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Would it be possible to use the warming engine for additional energy?


other_world
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Hey, everyone

Would it be possible to take advantage of the fact that the engine in the car heats up which could be used to "boil" the water to produce steam, which could be used to extract energy capable of powering the car?

This question has been bothering me for a long time and I decided to finally ask someone about it. I say right away that I don't even know if this all makes any sense (it was just a loose thought in physics class) so I sincerely ask you to explain in a relatively simple way why this can't be the case or what the obstacles are. 

thank you for giving me your time.

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24 minutes ago, other_world said:

he fact that the engine in the car heats up

When does this happen? Why does this happen? Trace the heating of the engine back to the cause and you will see the answer to you question.

 

 

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43 minutes ago, other_world said:

Would it be possible to take advantage of the fact that the engine in the car heats up

That's how the internal-combustion engine works in the first place (it's a heat engine). If it were practical to insulate the cylinders better and they could tolerate more pressure, the extra energy could be extracted from the air-fuel mixture directly (and more efficiently) without heating up the rest of the engine block and peripheral parts so much.

Edited by Lorentz Jr
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54 minutes ago, other_world said:

Hey, everyone

Would it be possible to take advantage of the fact that the engine in the car heats up which could be used to "boil" the water to produce steam, which could be used to extract energy capable of powering the car?

This question has been bothering me for a long time and I decided to finally ask someone about it. I say right away that I don't even know if this all makes any sense (it was just a loose thought in physics class) so I sincerely ask you to explain in a relatively simple way why this can't be the case or what the obstacles are. 

thank you for giving me your time.

Rather than extract heat from the engine block, you could in principle raise superheated steam from the far greater heat output in the exhaust.

This is the principle employed in Combined Cycle Gas Turbine (CCGT) power stations where each gas turbine exhausts into a Heat Recovery Steam Generator (HRSG) for driving a supplementary steam turbine.

This increases station electrical output by about 50% for a given fuel consumption.

Not a very practical proposition for a car though.  

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1 hour ago, Lorentz Jr said:

That's how the internal-combustion engine works in the first place (it's a heat engine).

And what happens to heat engine efficiency if you lower the temperature of the hot reservoir? 

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1 hour ago, other_world said:

Would it be possible to take advantage of the fact that the engine in the car heats up which could be used to "boil" the water to produce steam, which could be used to extract energy capable of powering the car?

This question has been bothering me for a long time and I decided to finally ask someone about it. I say right away that I don't even know if this all makes any sense (it was just a loose thought in physics class) so I sincerely ask you to explain in a relatively simple way why this can't be the case or what the obstacles are. 

I don't know how long is a long time for you, but do you remember old fashioned steam railway engines or steam powered traction engines, steam rollers or other steam propelled equipment, or have you seen pictures of them ?

They had one thing in common, they were big and very heavy. All that machinery to provide steam propulsion is very bulky and heavy.
And yet their makers knew about thermondynamics and mechanics and made them about as efficient as it is possible to be.

With various grades of liquid or liquified gas fuels it became possible to use different and far lighter mechanics for the propulsion drive.

Now that is where the internal combustion propulsion is at today.

A far ligher drive mechanics meaning a far lighter chassis meaning far more efficient use of the fuel.

Furthermore it doesn't require to carry either a large and weighty tank of water or additional weighty mechanics to recover the water from the steam and recycle it.

And don't forget that some heat is extracted in cold countries to heat the passenger cabin.

So yes, it is possible but just not practicable, there are better ways to use the fuels.

Note also the even more and smaller engines such as racing car engines wear out far more quickly than engines designed for road vehicles.

It is somebodie's law that says the more efficient and highly tuned a car engine is the more servicing it needs and the shorter its service life.

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23 minutes ago, swansont said:

And what happens to heat engine efficiency if you lower the temperature of the hot reservoir? 

I'm not sure I understand the relevance of that. My point was that one high-temperature/high-pressure heat engine (improved cylinders) is more efficient than two low-temperature/low-pressure heat engines in tandem (the OP's proposal).

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7 minutes ago, Lorentz Jr said:

I'm not sure I understand the relevance of that. My point was that one high-temperature/high-pressure heat engine (improved cylinders) is more efficient than two low-temperature/low-pressure heat engines in tandem (the OP's proposal).

I don’t see where the OP says anything about low-temperature heat engines, and offering an alternative doesn’t really answer the question being asked.

And my comment was in terms of the OP’s proposal: if you try and extract the energy you lower the temperature, making the engine less efficient.

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11 minutes ago, swansont said:

offering an alternative doesn’t really answer the question being asked.

That's true. I was trying to point out that the general concept of extracting useful energy from heat is already built into the design of the engine itself, just in case the OP didn't know that.

Quote

And my comment was in terms of the OP’s proposal: if you try and extract the energy you lower the temperature, making the engine less efficient.

Well, heat is already extracted from the engine by the cooling system, so I thought the OP meant using the heat instead of throwing it away.

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6 hours ago, other_world said:

 

Would it be possible to take advantage of the fact that the engine in the car heats up which could be used to "boil" the water to produce steam, which could be used to extract energy capable of powering the car?

 

Hypothetically, yes; the coolant temperature is often higher than boiling point of water - from added glycol - but without running the engine at lower than ideal temperatures (with reduced efficiency) it won't produce a lot of steam. The waste heat from the vehicle's cooling system could also power a Stirling or an Organic Rankin Cycle engine.

In practice these options would be a bulky and heavy additional load for a vehicle to carry and are not practical. Likewise storing the heat as hot water in dedicated tanks and offloading it for use - say home heating - would be impractical.

I have some small hope that we will see significant improvements in thermo-electric technologies, including potentially optical rectennas aka nantennas that can turn heat directly into electricity, with some quite profound implications, including the ability to harvest energy from the night sky or sun warmed ground as well as direct solar or utilise waste heat or enable large scale thermal storage. Maybe not ever going to be practical but given the potential it looks as worthwhile as spending big on fusion energy - but I would be surprised if they get as much as 1% of the funding that fusion gets.

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Driving a car here in the winter (Dakotas), we definitely put that waste heat to use, warming the cabin space.  Recovering heat from the coolant jacket is easy, getting it from the exhaust would not be economical as others have noted.  

Hardly anyone up here drove the old VWs in the winter, with the air-cooled engines, because the cabin heating systems simply couldn't capture enough radiated heat from the engine through passive airflow.  And on hot summer days, the Beetle would overheat and vapor lock.  

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It also had no power uphill and was reluctant to start on rainy mornings when we were late work... I wonder why it was so damn popular that they made a knock-off for the new millennium. Our much later GM pickup, now, that beast had heat to spare! But they're on it!

https://gmauthority.com/blog/gm/general-motors-technology/general-motors-propulsion-technology/general-motors-active-thermal-management-technology/

 

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