machine work
05-04-2006, 04:24 PM
#31
1.5 BAR
Join Date: Aug 2003
Posts: 1,194
Re: machine work
Originally Posted by Joseph Davis
Burn takes less time, so there is less time for it to transfer to the engine before going out the exhaust. Thermodynamic transfers are functions of time. Also, as exhaust density goes up combustion chamber surface area remains unchanged... 95 percent of those hot exhaust molecules never come in contact with chamber surface to transfer that "more heat from more fuel" which is incorrect anyway as fuel follows tq not hp and rpm. Go ask for the 75 year old basic engineering text already, spoonfeeding basicknowledge into the Grand Canyon is getting tedious.
05-04-2006, 07:25 PM
#33
3.0 BAR
Join Date: Nov 2004
Posts: 2,313
Re: machine work
baldur, not to be a dickface, but are you just completly ignorant.? Basic knowledge of thermal energy will show jd is in the "in" he knows exactly what he is talking about. Just do some fast searchs and what you will come up with will back jd up even more.
05-04-2006, 07:30 PM
#34
1.5 BAR
Join Date: Aug 2003
Posts: 1,194
Re: machine work
Let's see what engineering masters Lotus and their engine simulation says about my theories vs yours.
The red line is the heat transfer into the cylinder head.
Now lets change the parameters and observe piston temperature and rate of heat transfer.
It's just basic ------- engineering that the more POWER the engine is making the more heat is dissipated by combustion. Added on top is the heat created by more friction at higher revs.
The red line is the heat transfer into the cylinder head.
Now lets change the parameters and observe piston temperature and rate of heat transfer.
It's just basic ------- engineering that the more POWER the engine is making the more heat is dissipated by combustion. Added on top is the heat created by more friction at higher revs.
05-04-2006, 07:43 PM
#35
0.0 BAR
Join Date: Feb 2003
Posts: 0
Re: machine work
Which engine? Naturally asphixiated? Apples to oranges?
I'm also leery of the claimed rate of thermal transfer is? ie - how engine temps spike and reach peak about a full *minute* after you turn off the ignition key... which doesn't even account for the fact that kW is an expression of power, not of transfer over time
Lotus, huh? URLs come back to a dir under your name. Such mastery.
#1 rule of racing is read Ricardo's High Speed Combustion Engine, because you aren't going to figure out anything Sir Harry didn't, but you might just ---- everything up if you don't know what he does.
I'm also leery of the claimed rate of thermal transfer is? ie - how engine temps spike and reach peak about a full *minute* after you turn off the ignition key... which doesn't even account for the fact that kW is an expression of power, not of transfer over time
Lotus, huh? URLs come back to a dir under your name. Such mastery.
#1 rule of racing is read Ricardo's High Speed Combustion Engine, because you aren't going to figure out anything Sir Harry didn't, but you might just ---- everything up if you don't know what he does.
05-04-2006, 07:50 PM
#36
1.5 BAR
Join Date: Aug 2003
Posts: 1,194
Re: machine work
Yes the imaes are under my directory because I made them with Lotus engine simulator.
The model I made is naturally aspirated, not that it matters on this subject.
kW is an expression of power in any form. As an expression of energy over time it becomes kW/[insert unit of time measure here].
The model I made is naturally aspirated, not that it matters on this subject.
kW is an expression of power in any form. As an expression of energy over time it becomes kW/[insert unit of time measure here].
05-05-2006, 11:35 AM
#38
0.0 BAR
Join Date: Feb 2003
Posts: 0
Re: machine work
Originally Posted by baldur
kW is an expression of power in any form. As an expression of energy over time it becomes kW/[insert unit of time measure here].
Then print me up some charts with your AdVaNcEd EnGiNe SiMuLaToR that expresses heat transfer over time.
Nice to note that while the computer sim plots "heat transfer" to piston as going through the roof, the actual piston temperature barely rises - ah, so it does transfer it's heat via skirt to the bore, much as I stated.
If temperatures go through the roof with hp to the point, then why oh why do people shoot for a lower bmep and high revs as a tried and true method for sidestepping knocklimit? It's what Smokey Yunick did with his DIY destroked SBC entry into F1... it's what is going on in every B-VTEC on the face of the planet...
Wait, here, I'll connect the dots for you:
Originally Posted by baldur
There's the most heat buildup at high rpm though
Originally Posted by baldur
There's less heat produced per cycles but there are a lot more cycles.
Originally Posted by baldur
More fuel gets burned at high speed, hence more heat .
Originally Posted by baldur
Yeah and heat going into the exhaust doesnt get dissipated partially into the head?
Originally Posted by baldur
Now lets change the parameters and observe piston temperature and rate of heat transfer.
None of which touches on the time/temperature/density nature of detonation, disproves any statement I have made, yet all of it is a big fat ------- waste of time.
PS if you want a *correct* engine simulation performed, contact Per Andersson at Linkoping University in Sweden. He won't come off the software, but is more than happy to run a few engine models to help a ------ out. AFAIK, they have the most advanced software engine sim in the world - the archived and publicly available masters/doctoral thesis and published papers that they host for the world to read for free far eclipse most of the SAE publications of the last decade (I'm thinking of the blurry half blackened xerox copy O-ring paper, last SAE paper I paid for and will ever pay for).
Originally Posted by JDMFantasy2K
Wow my thread just turned into advanced engine physics
05-06-2006, 11:32 AM
#40
1.5 BAR
Join Date: Aug 2003
Posts: 1,194
Re: machine work
Heat transfer and temperature don't have a linear relationship.
The piston temperature goes up by 60 degrees celsius.
This heat isn't dissipated by the movement of the parts, so the revs don't affect heat transfer into the cylinder wall. There's more oil being thrown at the pistons at high revs though
Heat dissipation rate is purely a function of the temperature differential. A hotter piston will dissipate its heat faster than a colder one.
At low to mid revs, pressure is the primary cause of detonation. As the revs go up, the heat becomes a more and more significant factor. How significant depends a lot on the combustion chamber design.
Now, of course this only applies when you have a steady load so the engine can actually build up some heat.
My final point is: this is why (improperly) modified engines primarily blow up when doing top speed runs or other situations where they see full throttle and high revs for a prolonged period.
The piston temperature goes up by 60 degrees celsius.
This heat isn't dissipated by the movement of the parts, so the revs don't affect heat transfer into the cylinder wall. There's more oil being thrown at the pistons at high revs though
Heat dissipation rate is purely a function of the temperature differential. A hotter piston will dissipate its heat faster than a colder one.
At low to mid revs, pressure is the primary cause of detonation. As the revs go up, the heat becomes a more and more significant factor. How significant depends a lot on the combustion chamber design.
Now, of course this only applies when you have a steady load so the engine can actually build up some heat.
My final point is: this is why (improperly) modified engines primarily blow up when doing top speed runs or other situations where they see full throttle and high revs for a prolonged period.
