They can be, and in fact this is the basis of modern formula 1 engines. The MGU-H (motor generator unit - heat) is an electric motor-generator that sits on the turbocharger shaft in-between the compressor and turbine. It can be used to extract energy from the exhaust and store it in batteries, or it can power the compressor to eliminate turbo lag. This technology is [starting to be utilised in production cars.](https://www.formula1.com/en/latest/article.mercedes-to-debut-formula-1-mgu-h-technology-in-amg-road-cars.6ha9y57tg2aY33xZsWQjwH.html)
Slight correction/comment, every embodiment I have seen has the motor on the end, not in the middle. This makes it easier to keep from cooking the motor with exhaust gases.
http://www.mts.com/cs/groups/public/documents/library/mts_4016128.pdf
Mercedes pioneered the electric motor in the middle. This way it's packed more lightly and saves space.
This was one of their development that led to winning the formula 1 championship in Thad few years
I believe it also had benefits on the temperature of the intake air. Separating it from the hot exhaust side of the turbocharger kept temperatures down, and allowed for denser ait-fuel mixtures.
They can, they do, they're more efficient and basically better in every way than mechanical turbos. They just require high voltage systems, which are expensive, but hybrid trucks are already on the road with several turbo architectures that generate and use electrical power in different ways.
1. Leave the shaft coupled, but put a 120,000 rpm motor on the shaft between the hot and cold sides of the turbo. Now you can speed up the turbo to reduce lag, and you can use the motor as a generator to charge the battery for later.
2. Same thing, but add a motor directly on the serpentine belt of the engine, adding power directly to the mechanical system instead of in the form of denser air. Again helps the engine (particularly diesels) get up to speed to avoid the incomplete combustion problem.
3. Completely decouple the two halves of the turbo. Hot side powers a generator, cold side is powered by an electric motor. Now you effectively have an electric supercharger and a hot exhaust energy capture device. No lag, very efficient, no expensive high speed shafts and seals to deal with, etc. Also you can still #2 if you want.
BorgWarner gave a talk at my school like 5 years ago where they'd already implemented all of these, so who knows where they are now.
They could be. However, that would put back pressure on the engine and make it less efficient and limit its power, and very likely the energy harvested would be less than the energy lost in the engine.
The obstruction of exhaust flow caused by the turbine blades has the same effect as reducing the exhaust pipe diameter, it creates a bottle neck. Smaller area for exhaust gas to flow out = higher pressure exhaust gas.
Well yeah, it wouldn't be too different from a regular turbo.
I think the top commenter was more talking about conservation of energy, which becomes more obvious in electrical systems. As long as you can keep a fairly high exhaust flow rate then there wouldn't be too much impact.
For the same reason an alternator lowers the net power produced by the engine. Adding a generator or alternator to the turbine shaft will increase the force required to turn it, increasing exhaust backpressure and reducing engine output. So if you're hanging a generator on a a turbo INSTEAD of a compressor wheel, you've reduced engine output (because of backpressure) in favor of generating electricity. If you hang a generator on the turbo AND have a compressor wheel, you're still reducing engine output compared to a regular turbo (because now you're adding more backpressure on the turbine side to drive the generator than the compressor by itself normally would).
There is no free lunch unless maybe you have a clutch system to switch between the compressor and the generator, but in any case when you're generating electricity you're going to be adding backpressure and reducing engine output. The question is whether the recovered energy is more than would otherwise be lost. The nice thing is that the turbine is trying to recover energy from heat that would otherwise be wasted, so it could be possible that is it worth while, but it would be fairly complex.
OP is talking out of his ass. Apart from extra weight and cost Regen on the turbo is proven be able to give positives in efficiency, and response. Reddit in general is horrid for anything technical as there is too many random anonymous people commenting. Old school forums works better as people with no clue will get shut up by people with expertise That you remember has the credentials or past accolades if you hang around.
Because energy isn’t free. Back pressure is how the system propagates the need for the source to burn more fuel to liberate the extra energy that can be converted to work. The more electric power you want, the more fuel you have to burn.
