds of white smoke which indicated unburnt fuel. The problem was in the timing so I made a disk with degrees marked and fitted it to the aux. shaft which rotates at half speed. The cams were reset and this was followed by another test and at last the engine fired but would not sustain continuous running. My temporary fuel control was very hit and miss so to speak, so that is the next thing to do to allow better control.

This account has rambled on some what however, it does show that with persistence you can achieve an outcome. I have included a photo of the pinal nozzle and I am happy to answer any question you have. The best advice I can give is to suggest that you test the critical parts at the time to ensure that they can produce what you are expecting. I also agree that you can't put a pressure gauge in the line between the pump and the injector because of the air problem. The amount of fuel is very small and it rises quickly to the "pop" pressure and then immediately drops to almost zero until the next cycle. Air in the system no mater how small will prevent the system from working. Also, I have used copper tube for the delivery to the injector and to date it has not failed however, I have purchased some 3mm stainless capillary tube to use.

My current build is a vertical air blast injection engine which has its own unique set of problems and a further engine at the startup stage is a Fairbanks Morse 3 cylinder R80 engine.

Bruce

snip

Note, the coin is approximately 16 mm

Reading back (to before my join date) - - - - muchly appreciating your notes!!

 

[ajoeiam]

Hello everyone.
...............................................
This thread actually started a few days ago on the general engine discussion forum, but it seemed like it really belonged on this forum, so here it is.
How to fit mismatched rings and piston and cyl bore??
................................................

I have wanted to build a diesel for a long time, actually a 2 stroke complete with Roots blower. Why not bite off more than I can chew? I call it being greedy; and it usually gets me in trouble. EDIT:I have since revised my expectations and have dropped the blower and 2 stroke concept.
About a year ago, I found Find Hansen's beautiful engines on Youtube, and that almost pushed me into the project. Then I ran across his new video of the build of an A-Frame diesel. Darn! Then I found this great forum with lots of smart and helpful and friendly members. That's a rare combination to find on the internet! So I dove in head first.

The selection of 33mm bore x 66mm bore had an odd beginning. In one of my junk piles I had some short pieces of 8" welded steel pipe (actually 8-5/8" O.D.). I thought, that could make a great flywheel, what size cylinder would it go with?

So the first item is the one that for me, took the least amount of decision making. Like using 4 spokes or 5 spokes? The 5 curved spokes spoke to me. It is bolted construction, with inner and outer rim, 5 spokes and a hub, and hidden bolts.

I started by slicing off 3 pieces of the 8-5/8" O.D. x .30 wall welded steel pipe: rim, inner rim, spokes. I used a Harbor Freight $120 portable band/hack saw and had to saw all the way the way around each ring. I sawed them all in one session, using plenty of oil on the cuts. The Lennox blade held up fine. The saw didn't whimper.

My lathe is a Grizzly 10x22 and that pipe definitely pushed the limit, but I got the outer rim roughed out, clamping from the inside out with the 6-1/4" 4 jaw. Indicating the rings in to get them to run optimally for least amount of material removal was a chore. The outer ring was the first part rough machined. To make the inner spoke ring, I sawed out a 2" section of one of the pipe slices, and clamped it to force it into an 8" O.D. Then I welded it, multiple passes, grinding out the flux and inclusions between passes, One thing that really helped the welding was preheating the joint area with a Mapp gas torch. Welding that 5/16" wall just wouldn't have worked, not a my skill level anyway. Then I rough machined the new not trying to get 100% cleanup.
I machined the last ring to the finished cross section of the spokes.
The hub was rough turned from 12L14. It has an O.D. groove the width of the spokes, and has 5 flats machined into that groove.
I rough cut the 5 spokes to length plus about 1/8". It is bolted construction, with each spoke attached to the rim with a single 8-32 bolt, with the head counterbored into the rim. After all 5 spokes were attached to the rim, I fit them to the hub and determined how to trim the ends of the spokes and install the bolts.

After it was all lightly bolted together I chucked it in the lathe and pushed it around to get minimal runout and wobble, which ended up being about 30 thou. I tightened the bolts up, using a generous amount of 680 loctite. I then trued it up ont he lathe, changing the chucking at least 4 times.

