What is the mechanism that creates heat in combustion engines?

[Cogman]

Originally posted by: Paperdoc
Again, the heat "generated" by friction between moving parts is not new energy. ALL of the heat originates in what is released in the chemical reactions we call "burning" or "combustion" - the conversion of gasoline and oxygen molecules to CO2 and H2O releases a whole lot of energy as heat. The heated gases (the products of the combustion reactions are gases) cause motion of the pistons, thus converting heat into mechanical kinetic energy distributed among all the moving parts. A small amount of this kinetic energy is converted back into heat by the friction process, but this the same energy that we started with: it WAS energy stored by ancient chemical processes in the form of chemical bonds in the fuel, and then converted to heat energy by combustion, and thereafter into kinetic (moving mass) energy in the engine.

Old rule of Thermodynamics: Matter (and Energy, since Einstein and others demonstrated the quantifiable relationship between these) can neither be created nor destroyed. They can be converted from one form to another, but there is no mysteruious external source. In the internal combustion engine, ALL of the energy moving around comes from that stored in the chemical bonding structure of the fuels (gasoline and oxygen).

Well, all except your last statement was pretty spot on. And I only take exception to a part of it.

Matter CAN be created and destroyed, however energy cannot. Energy is the basis for all matter, hence matter can be converted into energy (destroyed), and energy into matter (created). I guess you could say that matter just doesn't disappear.

A good example of matter being converted into energy would be the collision of antimatter with matter. The result is a burst of gamma radiation, and both particles disappeared. Now, I don't know of a good example of energy going back to matter, but I am guessing it is possible as there are few things that go one way and cannot go the other way.

A better statement would be that the amount of energy in the universe is constant. (As far as we know )

 

[KIAman]

A better question would be "What is the optimal way to convert thermal energy into mechanical energy?" A piston engine is not the answer

 

[Paperdoc]

RE: Cogman's comment:
We agree, just use different ways to say it. In fact, I'm saying matter and energy are interconvertable (sort of). So the conversion of matter to energy is just a part of that same rule - it's a conversion, not a destruction. In fact, we used to phrase the rule as:" Mattergy can be neither created nor destroyed."

 

[natto fire]

Originally posted by: cusideabelincoln
The friction between the piston rings and cylinder walls, the crankshaft and rod bearings, camshaft(s) and bearings and lifters/rockers, and everything else that moves also creates quite a bit of heat as the molecules excite each other during the motion. Just think: You have tight fitting pieces of metal in direct contact and moving anywhere from 1500 to 8000 RPMs, and that creates a lot of frictional heat. Of course, the pistons and rings have to move up and down every RPM, so it travels roughly twice the distance of the cylinder wall every revolution.

Yes. So much heat that the engine would fail in a matter of seconds or minutes were this actually the case. All of those parts you describe actually have a very thin layer of oil between them which cuts down on the friction tremendously. Not to mention the fact that all of the energy comes from the gasoline combustion.

 

[OCedHrt]

Originally posted by: f95toli

Originally posted by: JeffreyLebowski
why can't we capture the heat from the engine instead?

Because you would waste MORE energy that way, due to the fact that the conversion to electrical energy is not 100% efficient. The motor would just use more fuel in order to generate the energy going to the battery.
Remember that you HAVE to generate heat in order to get any useful work from a process; that is one of the basic laws of thermodynamics.

I think there is some confusion here? The question is why can't the heat generated from the combustion (not used) be captured to generate electricity in the use of hybrid vehicles. Yes, this is not a highly efficient process but a gain is still a gain.

Are you saying that in order to capture the unused heat the engine has to generate more heat, and thus burn more fuel?

 

[Cogman]

Originally posted by: OCedHrt

Originally posted by: f95toli

Originally posted by: JeffreyLebowski
why can't we capture the heat from the engine instead?

Because you would waste MORE energy that way, due to the fact that the conversion to electrical energy is not 100% efficient. The motor would just use more fuel in order to generate the energy going to the battery.
Remember that you HAVE to generate heat in order to get any useful work from a process; that is one of the basic laws of thermodynamics.

I think there is some confusion here? The question is why can't the heat generated from the combustion (not used) be captured to generate electricity in the use of hybrid vehicles. Yes, this is not a highly efficient process but a gain is still a gain.

Are you saying that in order to capture the unused heat the engine has to generate more heat, and thus burn more fuel?

Tell me how the process would work and I'll tell you why it wont work. AFAIK there are two ways to convert heat into energy. The first, boil water and push the steam through a turbine. The added weight of the water and turbine would more then kill the amount of energy you would recover (as it would take even more energy to start and stop).

The next would involve sterling engines. More efficient then the turbine, but would require a large amount of them to get the same amount of power out. Again, the weight offsets any gain that would be accomplished by collecting the heat.

