Questions concerning Engine Head in relation to Engine Performance 1

[MechAeroAuto]

http://www.coatesengine.com/csrv.html

http://www.coatesengine.com/engine_of_the_future.html

" A five-litre poppet vavle engine tested on a dynomometer under the same loads and conditions at 5500 produced 480 BHP and 454 foot pounds of torque. The maximum RPMs on the poppet valve engine were 5700 RPMs; the Spherical Rotary Valve Engine in comparison reached 14,850 RPM's"
"

is it possible to get that kind of engine performance just by changing engine heads? i would think that would require significant balancing of the crankshaft, and replacement of the pistons with lighter ones.

"Because the valves rotate away from the combustion chamber and are vented and charged on the opposite side of each sphere, this creates a lower combustion chamber temperature, allowing for higher compression ratios to be used thus creating an extremely efficient engine. Some of the Coates Spherical Rotary Combustion Engines are at 12 to 1, 13 to 1, 14 to 1 and 15 to 1 compression ratios depending on the application."

again, this seems too good to be true. i would think you would have to alter the timing and fuel.

 

[MikeHalloran]

I recall reading about an engine with cylindrical, not spherical, rotary valves, in Popular Mechanics, 40 years ago. It never reached production in detectable volumes. I think it used a single overhead 'cam' that had both exhaust and intake channels in it.

You have to pay very close attention to the balance of any engine at high rotational speeds. I don't think they're claiming that just any old five litre production engine will survive with just a head conversion. I'd assume the timing and fuel also has to be adjusted.

I can accept the high rotational speeds. What I wonder about is how they keep the 'cams' from warping from thermal stress, and contacting the concave sealing surfaces. I.e, after the 14,000 rpm dyno run, will it idle, or just seize?




Mike Halloran
Pembroke Pines, FL, USA

 

[RobWard]

The surprising thing, to me, would seem to be that the rest of the engine holds together just fine at over 2.5 times it's usual max RPM...

Something here doesn't sound right.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[patprimmer]

This has been discussed at length in a previous thread

Please do a search of the site and save us the trouble of going through it all again.

I think the consensus was snake oil.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MechAeroAuto]

do you know how i could find this forum? i've tried searching for it but it brings nothing up.

 

[icrman]

I've run into the same problem. This search engine here doesn't work all that great.

Anyway at that rpm the recip loads would be a bit high.
Poppet valve float is a big limit to rpm limits. And also they are a bit restrictive to flow.

 

[MechAeroAuto]

what about the higher compression ratio's? they claim that their head is less restrictive. would they lower the temp enough that pressure inside the cylinder would decrease enough to run such high ratios?
do you think you would be able to run the engine that fast just be replacing the heads? i could maybe see an extra thousand rpm's. . . but not an extra 9000. let me know what you think.

 

[patprimmer]

A rotary valve head can have immensely improved airflow, so the rpm mentioned is not out of the question from an airflow point of view.

There will however be problems in other regards, not the least of which will be inertia loads from reciprocating parts and flame speeds..

The heat generated from the compression will in fact be more due to the extra VE and could induce detonation, but the hot spot on the exhaust valve will be reduced, thus reducing pre-ignition.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patdaly]

Here you go:

http://www.eng-tips.com/viewthread.cfm?qid=53549

The bigger one evidently is gone.

This is obviously one of those inventions bought up by big oil, just like the 200 MPG carb. ;-)