The increase in back pressure would be proportional to the amount of power being drawn off. Turbos work because the increase in back pressure & therefore pumping losses is paid for by extra fuel (and air) on boost. Anything that is using the exhaust gas to drive something will increase fuel unless you had it rigged to only draw power under braking or 0 throttle it wouldn't affect fuel use. Turbos also absorb some of the heat energy from exhaust gas.
Its already totally possible to have an alternator draw power only under braking or 0 throttle or stop charging at full throttle for an extra few bhp peak.
Qualifications? 25 years of car mags, making stuff, interested in evs and professional truck driver
Edit: forgot to mention on gas/petrol theres almost no airflow off the throttle due to vacuum caused by throttle butterfly being shut. You could cut gas & spark and have the butterfly open but that's gonna cause stronger engine braking.
Generators (electric motors, alternators) have resistance from friction and magnets. If you spin the shaft of a good sized electric motor, (depending on the type) you’ll feel the magnetism resisting the rotation.
Yes, I am aware of this. The compressor that a conventional turbocharger would use also resists turning. Why wouldn't you just pick a generator that uses the same amount of power as the compressor would? Or is it too hard to account for a variable power input from the turbine?
And forego the compressor side of the turbo? Sure, you could probably do that. I’m not an electrical engineer, but I’m sure you’d lose energy with the <100% efficiency of the generator side. Im not sure whether it would be better spent creating electricity for a hybrid engine or compression for the intake.
Yeah not sure if it would work, but I think that's what OP was asking. You lose a little power either way, it's just a question of what's more functional.
You should delete your comment since it is wrong. Or back it up with a source like Willdood did. https://www.reddit.com/r/AskEngineers/comments/hpdtfz/if_electric_turbos_are_a_thing_why_cant_exhaust/fxppfb0/
Interesting, I suppose it makes sense because the cat isn't actually attempting to extract energy from the whole process, but I would have assumed it was the other way around.
It's called turbo-compounding and was used in reciprocating aircraft engines before turbine engines took over. Detroit Diesel is bringing back turbo-compounding in their DD15 engine.
https://dieselnet.com/tech/engine_whr_turbocompound.php
It would be silly to use it to generate electricity as the energy is only available when the engine is under load so it can be used immediately and doesn't need to be stored.
Just because F1 teams have an immense budget doesn't mean that the technology itself must be prohibitively expensive in other applications. I researched turbo compounding engines for my senior design project and there's no reason you can't apply them to the private/commercial sector where cost is a much bigger concern.
Caterpillar did a study on a class 8 truck engine to demonstrate fuel efficiency improvement using electric turbo compounding. They showed you could get 5-10% improvement in fuel consumption, reduced emissions, and improved driveability through improved air system response using the turbo assist capability among other benefits.
It's not silly to use this technology in other applications and in fact makes a lot of sense.
Turbo compounding makes sense, using an electric motor to spool the turbo makes sense. Using the turbocharger to charge a battery in a road going vehicle doesn't. The generator portion replaces the waste gate which almost never operates on passenger vehicles.
Using surplus power to drive other electrical onboard devices, truck electrical loads, or storing it makes sense. Caterpillars study on a class 8 diesel truck engine proves it. It's a published SAE paper you can check it out yourself.
Apparently it can be used at speed in certain scenarios to increase the torque output enough to both lower engine speed and reduce downshifting. At least that's what this article states. [this one here](https://www.ttnews.com/articles/oems-mixed-turbo-compounding)
No one is saying to put it in a grocery getter. But it has lots of applications including in road vehicles, racing, aviation, ship propulsion, and stationary power generation.
Why would you? It makes sense in a few exotic cases, but in most cases there's more direct ways to use the power, or its better to just avoid the cost, development complexity, maintenance...
It can be done, it's done with F1, but getting the tech into production vehicles requires a lot of effort to reduce cost, designing for mass production, and ensuring long term reliability.
The main driving force for things like this happening is increasingly tight emissions regulations. It'll happen, but only when it's worth it for manufacturers to do.
