Return of the Mazda Rotary!

[Payman]

The energy generated would be less than the power expended to overcome the aerodynamic drag of the turbines.

Easy answer, but it loses lustre when you take the turbines out of the vehicle's aerodynamic flow. You can have an intake faired with the bodywork the size of a pitot tube... 1 cm across. At speed the ram air can spin the turbine at high rpm and generate power.

[giant_mtb]

Easy answer, but it loses lustre when you take the turbines out of the vehicle's aerodynamic flow. You can have an intake faired with the bodywork the size of a pitot tube... 1 cm across. At speed the ram air can spin the turbine at high rpm and generate power.

Yeah, I mean, look at all the fancy aerodynamic ductwork some supercars have for air intake or radiator cooling. Their bodies are still aero as frig.

[MX793]

Easy answer, but it loses lustre when you take the turbines out of the vehicle's aerodynamic flow. You can have an intake faired with the bodywork the size of a pitot tube... 1 cm across. At speed the ram air can spin the turbine at high rpm and generate power.

What you're proposing amounts to a perpetual motion machine, which violates the 2nd Law of Thermodynamics.

[Laconian]

Laws were made to be broken, man...

Don't be a physics fascist!

[FoMoJo]

We might think of the universe as a perpetual motion machine .

[Laconian]

No way, entropy will destroy everything. We're all racing towards energy equilibrium.

[Payman]

What you're proposing amounts to a perpetual motion machine, which violates the 2nd Law of Thermodynamics.

No, I'm proposing a range extender. You won't get anywhere close to the power expended to propel the car, but you can trickle charge the batteries as you drive.

[giant_mtb]

No, I'm proposing a range extender. You won't get anywhere close to the power expended to propel the car, but you can trickle charge the batteries as you drive.

Yeah, if anything it would help keep the electronics/fans/AC goin' without draining as much from actual propulsion energy.

[Payman]

Similar idea of an electric gyrocopter. Electric motor/propeller drives the craft forward, causing the freewheeling rotor to spin and create lift. You can harness that huge windmill by gearing it to a generator to send charging power back to the batteries.

[Payman]

Yeah, if anything it would help keep the electronics/fans/AC goin' without draining as much from actual propulsion energy.

Yes, that too. Airliners have emergency ram air generators that deploy into the airstream to power all the flight systems if there's a catastrophic loss of power.

[Soup DeVille]

No, I'm proposing a range extender. You won't get anywhere close to the power expended to propel the car, but you can trickle charge the batteries as you drive.

Yes,
you are.

TANSTAAFL.

[Soup DeVille]

Yes, that too. Airliners have emergency ram air generators that deploy into the airstream to power all the flight systems if there's a catastrophic loss of power.

To answer your question: why don't they just leave those on all the time then?

[Payman]

To answer your question: why don't they just leave those on all the time then?

Because you don't need them when the engines are generating power.

[Soup DeVille]

Because you don't need them when the engines are generating power.

If it was a net positive process; if it produced more power than it used, why wouldn't they leave them on all the time? 

[Payman]

Yes,
you are.

TANSTAAFL.

No, I'm not.

[Payman]

I see I'm up against the "heavier than air flight is impossible" crowd.   

[Soup DeVille]

No, I'm not.

Yeah, you're misunderstanding a basic fact. You can't get something from nothing. Nothing is more than 100% efficient. Most things never even come close.

You don't create energy, you just change its form; and everytime you do, you lose some to the process. Your plan is taking kinetic energy from the wind and the motion of the car, turning it into electrical energy, just to turn it back to kinetic energy to push the car into that same wind.

Its a net negative process, no matter how you add it up.

[Soup DeVille]

I see I'm up against the "heavier than air flight is impossible" crowd.   

Well, then you best do ot and prove us wrong.

[Payman]

Yeah, you're misunderstanding a basic fact. You can't get something from nothing. Nothing is more than 100% efficient. Most things never even come close.

