Turbo Alternator: How Can It Increase Vehicle Efficiency?

  • Thread starter Ayrity
  • Start date
  • Tags
    Alternator
In summary, the conversation discusses the idea of using a turbocharger to generate electricity for a car's electrical systems, instead of relying on the traditional alternator. The proposed setup involves using a gear reduction or pulley system to slow down the turbo's speed and make it suitable for turning the alternator. The conversation also mentions the potential benefits of this setup, including increased efficiency and reduced parasitic losses. However, there are concerns about the practicality and feasibility of this idea, such as the added weight and space requirements, as well as the potential power loss to the wheels.
  • #1
Ayrity
92
0
Im a mech engineering student and I am very interested in alternate fuels, and better mpg. So I was thinking and did some research on the topic I am posting about and found very little so I am looking to experienced moders for some input.

what if you were to hook up a turbocharger so that the exhaust spun the turbo shaft but instead of turning a compressor blade, it was used (through a gear reduction, or pulley system to slow the rpm to a usable rate) to turn the alternator? then you could use a smaller serp belt on the engine, and you could see some increased efficiency because of the decrease of parasitic loss. the most difficult parts of a project like this would be to make sure that at idle, the car was spinning the turbo at a fast enough speed to produce the amount of electricity needed, and that to reduce the gearing (i use the term loosely because it might not be best to use "gears" to do this) from the turbo spinning at very high rpm, to what the alternator is used to seeing.

It would be best to be able to use the stock alternator, thus reducing cost and the pain of replacing it, and/or moding the wiring from it. other than that the game is on for ideas to improve this concept.

I know BMW is using a similar idea involving capturing the heat loss from an engine/exhaust to run a small steam turbine to run the electrical system, but I think that the turbo idea might be a better one as far as a bolt on goes.

as far as added back-pressure goes, you could put in a free flow exhaust, and the turbo all together and thus roughly maintain "stock" back-pressure.

any input?
 
Engineering news on Phys.org
  • #2
I would think a hydrolic drive off the turbo would work better
then a mess of gears or belts
and you could then drive other systems too like
water/cooling pump, A/C pump, power steering, in addition to the alt
maybe some fans too
 
  • #3
It's a good idea, but here are a few things to consider:

- Parasitic losses to the battery charging alternator are low, and are only incurred when the alternator is actually generating power (not all the time).

- The speed range of a turbo is huge. To gear this down to suit a normal alternator would require a very large turn-down ratio. This means that while the turbine isn't spooled up (a high proportion of the time) your alternator won't be able to generate a large amount of power, and (more importantly) the effective inertia of the system would be very high.
 
  • #4
actually I have a mazda3 (just got it woohoo awesome) and it already has the power steering and radiator fans totally electric, so doing the alternator would be such a great power saver for me. But the a/c pump would be great to take off the engine too.

what do you mean exactly by a hydrolic drive? like a water pump basicly with hydrolic fluid?
 
  • #5
and to brewnog, i think that because of the way my car is set up (look at my last post) the demands of the alternator are higher. and I have seen reports of people disconnecting their alternator from the battery to see what kind of mpg improvements they get, low reports are something like an 8% increase from what I can tell, and that is huge over the lifetime of the car.

and to compensate somewhat for the turn down ratio, maybe in combo with a bank of capacitors, you could use a small CVT like out of a snowmobile or even a large chainsaw?

by the way, thanks for the "it's a good idea but here are some things to overcome" comment, its stuff like this that makes me love this forum. people helping people instead of telling them it can't be done :)
 
Last edited:
  • #6
hydraulic a small pump useing oil like fluid
most are displacement types rather then vane so they work at higher pressure
and lower volume
a accumulator [ tank with air pressure ] can keep power up to motors
to drive the accessories as needed when turbo is not at full speed
but a accessorie drive turbo need not be sized for peak power like a compressor turbo is
a much smaller unit could be used and partly bypassed at full power to cut back pressure
and keep the unit spinning at lower RPM maybe even at idle
 
  • #7
that is true, it could be much smaller possibly. maybe a turbo that is meant for a motorcycle?
 
  • #8
It's a cool idea, I thought about that once before. You could definitely find a small enough turbo to do it, and the wastegate would keep it from over spinning. In reality though it would not be worth the extra weight of the turbo, the plumbing, the oiling system, the space it would take up, and the extra heat and parasitic effects on the motor. on the other hand though, it would sound badass. Especially when you turn your lights on and hear it whine :)
 
  • #9
In principle, the idea is sound. There are plenty of people using turbines to generate eletricity, and exhaust pressure and temperature are where the biggest inefficiencies of cars are.