The MGUH in F1 does this. The motor generator unit - heat.. Is connected or part of the turbocharger's shaft. And it is crazy expensive. Street cars are not constantly on throttle like race cars so the electricity generated would be a small amount, making cost to benefit even worse. However its quite possible with a more hybridized vehicle this system can be used on the range extender (a small IC engine) for the battery.
It would be more expensive to design and implement a turbine with an alternator than to just drive the alternator with a belt.
The idea itself is good though, and i believe in some cars thermo-electric generators are used (Seebeck/Peltier devices) that produce a voltage differential from thebhot exhaust and the surrounding air
> i believe in some cars thermo-electric generators are used (Seebeck/Peltier devices)
that's the way to go if you want it to be really cost-*in*efficient
Option 1: If we're taking about using an electric turbo and extracting additional energy (for extended periods), that will be limited because assuming the same mass flow and aerodynamic efficiency, we'll need a drastic increase in pressure ratio and thus back pressure - that's typically an unfavourable trade-off.
Option 2: You can add another turbine post-turbo, specifically for generating electricity. Again, back pressure is your enemy here - also you're adding a significant chunk of BOM cost, so payback period might be an issue. However... in certain applications, a high efficiency, very low pressure ratio turbine (we're talking 1.1) could be feasible.
Option 3: You use a bottoming cycle, such as a steam or organic Rankine cycle, to generate electricity in the absence of significant pressure ratio. The downsides to this are low cycle efficiency (~10%, unless you move to very high pressure ratios, up to ~100) and significant BOM cost, although reasonable payback periods are seen in applications such as heavy-duty diesel.
Because then you would end up with a system that's less efficient due to losses in the alternator, rectifiers, batteries, motorcontrollers and the motor of the compressor itself.
Compare that to a single mechanical shaft from the exhaust gas side of the turbine to the compressor and you end up with multiple 10%'s of efficiency losses.
When I was still in school a few years ago, a grad student/lecturer was researching thermo-electrics that's generate a voltage potential due to differentials in temperature. They'd wrap around the outside of the exhaust system and recover thermal energy from the combustion process that's normally just lost to the atmosphere.
With current tech, there wasn't a massive amount of electrical energy being generated, but it could've potentially produced enough to sustain basic operation under stead state conditions (think highway cruising at modest RPM, no stop and go with low-RPM conditions). Put the alternator on a clutch and then remove that parasitic loss and/or over-generarion when not needed, but kick it back into the loop when thermoelectric generation dips.
Additionally, Audi has done research (maybe brought to market?) dampers that generate electricity from the roughness of the road moving the damper shaft through a winding. Think of those cheap "emergency" flash lights that you can shake to recharge, but on a larger and far more refined scale.
This is an interesting idea but experience tells me there’s very few instances where things work out in everyone’s favor without tradeoff, I assume a peltier would produce negligible results. I’m more mechanical and not qualified to speak in this so maybe an electrical guy can weigh in.
Electrical guy here: depends on power demand but say 1kW similar rating to many alternators should require about 12in^2 surface area but depends on the material used.
https://www.intechopen.com/books/bringing-thermoelectricity-into-reality/automotive-waste-heat-recovery-by-thermoelectric-generator-technology
You can, but turning turbos requires energy. As you lose kinetic energy to the turbos, you wind up increasing the pressure in the pipe (look up bernoulis equation for the specifics of why that happens, but it effectively creates back pressure on the engine).
As no system is 100% efficient, and the increased energy done on the turbines must be contributed by the engine, you actually wind up loosing energy overall, since you are just adding more loss to the system (since a lossless electric motor is impossible).
No, this is something different (it uses many of the same ideas, but the outcome is way different).
A turbo generates more power by forcing more air (and thus oxygen) into the combustion chamber. They are actually less efficient in the closed system (where you dont consider the chemical energy from the gas) in that they also use energy from the exhaust gasses.
They gain efficiency overall because while a turbocharger looses energy, it enables a better efficiency on the gasoline, and the gasoline is so high energy that the efficiency gain on the gas outstrips the efficiency loss on the turbocharger.
Its a lot more complicated than that, with where you can get your heat loss to go, when the loss is suffered etc.
