supercharged V12 2 stroke

[JAParticipant @ja]

Dean

I am sure you have looked into this in great detail but I don't believe all blown four stroke engines have large valve overlaps. Pressure is far more effective at scavenging than a working exhaust system so the need for, let's say, 60 degrees of overlap disappears. In fact with an external fuel system, carburettor or injection, all you would be doing is blowing fuel down the exhaust system. Not what you want with a petrol engine and if you are interested in fuel consumption. However if you are burning methanol, with its low calorific value and, particularly, high latent heat of evaporation, large overlaps can be a major advantage due to the evaporative cooling from the fuel. This comes at the expense of fuel consumption. Alfa Romeo used this system in their early 1950s GP engines, they had a fuel consumption of something like 3/4 m.p.g.

JA

[Mark CParticipant @markc]

I was under the impression that forced induction (super/turbo charging) was intended to increase the volumetric efficiency of an engine – two or four stroke. All you are trying to do is fill the cylinder each time instead of only part filling it due to gas flow restrictions through valves/ports and inlet tracts etc.

Obviously, once you can fill the cylinder 100% and that's good – a little more would be better and clearly a LOT more would probably be just about right – but then we discover that we need stronger engine bits, special fuel, better cooling and all sorts of other problems to fix until we end up with ……. an F1 engine

Mark

[John OlsenParticipant @johnolsen79199]

Valve overlap is not the same thing as having the exhaust open after the transfer port closes. With overlap, the exhaust opens first, then the inlet opens, then the exhaust closes, then the inlet closes. The timing won't generally be as extreme on an engine designed for supercharge. This arrangement allows the mixture being blown in to scavenge the cylinder effectively, then after the exhaust closes it can build up pressure in the cylinder until it is higher than would usually be the case with a normally aspirated engine, giving higher power. Yes, this does also lead to higher temperatures, so there is a limit to what any given engine will stand.

With a standard two stroke arrangement, it is inherently impossible for the transfer to remain open after the exhaust closes, so you can't build up a positive pressure in the cylinder, apart from tricks with the exhaust system. Blowing will improve the scavenging and so reduce the dilution with exhaust gas that usually occurs, but at the expense of fuel economy.

John

[Clive HartlandParticipant @clivehartland94829]

SAAB tuned their 3 Cyl. 2 strokes by the exhaust method and by putting a carb. on each cylinder. I was lucky enough to see Carlson in Kenya with his tuned SAAB 95, the engine was a lovely thing to see. Three very large carburetters took up a lot of space in the engine compartment.

I watched as he revved the engine and the Tacho reached 9000 rpm. My SAAB 95 would do just 87mph flat to the floor. Carlson was balked on a hill where a Mercedes had become stuck in the mud, all he did was jump out and with help tipped the SAAB over and back on its wheels and went on his way.

I ever regret selling both my SAAB 95 and the SAAB 96 that I had. For a new FORD Escort.

Clive

[dean clarke 2Participant @deanclarke2]

Ok, so i think it will help if i explain what i mean by super charged. the object of super/turbo charging any engine is to increase its ability to intake the air fuel mix over and above what its naturally capable of, right? So that being said you can super charge it by forcing more mix in. weather or not you achieve positive pressure in the combustion chamber is not the be all and end all (ideal but not the only end result) there are a number of efficiency losses in a model 2 stroke engine but by adding intake pressure you can remove these and gain a large power increase but still without reaching positive combustion chamber pressure. using the increased transfer pressure to help remove the leftover exhaust gases is also another plus to supercharging this engine, ( without the excessive fuel consumption), also the desgin of this v12 is with 2 con rods to 1 big end journal. this gives a 90 deg lag over tdc at number 1 to number 2 cyl. this equals a significant loss of crankcase suck effort, hence the addition of the super charger. So all this equals a super charged 2 stroke V12.

