Scion tC Forums banner
1 - 20 of 39 Posts

·
Registered
Joined
·
290 Posts
Discussion Starter · #1 ·
Just posing a question for thought here.

I was reading an article about ceramic engines in development, with the bonus being that they don't need any form of a cooling system. The more heat you can keep in the engine, the more efficient the engine runs dues to less thermal loss.

Now, i know we don't have ceramics in our engines, but we do have a fairly large normal temperature span, Would installing a "hotter" thermostat in our cooling system and essesntially keeping the engine hot-er increase thermal efficiency to any point noticible, or would it be pretty much worthless. I have heard of some drag teams running almost no cooling system at all, so i assume there is some truth to this. Im not too worried about overheating, so long as i watch the temps that will be fine. any thoughts or technical refrences would be cool.
 

·
Registered
Joined
·
290 Posts
Discussion Starter · #3 ·
The internal components shouldn't excede tolerances if it's still in the normal operating temp. range... that would be bad design. not thinking of running above the normal temp, just in the high side of it...
 

·
Registered
Joined
·
272 Posts
excessive heat will make the parts exceed their tolerances and seize...
also on the hotter side of things there is more chance for detonation.

i havent really gone into this myself, Im sure lo bux will jump in soon for a theory lesson
 

·
Former '05er
Joined
·
12,467 Posts
More heat improves thermal efficiency, that's why thermostats have gone from 160 back in the old days to 195 in modern high efficiency engines.

Here's the problem: the engine's components absorb heat and pass it to the cooling system. The absorbed heat is wasted because it is not used to expand the gas in the cylinder, it is used to add heat to the engine's components. In a ceramic (or adiabatic) engine, this heat is not lost because the components don't absorb it. In a metal engine, the kinetic energy (the stuff that actually moves the piston) is created with the heat left over after the materials are completely heat soaked. So the cooler you run the cooling system, the more heat gets diverted to heating the engine components. This is what led Detroit engineers to 195 degree thermostats some years ago.

On the other side of the problem, you have the specter of detonation from too much heat. Our universal gas law says the fuel/air mixture will gain heat as it is compressed, and at some point, it will auto-ignite from the increased temperature. So we have to keep the combustion chamber cool enough to prevent this from happening. There are a few ways we can do this.

The fuel itself has a heat of vaporization, so the type of fuel will help remove heat from the compression process. Alcohol fuels like methanol and ethanol are excellent for this because they require significantly more heat than gasoline to vaporize. Methanol and nitromethane are wonderful for engines running a total of about 30 seconds with only 4 seconds at full output. These fuels just don't really need much additional cooling in a drag racer.

Running an air/fuel mixture on the rich side of stoichiometric also helps because the excess fuel also absorbs heat and reduces the tendency to auto-ignite. This is one of the prime reasons why tuners start rich and go lean in the search for power. Rich is relatively safe, and leaner becomes increasingly dangerous.

We can also run the cooling system at a lower average temperature to help reduce combustion chamber temperatures, but as we already noted, this will lose thermal efficiency. The ideal cooling system would maintain a fully heat soaked combustion chamber without promoting detonation from auto-ignition. Given the current state of automotive cooling system design, there is a lot of opportunity for improvement, but the cost of those improvements isn't very economical.

I have toyed with the idea of a reverse flow cooling system with independently computer controlled valves for each cylinder to allow a closed-loop control for combustion chamber temperature. The concept is to maintain full heat soak while monitoring for knock and adjusting coolant flow to keep the engine on the verge of knock without actually causing detonation. Unfortunately the sensor array and the controls to do this are prohibitively expensive, and the efficiency gains over the present design do not warrant this kind of investment in a mass produced machine. Even a one-off would be absurdly expensive and the payoff would be tiny.

Ceramics are the great hope. Cummins has had engines since the 80's that run at or above 98% thermal efficiency, but they just don't do it for very long. The other thing conspiring to squash this technology is the oil companies would cringe with fear if we suddenly improved the thermal efficiency of the entire fleet by a factor of three. Sales would drop precipitously, and there would be no need for lubricating oil in these ceramic engines, so a whole product line would go away. Not very enticing to an oil-based economy.