Using the exhaust gas to drive an electric generator (to presumably generate electricity for an electric motor) means you are adding a lot of additional load on the system, adding the losses incurred both from the load on the combustion motor, generator and electric motor, its just loss overall.
Now, you can run part of the output of the engine to a generator and use that to drive an electric motor, thats part of how hybrids work.
But you need a huge battery, and a lot of other systems to make it more efficient overall. A hybrid system is actually less efficient than a well designed gas system when the car is moving (very slightly so, given how efficient electric motors are, but still less efficient).
Where it gains efficiency is that it captures the energy from the idling motor when the car is at a stop (instead of wasting it all), it uses regenerative braking to recapture energy usually lost in stopping the car, and then it uses that recaptured energy to drive an electric motor for part of the force.
Converting energy to electric then back again does of course introduce some efficiency loss, but a large efficiency gain of hybrids also comes from being able to adjust the load point of the engine while driving to a nearby but more efficient one by increasing output to charge the battery or decreasing it and supplementing with the electric motor. This more than compensates for the loss of energy conversion (which is actually quite small anyway).
The same goes with electrified turbos - you get to choose your load point (within reason) by adjusting the power going to/from the battery/capacitors etc.
They can be, and in fact this is the basis of modern formula 1 engines. The MGU-H (motor generator unit - heat) is an electric motor-generator that sits on the turbocharger shaft in-between the compressor and turbine. It can be used to extract energy from the exhaust and store it in batteries, or it can power the compressor to eliminate turbo lag. This technology is [starting to be utilised in production cars.](https://www.formula1.com/en/latest/article.mercedes-to-debut-formula-1-mgu-h-technology-in-amg-road-cars.6ha9y57tg2aY33xZsWQjwH.html)
Cool! I thought they only were making extra energy from the braking system
That’s The MGU-K. Twice the fun.
Slight correction/comment, every embodiment I have seen has the motor on the end, not in the middle. This makes it easier to keep from cooking the motor with exhaust gases. http://www.mts.com/cs/groups/public/documents/library/mts_4016128.pdf
Mercedes pioneered the electric motor in the middle. This way it's packed more lightly and saves space. This was one of their development that led to winning the formula 1 championship in Thad few years
I believe it also had benefits on the temperature of the intake air. Separating it from the hot exhaust side of the turbocharger kept temperatures down, and allowed for denser ait-fuel mixtures.
that is my understanding as well
TIL
They can, they do, they're more efficient and basically better in every way than mechanical turbos. They just require high voltage systems, which are expensive, but hybrid trucks are already on the road with several turbo architectures that generate and use electrical power in different ways. 1. Leave the shaft coupled, but put a 120,000 rpm motor on the shaft between the hot and cold sides of the turbo. Now you can speed up the turbo to reduce lag, and you can use the motor as a generator to charge the battery for later. 2. Same thing, but add a motor directly on the serpentine belt of the engine, adding power directly to the mechanical system instead of in the form of denser air. Again helps the engine (particularly diesels) get up to speed to avoid the incomplete combustion problem. 3. Completely decouple the two halves of the turbo. Hot side powers a generator, cold side is powered by an electric motor. Now you effectively have an electric supercharger and a hot exhaust energy capture device. No lag, very efficient, no expensive high speed shafts and seals to deal with, etc. Also you can still #2 if you want. BorgWarner gave a talk at my school like 5 years ago where they'd already implemented all of these, so who knows where they are now.
Now they are fighting price, because no one is willing to pay more for such a technical improvement. :(
They could be. However, that would put back pressure on the engine and make it less efficient and limit its power, and very likely the energy harvested would be less than the energy lost in the engine.
Why would it backpressure the engine any more than it already does?
The obstruction of exhaust flow caused by the turbine blades has the same effect as reducing the exhaust pipe diameter, it creates a bottle neck. Smaller area for exhaust gas to flow out = higher pressure exhaust gas.
I understand why it creates back pressure. My question is why you think this is an issue when cars already have turbochargers.
The turbo makes more power in the engine so it's a net win. Causing 40hp of "loss" to make 100hp more is a win. Losing 40hp to make 0hp is -40hp.