Dean

p.s. scavenging pumps are recovery pumps and strictly speaking not the correct label for intake pressure pumps. plus "super charged" sounds way more "heavy metal" don't you think? LOL i will keep you all updated with progress

[dean clarke 2Participant @deanclarke2]

Ok, so i have finished the front housing now, yay 1 more part down. this holds 2 21 x 12 x 5 ball races to carriy the front of the crankshaft. the rear end being held on a single ball race of the same dimensions. here are also the quad carb bodies i have roughed out along with the manifold.

Blower case is the next challenge, will post these photos as soon as i have done it.

cheers for now

dean

[dean clarke 2Participant @deanclarke2]

ok, so i had quite a bit of success over the weekend but also a somewhat frustrating disaster. got the supercharger case all but finished and both end caps machined up , made the offset turning fixture to machine the bearing holes for the blower rotor. this turned out to be not quite as straight forward as i thought as you will see in the latest photo updates.

having made the fixture i inadvertantly fitted the cover up 180 deg out and machined the wrong side, OOPS, bugger. oh well start that part again…………….

dean

[dean clarke 2Participant @deanclarke2]

Hey guys , just thought i'd give you all an "assembled so far" bunch of photos of whats been done on this project up to date. i only have the blower rotor and vanes left to complete, then onto the crank.

cheers

dean

will keep posting progress if anyone's interested in seeing it?

dean

[Ady1Participant @ady1]

Lots of armchair watchers methinks.

People in here tend not to clutter a good build thread with fluff until after its completion

We are watching, and are impressed

[RJWParticipant @rjw]

Count me in 1000% Dean, antique clocks and watches are my bread and butter, but engines are my lifelong passion, I was manufacturing and installing automotive turbocharging systems for a living way back in 1979!
I'm in awe of your progress with this project 'Superb' is all I can say!

John.

[dean clarke 2Participant @deanclarke2]

Well started the crank tonight, here are a couple of photos of the first two stages of machining

1st is bar stock cut to length and faced and centered both ends

2nd shot shows the front main fournel roughed out to go into a collet chuck.

3rd photo shows machining the flywheel diameter.

cheers for now

dean

[dean clarke 2Participant @deanclarke2]

So heres the photos, LOL

dean

so the sequence goes something like this, make the blank then machine the flywheel dia. then maching the front bearing to 1mm oversize and mark out all the flywheel, bigend and center main bearings. next its off to the mill for indexing all the bigend location marks, mill out the bulk of material for the be to leave a small oversize square. this reduces the turning in the lathe for the b.e. journel. once all the b.e. and main journels have been roughed out i grind the b.ends to final size followed by the mains. Big end journels are turned with the crank mounted in a special fixture. finally cut all the chamferes on the flywheel faces and deburr and polish.

dean

[dean clarke 2Participant @deanclarke2]

OK so another fine day in paradise and we saw the completion of stage two machining of the V12 crank. all B.E pins and main bearings have been roughed out to oversize by 1 mm ready for final machining to size.

Hopefully i will be able to finish machine and grind the crank this week, before christmas. Next will be the center main split bearings, backplate cover and blower drive.

cheers for now

dean

[doubletopParticipant @doubletop]

Dean

Apart from a general sense of inadequacy the last sequence of shots was an "I've just learned something useful" moment.

Keep them coming

Pete

[Clive HartlandParticipant @clivehartland94829]

The vane type rotor, what ratio drive are you going to use? How does it equate in volume passed to give an adequate supercharge pressure.

Clive

[Ady1Participant @ady1]

All these fancy words like blower and scavenge pump and supercharger stirred the family braincell into remembering a book I once read

I was Tubal Cains "Diesel Engine Design" and it contains a huge amount of detail on different routes used for different engines and their advantages/problems

This is part of the crankshaft section

supercharger section, etc etc

Edited By Ady1 on 21/12/2013 12:33:17

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

As the picture of the difference 2 stroke engines is showing clearly the pressure in cylinder will be disappeared after the transfer port is closed while the exhaust port is still open, "Supercharging" is incorrect to use in 2 stroke engine. Also we will call it for blower/scavenge blower instead "supercharger". 4 stroke engine with supercharger will give more power due there is enough pressure in cylinder before compression stroke begins.