In practice, adding a turbine means that the engine has to work harder to get the exhaust out - and that means less power at the wheels. With a turbocharger, this is going to be more than offset by the increased volumetric efficiency of the engine - but if you're dumping all the energy into the battery you may well notice the power loss.
 
  • #10
Having an extensive automotive background I thought of this as well. The battery powers the vehicle the alternator charges the battery as well as supplying some power to the car.It would work but would have to go under the vehicle where it is very wet so it would need to be put into a water resistant box.
 
  • #11
NateTG said:
In principle, the idea is sound. There are plenty of people using turbines to generate eletricity, and exhaust pressure and temperature are where the biggest inefficiencies of cars are.

In practice, adding a turbine means that the engine has to work harder to get the exhaust out - and that means less power at the wheels. With a turbocharger, this is going to be more than offset by the increased volumetric efficiency of the engine - but if you're dumping all the energy into the battery you may well notice the power loss.
There is little loss of power with the turbo inline you would have to size it to your exhaust pipe. my truck would require a 3 " turbo.
 
  • #12
brewnog said:
It's a good idea, but here are a few things to consider:

- Parasitic losses to the battery charging alternator are low, and are only incurred when the alternator is actually generating power (not all the time).

- The speed range of a turbo is huge. To gear this down to suit a normal alternator would require a very large turn-down ratio. This means that while the turbine isn't spooled up (a high proportion of the time) your alternator won't be able to generate a large amount of power, and (more importantly) the effective inertia of the system would be very high.
Loss from belt driven accessories is 10-15% then fan being the biggest at 20%.
 
  • #13
Welcome to PF. You'll note that this thread is 3 years old, it's a good revival!

cobra5.0 said:
Having an extensive automotive background I thought of this as well. The battery powers the vehicle the alternator charges the battery as well as supplying some power to the car.It would work but would have to go under the vehicle where it is very wet so it would need to be put into a water resistant box.

Water resistance is the least of your worries. Do you have an idea what size battery is required to power a car? Have you looked at what this weighs and costs? Take a look at any of the 3rd generation hybrids in production at the moment and look at some of the engineering challenges they've faced.

cobra5.0 said:
There is little loss of power with the turbo inline you would have to size it to your exhaust pipe. my truck would require a 3 " turbo.

Turbochargers aren't 'sized' to the exhaust pipe diameter, they're sized principally to give a specific air mass flow at a given pressure ratio. A '3 inch turbo' doesn't mean anything. The turbo "size" is comprised of the frame size, compressor wheel size, turbine wheel size, compressor housing A/R ratio, turbine housing A/R ratio, compressor wheel trim, and turbine wheel trim.

cobra5.0 said:
Loss from belt driven accessories is 10-15% then fan being the biggest at 20%.

No, the biggest losses are thermal (heat to coolant and oil, heat to exhaust, and heat to intercooler where fitted). Losses to belt driven ancilliaries depends entirely on what's being driven and what conditions those driven equipment are being run at. The cooling fan losses are generally a couple of percent of heat in fuel, not 20% as quoted.

I'm not sure what your 'extensive automotive background' comprises, but until people here know you, if you wish to throw figures around, you might wish to provide some references to back them up.
 
Last edited:
  • #14
brewnog said:
Welcome to PF. You'll note that this thread is 3 years old, it's a good revival!
Water resistance is the least of your worries. Do you have an idea what size battery is required to power a car? Have you looked at what this weighs and costs? Take a look at any of the 3rd generation hybrids in production at the moment and look at some of the engineering challenges they've faced.
Turbochargers aren't 'sized' to the exhaust pipe diameter, they're sized principally to give a specific air mass flow at a given pressure ratio. A '3 inch turbo' doesn't mean anything. The turbo "size" is comprised of the frame size, compressor wheel size, turbine wheel size, compressor housing A/R ratio, turbine housing A/R ratio, compressor wheel trim, and turbine wheel trim.
No, the biggest losses are thermal (heat to coolant and oil, heat to exhaust, and heat to intercooler where fitted). Losses to belt driven ancilliaries depends entirely on what's being driven and what conditions those driven equipment are being run at. The cooling fan losses are generally a couple of percent of heat in fuel, not 20% as quoted.

I'm not sure what your 'extensive automotive background' comprises, but until people here know you, if you wish to throw figures around, you might wish to provide some references to back them up.