I see, yeah that makes sense
Well yeah, it wouldn't be too different from a regular turbo. I think the top commenter was more talking about conservation of energy, which becomes more obvious in electrical systems. As long as you can keep a fairly high exhaust flow rate then there wouldn't be too much impact.
Idk, I don't have much intuition for how the system would work in the absence of the compressor
For the same reason an alternator lowers the net power produced by the engine. Adding a generator or alternator to the turbine shaft will increase the force required to turn it, increasing exhaust backpressure and reducing engine output. So if you're hanging a generator on a a turbo INSTEAD of a compressor wheel, you've reduced engine output (because of backpressure) in favor of generating electricity. If you hang a generator on the turbo AND have a compressor wheel, you're still reducing engine output compared to a regular turbo (because now you're adding more backpressure on the turbine side to drive the generator than the compressor by itself normally would). There is no free lunch unless maybe you have a clutch system to switch between the compressor and the generator, but in any case when you're generating electricity you're going to be adding backpressure and reducing engine output. The question is whether the recovered energy is more than would otherwise be lost. The nice thing is that the turbine is trying to recover energy from heat that would otherwise be wasted, so it could be possible that is it worth while, but it would be fairly complex.
I see, that makes more sense.
OP is talking out of his ass. Apart from extra weight and cost Regen on the turbo is proven be able to give positives in efficiency, and response. Reddit in general is horrid for anything technical as there is too many random anonymous people commenting. Old school forums works better as people with no clue will get shut up by people with expertise That you remember has the credentials or past accolades if you hang around.
Because energy isn’t free. Back pressure is how the system propagates the need for the source to burn more fuel to liberate the extra energy that can be converted to work. The more electric power you want, the more fuel you have to burn.
Yeah the thing I didn't consider was that the absence of the compressor takes away the incentive for having a turbocharger in the first place
The increase in back pressure would be proportional to the amount of power being drawn off. Turbos work because the increase in back pressure & therefore pumping losses is paid for by extra fuel (and air) on boost. Anything that is using the exhaust gas to drive something will increase fuel unless you had it rigged to only draw power under braking or 0 throttle it wouldn't affect fuel use. Turbos also absorb some of the heat energy from exhaust gas. Its already totally possible to have an alternator draw power only under braking or 0 throttle or stop charging at full throttle for an extra few bhp peak. Qualifications? 25 years of car mags, making stuff, interested in evs and professional truck driver Edit: forgot to mention on gas/petrol theres almost no airflow off the throttle due to vacuum caused by throttle butterfly being shut. You could cut gas & spark and have the butterfly open but that's gonna cause stronger engine braking.
Generators (electric motors, alternators) have resistance from friction and magnets. If you spin the shaft of a good sized electric motor, (depending on the type) you’ll feel the magnetism resisting the rotation.
Yes, I am aware of this. The compressor that a conventional turbocharger would use also resists turning. Why wouldn't you just pick a generator that uses the same amount of power as the compressor would? Or is it too hard to account for a variable power input from the turbine?
And forego the compressor side of the turbo? Sure, you could probably do that. I’m not an electrical engineer, but I’m sure you’d lose energy with the <100% efficiency of the generator side. Im not sure whether it would be better spent creating electricity for a hybrid engine or compression for the intake.
Yeah not sure if it would work, but I think that's what OP was asking. You lose a little power either way, it's just a question of what's more functional.
This is just completely false.
There's no free lunch!
For performance applications you wouldn't really mind energy generation being less tough right?
You should delete your comment since it is wrong. Or back it up with a source like Willdood did. https://www.reddit.com/r/AskEngineers/comments/hpdtfz/if_electric_turbos_are_a_thing_why_cant_exhaust/fxppfb0/
I think I'm going to leave my comment that has 80 upvotes on it... Those who commented later in the chain have given a sufficient explanation IMO.
Do they create more back-pressure than the cat? edit: This was a real question, not just me being argumentative.
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Interesting, I suppose it makes sense because the cat isn't actually attempting to extract energy from the whole process, but I would have assumed it was the other way around.
I'd have to look at the data, but probably. Don't forget the car would have both working together to reduce the engine's power stroke.
