Joe, sure, I'd love to take a look.
Fantastic work. Amazing to see the bag fill and build pressure.
Andrew in Melbourne
Now THAT is cool!The Latest Version of the Roots Blower is WORKING !
Finally! I have been around the world twice on this and ended up back with the original 3-lobed design, but totally revamped. I ended up with better bearings and gears, and tighter clearances. But that still wasn't enough. The ratio of the clearances to the effective swept volume was still too much to stop the "slippage" between the rotor lobes. See post #75 for more about this.
The last set of 3 lobed rotors are made out of Teflon so that the clearances can be kept to a minimum without galling, but they ALSO had to be made somewhat flexible such that under centrifugal force, they would expand in such a way that the mating rotors would conform to each other, and seal to each other, without binding up. This was accomplished by drilling larger thru-holes in the 3 lobes to make the walls of the lobes thinner in certain areas so that they had flexibility where needed, and rigidity where needed in other areas.
Here is a quickie video that I made of the roots blower powered by a little drill press at approx 2500 rpm. The tubing filled with blue tinted water serves as a pressure gauge. The Roots blower is a positive displacement blower that moves air, but doesn't build significant pressure (unless modified extensively). At most, the blower would build up maybe 20" of water. BUT, it pumped a lot of air.
I fastened a 125,000 cc plastic trash bag to the outlet of the blower and it filled in about 55 seconds, running at 2500 rpm. Previous versions had taken from 2 and half to over 4 minutes.
If we just say that the blower output 125,000 cc's in one minute, and divide that by the proposed 56 cc displacement, that is 2232 cylinder fills in one minute. Since this is for a 2 stroke, the blower rpm of 2500 might support an engine rpm of ..... maybe 1500?? Hard to say.
Here is the amateurish video, but I think it gets the point across. Honestly, I was a bit surprised at how well it filled the plastic bag.
View attachment 135788
Will the Blower Pump Enough Air?
Here are some thoughts and questions about this Roots blower.
First off, we know this application works in real life in the 100's of thousands of 2-stroke Detroit Diesels that were produced. I remember here in the US, that the Greyhound buses would always go flying by on the interstate, with that familiar blown 2-stroke sound.
I know this blower pumps air. The 125,000 cc plastic bag was stretched tight after just over a minute of pumping at 2,500 RPM.
View attachment 135828
Here is the inside of the blower and each lobe space calculates out to 11.3 cc's, and one complete revolution should pump six lobe spaces, or (at 100% efficiency) 67.8 cc. At 2500 rpm, that is 169,500 cc's. Does that mean the blower is 125,000/169.500= 74% efficient. That is extremely hard to believe, but maybe since the pressure only builds up to 15 or so inches of water, maybe that is true.
View attachment 135830
So here is the real question(s). How many revs of the blower would be needed to purge a 56 cc cylinder? And how about a method to test to see if it will actually purge 56cc while at operating speed? This is a head-scratcher.
Now THAT is cool!
Good go there sir!!!!!!!!!!!
This may be time for the equivalency testing situation.
(Sometimes trial and error beats a lot of calculations and might even be faster - - - grin!)
Engine displacement and rpm:
56cc x 2500rpm: One cylinder fill per Rev.
=> 140litres per minute:
Your pump makes 125litres per minute... but at 1.04barG. = 130l/min.
So maybe the engine will run? but won't run really well. So can you make a blower half as long again, (or whatever?) to exceed the displacement (at atmospheric pressure) and even give you some boost?
Probably of no use whatsoever...but, as an aside,
I think that modern motorcycle scooters a la Vespa and Lambretta, but now made by Piaggio, and lots of others (not the electric toy scooters like single wheeled skate-boards with a steering handle), have 125cc engines with small blowers to boost their inlets. I have also seen an electric blower to boost and engine...
Universal 3" Electric Turbocharger Air intake for Car/Motorcycler/Truck/ATV/RV – Grandado.com ...
Mini Turbocharger For Small Engines Motorcycle RHB31 For ALTO | eBay
It may be possible to get enough information from these to understand what actual volume and pressure they produce, and for what size/power of engine, so you can get some better clues as to sizing your blower?
Thanks for previous compliment, but I don't really deserve any, as I have more "stupid" ideas issuing from my brain than "sensible".
Enjoy what you are doing, as we enjoy your posts!
AMR500 will produce 1.8 pressure ratio or ~12psi of boost. High performance engines will have peak primary pressure ratio of ~1.5 just before transfers open. There must be pressure to push the charge through the ports against cylinder pressure which takes time to drop. Slower engines give a bit more time for blowdown and transfer. Obviously, engines run at part throttle when crankcase pressures are much lower, but the effect on power is clear.
The key will be making the blower components as precise as possible.
Here's some motivation. superchargedsaitopics
https://www.rcuniverse.com/forum/glow-engines-114/1580599-roots-supercharged-saito-engine.html gets interesting at post 18.
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