What I meant is if your vehicle has 1.5" exhaust the turbo outlet will be 1.5" if you have 3" exhaust your turbo outlet will 3".
I received a 25HP increase by eliminating my belt driven fan to an electric one. And throwing out the smog pump gave me a 10hp increase. Under-drive pulleys also gave me a 15hp increase. Which technically is not and increase just freeing up lost HP from the engine. So if the manufacturer say the vehicle has 225hp you need to subtract the belt driven accessories to have a true HP output. I also relocated my oil filter and the electric fan hardly comes on even in the hottest summer day's. I have done all my own work on my mustang which includes new heads intake cam 1.7 ratio rocker arms. With the new cam shaft I have .554 lift on intake and exhaust.Drive shaft loop, Airbags in the rear coil springs. B&M short throw shifter and a new Center line racing clutch. And the HP rating for vehicle's is from the flywheel not rear wheel unless specified by the manufacturer. By throwing out the smog pump I dropped about 25lbs off the car weight and received about 15% increase in mileage. And it still met emissions standards.
 
  • #15
http://www.barber-nichols.com/products/specialty_products/turbo_alternators/default.asp
They can build it for you. Apparently Turbo Altenators have been around since the 80's
 
  • #16
What turbo manufactures have done to improve the peak efficiency around wide rpm is .
1)variable geometry exhaust housing, this not used much in gas as temps to high but idea is a variable vanes/deflectors in the housing that can keep efficiency up over engine rpm band .
2) twin scroll housing, this is were the exhaust housing has two different A/R compartments,. one for low speed response and larger for high rpm . there a flap to control when it opens (there still normal wastgate still used) .RX7 used this for many yrs on there turbo 13b engines (87-91).
3)Sequential turbos , this is were there 2 turbos, its similar to twin scroll idea. One turbo is run at low speed/boost and then second kicks in . Later 92+ RX7 went to this system and so did Toyota supra turbo's at end.
http://ecomodder.com/forum/showthread.php/turbo-powered-alternator-13746.html
 
  • #17
cobra5.0 said:
What I meant is if your vehicle has 1.5" exhaust the turbo outlet will be 1.5" if you have 3" exhaust your turbo outlet will 3".

Not true. The turbine outlet connection will have greater diameter than the duct running from the manifold, this ensures the back-pressure on the turbine wheel is not increased due to an inadequate pipe diameter, and promotes expansion over the turbine.
 
  • #18
brewnog said:
Not true. The turbine outlet connection will have greater diameter than the duct running from the manifold, this ensures the back-pressure on the turbine wheel is not increased due to an inadequate pipe diameter, and promotes expansion over the turbine.

My truck has a 3" exhaust and the outlet side of the turbo is 3" diameter. By outlet size I mean as the exhaust passes through the turbo. The boost side that goes to the intake on my application is also 3 ".
 
  • #19
So turbine 'inlet' then, not 'outlet'.

Anyway, I still don't see what a nominal pipe diameter has to do with anything. When turbocharging an engine, the existing exhaust pipe wouldn't even enter into the considerations as far as turbomachinery sizing would go.
 
  • #20
Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.
 
  • #22
I'm well aware of this; that's what my post (about minimising turbine outlet back-pressure) was about! I just didn't understand why you claim that a turbo is sized based on the existing vehicle's exhaust pipe size. The existing pipe diameter is completely irrelevant.
 
  • #23
To reduce back pressure it requires to as large as possible. To match turbo and exhaust size makes installation easier.
 
  • #24
Turbo is matched to work with the engine.I f you over boost the motor it can blow up. so the exhaust for ease of installation is matched to the turbo.
 
  • #25
The idea of converting th power from a turbine to mechanical power is easier done with http://en.wikipedia.org/wiki/Turbo-compound_engine" [Broken] where the turbine is connected to the crankshaft (which in turn is connected to the alternator). Here is the system used by Scania where the exhaust goes through a traditional turbocharger (1-2) and then through a blowdown turbine (3) connected to the crankshaft (6) through some gearing (5) and hydraulic coupling (4):

Scania-turbo-compound.jpg
 
Last edited by a moderator:
  • #26
The whole idea is to limit parasitic loss from the crankshaft. Having a exhaust driven alternator would eliminate that.
 