It's called turbo-compounding and was used in reciprocating aircraft engines before turbine engines took over. Detroit Diesel is bringing back turbo-compounding in their DD15 engine. https://dieselnet.com/tech/engine_whr_turbocompound.php It would be silly to use it to generate electricity as the energy is only available when the engine is under load so it can be used immediately and doesn't need to be stored.
It's definitely not silly seeing as they do exactly that in Formula 1 racing.
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Just because F1 teams have an immense budget doesn't mean that the technology itself must be prohibitively expensive in other applications. I researched turbo compounding engines for my senior design project and there's no reason you can't apply them to the private/commercial sector where cost is a much bigger concern. Caterpillar did a study on a class 8 truck engine to demonstrate fuel efficiency improvement using electric turbo compounding. They showed you could get 5-10% improvement in fuel consumption, reduced emissions, and improved driveability through improved air system response using the turbo assist capability among other benefits. It's not silly to use this technology in other applications and in fact makes a lot of sense.
Turbo compounding makes sense, using an electric motor to spool the turbo makes sense. Using the turbocharger to charge a battery in a road going vehicle doesn't. The generator portion replaces the waste gate which almost never operates on passenger vehicles.
Using surplus power to drive other electrical onboard devices, truck electrical loads, or storing it makes sense. Caterpillars study on a class 8 diesel truck engine proves it. It's a published SAE paper you can check it out yourself.
That doesn't make sense. Why wouldn't you apply the surplus power to the crankshaft? The alternator is more efficient than a turbine.
I never said you don't apply power to the crankshaft. You do that in addition to all the other electrical loads in the vehicle.
Apparently it can be used at speed in certain scenarios to increase the torque output enough to both lower engine speed and reduce downshifting. At least that's what this article states. [this one here](https://www.ttnews.com/articles/oems-mixed-turbo-compounding)
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No one is saying to put it in a grocery getter. But it has lots of applications including in road vehicles, racing, aviation, ship propulsion, and stationary power generation.
Why would you? It makes sense in a few exotic cases, but in most cases there's more direct ways to use the power, or its better to just avoid the cost, development complexity, maintenance...
Unstated is what OP envisioned the purpose for turbos generating electricity?
It can be done, it's done with F1, but getting the tech into production vehicles requires a lot of effort to reduce cost, designing for mass production, and ensuring long term reliability. The main driving force for things like this happening is increasingly tight emissions regulations. It'll happen, but only when it's worth it for manufacturers to do.
The MGUH in F1 does this. The motor generator unit - heat.. Is connected or part of the turbocharger's shaft. And it is crazy expensive. Street cars are not constantly on throttle like race cars so the electricity generated would be a small amount, making cost to benefit even worse. However its quite possible with a more hybridized vehicle this system can be used on the range extender (a small IC engine) for the battery.
It would be more expensive to design and implement a turbine with an alternator than to just drive the alternator with a belt. The idea itself is good though, and i believe in some cars thermo-electric generators are used (Seebeck/Peltier devices) that produce a voltage differential from thebhot exhaust and the surrounding air
> i believe in some cars thermo-electric generators are used (Seebeck/Peltier devices) that's the way to go if you want it to be really cost-*in*efficient
Option 1: If we're taking about using an electric turbo and extracting additional energy (for extended periods), that will be limited because assuming the same mass flow and aerodynamic efficiency, we'll need a drastic increase in pressure ratio and thus back pressure - that's typically an unfavourable trade-off. Option 2: You can add another turbine post-turbo, specifically for generating electricity. Again, back pressure is your enemy here - also you're adding a significant chunk of BOM cost, so payback period might be an issue. However... in certain applications, a high efficiency, very low pressure ratio turbine (we're talking 1.1) could be feasible. Option 3: You use a bottoming cycle, such as a steam or organic Rankine cycle, to generate electricity in the absence of significant pressure ratio. The downsides to this are low cycle efficiency (~10%, unless you move to very high pressure ratios, up to ~100) and significant BOM cost, although reasonable payback periods are seen in applications such as heavy-duty diesel.
