Thermal Efficiency Discussion

[RobertISaar]

hopefully, this ends up as a very long thread, filled with good information, or at least theories that have merit...

so, what is thermal efficiency(specifically, the thermal efficiency of an otto cycle engine, since by a large margin those dominate the US market)?

it's how much of the energy contained in the fuel is actually used to power the engine, rather than getting "lost" as exhaust or cooling. it's commonly quoted that roughly 1/3 of the energy contained in gasoline is actually used in a useful way(driving the piston down its bore, which turns the crank, which powers the transmission, which turns the axle, which turns the wheels, with each step losing efficiency along the way), the other 2/3 is lost to the exhaust system and to the cooling system.

now, 33% isn't that great... you could be making 3 times the torque or achieving 3 times the fuel efficiency, depending on how far your foot is in the throttle, obviously.



so, now that we know what we're working up against, what can be done to convert the energy lost in the cooling system and exhaust system and use it to drive the engine?



friction = bad, no exceptions. friction takes useful energy to make more heat, which ends up in the cooling system.

heat IS energy. pressure IS energy. anything that can be done to keep those two things inside the combustion chamber and not the surrounding metal will keep energy out of the cooling system. when the spent air/fuel charge comes out through the exhaust port is another place for it to sink into the surrounding metal. the exhaust manifolds and downpipe as well. you could actually help cold-start emissions quite a bit if you kept all of the heat coming out of the engine intact until it hits the catalytic converter.



other suggestions???

one way of extracting energy from the exhaust is obviously a turbocharger, though with increased airflow/airmass caused by boosting, don't expect to see any MPG benefit. if you're looking for more power, it's a great way to go about it, since at least the energy left in the exhaust will be doing something.

there was some brief discussion before about coating internal parts with substances that would reject heat... seems like a good place to cut cooling system losses.

it seems like the cooling system is the low-hanging fruit... extracting work out of the exhaust(besides a turbo) seems to be difficult. using the exhaust to heat up the coolant to normal operating temps faster is actually getting used on some common cars now(prius is one IIRC).

neat fact: a hotter engine absorbs less usable energy into the cooling system due to the temperature differences. a 1500*F flame hitting a 70*F piece of metal gets more of it's heat sapped away than the same flame hitting a 210*F piece of metal. this is why some rather "radical" engines(NASCAR) run really hot thermostats/coolant temps.

another neat fact: aluminum conducts heat a LOT better than iron... thus, an aluminum head will transfer more heat out of the combustion chamber than an iron-head engine of the same design would. because of this "feature", you'll generally run more advance since the engine will be less likely to detonate/pre-ignite. one way to help minimize heat loss regardless of head material would be to minimize surface area.





MOAR THOUGHTS!?!???

[EagleMark]

I think Smokey Yuinick knew this in early 80s, or at least did something with the knowledge. Went against all we are taght about cool air and fuel.

http://www.legendarycollectorcars.co...clusive-video/

[1project2many]

Good start. This subject is very near and dear to me and I've got plenty of years learning, reading, and trying different approaches to improving engine efficiency and in turn, thermal efficiency.

The cooling system is a necessary component and will continue to be so as long as we keep introducing 2/3 more fuel into the chamber than we need to move our cars. What we need to do is find a way to reduce the necessary fuel to that amount necessary to move the vehicle. One of the reasons the mixture must be so rich is because of the amount of inert gas in the combustion chamber. Nearly 79% of what we injest in the engine won't add power and actually inhibits combustion. In order to get enough fuel molecules next to the available oxygen molecules we simply dump too much fuel into the cylinder. The reaction starts and continues until almost all O2 is consumed and the unused fuel is ejected as unburned hydrocarbons to be treated in the converter. Altering the balance of nitrogen and oxygen to favor O2 means less fuel can be used without combustion failing, and less gas needs to be pumped to produce the same power output. The first attempt that I'm aware of was around the beginning of the 20th century using special membranes to separate O2 and N2. The fact that we rarely hear of this suggests the results were less than favorable but the idea is still correct.

[EagleMark]

May be the same issue rarely talked about in the Yunik fiero, even aircraft grade oil had a hard time dealing with heat. Standard car oil did not last at all! That was early 80s, was synthetic around then?

[gregs78cam]

I have a read quite a lot about the work that Smokey did, and I think he had the right idea, heat up the air/fuel mixture (more heat stays in the engine) and mix it very well to get the most efficient combustion possible. I have been wanting to try my hand at making it work, just don't have time or money required. As far as coating engine components, if I had known about it when I was building my 383 I would have done it. I think it would go very well with making Smokey's ideas work.

[RobertISaar]

i've always wondered what the overwhelming amount of nitrogen did to the burn rate / completeness...

if we moved up to 100% oxygen.... would that also significantly alter the stoich ratio for a given fuel? it seems like it would have to.



i've also heard of the various theories and how the "adibiatic" fiero worked.... or didn't work. the big issue is that the engine ran so hot that it required a very expensive oil that didn't last very long. it also had absolutely horrible drivability until it was fully warmed up. but, the idea of using the exhaust to heat up..... well, everything, it's interesting.

[gregs78cam]

Now that you bring up oil, I read an article, and subsequently contacted the company to see if they would be producing anything for automotive applications, they said no.

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

Short story, spherical rotary valves, no oil in top of head, much better flow, higher compression, much less friction, higher revving, more power, better economy. Only for Harleys, and commercial generators.......as of like 8 years ago or so.

Think something like this, direct injected, and turbos.

Turbos bring up another question I have. Can a turbo be sized appropriately, and tuned to actually make boost while at a steady state of output. I mean say for instance start with a 2.0L (really I am thinking something around 600cc-1.0L) engine, setup and tune the combination to make 3-5 psi while cruising. Not much but enough to offset the pumping losses, and use the exhaust velocity to do something useful.

[bentrod]

Man I remember being younger and reading that hotrod article like 10 times. When it came out I believed with in 2 years, that was the future of cars, all cars.

But what happened? For all the lame excuses that could come up, from auto manufacturer's laziness to oil company conspiracies, you'd think SOMEONE, SOMEWHERE would after 20+ years figure out how to mass produce an engine like the one he made.

There is clearly money to be made on making an engine with the stats he provided. Yet no one, not even greedy mega multimillionaires (who could hire Smokey and a team of 10 engineers) could figure out how to mass produce it and make conventional engines as a thing of the past?

Was it too good to be true? Was hotrod lying to us? Why don't we see more of these cars around now? What went wrong?

Maybe it's getting older that makes more skeptical but something tells me we are missing the whole story about that 230hp iron duke.

[RobertISaar]

Turbos bring up another question I have. Can a turbo be sized appropriately, and tuned to actually make boost while at a steady state of output. I mean say for instance start with a 2.0L (really I am thinking something around 600cc-1.0L) engine, setup and tune the combination to make 3-5 psi while cruising. Not much but enough to offset the pumping losses, and use the exhaust velocity to do something useful.

what kind of cruise RPM would be desired? around 2,500(with a 2L)? because i can definitely see turbine housings small enough for that to be a reality.

[gregs78cam]

yea, 2000-2500 rpm, 4K-5K with a <1L. Turbos are great at making better than 100%VE at WOT, why not at cruise?