[MuzzerParticipant @muzzer]

Yes, you can't really "supercharge" a 2-stroke even with exhaust valves and proper injection. The blowers and turbochargers are primarily to ensure scavenging. However, when you have a V engine like this, you aren't going to get any effective crankcase pressure when you need it, so the transfer ports aren't going to do much for you. The use of a supercharger (scavenge pump?) is probably a sensible choice here, given that Dean is aiming to get this impressive beast working. At least there is a decent chance of the cylinders getting some mixture……..as he explained back on the 8th.

Is this a CI (diesel) or will it have spark plugs? That's a lot of parts either way! Good luck, lots of people watching and wishing you well – no pressure, then!! It'll make a fantastic noise / smell….

Edited By Muzzer on 21/12/2013 18:28:33

[dean clarke 2Participant @deanclarke2]

Hi guys and thanks for the comments and info etc. Hi jen, I accept what you are saying about 2 strokes with the port timing etc, and if you want to call it a scavenge pump then thats fine with me, each to his own, i will use the term supercharger as it will be forcing more mix into the engine than could otherwise be done. however without going into too much detail (secret squiral suff etc) LOL. the engine is arranged with porting and exhaust dimensions to allow some amount of positive charge in the combustion chamber, this is managed by using the rather large expansion pressure of combustion to act as a back door as it escapes out the exhaust system to allow positive transfer pressure to reach the combustion chamber. it is somewhat more involved than what i've just said but it does work. there are a few variables that need a bit more experimentation to finalise as it becomes a balancing act of appropriate pressures which will dictate drive speeds etc. Oh well i guess thats all for now will keep you all posted on the progress. The exhaust back pressure is also what helps stop excessive fuel consumption to a certain extent.

cheers for now

dean

p.s. before anyone asks i have done some experiments and yes the theory is sound and will run, actually it will run very well i think but like my nanna always used to say " the proof is in the pudding" so we shall see.

[dean clarke 2Participant @deanclarke2]

Oh yea sorry i forgot to answer you muzzer, this is a glo engine running on methanol and nitro methane with a bit of good ole caster oil to stop the welding of internal parts.

dean

[doubletopParticipant @doubletop]

Posted by dean clarke 2 on 21/12/2013 23:59:36:

 

" the proof is in the pudding" so we shall see.

Can't wait; and with the progress so far I can't see us having to wait until until Christmas 2014 for the pudding

One of the many watching with interest….

Pete

Edited By Doubletop on 22/12/2013 07:09:19

[dean clarke 2Participant @deanclarke2]

Ok so a quick update to let you know where I'm up to. I have made the fixture to turn the crank big end journels and found a slight problem, the fixture, with the crank in, was too big for the inside dia of my 3 jaw chuck. bugga!! now what to do. Luckily i have a larger 4 jaw self centering chuck so with a slight modification with a boring bar i can now machine the big ends, yay!! So i am now in the middle of making the tools to turn the journels. will post the photos if all goes well, maybee in the next few days depending on how much shed time my wife lets me have. LOL.

cheers

for now

dean

Edited By dean clarke 2 on 28/12/2013 03:06:20

[David Tweddle 2Participant @davidtweddle2]

Hi Dean if you need a test bed to run it in, my 72" Piper Cub is nearly completed and needs a decent power unit.

Keep up the brilliant work and I will sit back and learn from a true maestro .

Regards David

[dean clarke 2Participant @deanclarke2]

LOL yea sure no problem David just cruise on down to cambridge N.Z and we'll bolt it in. I was thinking that I might actually build an ME 109 to put it in, control line of course, about 76" span, what do you think? LOL. Hopefully i will have the crank finished tonight. I am in the middle of building a custom tool post for the lathe to eliminate the toolpost flex from the standard (not very ridged) toolpost. I knew i should have got the bigger lathe. oh well. will post the photo update later tonight all going well

dean

[doubletopParticipant @doubletop]

Dean

Cambridge NZ? That means there is some chance of seeing this creation in the flesh. ME109 or just on the bench

Pete (Wellington NZ)

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