Then the outer rim was attached using (5) 10-32 set screws that fit into pockets on the I.D. of the outer rim. After it had a final alignment, one last set of clean-up cuts were needed to get the non-painted surfaces all pretty looking. Lastly was several sessions of epoxy and JB Water Weld. I was shocked at how well that combination worked. i cleaned with acetone, and lightly preheated before applying epoxy, and used a heat gun to get the epoxy to flow properly. If this wheel were dropped hard enough to break it, I think a cast iron one would have broken too.

Here are the final as-built specs for the flywheel.
Outer rim O.D. 8.58"
Outer Rim width 1.99"
Inner rim 1.13 wide x . 25 thick
Spokes (5) at .88" x .20" cross section
Hub 2.30 long x 1.82 O.D.
Hub Bore .75"
Weight 7.96 pounds

........................................
Starting with a chunk of 8" nominal welded steel pipe.
View attachment 108091

Three slices of pipe.
View attachment 108092

L to R, Outer rim, spokes, inner rim.View attachment 108093

The bolted assembly with the epoxy and bolts visible.
The JB water weld has NOT been applied yet.
EDIT: Each spoke is machined for a snug fit into its loacation, including a snug fit into the matching groove in the hub. There is one 8-32 bolt radially thru the inner rim into the spoke. There is also a 10-32 bolt that goes thru the spoke radially into the hub.When these 10 screws were all tightened and secured with Loctite 680, the flywheel became a rigid unit. The outer rim was a slip fit onto the inner rim, and epoxy was was used to secure it in place (and possibly kill some vibration) and was also secured with setscrews radially outward from the inner rim into pockets in the outer rim. This method allowed the outer rim to be aligned with the hub to minimized radial and axial runout. The additional epozy and JB water weld fillets are mainly for cosmetic purposes, but I am sure they also will contribute to strength and vibration damping.
View attachment 108094

After filling, sanding, priming and painting, here is the Glamour photo
of the finished flywheel, using special lighting,
and the photo editor, for those extra special high-lites, LOL.
View attachment 108095

More to come, but not really fast.
Lloyd

You don't mention it explicitly but - - - - am I understanding correctly - - - your inner flywheel ring was made from the same 8" pipe with a slot cut into it so that you could fit this inner ring into the outer ring (uncut 8" pipe)?

I've thought of making a flywheel from say a chunk of 1" or 1-1/2" thick steel cut into shape using a cutting torch.
Likely could also be made stacking some bits of 3/4" thick steel cut in similar fashion.

 

[ajoeiam]

Bruce,

snip

Just for show-and-tell, this is a hydraulic burst test fixture that I made to test high pressure air tubes. Capability is to approx 30,000 psi. The black tube on the right is 1.25 O.D. x .095 wall 2024T3. Out of the picture on the left is a Harbor Freight hydraulic hand pump that goes to 8,000 psi, and serves as the first stage of the hyd system. The 2 long steel tubes to the left of the black tube are a hyd multiplier with a large input piston on the far left, that drives a smaller piston that is in the tube on the right. Multiplication is about 4 to 1.
When testing the black aluminum tube on the right, the first failure occurred at 9,000 psi when the tube swelled and an o-ring popped. I fixed that so that the o-ring held pressure again, and then the retaining screws for a valve plug in the end of the tube plowed their way thru the aluminum tube. The failure was quick and definitive, but the tube never did really "burst". I did test some 7/8 x .065 A513 Ty5 ERW DOM steel tube and it did actually burst at 16,000 psi, which was several percentage points above the predicted failure. The test was reassuring.
Lloyd
View attachment 108273

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!!

 

[ajoeiam]

delete (please - - - for one of the admins)

 

[ajoeiam]

Here is some more work completed on the Roots blower rotors and housing. This is just to check the fit, and next will be work on the gear train, machining the air inlet and outlet ports, and then actual testing of the blower function.
There is a temporary Lexan cover on the front to allow observation of the gears during operation. Two idler gears will be needed to get the rotors to rotate into each other (one CW, and one CCW) for proper airflow and meshing. Using 2 idlers will also make it easier to sync the rotors together. The final version probably will not have idlers. Lots more to do.
snip
Lloyd

When you are checking your 'blower' besides checking for volume and pressure would you be able to check for vacuum producible?