So, that's the theory. Yes, a hotter thermostat raises combustion efficiency. It brings problems with it, and brings the user a little closer to the edge of disaster. All the information about the parts expanding beyond service limits fails to realize these parts were all designed to run at a given temperature and as long as the engineer and machinist know what that is, the pieces can be designed to work just fine.
 

·
Registered
Joined
·
1,704 Posts
i read the first paragraph..... what i understand is... find the optimal temperature so that heat doesn't go into heating the engine and goes into kinetic energy... but theres a balance between overheating and finding that optimal temperature...

if im wrong, i blame it on me being a biology major
 

·
Registered
Joined
·
290 Posts
Discussion Starter · #11 ·
That seems to be what i was thinking, lo bux pretty much affirmed my suspicions... i guess the only real way to find out will be to test it out. so long as i can keep the intake temps low enough, i don't think i'll have to worry about detonation. Just gotta find a way to do this without blatently voiding the warrenty. Maybe by carefully covering the radiator untill i find a balance, then record average MPG for all the highway cruising i do. Im not worried about overheating too much, as i'll be watching the temps like a hawk. Does anybody know what the Hot end of the normal temp range is specifically?


anyways, thanks for input

Also, in my area gas is predicted to go well above 2 bucks a gallon for low grade.. anything if i can save 5 bucks a week on gas, im gonna
 

·
Registered
Joined
·
290 Posts
Discussion Starter · #12 ·
Sorry, last post was early am... Im gonna go about this a little more organized than cardboard. Going to find a higher pressure radiator cap, and try raise the temps with a new thermostat if i can. If anybody has numbers (max psi for cooling system, temp range) etc that would be helpfull, many thanks
 

·
Former '05er
Joined
·
12,467 Posts
22 psi is generally accepted as a reasonable limit for street cars. TRD makes a high pressure cap, but it's either 1.3 kgf/cm^2 or 1.5 kgf/cm^2.

High pressure helps heat transfer a lot. Blocking off the radiator will not necessarily give you the results you expect unless the engine is working at a consistent load. It is highly improbable the engine in a street car works at a consistent load. Starting with the thermostat is a good idea, but I'd bet you already have an 82 degree C thermostat. Just something to think about.
 

·
Registered
Joined
·
290 Posts
Discussion Starter · #15 ·
I know 2 mpg, or less doesn't seem like a lot, but thats still an extra 25 mi per tank...
but i fill up 3 times a week, or 156 times a year... thats almost 4000 miles by the years end... or i guess by some sorts of fuzzy math, at 1.90 per gallon, almost 295 a year in savings. to me i think thats worth 50 bucks in parts... as long as i am carefull. I know i can save more by changing my driving style... but who honestly likes to do that?

Anyways, found a cap thats supposed to be 20 psi, and looking for a high temp. t-stat. now... i guess i'll see if it really works. I doubt honestly i'll even see 2 mpg increase... but at least i tried.
 

·
Registered
Joined
·
61 Posts
Just something to think about.... if you raise the temp. too much, you could start seeing some self-ignition and knock. To combat this, a higher octane fuel could be used which would negate any price savings.
 

·
Former '05er
Joined
·
12,467 Posts
Originally posted by hamster@Mar 8 2005, 07:41 PM
if im wrong, i blame it on me being a biology major
Don't discount your Biology major. We need someone like you to figure out a bacteria that will produce crude oil from biomass as byproduct of its existence. If you can figure out how to do this, you will be the richest man in the world. I bet some really bright minds are working on this right now because we are going to run out of the oil under the ground, and when we do, we need something CHEAP to replace it. So far, there isn't anything.

What are you waiting for? There's a whole global economy to save!!!
 

·
Registered
Joined
·
290 Posts
Discussion Starter · #18 ·
Just ran through the first tank of highway gas... ended up getting 405 miles on 12 gallons, or almost 33 mpg... before i was getting 30 or so. I installed the TRD high pressure cap, and a 230 deg. thermostat. 3 mpg is ok in my book... awfull near the red line on the temp gauge though...



will post more later
 

·
Former '05er
Joined
·
12,467 Posts
So you are seeing a 10% increase in thermal efficiency? That's incredible. Are you running synthetic oil or conventional?
 

·
Registered
Joined
·
1,704 Posts
this stuff is interesting... as for finding a microbe that produces crude oil... u know i never looked into that as i bio major.. i was thinking drug industry.... thanks again lance... you gave me something to think about
 
1 - 20 of 39 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top