Hello Enfieldbullet.
Thanks for your technical arguments and the opportunity to explain a few things.
You write:
“first and foremost, thats a cool new rotary valve design, i`ve never seen it before and i think it could be really cool to build an engine using it. but your 40,000 rpm is just...too much. modern F1 engines arrive at 18.000 rpm. you could probably do a little faster on a reciprocating otto cycle but not much, not nearly 40.000 rpm.
that`s because your flame front has to consume the fuel in the combustion chamber at every powerstroke and at 40.000 there isn`t enough time for that to happen. your engine would do a full turn at almost every 1 millisecond and you would have 0.5 milliseconds for combustion to occur. combustion cannot happen that fast normally, i think i remember 3 milliseconds quoted in a book in high-turbulence designs. maybe you would just have a lot of combustion happening in the exhaust pipes, and that you make a pretty inefficient engine”
50,000rpm sounds as too much, but it is not too much.
Let me explain it.
The Ducati Panigale 1299 has 116mm bore, 60.8mm stroke and runs reliably till 11,500rpm of the rev limiter.
In the 24.8mm bore x 13mm stroke PatRoVa model engine (same bore to stroke ratio with the Ducati), the flame has to travel a 116/24.8=4.7 times smaller distance.
Provided the flame front propagates at the same rate (speed) in the Panigale 1299 and in the PatRoVa model engine, the second burns the mixture until at least 11,500*4.7=53,800rpm
Actually, the flame in the Ducati Panigale extends slower than the flame in the PatRoVa model engine because the shape of the combustion chamber of the first is not good: it is a thin disk (116mm diameter, 5.24 mm average height for 12.6:1 compression ratio), with deep valve pockets on the piston crown and necessarily abnormal shape of combustion chamber walls.
In the one case the flame extends at the two only dimensions (thin disk), while in the second case, wherein almost all the mixture is concentrated into the chamber formed between the two disks of the rotary valve (the clearance between the flat piston crown and the cylinder head is quite small: the limitation is to avoid the piston-cylinder head collision at high revs), the flame extends in three dimensions and proceeds faster with lower thermal loss.
So, as regards the combustion, 50,000rpm is OK for the oversquare PatRoVa model engine.
From the practical viewpoint, take the OS.18TZ model engine (
http://www.pattakon.com/tempman/osmz2110-dynotest-rcnitro.pdf ).
2-stroke with 16mm bore and 15mm stroke.
The dyno test in the above PDF shows the peak power at 30,500rpm and the maximum rpm at 42,500.
Here is the port timing (quote from
http://www.pattakon.com/pattakonPatAT.htm ) :
Its is a tiny engine that provides 750bhp/lit. To achieve such high specific power it is required the efficient burning of a good quantity of fuel inside the cylinder.
You also write:
“secondly, at 40.000 rpm in a reciprocating engine, the inertial forces on the piston would be a HUGE problem and you would need a super strong material or a super dimensioned part. but the more massive the part is the slower the engine`s top speed would be. which brings me to the third point”
The abovementioned OS.18TZ model engine revs reliably at 42.500 rpm wherein the mean piston speed is 21m/sec and the maximum acceleration of the piston (with, say, connecting rod to stroke ratio 2.0) is 19,000g (g=9.81m/sec^2).
With 13mm stroke versus the 15mm stroke of OS.18TZ, the PatRoVa model engine has a mean piston speed of 21.7m.sec at 50,000rpm and a peak inertia acceleration of 23,000g. With longer connecting rod (say, 3*stroke=39mm from center to center) the maximum acceleration of the piston falls at 21,000g (only 10% higher than in the OS.18TZ).
An advantage of the 4-stroke is that its piston is shorter than of a 2-stroke because it needs not to cover and uncover ports on the cylinder liner. It also runs colder (it burns every other reciprocation; and there is no side of its piston skirt thrusting over hot exhaust port).
According the previous, when a 4-stroke model engine with 13mm piston stroke is operating at 50,000rpm, the inertia forces on the piston is not a problem (at least not a huge problem) and the existing materials used already in the model engines are OK.
You also write:
“third: it`s not just because your valves are revolving that they don`t take force to turn. they do, just like poppet valves. and by the apparent size of the drawing their moment of inertia would be pretty big. you could make their diameter smaller, but then breathing would become an issue(must reach a compromise here).”
No. There is no comparison of the loads.
With a rotary valve rotating at constant angular speed, the only resistance is the friction between the valve and the cylinder head. But there is no force pushing the PatRoVa rotary valve onto the cylinder head. So the friction is quite small. The sprocket has to provide this small torque to the rotary valve, and this is all.
Note: the rotary valve does not accelerate / decelerate during each crank rotation; it just rotates with half crankshaft speed.