AIUI a blower can function as a vacuum as well.

 

[djswain1]

Hi Bruce, I appreciate your sticking with me and offering your voice of experience. And believe me, I do appreciate the advice. But I also often have to prove things to myself, and who knows, I might eventually end up right where you are pointing me. When I was actually being paid for being a manufacturing engineer, creative, cost effective solutions were my forte, and managers would often ask good naturedly in Monday meetings what solutions I had cooked up in my shop over the weekend. I loved the challenge, but of course the stakes were higher there, LOL.
But the challenge of this creative hobby is what makes it so special, isn't it? Enough rambling, ha, ha.

I did indeed install a spring loaded check ball on the input to the injector. I also managed to get the air out of the system and fill it for the first time with water and emulsified oil coolant. I didn't want to use diesel until I was close to happy. Didn't want the extra mess yet. I was also able to pressurize the system up to 1500 psi and bleed it and find the leaks, and also get it to inject. Kinda disappointing. The discharge was more like someone using the toilet than a nice mist from a perfume bottle.

This injector is supposed to (in my mind anyway) take an inlet pressure of maybe less than 1000 psi and boost its internal pressure with a cam driven piston, to a point high enough to make the injector pop open. I was not planning on a direct ecumenical connection from the cam to the injector pintle. But I know this is old territory for many people and I also am keenly aware that there are very few "new" solutions to these problems. Most of the new solutions are ones that somebody else already developed and that I am just not aware of.

I have to follow along the general theme that I have in mind for the injector, and when I have exhausted that, then I will take a different approach, and who knows, probably end up where you did, LOL.
Lloyd

An injector with integrated pump is called a "unit injector" in case you don't know. Interesting build will be following along

 

[Lloyd-ss]

An injector with integrated pump is called a "unit injector" in case you don't know. Interesting build will be following along

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.

 

[Lloyd-ss]

When you are checking your 'blower' besides checking for volume and pressure would you be able to check for vacuum producible?

AIUI a blower can function as a vacuum as well.

Sure, testing for vacuum will be easy once I get it operating.
It has been mentioned before about how "scaling" kind of falls apart as the models get smaller and smaller. I think the roots blower will have that problem, too. On the full size units, there is a few thousandths of an inch clearance between all mating surfaces. On the model version, the clearances will probably be about the same because that is about as accurately as I can make the parts. So, the clearances, and therefore the leakage, are a far bigger percentage on the model unit compared to the real unit. Something will need to compensate. More overdrive?
Lloyd

 

[Lloyd-ss]

Hi Lloyd,
Nicely made parts!
Looking at the way the rotors mesh together, you may need to alter the profiles to make them work when they are geared together.
In the picture of both rotors mounted on pins, it appears that the rotor on the right would need to rotate a lot more than the one on the left in that part of the rotation.
When you meshed them in autocad, did you do so by rotating both through the same angle?
From your cad model, you should be able to derive the areas of displacement between the rotors and calculate the theoretical flow rate.
I like your manual mill setups - I do a lot of that kind of rotary table work myself.

Pete.

Hi Pete, I took your advice and calculated the area of each "empty" lobe space. It looks like each lobe space is approx 0.36 cuin, and that each rotation should transfer thru 3 lobe spaces for a displacement of 1.08 cuin per revolution or 17.7 cc/rev. Given that the proposed swept cylinder volume is 56 cc, that means at least 3.2 revs of the blower to fill the cylinder if the blower is 100% efficient. If the efficiency is really only 50%, then the overdrive might need to be 6.4 to one????? Hmmm. I need to double check that. Thoughts? The detroit diesel blowers only run at about 1.5 overdrive, but there are so many variables. Maybe the displacement is equal to 6 lobe spaces per rev, rather than 3?
Lloyd