What is the mechanism that creates heat in combustion engines?

[AstroGuardian]

I would like to hear your opinions including all the factors that apply.

 

[bobsmith1492]

Is this a joke?

You are burning gasoline. Burning creates heat. There is no opinion involved.

There may also be some thermodynamic activity involving the expansion and compression of gasses but the net effect is... you're burning gasoline!

 

[Howard]

comBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANGBANG

Why is this in HT?

 

[AstroGuardian]

Where else?

Bobsmith is not entirely right. That's why i posted this topic. More opinions? Other factors?
Hm?
Bobsmith, what do you think?

 

[Cogman]

Then answer is in one of you other posts on the exact same topic. There is no mystery why engines generate heat. In fact, we can even pretty accurately calculate how much heat it will produce.

 

[sonoma1993]

and there are moving parts inside the engine, moving parts create friction.and friction creates heat

 

[Howard]

nm

 

[Rubycon]

Rapid oxidation (combustion), friction, heat of compression all are contributing factors.

 

[silverpig]

The creation of carbon-oxygen and hydrogen-oxygen bonds releases energy in the form of kinetic energy of the molecules. This is essentially the definition of thermal energy.

 

[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.

 

[jagec]

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.

Considering that the fuel being burned is what creates the mechanical energy necessary to compress the mixture in the next stroke, you can safely say that, directly or indirectly, ALL of the heat created in a combustion engine comes from burning fuel. Keep in mind, too, that the adiabatic heating created from the compression of the mix is balanced by the adiabatic cooling which occurs from the piston moving down during the power stroke. Of course, entropy will have risen by that point, and the chemical reactions which occur simultaneously complicate the actual calculation of net heat gain, but suffice to say, that "over half" figure is completely false.

If you want numbers, grab a thermo book and thumb through the enthalpy tables, or check out the NIST thermo tables, but it will be a fairly theoretical exercise. A more direct way of measuring how much heat arises from frictional losses and pumping losses would be to set up a test engine driven by an electric motor, with a noncombustible fluid in place of gasoline and heating elements arranged to keep the various parts of the engine at their normal operating temperature. Supply current to the motor until you reach the engine speed of interest, and then simply measure power consumption. The power the (electric) motor consumed, times its efficiency, gives you the heat produced through secondary processes.

 

[wwswimming]

http://thermosciences.stanford.edu/

entropy, enthalpy, exothermic reactions.

basically, the energy acquired in the form of sunlight many moons ago is rendered to a refine-able
form, the form of oil, which is then refined to a combustible form, the form of gasoline.

one of the reasons you don't smoke when filling up the car.

POOF !

maybe if you post the question again ...

 

[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.

 

[BrownTown]

Originally posted by: AstroGuardian
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.

You read wrong, all of the energy is from the combustion of the the fuel. The compression is caused by the rotation of the shaft which is itself due to the combustion of the fuel. ALL of the energy in an internal combustion engine is coming from the combustion of the fuel, be it directly or indirectly. IF you want to get really technical the C=O and O-H bonds in the product are lower energy than the C-C and C-H bonds in the reactants, the energy lost from the chemical bonds is gained in terms of heat via the combustion. This is 9th grade chemistry and this is really a pretty silly thread to be "highly technical".

 

[JeffreyLebowski]

Well technically, the heat is unused energy fro mthe combustion of the fuel. By radiating the heat you are actually loosing energy.

Don't they have rechargable batteries in some cars that are recharged by the heat created from braking? why can't we capture the heat from the engine instead?

 

[Born2bwire]

Originally posted by: JeffreyLebowski
Well technically, the heat is unused energy fro mthe combustion of the fuel. By radiating the heat you are actually loosing energy.

Don't they have rechargable batteries in some cars that are recharged by the heat created from braking? why can't we capture the heat from the engine instead?

No, they do not regain energy from the heat, they turn the engine into a generator. The electromotive force from the generator and other losses in energy causes the vehicle to slow down.

 

[silverpig]

Originally posted by: BrownTown

Originally posted by: AstroGuardian
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.

You read wrong, all of the energy is from the combustion of the the fuel. The compression is caused by the rotation of the shaft which is itself due to the combustion of the fuel. ALL of the energy in an internal combustion engine is coming from the combustion of the fuel, be it directly or indirectly. IF you want to get really technical the C=O and O-H bonds in the product are lower energy than the C-C and C-H bonds in the reactants, the energy lost from the chemical bonds is gained in terms of heat via the combustion. This is 9th grade chemistry and this is really a pretty silly thread to be "highly technical".

Here, I'll "highly technical"-ize it.

Not ALL of the energy comes from the fuel. The battery starts the engine

Yeah I know the alternator recharges the battery, which is run by the engine, but you need an initial battery start up the first time you start the car.

It's dumb I know, but it's in the spirit of the forum.

 

[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.

 

[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.

 

[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.

 

[gsellis]

I invoke Occum's Raisor (Razor). BobSmith wins. Burning gasoline is the simpliest answer.

 

[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.

 

[BrownTown]

Originally posted by: silverpig

Originally posted by: BrownTown

Originally posted by: AstroGuardian
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.

You read wrong, all of the energy is from the combustion of the the fuel. The compression is caused by the rotation of the shaft which is itself due to the combustion of the fuel. ALL of the energy in an internal combustion engine is coming from the combustion of the fuel, be it directly or indirectly. IF you want to get really technical the C=O and O-H bonds in the product are lower energy than the C-C and C-H bonds in the reactants, the energy lost from the chemical bonds is gained in terms of heat via the combustion. This is 9th grade chemistry and this is really a pretty silly thread to be "highly technical".

Here, I'll "highly technical"-ize it.

Not ALL of the energy comes from the fuel. The battery starts the engine

Yeah I know the alternator recharges the battery, which is run by the engine, but you need an initial battery start up the first time you start the car.

It's dumb I know, but it's in the spirit of the forum.

well, yeah, it definitely is in the spirit of this forums since that spirit seems to be to take the simplest questions and act like they are absurdly complicated and then act like we are all geniuses for taking 20 posts to solve a simple problem?

 

[CycloWizard]

Originally posted by: AstroGuardian
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.

I never said it was a silly topic. If I thought it was, I wouldn't have spent the last nine years of my life studying chemical engineering, nor would I have bothered to post in your thread. Just calm it down a notch with all of the thread posting and no one gets hurt.

 

[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).