Forced induction 100cc

[Grumph]

Yeah I am hoping that the fuel injection system is going to make the fueling control much better, I am looking forward to the kit turn up as I can't really design the rest of the intake system until that arrives. I know I am going to need a blow off valve but though I wouldn't need a safety dump valve with the fuel injection, as even if the intake had a back fire there would not be enough fuel in the air to create conditions for a ignition, thoughts?

I am planning on going to the library this weekend to have a look at those two books, hopefully they are returned on time

-Sketchy

If the Irving book is a later edition without the singles info, PM me & I'll scan and email it to you...I can't post pics on this site....

Explosion valve will IMO be needed not for potential ignition bangs but the whole system will see a pressure rise and I reckon you'll need to protect the $$$ blowoff valve. We had only one genuine backfire with plenum ignition....split the plenum and scared shit out of the guy sitting on the bike. Amazingly it kept running - badly - so got shut down toot sweet. Backed off the explosion valve spring tension a couple of turns after that which rendered it a bit too sensitive but at least we knew we weren't going to have another huge bang.

[bucketracer]

The Plenum

ok its not supercharged but it is a working plenum and on a 2-stroke no less.



The idea behind this plenum was as a way of getting around the restrictive 24mm carb rule, the idea being that the motor would draw from the plenum through a bigger inlet tract while the carburator was still a legal 24mm.

The theory is, that as the motor only sucks for about half a crank shaft rotation, the 24mm carb at wide open throttle would have a full crank shaft rotation or twice the time to re fill the plenum and therfore potentialy flow twice the air than it would have. The prototype plenum on TeeZee's 125cc bike started at 1000cc.



To form a seal and cushion for the blow off plate, the top of the case was milled flat then a thin bead of silicon glue laid on it. Strips of sellotape were put on the blow off plate as a parting agent, then the plate was lightly screwed down on the silicon glue to form a flat seal surface.



TeeZees plenum, is 4x the cylinder volume and the on track throttle response feels soft, a bit like winding on a std FXR. This soft feel helps with getting the throttle on earlier in a corner than you can when the engine has the typical 2-stroke hit. TeeZee thinks this softening of the throttle response is a real help with on track drivability.

EngMod2T suggests a volume 8x the cylinder would be better for power and low end torque. In researching plenums 10x or more for supercharged engines was the go, in fact the talk was for supercharging and power the plenum cant be to big and the size was more likely to be restricted by the space available.



When its running TeeZees plenum is full of combustibale fuel/air and goes bang quite often, particularly on over rev and the original 4mm blow off plate got bent out of shape but the 10mm one has stood up OK. The green scotch bright glued to the stop plate forms a blow off cushion, its needed as the pops can be quite robust.

We had thought the explosive mixture might blow the casing apart but after a lot of pops and bangs that has not happened.

[Sketchy_Racer]

Well I was hoping to be telling everyone that the super charger is no complete but it would appear I have made a cock up.

When I made the shafts I must have made them to much of an interference with the rotors as I have had some distorion of the shafts and I can't get my gears to mesh well enough. I have run the super charger on the end of drill at 2500RPM and it certainly moves a lot of air!

So I'm going to have to leave it where it is for the rest of next week as I have had a big job come in so wont get any machine time to re-make the rotors, shafts and gears. It's not as bad as it may seem, the beauty with CNC is now the programs are there it is literally a case of put the blanks in the mill, set the datums and hit the go button.

Aside from that I have figured out how I am going to put the pulley belt on the end of the crank and cut the cases out to give me clearance to run the belt. The belt will be a poly V belt 15mm wide.

Also the next part it going to be making some mounts to hold the supercharger. Looking back I should have built them into the housing but it's not a big problem.

I fitted the oil cooler and adaptor plate, happy with how that came out, the oil cooler is off a old harley and is nice and light with a good volume.

This week will be mounting the supercharger and getting the belt drive to it sorted, then hopefully the fuel injection kit will have turned up so I can look at getting all that mounted, and finish the intake system.


Cheers,

-Sketchy

[bucketracer]

Bad luck with the shafts, still its a very interesting project and very impressive engineering.

[bogan]

Change some other bits while you're there

[TZ350]

Hi Sketchy

pressure wave superchargers I didn't know they existed untill I was inspired by your project to look at superchargers on the net.

http://en.wikipedia.org/wiki/Exhaust...ssure_charging

Exhaust pulse pressure charging (EPPC) is a system for supercharging two-stroke diesel engines of the loop-scavenge type. Loop-scavenge engines cannot be pressure-charged in the same way as uniflow engines or four-stroke engines because the inlet and exhaust ports are open at the same time.

http://en.wikipedia.org/wiki/Pressure_wave_supercharger

A pressure wave supercharger The process is controlled by a cylindrical cell rotor whose speed is synchronised with the engine crankshaft speed via a belt or chain. Individual cells alternately open and close the exhaust gas and fresh air apertures, when the aperture on the exhaust gas side is reached pressurised exhaust gas flows into the cell and compresses the fresh air there.



