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

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Lloyd-ss

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Pressure and Volume Test Results from Roots Blower.

The Roots Blower that I made has a pair of 3-lobed rotors 44mm in dia and 27.8 mm thick. The p.d. and the C to C distance is 29mm. The inlet and outlet ports ar 20mm x 16mm. Each lobe has 3 "empty spaces" of about 5.9cc. Each revolution pumps 6 empty spaces from the inlet port to the outlet port, so the pump through-put at 100% efficiency could be 35.4 cc/rev . As a side note, because the Roots is symmetrical inside, if the direction of rotation of the rotors is reversed, the in and out directions are swapped.
BlowerRotorsInHousing.jpg

Because the 2-stroke diesel that I have in mind is about 56.4, even if the Roots operated at 100% eff, the rotors would need to run at 1.6 to 1 (60% overdrive) to keep up with the piston movement. 100% eff, no way!

Here are the test results fro the various rotor speeds:

1,040 rpm
Maximum developed pressure (with outlet blocked)(in inches of water column):
7.12" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.182" hole:
2.37" W.C.
19,820 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.375" hole:
0.22" W.C.
25,770 cc/min
Theoretical swept volume of the Roots blower at 1040 rpm (at 35.4 cc/ blower rev):
36,820 cc/min, max theoretical

1,510 rpm
Maximum developed pressure (with outlet blocked)(in inches of water column):
12.75" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.182" hole:
4.63" W.C.
27,690 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.375" hole:
.62" W.C.
42,760 cc/min
Theoretical swept volume of the Roots blower at 1,510 rpm (at 35.4 cc/ blower rev):
53,454 cc/min, max theoretical

2,150 rpm
Maximum developed pressure (with outlet blocked)(in inches of water column):
21.75" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.182" hole:
8.25" W.C.
37,090 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.375" hole:
1.25" W.C.
60,880 cc/min
Theoretical swept volume of the Roots blower at 2,150 rpm (at 35.4 cc/ blower rev):
76,110 cc/min, max theoretical


How does the scaling to Detroit Diesel 1-71 look?
As I stated previously, this little Roots blower is approximately 1/5 th linear scale to 1-71 Roots.
The swept volume of the DD roots blower, per rev, is equal to about one cylinder's worth of air per engine rev. In other words, 71 cuin of air per rev, or 1,163 cc of scavenge air per revolution, or 1,163,000 cc of air per minute at 1,000 engine rpm. (Note- edit made to this paragraph to correct math errors)

The blower I am working on is supposed to be 33mm bore x 66mm stroke, for 56.4cc/rev. Doing the simple math:
56.4 x 500 rpm = 28,200 cc/min (for 1 cyl fill of air per rev)
56.4 x 1,000 rpm = 56,040 cc/min (for 1 cyl fill of air per rev)
56.4 x 1,500 rpm = 84,600 cc/min (for 1 cyl fill of air per rev)
56.4 x 2,000 rpm = 112,800 cc/min (for 1 cyl fill of air per rev)

Looking at the performance per rev chart, above, it looks like approx 1,510 rotor rpm might be a good starting point for 1,000 rpm engine speed, which would require at least a 1.5 to 1 overdrive for the 2 rotors.
There might be some mistakes in my math or logic, so please let me know if you spot anything.

Lloyd
 
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Richard Hed

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Pressure and Volume Test Results from Roots Blower.

The Roots Blower that I made has a pair of 3-lobed rotors 44mm in dia and 27.8 mm thick. The p.d. and the C to C distance is 29mm. The inlet and outlet ports ar 20mm x 16mm. Each lobe has 3 "empty spaces" of about 5.9cc. Each revolution pumps 6 empty spaces from the inlet port to the outlet port, so the pump through-put at 100% efficiency could be 35.4 cc/rev . As a side note, because the Roots is symmetrical inside, if the direction of rotation of the rotors is reversed, the in and out directions are swapped.
View attachment 128952

Because the 2-stroke diesel that I have in mind is about 56.4, even if the Roots operated at 100% eff, the rotors would need to run at 1.6 to 1 (60% overdrive) to keep up with the piston movement. 100% eff, no way!

Here are the test results fro the various rotor speeds:

1,040 rpm
Maximum developed pressure (with outlet blocked)(in inches of water column):
7.12" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.182" hole:
2.37" W.C.
19,820 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.375" hole:
0.22" W.C.
25,770 cc/min

1,510 rpm
Maximum developed pressure (with outlet blocked)(in inches of water column):
12.75" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.182" hole:
4.63" W.C.
27,690 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.375" hole:
.62" W.C.
42,760 cc/min

2,150 rpm
Maximum developed pressure (with outlet blocked)(in inches of water column):
21.75" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.182" hole:
8.25" W.C.
37,090 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
.375" hole:
1.25" W.C.
60,880 cc/min


How does the scaling to Detroit Diesel 1-71 look?
As I stated previously, this little Roots blower is approximately 1/5 th linear scale to 1-71 Roots.
The swept volume of the blower per rev, is equal to about one cylinder's worth of air per rev. In other words, 71 cuin of air per rev, or 1,163 cc/rev, or 69,780 cc/rev. That works out to 4,186,800 cc/minute of air.