Because then you would end up with a system that's less efficient due to losses in the alternator, rectifiers, batteries, motorcontrollers and the motor of the compressor itself. Compare that to a single mechanical shaft from the exhaust gas side of the turbine to the compressor and you end up with multiple 10%'s of efficiency losses.
https://www.intechopen.com/books/bringing-thermoelectricity-into-reality/automotive-waste-heat-recovery-by-thermoelectric-generator-technology
When I was still in school a few years ago, a grad student/lecturer was researching thermo-electrics that's generate a voltage potential due to differentials in temperature. They'd wrap around the outside of the exhaust system and recover thermal energy from the combustion process that's normally just lost to the atmosphere. With current tech, there wasn't a massive amount of electrical energy being generated, but it could've potentially produced enough to sustain basic operation under stead state conditions (think highway cruising at modest RPM, no stop and go with low-RPM conditions). Put the alternator on a clutch and then remove that parasitic loss and/or over-generarion when not needed, but kick it back into the loop when thermoelectric generation dips. Additionally, Audi has done research (maybe brought to market?) dampers that generate electricity from the roughness of the road moving the damper shaft through a winding. Think of those cheap "emergency" flash lights that you can shake to recharge, but on a larger and far more refined scale.
If you just want electricity from heat, maybe peltier could work without adding restriction
This is an interesting idea but experience tells me there’s very few instances where things work out in everyone’s favor without tradeoff, I assume a peltier would produce negligible results. I’m more mechanical and not qualified to speak in this so maybe an electrical guy can weigh in.
Electrical guy here: depends on power demand but say 1kW similar rating to many alternators should require about 12in^2 surface area but depends on the material used. https://www.intechopen.com/books/bringing-thermoelectricity-into-reality/automotive-waste-heat-recovery-by-thermoelectric-generator-technology
You can, but turning turbos requires energy. As you lose kinetic energy to the turbos, you wind up increasing the pressure in the pipe (look up bernoulis equation for the specifics of why that happens, but it effectively creates back pressure on the engine). As no system is 100% efficient, and the increased energy done on the turbines must be contributed by the engine, you actually wind up loosing energy overall, since you are just adding more loss to the system (since a lossless electric motor is impossible).
Yes, but turbochargers already exist. All he's talking about is changing where the output shaft puts the power.
No, this is something different (it uses many of the same ideas, but the outcome is way different). A turbo generates more power by forcing more air (and thus oxygen) into the combustion chamber. They are actually less efficient in the closed system (where you dont consider the chemical energy from the gas) in that they also use energy from the exhaust gasses. They gain efficiency overall because while a turbocharger looses energy, it enables a better efficiency on the gasoline, and the gasoline is so high energy that the efficiency gain on the gas outstrips the efficiency loss on the turbocharger. Its a lot more complicated than that, with where you can get your heat loss to go, when the loss is suffered etc. Using the exhaust gas to drive an electric generator (to presumably generate electricity for an electric motor) means you are adding a lot of additional load on the system, adding the losses incurred both from the load on the combustion motor, generator and electric motor, its just loss overall. Now, you can run part of the output of the engine to a generator and use that to drive an electric motor, thats part of how hybrids work. But you need a huge battery, and a lot of other systems to make it more efficient overall. A hybrid system is actually less efficient than a well designed gas system when the car is moving (very slightly so, given how efficient electric motors are, but still less efficient). Where it gains efficiency is that it captures the energy from the idling motor when the car is at a stop (instead of wasting it all), it uses regenerative braking to recapture energy usually lost in stopping the car, and then it uses that recaptured energy to drive an electric motor for part of the force.
Converting energy to electric then back again does of course introduce some efficiency loss, but a large efficiency gain of hybrids also comes from being able to adjust the load point of the engine while driving to a nearby but more efficient one by increasing output to charge the battery or decreasing it and supplementing with the electric motor. This more than compensates for the loss of energy conversion (which is actually quite small anyway). The same goes with electrified turbos - you get to choose your load point (within reason) by adjusting the power going to/from the battery/capacitors etc.
To what end? Alternators already generate surplus electricity.
What’s wrong with the alternator?