  • #27
Curiously, I have been interested in this subject for several years and just started a prototyping effort:
turbo_120.jpg


So I bought a turbo-charger a couple of years ago and finally started blue-printing it:
turbo_130.jpg


I'm building a brass-board based upon a 1.4kW rated, brushless motor normally used for ducted fan, RC models:
turbo_250.jpg


In my case, the energy recovered from the exhaust stream will be dumped into a Prius traction battery (aka., plug-in Prius style.) Sensing the higher battery SOC, the car will simply draw it down by powering the drive system. A back-of-the-envelope thermodynamic analysis suggests my goal of 20 kW may be achievable:
turbo_110.jpg


Most folks get hung up on "back pressure" effects which exist but given the typical turbo pressure ratios of 2-to-1 are nearly half an order of magnitude smaller than the power gain from the alternator:
turbo_200.jpg


Feel free to check my math but at full-throttle, 4,500 rpm, the 1.5L engine in my 2003 Prius will lose about 250 watts when the turbine is running at a 2:1 pressure ratio for an expected gain of 1.4 kW with this first prototype. If it works as expected, I'll scale the alternator to 20 kW and the back pressure effects will only slightly change. One reason for testing is to gain quantitative numbers to refine the math model.

Think of back-pressure this way, the turbo-alternator and exhaust pipe have expanded the definition of the "engine." To only pay attention on "back pressure" ignores the rest of the engine, the turbo-alternator that is producing power. It is like looking at just the compression stroke energy loss and forgetting that a power generation stroke follows. <grins>

There have been a number of technical problems to overcome in this project and 'lessons learned.' But that is why we experiment, to find out what works and what is Escher engineering.

Bob Wilson
 
  • #28
This is an interesting topic. Here the question is, does a turbo connected to an alternator have less net energy losses than a belt drive.

The cooling fan argument is irrelevant. Yes there is a gain in hp from converting to an electric fan. The reasons for this is because 1) the electric fan weighs MUCH less than the belt driven fan and clutch system and 2) the electric fan is only on at a certain temperature, which likely occurs at a very small fraction of a given persons driving time (rather than the whole time that the engine is running).

Now let's analyze where there will be net energy losses in a belt driven alternator. There is frictional losses between the belt and the pulley's, bearings, and there are also net losses due to the electrical efficiency of the alternator itself.

Where are there net losses in turbo driven system? The turbo takes energy to spool up, there are losses due to exhaust flow which get by the turbine blades without actually helping to spool the turbo, losses in the bearings, losses in every moving part used to help drive the alternator, and then the alternator itself again. How will this rob energy from the engine? The backpressure to adequately spool the turbo will pose resistance on the exhaust strokes of each piston.

I'm really interested in seeing the result of this. Personally I don't think you will see a reduction of energy losses; I think there will be more losses with the turbodrive.

The alternator is already a fairly efficient system. When the alternator is not generating power, it poses very little resistance on the system. which gradually increases as the electrical load and need increases.
 
  • #29
This is an interesting topic. Here the question is, does a turbo connected to an alternator have less net energy losses than a belt drive.
Uh, my prototype is exploiting the waste heat in the exhaust gas. In the Prius, there is no belt driven alternator.

The cooling fan argument is irrelevant. Yes there is a gain in hp from converting to an electric fan. The reasons for this is because 1) the electric fan weighs MUCH less than the belt driven fan and clutch system and 2) the electric fan is only on at a certain temperature, which likely occurs at a very small fraction of a given persons driving time (rather than the whole time that the engine is running).

Now let's analyze where there will be net energy losses in a belt driven alternator. There is frictional losses between the belt and the pulley's, bearings, and there are also net losses due to the electrical efficiency of the alternator itself.

Where are there net losses in turbo driven system? The turbo takes energy to spool up, there are losses due to exhaust flow which get by the turbine blades without actually helping to spool the turbo, losses in the bearings, losses in every moving part used to help drive the alternator, and then the alternator itself again. How will this rob energy from the engine? The back-pressure to adequately spool the turbo will pose resistance on the exhaust strokes of each piston.
I think you are analyzing a traditional vehicle, not a Toyota hybrid electric. My 2003 Prius only has one belt and it runs the air conditioner compressor and engine water pump. Everything else comes from the two motor generators, MG1 and MG2.

I'm really interested in seeing the result of this. Personally I don't think you will see a reduction of energy losses; I think there will be more losses with the turbo drive.
Remember my goal is to exploit the wasted heat in the exhaust stream. Think of the turbo as expanding the existing 13-to-1 power stroke to 14 or 15-to-1. We're not letting the exhaust gas reach atmospheric pressure until it gives up some of its latent energy, its momentum to the turbine. <grins>

If there were no 'back-pressure,' the exhaust gas would not even pass through the turbine. But because it is 'hot gas' and expands as it gives up its momentum, we get the last ergs. Don't treat this hot, gas as an incompressible fluid but just another expanding gas that cools a little more as it gives up its momentum.

Bob Wilson
 
  • #30
bwilson4web said:
Uh, my prototype is exploiting the waste heat in the exhaust gas. In the Prius, there is no belt driven alternator...