You don't create energy, you just change its form; and everytime you do, you lose some to the process. Your plan is taking kinetic energy from the wind and the motion of the car, turning it into electrical energy, just to turn it back to kinetic energy to push the car into that same wind.

Its a net negative process, no matter how you add it up.

It's not creating energy; it's redirecting energy (airflow) to generate electricity. So what you're saying is that electricity generated would be negated by the extra energy required by the motor to compensate for parasitic loss caused by the intake and turbine/alternator setup?

[CaminoRacer]

The problem is that the wind is generated from the car moving itself. If it was natural wind, yes you could power something from it.

[Soup DeVille]

It's not creating energy; it's redirecting energy (airflow) to generate electricity. So what you're saying is that electricity generated would be negated by the extra energy required by the motor to compensate for parasitic loss caused by the intake and turbine/alternator setup?

It would be negated by the extra energy required to create the airflow. The parasitic loss would be the disturbance of the airflow- yes, even in a NACA duct.

[MX793]

It's not creating energy; it's redirecting energy (airflow) to generate electricity. So what you're saying is that electricity generated would be negated by the extra energy required by the motor to compensate for parasitic loss caused by the intake and turbine/alternator setup?

Let me put numbers to it.

You have an electric vehicle with typical car aerodynamics.  It requires 25 kW of power to maintain 65 mph on flat ground in still air (power to overcome drag and rolling resistance).  You attach to that car one or more little wind turbines that, cumulatively, generate 5 kW of power at 65 mph.  The drag they will add to the car in order to create that 5 kW will require the propulsion motor to put out more than 5 kW to overcome in order to maintain speed.  Let's say 6 kW of additional drag.  So now the car needs 31 kW to maintain 65 mph, but the turbines are kicking back 5 kW, so you're at 26 kW total propulsive power to do 65 mph.

Let's say you have 50 kW-h of battery charge.

The car without the wind-turbine "range extender" can travel for 2 hrs at 65 mph, 130 miles

The car with the wind turbine "range extender" can travel for 1.92 hrs at 65 mph, or 124.8 miles.

The range extender will not extend range.

Even assuming a 100% efficient turbine (power generated equals the drag incurred), which is impossible due to the laws of thermodynamics, you can do no better than match the range of the scenario when you have no turbine.  The only way for that to extend range is for the turbine to have a greater than 100% efficiency, which also violates the laws of thermodynamics.

[MX793]

Yes, that too. Airliners have emergency ram air generators that deploy into the airstream to power all the flight systems if there's a catastrophic loss of power.

Which requires that they throttle up the engines (and burn more fuel) to overcome the added drag of the emergency generators.  That power isn't gotten for free.  It's using the plane's kinetic energy to turn those turbines, and since the engines are the things imparting that kinetic energy, either the plane slows down at the same fuel consumption rate, or they throttle up (increase consumption rate) to maintain speed.

[Soup DeVille]

Which requires that they throttle up the engines (and burn more fuel) to overcome the added drag of the emergency generators.  That power isn't gotten for free.  It's using the plane's kinetic energy to turn those turbines, and since the engines are the things imparting that kinetic energy, either the plane slows down at the same fuel consumption rate, or they throttle up (increase consumption rate) to maintain speed.

I think he's talking about a RAT, which is an emergency device for when the engines stop.

https://en.m.wikipedia.org/wiki/Ram_air_turbine

In this case, they add drag and slow the plane down- but allow you to maintain hydraulic and electric power.

[Laconian]

Maybe a louver could open during braking? But then why not just do regen braking instead...

[MX793]

Maybe a louver could open during braking? But then why not just do regen braking instead...

Regen braking would be (is) far more efficient.  Which is why all contemporary hybrids and EVs utilize it.

[Soup DeVille]

Of course if you had some sort of wind generator where you could sit by the side of the road and capture energy from the breeze of passing cars...

Well, that's one step away from putting a small windmill on the Thanksgiving table and trying to put some of that hot air to a useful purpose...

[Payman]

Let me put numbers to it.

