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?

[Playtoy_18]

I am interested and am playing with the ideas of thermal efficiency as well a small bit.
One big issue I see is with all the energy conversions taking place.
From chemical to heat to mechanical etc..
The heat is a necessary evil,as the expansion of the chemical combustion reaction is what transfers to mechanical energy.
I am trying to make those conversion processes more efficient in order to coax more efficient power.
One thing i've been playing with is the use of specialized coatings.
Coating the piston and chamber will help retain heat where it can be used in the cylinder instead of wasting it into the cooling system.
At the same time however,the fuel delivery must also take a new turn.
One big issue with fuel is atomization,fuel will only be consumed in the combustion process from the surface of a droplet of fuel as I have been taught.
So to actually use less fuel,the fuel must be almost completely vaporized or else the rest of the droplet goes right out the exhaust.
Direct injection helps accomplish this,as the ecoboost from Ford has shown.
Offhand I think the v6 twin turbo in the f150's is running about 12psi,10:1cr and over 350hp from a 3.5.
I want to say the sho or one of them is actually running higher boost and cr as well.
I believe it is from some of the benefits of such higher pressures/better atomizatin as well as the excellent effects of controlling cylinder temps.

I'm trying to negate alot of the parasitic effects of the mechanical parts as well using dry film and ceramic coatings as well as thermal transfer and barrier coatings.
Coming up on some actual engine testing,and i'm anxious to see if it is going anywhere.
I have both of smokey books and honestly alot of where my ideas come from,I admire the hell out of him.
Interesting topic,subscribed.

[RobertISaar]

fuel vaporization is a big issue... one reason why i would hesitate to coat the intake valves with anything that would prevent it from heating up. if anything, let that run hotter, the fuel charge spends some significant time sitting on it.

it would be neat if there were some type of coating(catalyst?) that could be applied to the backside of the valve that either reduced the temperature necessary for gasoline to vaporize, or otherwise would help it along.

[Playtoy_18]

http://www.techlinecoatings.com/arti...ve_Article.htm

I used the same product on the inside of a carb manifold,he had to rejet down two sizes and play with the plug gap when tuning it afterwards.
Offhand I would say in general it definately helps keep the fuel in the airflow and off the walls.

*sorry,that covers the front and not so much back of valve.
The dry film product creates a "boundary level turblulence" that promotes flow as well as keeping the fuel suspended and off the port walls.

[1project2many]

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.

Yes. The balanced ratio of oxygen to fuel is about 11:1. The end components are primarily CO2 and H20. But 100% oxygen carries it's own set of problems. Oxygen prefers to bond with other atoms such as Hydrogen and Carbon. Given the chance, O2 will quickly break apart to form bonds with these elements. In a warm engine with sharp edges and hot spots, increasing heat from compression is all the chance that O2 needs. Ignition can easily start well before the spark and with no inert gas to inhibit the reaction, fuel quickly burns. Additionally, free oxygen and excess heat can cause internal engine parts to burn or melt which rarely leads to long engine life.

Can a turbo be sized appropriately, and tuned to actually make boost while at a steady state of output.

Yes. That was a major part of Smokey's hot vapor engine.

fuel vaporization is a big issue... one reason why i would hesitate to coat the intake valves with anything that would prevent it from heating up.

But, and this is a big but, fuel that has changed phase and become a gas will expand and force much needed oxygen out of the engine. The turbocharger on the hot vapor engine played a dual role. First, it served as a giant mixer, a homogenizer, to turn fuel and air into a consistent mixture. Second, and more importantly, it kept the gaseous fuel from forcing oxygen back out of the engine.

So to actually use less fuel,the fuel must be almost completely vaporized or else the rest of the droplet goes right out the exhaust.
Direct injection helps accomplish this,as the ecoboost from Ford has shown.

What direct injection really accomplishes best is to move the vaporization phase away from the intake pathway and into the cylinder. Not only does this prevent O2 displacement but it allows the beginning and end of combustion to be better timed to specific positions of the piston and crankshaft.

it would be neat if there were some type of coating(catalyst?) that could be applied to the backside of the valve that either reduced the temperature necessary for gasoline to vaporize, or otherwise would help it along.

You've got the catalyst in your car already. Platinum and Palladium are excellent catalysts for combustion. We just need a binding agent that can be applied to engine parts and will withstand the heat of combustion. Anyone interested in mixing ground up cat ceramic with thermal barrier coatings?

[Playtoy_18]

Don't the platinum and palladium have it's reactions after combustion though?
I thought we were talking about using the fuel more efficiently,after it's burned and needs a catlyst for emissions then the idea pertains more towards controlling emissions versus controlling combustion/fuel efficiency/vaporization etc..