18 Cylinders Isotta Fraschini (straight six-cylinder x3 )

[Foketry]

As I worked with piston and combustion chamber designers on a couple of engines: "modern thinking" - as of the late 1980s~90s. was to simply flatten the piston and head as much as possible. On CAD: Draw a sphere at BOTTOM dead centre and it should touch the cylinder walls, head and piston with very little overlap. That minimises heat loss to the metal when a spherical flame develops as the piston travels down the bore. (This was developed in laboratories with single cylinder "see through" engines, lazers, etc.).
On Model (seriously small engines, sub-50cc per cylinder) the heat losses to adjacent metal are much worse than your small car engine, and low compression makes things worse.
I would therefore, remembering that the piston does not rotate, simply mill a small pocket for the spark-plug, and a curved bottom groove from there to the middle of the piston, with maybe a SLIGHT dishing of the piston crown). The flame generated by the spark ignition will then progress up the channel to the centre of the piston to meet the remainder of the charge and burn that as the piston travels down the bore.
I have done a quick sketch... - Hope it makes sense?
View attachment 137194
Ask more questions if you wish...
K2.

to facilitate the ignition of petrol, through the spark plug, in addition to the first version, I designed 2 other versions, similar to each other, the last one has an inclined plane.
What could be the best solution?
I remind everyone that the spark plug is located on the cylinder, next to the piston, not above as per image post #30

 

[Foketry]

Hallo Foketry
The engine must work with your piston design as on -30- flame travel is short , first runs on glow fuel wiht glow plugs
the v 10 engine is the project i am working on (bore and stroke 26mm )my own design and make
gr

Hallo Leerkracht
Beautiful engine, is the glow plug on the head or in the cylinder?

 

[leerkracht]

Hallo Foketry
the plug is in the hemi shape head
keep your piston so simpel as possible , the modelengines from the beginning has a baffle (on two stroke engines ) this work wel , your pistons with a dome and a plug on the side wil work , for testing make a simple 1 cilinder
gr

 

[Steamchick]

Hi Foketry: post#41 - My vote is no 3: the inclined groove, but even as small as 1/8" parallel sided will shoot the flame to the middle of the piston. - Possibly smaller? - and parallel is OK. Or a vee-groove, or round bottomed? Or even a 1/8" hole drilled from the spark plug centre to centre of piston will work. Basically, fill as much of the cylinder as possible up to the crown face, but have the combustion chamber in the middle and across the surface of the crown Of course, the notch on the side of the crown to clear the spark plug must be all the way up the side, so an "open channel" to the crown centre is quite reasonable to ignite the "flat pancake" of gas as it approaches TDC. With any "side positioned" ignition source the flame front will "wrap around" the "pancake" of gas at TDC and pre-ignition will occur opposite the spark plug when flame fronts turn and collide. Ignition advance must be set as early as possible without this pre-ignition (detonation for flame front shock waves colliding) occurring before TDC has passed.
K2

 

[leerkracht]

there is a saying (there is a difference in theory and practice , but in practice the difference is even greater than in theory)
gr

 

[Steamchick]

Leerkracht: I like that one!
Theory is like a map: It is a "human" representation of what we should expect, and where we should go. In fact, "Theory" means it has been proven by some so we tend to believe it is relatively useful (within the scope of the proof). But like all "virtual" information, (Imagination, memory, Maps, Drawings, TV, Internet, etc.) it isn't really there, it is just an impression so we can decide where to go and what to do. And then it becomes real, and is more than likely going to be close to what we expected. But "Life" does have a laugh when reality isn't what we expect! - e.g. Columbus not finding India? Buzz Aldrin finding that the Moon is not made from Cheese? People thinking that the atom was the smallest indivisible particle, or the Earth is the centre of creation?
I do like theory, because if it says something will fail I would rather not waste time trying to prove the theory wrong. (I am not a "Galileo"). Especially if it risks hurting me or my loved ones.
But I do enjoy it when someone succeeds by using theory (Higgs with his Boson?), and also when they succeed despite the theory saying "it will fail" - though I can't think of any examples just now...
K2

 

[Foketry]

Another piston with V-milling, easier to make.
I will do a test on a single cylinder with at least 2 types of pistons to see if there are any appreciable differences.
Another solution could be to place the spark plug on the head with a recess similar to Holt 75 but it would be different from the original Isotta Fraschini project.