I kind of overlooked your post at first, but yeah prius's have their alternator/motor wedged in between the engine and trans (not belt driven but it does take energy to spin it).

My question is how much force is required to spin the turbodrive alternator when it's at full output and how much backpressure will that create in the exhaust?
 
  • #31
Allenman said:
I kind of overlooked your post at first, but yeah prius's have their alternator/motor wedged in between the engine and trans (not belt driven but it does take energy to spin it).

My question is how much force is required to spin the turbodrive alternator when it's at full output and how much backpressure will that create in the exhaust?
That is one of the reasons why this prototype is important.

Sad to say, it is difficult to find the performance specs for turbines. I did find mass-flow, efficiency charts for the turbo charger I'd bought several years ago but my best case estimate including injecting enough water for 20 kW is not even close to the graph (see earlier post.) I've sadly oversized the turbine by nearly half an order of magnitude. But I can still get useful data and use it for system integration and test.

I have found a motorcycle turbo that is more correctly sized for the gas flow of the 64 hp of my 2003 Prius but before I spend any more money, I want to make sure the system elements work well enough to trust exchanging the turbo. There are 'devils in the details' and I don't think I've figured them all out, yet.

BTW, the 250 W, back-pressure model is for a 2:1 pressure ratio of the turbine. It turns out whatever the actual pressure ratio of the real turbine, you can multiply it minus 1 times 250 W to estimate the back-pressure overhead. But then that is why we experiment.

Bob Wilson
 
Last edited:
  • #32
Hey i was just letting you know I'm watching this and thinking something of the same thing as you guys are...but I'm doing it in a race car I'm building, I'm plan on doing it in a Dodge Charger, and want all parasitic loss of the drive train, currently using a supercharger, but to get the boost i want, i will need to switch to a turbo and it hit me today, that a turbo pulley/belt system like on the engine, using the OEM accessories and making something for them to mount to and run them in the same style but using a turbine to power all the accessories insead of making to motor do it. Just letting you know I'm watching, and hoping to hear good things. Might be trying this.
 
  • #34
Bob Wilson, I think you're onto something. Rather than using existing parts and trying to cobble them together in series, you may want to make an alternator that's driven by the turbine section. So basically, you remove the compressor and replace it with the stator-assembly from an alternator. Replace the compressor-housing with the alternator rotor.

Due to the high velocities, you're going to get very high voltage AC output. A buck-regulator with induction-coil can be used to store the high-voltage and have it be returned slower as lower-voltage. Then rectify as necessary. Although the Prius uses 288v batteries, so this might actually be a match made in heaven.
 

1. What is a turbo alternator and how does it work?

A turbo alternator is a device that uses the exhaust gases from a vehicle's engine to power a small turbine, which in turn drives an alternator to generate electricity. The exhaust gases spin the turbine at high speeds, which then powers the alternator to produce electricity.

2. How does a turbo alternator increase vehicle efficiency?

By using the exhaust gases that would otherwise go to waste, a turbo alternator is able to generate electricity without using any additional fuel. This reduces the load on the engine and allows it to operate more efficiently, resulting in increased fuel efficiency.

3. What are the benefits of using a turbo alternator in a vehicle?

In addition to increasing fuel efficiency, a turbo alternator can also help reduce emissions by utilizing the exhaust gases. It can also provide additional power to the vehicle's electrical systems, reducing strain on the battery and improving overall performance.

4. Are there any drawbacks to using a turbo alternator?

One potential drawback is that a turbo alternator adds additional weight and complexity to a vehicle's engine, which can affect its overall performance. It may also require regular maintenance and can be more expensive to repair or replace compared to a traditional alternator.

5. Is a turbo alternator suitable for all types of vehicles?

A turbo alternator can be installed in most types of vehicles, but it is most commonly used in larger vehicles with diesel engines. It may not be as effective in smaller vehicles with gasoline engines, as the exhaust gases may not be strong enough to power the turbine efficiently.

Similar threads

Replies
13
Views
5K
  • Mechanical Engineering
Replies
12
Views
5K
  • Mechanical Engineering
Replies
18
Views
2K
Replies
2
Views
1K
  • Mechanical Engineering
Replies
6
Views
262
  • Mechanical Engineering
Replies
16
Views
2K
  • Mechanical Engineering
Replies
6
Views
3K
  • Mechanical Engineering
Replies
24
Views
9K
  • Mechanical Engineering
Replies
20
Views
3K
  • Mechanical Engineering
Replies
4
Views
6K
Back
Top