The next problem is that no matter what system you use to collect the heat, it is pretty much impossible to collect all the heat the escapes. so you are looking at very minimal gains (most likely losses) + added weight/complexity. And heck, if the system breaks down ever you are basically just carrying around dead weight which would hurt energy efficiency even more.

 

[CycloWizard]

Originally posted by: Cogman
Tell me how the process would work and I'll tell you why it wont work. AFAIK there are two ways to convert heat into energy. The first, boil water and push the steam through a turbine. The added weight of the water and turbine would more then kill the amount of energy you would recover (as it would take even more energy to start and stop).

The next would involve sterling engines. More efficient then the turbine, but would require a large amount of them to get the same amount of power out. Again, the weight offsets any gain that would be accomplished by collecting the heat.

The next problem is that no matter what system you use to collect the heat, it is pretty much impossible to collect all the heat the escapes. so you are looking at very minimal gains (most likely losses) + added weight/complexity. And heck, if the system breaks down ever you are basically just carrying around dead weight which would hurt energy efficiency even more.

There are other ways that would work, such as Peltiers, but they are simply not cost effective.

 

[Cogman]

Originally posted by: CycloWizard
There are other ways that would work, such as Peltiers, but they are simply not cost effective.

Hmm, you might be able to get a positive return on pelters, but like you said, they are not cost effective at all. there efficiency is low, cost is high, and if I recall correctly once they are heated the current stops.

 

[AstroGuardian]

Originally posted by: Cogman

Originally posted by: AstroGuardian

Originally posted by: CycloWizard

Originally posted by: AstroGuardian
I was waiting for Silverpig to show up and is flawless as always

I would apreciate if Cogman writes more about how can the total amount of heat be calculated. I recently read that over the half of the heat generated comes from the mixture being compressed and not the fuel being burned as Bobsmith stated before.

I answered this very exactly in one of the other two threads you posted on this subject. Of course, you could only be bothered to post them - not actually read them.

The first thread was some kind of mistake cause it showed up on the forum hours later when i already sent the second one. I actually read everything and every thread.

And why do you think it's "silly" topic? I think it's more than serious. For example i am an Economist and an IT specialist. I have two Bachelor's Degrees i Economics - Finances and Computer sciences and i have unanswered questions. There are excellent people here at the forums which know far more in topics which are interesting for me. That's why this forum is here for. I appreciate what anyone has to say here.

So what about the 3rd thread, was that a mistake too? Double posting I can see, but triple posting after 2-3 hours is ridiculous.

The reason this question is ridiculous is because if you where awake during Chem, Thermal physics, or even biology, you would realize that the energy put out from a chemical reaction is a constant amount. And as someone else said, it in the order of difficulty of looking up "Energy released from combustion".

But since your initial question was "What creates the heat" It is even more ridiculous. Most teenagers could tell you that gas burns hot.

Sorry, your qualifications don't instantly make all your questions good. In fact, if anything dumb questions devalue the degrees you have.

Cogman, i hate to say this but if there were top10 stupidest answers to a question yours would be the No.1 Not mentioning you insulting me unprovoked. The question is simple and logical. "What creates the heat"? If you are frustrated and not having time to think about all the factors, let the others do that and everyone would be happy.

Please don't take this as an insult. That's not my point.

 

[CycloWizard]

Originally posted by: Cogman
Hmm, you might be able to get a positive return on pelters, but like you said, they are not cost effective at all. there efficiency is low, cost is high, and if I recall correctly once they are heated the current stops.

Yep. One of my roommates looked into using Peltiers to power the fans on a motherboard using heat from the CPU a few years ago for a course project. The payback period was like 350 years.

 

[jagec]

Originally posted by: Cogman
Tell me how the process would work and I'll tell you why it wont work. AFAIK there are two ways to convert heat into energy. The first, boil water and push the steam through a turbine. The added weight of the water and turbine would more then kill the amount of energy you would recover (as it would take even more energy to start and stop).

The next would involve sterling engines. More efficient then the turbine, but would require a large amount of them to get the same amount of power out. Again, the weight offsets any gain that would be accomplished by collecting the heat.

The next problem is that no matter what system you use to collect the heat, it is pretty much impossible to collect all the heat the escapes. so you are looking at very minimal gains (most likely losses) + added weight/complexity. And heck, if the system breaks down ever you are basically just carrying around dead weight which would hurt energy efficiency even more.

No matter what, you are still limited by the Carnot cycle. You will ALWAYS have "waste heat", but the secret to recovering more useful work from the same amount of heat is to improve the engine itself, not add additional doohickeys to try and convert more heat to work.
Better materials to support higher temperature operation, fewer frictional losses, and various adjustments to make an engine more and more closely resemble an ideal Carnot cycle are key to maximizing efficiency. Waste heat will always be there, and unless it can be used as straight "process heat" (which cars do in the winter), you can't convert it to a useful form of energy. Any sort of "energy recovery" from waste heat will decrease the efficiency of the engine by compromising the quality of the Carnot-cycle heat sink.