 

[Steamchick]

Better for combustion would be using a ball-ended mill, for a round bottomed groove. - (The V-groove has a small corner at the bottom for cooler gas to not ignite, and a possible stress raiser that could develop a crack in the piston. So I should prefer to avoid that shape.). Or milled with a square-ended milling cutter, from the side, with piston angled, so the groove gets shallower towards the middle of the piston, to virtually run-out at the middle of the piston.
I can do a sketch, if you think this is useful?
K2

 

[Foketry]

Better for combustion would be using a ball-ended mill, for a round bottomed groove. - (The V-groove has a small corner at the bottom for cooler gas to not ignite, and a possible stress raiser that could develop a crack in the piston. So I should prefer to avoid that shape.). Or milled with a square-ended milling cutter, from the side, with piston angled, so the groove gets shallower towards the middle of the piston, to virtually run-out at the middle of the piston.
I can do a sketch, if you think this is useful?
K2

I modified the piston using a 6 mm diameter ball end mill, similar to the diameter of the spark plug
Now the compression ratio is 7.4 , I think the piston project is now final but if you have any other suggestions they are welcome

 

[Steamchick]

Seems good!
Needs a real part running to prove it.
Well done Sir!
K2

 

[ddmckee54]

Foketry:

Are the cylinders going to be keyed somehow so that the spark plug will line up with the groove in the piston?

Don

 

[Foketry]

Foketry:

Are the cylinders going to be keyed somehow so that the spark plug will line up with the groove in the piston?

Don

sure, they will be aligned with the spark plug

 

[Steamchick]

Hi again, Thinking of "what can possibly go wrong".... I wonder if the combustion when cold will need a choke, to richen the mixture, but the engine will take a relatively long time to fully warm up and temperature to stabilise, during which time you'log need to fiddle the choke to keep it running, before the hot engine runs on the stoichiometric mixture? Purely an operational, not mechanical issue. A feature of the thick piston crown. Perhaps some of the thickness (mass) can be relieved from the underside of the piston? A horse shoe shaped grove?
But only my guess.
K2

 

[Foketry]

Hi again, Thinking of "what can possibly go wrong".... I wonder if the combustion when cold will need a choke, to richen the mixture, but the engine will take a relatively long time to fully warm up and temperature to stabilise, during which time you'log need to fiddle the choke to keep it running, before the hot engine runs on the stoichiometric mixture? Purely an operational, not mechanical issue. A feature of the thick piston crown. Perhaps some of the thickness (mass) can be relieved from the underside of the piston? A horse shoe shaped grove?
But only my guess.
K2

My brief experience tells me that it will not be a problem, to enrich the air-petrol mixture. it is sufficient to plug the venturi of the carburetor with a finger, the engine will become hot in a few minutes
There are 18 cylinders that heat, the exhaust temperature will reach 120-140 C degrees in less than 2 minutes

 

[Steamchick]

OK Foketry, I think (hope) you are right.
Thanks for reply,
K2

 

[Foketry]

I made some changes to the block design, some reliefs and ribs

 

[Foketry]

From drawing to the finished piece : crankshaft

the steel bar with the 2 references at the ends to drill the centers in phase for tail stock

to drag the crankshaft with the spindle I screwed a threaded pin

roughing

finishing before grinding with tool post grinder

glued wood shims to avoid bending and vibrations during turning

 

[Foketry]

I left 0.3 mm in all turned diameters for final grinding

For my grinding tool post I used a washing machine motor with an electronic speed control board and a Poly V belt, now after this test I have to build the safety protections, very important to avoid accidents.

The final check to verify the alignment, max error 0.03 mm, means 0.015 error on the rotation axis, more than satisfactory.

 

[Foketry]

The crankshaft almost completely finished, I am waiting to build the engine block and then make the last finishes and adjustments

the final pin with the cone will be fixed in its seat at the end, once the engine block has been made
On this cone which originally was to fix the propeller I will put a flywheel, large when necessary

 

[Vixen]

Beautiful crankshaft and toolpost grinder. Well done.

What was the spindle speed of your home made toolpost grinder?
What was the diameter, width and grit size of the stone?

Mike