The blower I am working on is supposed to be 33mm bore x 66mm stroke, for 56.4cc/rev. Doing the simple math:
56.4 x 500 rpm = 28,200 cc/min (for 1 cyl fill of air per rev)
56.4 x 1,000 rpm = 56,040 cc/min (for 1 cyl fill of air per rev)
56.4 x 1,500 rpm = 84,600 cc/min (for 1 cyl fill of air per rev)
56.4 x 2,000 rpm = 112,800 cc/min (for 1 cyl fill of air per rev)

Looking at the performance per rev chart, above, it looks like approx 1,510 rotor rpm might be a good starting point for 1,000 rpm engine speed, which would require at least a 1.5 to 1 overdrive for the 2 rotors.
Lloyd
Do you have the plans for this? I was working on a two lobed roots blower but got nowhere as I didn't have a quality enough mill--that is I didn't have ANY mill.
 

Peter Twissell

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Nice work Lloyd!
Good to see that your test results correlate well with calculated flowrates at higher rpm. This is to be expected, as the leakage in the blower is constant through the rpm range.
 

Lloyd-ss

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Do you have the plans for this? I was working on a two lobed roots blower but got nowhere as I didn't have a quality enough mill--that is I didn't have ANY mill.
Richard, yes I do have some drawings of the rotors and housing. They are just 2d autocadd drawings, but the mesh of the rotors seems to be good throughout 360 degrees of rotation. The rotors are not true cycloids, but close approximations of them. All features on the rotors are portions of a circle, as shown in the post about the actual machining of the rotors. Start by getting the gears first, so that you know what the exact center distance between the rotors needs to be. The size of the rotors and housing are fully scalable, so you could make whatever size you want. I will post the drawings in a few days after I get them prettied up with adequate dimensions. I think I can post both pdf's and dxf's or dwg's of the blower parts.

Just like standard involute gears, where the tooth faces roll against each other with no rubbing, the cycloid shape is supposed to do the same thing, all rolling without any rubbing.
Lloyd
 

Lloyd-ss

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Nice work Lloyd!
Good to see that your test results correlate well with calculated flowrates at higher rpm. This is to be expected, as the leakage in the blower is constant through the rpm range.
Thank you Pete! After reading your reply, I went back and did a few edits in post #61 to correct some fuzzy, late night, math and descriptions. I also added a "theoretical maximum" airflow at each test rpm speed, based on swept volume of the Roots rotors of 35.4 cc/revolution. That helps shed some light on the leakage in the blower as you pointed out.

I am a data junkie and love making spreadsheets and graphs to display the data in various ways. You never know what sort of unexpected trend might pop out at you, or how consistent and preditable the results might be. I might collect more data at the 2 remaining speeds on the little drill press, 585 and 3,000 rpm. There might be the makings of some actual pump curves, or at least my interpretation of a pump curve. The science of this adds a whole 'nother dimension of enjoyment of this hobby for me. But the cool thing is, you only need to get into the science as much as you want to, or even not at all. Great fun!

Also, I want to give a big thank you to ALL of the members of the forum who display and share their projects and ideas and comments. The challenges undertaken, and successfully completed, are true inspirations for a new novice member. 👍

Lloyd
 

Richard Hed

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Richard, yes I do have some drawings of the rotors and housing. They are just 2d autocadd drawings, but the mesh of the rotors seems to be good throughout 360 degrees of rotation. The rotors are not true cycloids, but close approximations of them. All features on the rotors are portions of a circle, as shown in the post about the actual machining of the rotors. Start by getting the gears first, so that you know what the exact center distance between the rotors needs to be. The size of the rotors and housing are fully scalable, so you could make whatever size you want. I will post the drawings in a few days after I get them prettied up with adequate dimensions. I think I can post both pdf's and dxf's or dwg's of the blower parts.

Just like standard involute gears, where the tooth faces roll against each other with no rubbing, the cycloid shape is supposed to do the same thing, all rolling without any rubbing.
Lloyd
When I was working on this, nearly 30 years ago, an engineer friend told me .012 clearance was good, but I thimpfk that is too much. I woujld thimpfk that a thou would be fine if one could achieve it. Is there any reason, other that making sure there is no actual contact, for making such huge clearances?
 

Lloyd-ss

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When I was working on this, nearly 30 years ago, an engineer friend told me .012 clearance was good, but I thimpfk that is too much. I woujld thimpfk that a thou would be fine if one could achieve it. Is there any reason, other that making sure there is no actual contact, for making such huge clearances?
Richard, Here are 2 pages from the DD 71 series manual and it does indeed call for a .012" clearance between the rotor tips and the housing. But it only calls for a .002" clearance between the interference points between the rotors. During operation, all of the air flow is along the outside wall of the housing (air does not pass in a straight line thru the rotors. It calls for inspection every 100k miles, so i guess they figure that is where the clearances are needed. The rotors are huge and maybe they get hotter and expand more than the housing. Funny that only 2 of the clearances have max tolerances specified.

My rotors started out too tight to easily roll all the way around. Sandpaper, files, and lapping compound finally got it to rotate with some contact, but no binding. The cycloid features (like an involute gear shape) should roll past each other, not slide past each other.

The cross section picture really shows how huge the blower is.
Lloyd

MaintMan-1.jpg

MaintMan-2.jpg
 
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