You have an electric vehicle with typical car aerodynamics.  It requires 25 kW of power to maintain 65 mph on flat ground in still air (power to overcome drag and rolling resistance).  You attach to that car one or more little wind turbines that, cumulatively, generate 5 kW of power at 65 mph.  The drag they will add to the car in order to create that 5 kW will require the propulsion motor to put out more than 5 kW to overcome in order to maintain speed.  Let's say 6 kW of additional drag.  So now the car needs 31 kW to maintain 65 mph, but the turbines are kicking back 5 kW, so you're at 26 kW total propulsive power to do 65 mph.

Let's say you have 50 kW-h of battery charge.

The car without the wind-turbine "range extender" can travel for 2 hrs at 65 mph, 130 miles

The car with the wind turbine "range extender" can travel for 1.92 hrs at 65 mph, or 124.8 miles.

The range extender will not extend range.

Even assuming a 100% efficient turbine (power generated equals the drag incurred), which is impossible due to the laws of thermodynamics, you can do no better than match the range of the scenario when you have no turbine.  The only way for that to extend range is for the turbine to have a greater than 100% efficiency, which also violates the laws of thermodynamics.

Good explanation, and I did learn this stuff a long time ago, but say the impellers were well designed and allowed the alternators to kick out 10 kw. Given the airflow and aerodynamic drag remains almost the same, you're telling me the drive motor must draw another 10+ kw to compensate. That doesn't seem right. I don't mean to sound dumb... it's actually an interesting discussion.

[Payman]

Of course if you had some sort of wind generator where you could sit by the side of the road and capture energy from the breeze of passing cars...

Well, that's one step away from putting a small windmill on the Thanksgiving table and trying to put some of that hot air to a useful purpose...

I met the guy up here who formed a company to do just that. Wind impellers/generators mounted into the divided highway medians. I don't think the cost advantages are there.

[MX793]

Good explanation, and I did learn this stuff a long time ago, but say the impellers were well designed and allowed the alternators to kick out 10 kw. Given the airflow and aerodynamic drag remains almost the same, you're telling me the drive motor must draw another 10+ kw to compensate. That doesn't seem right. I don't mean to sound dumb... it's actually an interesting discussion.

Yes.  If you put a 10kW wind turbine on a car, it will add >10kW of drag to the car.  The law of conservation of energy states that the turbine cannot add less than 10kW of drag (1st Law of Thermodynamics).  And, as energy conversion cannot be 100% efficient (2nd Law of Thermodynamics), the turbine must therefore incur more drag than the energy it generates.

Putting a wind turbine on the car is no different than attaching a trailing 5th wheel that turns a generator as it rolls along (actually, the 5th wheel generator would probably be more efficient, but still a net loss).  Like the turbine, the wheel would convert kinetic energy to create electricity.  The car's propulsion motor creates that kinetic energy.  To offset the drain of the KE being converted to electricity, the car's motor would have to increase it's output to maintain speed.  The amount the output increases would have to be at least as high as the power being generated, assuming 100% efficiency at the generator.  Every kW it generates in power is more than a kW of extra drag it imparts on the car for the reasons given above.  It would basically be a trailing regenerative brake that's always there, trying to slow the car down and taking power to overcome, while generating less power than it takes to overcome the drag of the wheel.

An even more simplified scenario would be to connect a battery to a motor, then have the motor's output shaft directly driving a generator, and then have the generator feed power back into the battery (with diodes to ensure that the electricity can only flow 1-way).  Due to losses in the system (resistance in the wires, friction in bearings, etc), the output of the generator into the battery will always be less than the output from the battery and the motor.  This means that the battery will eventually go dead, as it takes more mechanical power to turn the generator than electrical power the generator can create (or, more accurately, convert).

Suppose you want to use this motor to power some kind of equipment, like a conveyor belt.  If you attach both a generator and a conveyor belt to the motor, thinking that the generator's output will at least partially charge the battery and increase your run time, you'll find that battery will actually go dead faster than if you just ran the conveyor belt.