what limits RPM

[1953greg]

They are also limited by flame front speed during combustion. You can only burn a fuel/air mixture so fast. This is one of the primary limitations of RPM in a Diesel, the flame front speed is quite slow compared to gasoline.

is that whats called vapor expansion speed?

 

[wkpoor]

I think post 19 and 20 basically nails it.

 

[safeT1st]

Not the case

I have to disagree with you regarding diesel engines . The speed is limited by the rotating mass and the forces it generates . They are built strong and heavy . I have seen several diesel engines self destruct ( rods and pistons out the block) when the governor failed . At that point , the only way to stop it from blowing itself up is to shut off air flow or fuel . That's if you have the guts to get near it . Flame front does not become the limiting factor in a diesel engine .

 

[1953greg]

I think post 19 and 20 basically nails it.

+1

good thread

 

[gink595]

What limits rpm now is still up in the air, but what limits it later on will be the price of gas

 

[Cerran]

Flame front does not become the limiting factor in a diesel engine .

I would agree on large slow speed diesels that are scavenging and designed to turn very low RPMS for efficiency. For these engines rotating mass becomes the limiting factor. However, it certainly is the limitation on smaller diesels for passenger cars and pickups. To verify go look at the Tachometer on a modern diesel 1/2 to 1-ton truck versus a gasoline one.

is that whats called vapor expansion speed?

Actually that would be something different. That would be how fast the compressed gas entering the cylinder expands to fill the cylinder volume.

Flame front speed is how fast the leading edge of the flame travels in the fuel/air mix in the cylinder once ignited.

 

[safeT1st]

Becuase of the mass involved in a diesel inertia causes it to fly apart before it stops breathing reasonably well . I should add that my experience is with the large Detroits .... 16v149's etc . That's 149 cubic inches X 16 .

 

[safeT1st]

Point taken

I would agree on large slow speed diesels that are scavenging and designed to turn very low RPMS for efficiency. For these engines rotating mass becomes the limiting factor. However, it certainly is the limitations on smaller diesels for passenger cars and pickups. To verify go look at the Tachometer on a modern diesel 1/2 to 1-ton truck versus a gasoline one.

You and I are on the same wave length here . I wrote my previous post as you wrote yours .

 

[Fish]

so then if a 2 stroke would stay glued together, would lets say 20k be possible??

has anyone intentionally taken one to the limit w/ a tach attached?

neat topic

Actually at the Stihl schools at Bryan Equip. in Ohio, they did just that,
in the early 1990's, I believe they used an 026, or 034/036, I cannot
remember, but it got @ 17,000-18,000 for about 45 seconds or so, it seized,
he waited a minute or two, set the carb back to 1 turn out, and restarted
and started cutting some more.

Afterward, we took it back in and tore it down, to see the damage.








On a lighter note........

If this thread gets too deep, I might have to re-introduce you all to...........

THE FISHERIZED EAGER BEAVER!!!!!!!!!!!!!!!!!!!!!

And my patented MAGLEV bar/chain system..

Do a search, and open another beer, we had fun in those days.........

I actually used to get p.m.s asking me why I needed liquid nitrogen..........

 

[1953greg]

Becuase of the mass involved in a diesel inertia causes it to fly apart before it stops breathing reasonably well . I should add that my experience is with the large Detroits .... 16v149's etc . That's 149 cubic inches X 16 .

safe, i never knew how the nomenclature of the detroit diesels were til your post. back n the late 60's i remember a 6n71 that was in one of dads trucks. i knew it was an inline 6 but never knew what the 71 was. now i do!!

what do those 16v149's go in, euclids??

 

[safeT1st]

Engine model designation: Detroit Diesel

Yes , the last digits express the cubic inches per cyl. Ex: 4V53 = 4 cyl , 53 cubes per cyl . 6-71 = 6 cyl , 71 cubes per cyl . The nice thing about Detroits is their flexibility . Most any engine can be built to any configuration you desire ... and there are alot ! The 16 V's we built were two functional V8 blocks bolted together , two cranks bolted together , supercharged as all the early detroits are , turbo charged and intercooled . We built these from the ground up , dynoed them for break -in and shipped them to Fort Mcmurray for Syncrude . There they bolted generaters on the back and installed them in 200 ton Electrahaul trucks .

 

[timberwolf]

Flame speed is what I think to be the limit, provided mechanically it is built to take the RPM. Also rings and piston speed are a factor.

These can be overcome to some extent with shorter strokes and rod geometry. Also fuels can be used that maximize the flame speed.

 

[wood4heat]

Honda had four strokes turning 20,000 rpm in the sixties! I think the biggest limiting factor is piston speed and weight. Shorter strokes have lower piston speeds therefore can turn higher rpms. Lighter pistons can sustain higher speeds while putting smaller loads on the crank, rods, etc. If you want to take my theory to extremes I have a .25 rc engine that turns 45,000 rpm.

 

[gink595]

Honda had four strokes turning 20,000 rpm in the sixties! I think the biggest limiting factor is piston speed and weight. Shorter strokes have lower piston speeds therefore can turn higher rpms. Lighter pistons can sustain higher speeds while putting smaller loads on the crank, rods, etc. If you want to take my theory to extremes I have a .25 rc engine that turns 45,000 rpm.

I agree, I think manufactures could make these motors scream more. But I think they draw the line because the extra costs of more precision machining and engineering don't out weigh the power gains when they can just bump bore/stroke a couple mm. The reliability of a motor turning 20,000 cannot be that long and the fuel it would suck through, wow my saw only lasts a 1/2 hour now.
Yeah I remember reading of a (I believe a 125cc)Honda 6cyl. GP bike that turned 20 grand in the late sixties.

 

[timberwolf]

There is a limit too to how much the bore to stroke ratio can go over square due to piston weight and also the travel distance from the combustion chamber to the exhaust port, transfer ports to conbustion chamber ect.

 

[Lakeside53]

..and bearings... The main bearings in most saws are C3 clearance due to the tight interference fit in the case (the bearing actually gets "squeezed a little) and thermal considerations. Axial loading increases rapidly (square, expotentially? I forget) with speed, and among other issues, at some point the balls will "skid" rather than roll - not good... How do you solve this? Bearing selection, mounting methods, lube methods... all $$.


The MS200T is a high reving saw - it uses needle roller mains rather than deep groove, and the seals are of a different construction.

 

[cuttinscott]

so then if a 2 stroke would stay glued together, would lets say 20k be possible??

has anyone intentionally taken one to the limit w/ a tach attached?

neat topic

LOL I have a Dolmar 120si that pegged my 19,900 tach and went a tad farther. It was also modded and running on 20% nitro RC fuel

Scott

 

[zayder06]

my first post here,love all the info and found this possibly relative video
http://www.videovat.com/videos/1023/chainsaw-v8.aspx

 

[wood4heat]

Yeah I remember reading of a (I believe a 125cc)Honda 6cyl. GP bike that turned 20 grand in the late sixties.

The six cyl was a 250cc that only turned 17,000 rpm. There were two that could turn 20,000 rpm, a five cyl 125cc and I believe a two cyl 50cc which made something like 15hp. I think the 125 was over thirty! Can't remember what the 250 made but I would guess around sixty.

 

[wood4heat]

Ok did a little digging and found a cool site:

http://www.vf750fd.com/Joep_Kortekaas/1966.html

In 1966 the specs were as follows
50cc=21,500 rpm 16hp
125cc=21,500 rpm 38hp
250cc=18,000 rpm 60hp

Sorry if I'm derailing, I'm kinda of a Honda enthusiast/geek