If necessary, the upper sprocket can be elastically connected to the rotary valve shaft (to allow the rotary valve to rotate at more-or-less constant angular velocity despite the slightly variable angular velocity of the crankshaft (think how the clutch disk is connected to the clutch hub))
Parenthesis.
The requirements seem initially “opposite” / “incompatible”:
On one hand the PatRoVa rotary valve needs a stiff structure (which means heavy weight) wherein the high pressure acting on the two disks through the windows of the combustion chamber will cause only a tiny change in the clearance between the disks and the respective window lips:
On the other hand, the rotary valve should be capable for extreme revs without significant friction.
The above rotary valve (88mm diameter) has been tested alone (i.e. without a piston in the cylinder) at 11,000 rpm (i.e. 22,000rpm of the crankshaft) for several minutes without significant temperature increase of the cylinder head.
Are there any normal size reciprocating piston engines running at 22,000rpm?
End of parenthesis.
As regards the inertia loads, comparing the PatRoVa rotary valve with the poppet valve is like comparing the day with the night.
As a piston, the poppet valve accelerates and decelerates in synchronization with the crankshaft.
During, say, 240 crank degrees the poppet valve opens and closes (frequency:
1.5 of the crankshaft frequency).
Its restoring spring has to be strong enough to accelerate the poppet valve to close following the ramp of the camshaft.
In the Ducati Panigale 1299, the intake valve lift is 16mm for a piston stroke of 60.8mm. This means that the acceleration of the valve is (
1.5^2)*(16/60.8 ) =0.59 or 59% of the acceleration of thepiston.
Note: the opening and the closing of the valve is far from being pure sinusoidal;
the acceleration of the piston, due to the limited length of the connecting rod, is not sinusoidal , too.
But in the lump sum the acceleration of the valve is more than half of the acceleration of the piston.
With the intake valve weighing 46.8gr, the overall reciprocating “valve mass” is about 100gr (it is the valve mass plus half of the spring mass, plus a part of the mass of any linkage like, say, the cam follower).
At 11,500rpm the acceleration of the piston of the Panigale is about 5,600g; according the previous, the acceleration of the inlet poppet valve of the Panigale is more than 2,800g.
This means that the spring has to be capable to apply a restoring force of at least 280Kp (about 600lb) to the valve (actually more, for safety), otherwise the valve cannot follow the cam lobe. This means that the camlobe has to apply to the valve / valve spring an even stronger force (necessary for the acceleration of the valve / valve spring and for the compression of the valve spring) in order the valve to move as it moves.
For the motion of the conventional poppet valves they are required extreme forces (which means stress on the parts involves (including the timing chain or belt), friction, wear, cost etc.)
Ducati solved partially the problem by eliminating the restoring valve springs (Desmodromic cylinder heads: the valves not only open positively – as in the conventional valve trains – by they also close positively, without the need of restoring springs).
The Panigale seems ideal for the application of the PatRoVa rotary valve in full size.
But Ducati refuses to sell a Panigale without its expensive cylinder heads (they reasonably cost a dozen of times more than the PatRoVa cylinder heads), so we are looking for a Ducati Panigale with destroyed cylinder heads to modify it to PatRoVa.
I hope it is now clear:
There is no comparison. The load on the timing chain or belt of a conventional engine (say a sport single cylinder or a V-2) is dozens of times more than in the PatRoVa rotary valve.
By the way, a broken timing chain or belt is – typically - a catastrophe in the case of poppet valve engines (valves / piston collision, destroyed pistons and cylinders and casing). In comparison, all it requires a broken belt or chain in a PatRoVa engine is the replacement of the broken belt or chain.
You also write:
“also, a reciprocating engine with just 6cc reaching 4.5hp is just unrealistic. did you factor in the thermal problems? i mean, normally 2/3 of the power is lost as heat inside the engine and at the exhaust. and at just 6cc those small parts would have a hard time getting rid of the heat instead of melting. (also, parts weaken the hotter they are and reaching 40.000 rpm just gets more and more unrealistic)”
The OS.18TZ 2-stroke model engine with only 3cc capacity provides 2.28bhp at 30,500rpm (750bhp/lit).
With 6.28cc capacity the 4-stroke oversquare PatRoVa model engine has an easier task: only 4.5bhp.
As for the cooling of the parts, a 4-stroke is better / easier in this area than a 2-stroke.
You also write:
“lastly...you drawing shows a timing belt pulley. F1 engines use gears because timing belts simply lag too much at 18.000 rpm to give accurate valve timing, you wouldn`t be able to get away with that.”
If necessary, gear wheels can replace the timing belt and the sprockets.
On the other hand, as explained in the previous, the timing belt of the PatRoVa engine has a far easier job than the timing belts in the poppet valve engines.
Thanks
Manolis Pattakos