As the cell rotor continues to rotate and reaches the aperture on the inlet side the compressed air flows to the engine. Before the exhaust gas can flow the aperture is closed again and the exhaust gas column is reflected before entering the engine. The exhaust gas exits at high speed sucking further intake air into the cell behind it repeating the process.

Energy exchange in the pressure-wave supercharger occurs at sound velocity, resulting in good response even at low engine speeds, a common downfall of turbocharged engines. It combines the advantages of mechanical and exhaust gas supercharging.



http://www.idsc.ethz.ch/Research_Guz...e_Wave_Systems


So if a 2-stroke is already supercharged by the exhaust system, then would it be ok to extend the inertial pressure wave process to the inlet side as there will be no mechanical compressing involved only an open chamber with some ports.

A pressure wave supercharger, clever idea but probably not in the spirit of things for a F4 2-stroke....

[Sketchy_Racer]

I've never seen that before, very interesting! I'm sure if you built it no one would mind, I've been told the rule book is just a guide line anyway

Would be very simple to manufacture in comparison to the roots style as there are no gears just a simple vane pump really.

[TZ350]

I've never seen that before, very interesting! I'm sure if you built it no one would mind, I've been told the rule book is just a guide line anyway

Would be very simple to manufacture in comparison to the roots style as there are no gears just a simple vane pump really.

I am impressed by you building your own supercharger.

And yes it would be fun to try one of these wave rotor superchargers, a lot of info can be found here:- http://www.egr.msu.edu/mueller/projects_waverotor.htm

[bogan]

Doesn't strike me as being too rpm resilient. Won't the clearing of the rotor chambers do a lot better at a certain rpm? I also read that they often use this design in conjunction with a low pressure blower to chase the exhaust gases out of the rotor. Is a pretty neat idea though!
I really want to try one of them fandangled twin screw blowers now, got the 4 axis for it, just need the rotor dimensions...

[speights_bud]

Check out this video at around 1:20 mark, it uses the same idea

http://www.youtube.com/watch?feature...&v=m-ZWPnvC0wc

Cheers

-Sketchy

So i actually only just watched that video, these are exactly the same/are the pumps i used to build.

[Brian d marge]

So i actually only just watched that video, these are exactly the same/are the pumps i used to build.

what happens when the shaft stops suddenly?

Stephen

[speights_bud]

what happens when the shaft stops suddenly?

Stephen

Umm depends if the other one keeps going...

Had one the plant installer managed to get a spanner dropped in there it got real nasty, makes a hell of a mess of the rotors and housing beyond a 2mm oversize machine job. But it also damages shafts, bearings & shears off keyways etc. Have seen a 50mm shaft sheared off and them big ceramic seals aint cheap either!

They don't usually stop going around though, they just start eating themselves

If the clearances between the lobes and the housing/front plate aren't set right the lobes start rubbing and can pick up scoring the crap out of both faces, kinda like just feeding that 2-stroke some more right when its considering seizing up. Most likely to happen once machine is up to temp in working environment and was set too tightly on the bench.

This also happens when one particular dickhead machinist/colleague doesn't check his tooling and leaves a small radius in the housing corner and nobody finds out until re-assembly time and then its back into the machine for round 2.....

[pete376403]

Ferrari tried the pressure wave superchargers in F1 back when 1500 turbos were being run against 3.0NA motors. They worked but were abandoned becuase of problems and turbocharging had higher potential.

[Grumph]

Ferrari tried the pressure wave superchargers in F1 back when 1500 turbos were being run against 3.0NA motors. They worked but were abandoned becuase of problems and turbocharging had higher potential.

Brown- Boveri did a lot of work with Ferrari. I understand power wasn't a problem but the curve was rather like a 2 stroke coming on pipe.
Not what the car punters wanted. Turbos could be and were developed to give the characteristics wanted.

The screw type compressors are trick all right. Glen Smiths TQ used I believe a Lysholm blower. They had a shitload of trouble with it until they data logged it. Turned out that the blower acceleration rate was so high it was simply twisting the shafts like bamboo.
Lysholm made them a special blower in the end - oversize shafts and I believe magnesium rotors.Cost no object....
What was happening was when the thing lost traction the revs just went up instantly.
That thing had injection into the blower - and into the ports as well.

[Sketchy_Racer]

So I spent an hour or so last night designing the 2 lobe rotor. It's come out great and It will be much easier to maintain tolerance between the two which is also good!

I have also designed the cradle that will hold the supercharger and give me the ability to tension the belt. I am not running a separate tensioner bearing and pullet, rather I am moving the supercharger and locking it in place.

So that's todays project, go get the mount sorted.