Electrical Engineering needed. Would this work?

A while back I read an article about the demise of the GM EV test vehicles. Burt Rutan was interviewed about his experience in using one and his ideas about it. First of all he used it for quite a long time to commute to work and had no fault with it. He suggested the following: Build a car that runs on electric power all the time. It would be a plug in electric with an onboard state of the art, small displacement diesel powered generator that would auto-start to provide power after the batteries reach a certain discharge level. The research I've done indicates that this wouldn't work, but I'm not so sure.

So, GRM electrical geniuses, what is your take on this idea?

In reply to Graefin10:

Yep. This is basically how the Volt works - using a gasoline generator. Your idea is also exactly how the Top Gear crew built their hybrid.

Diesel Locomotives?

Granted this is not a battery fed system but rather a generator running the motors with a "produce as needed basis". It could work, but you would need to know the efficiencies of all components. A high efficiency motor with light weight and all that may make it feasible. You would still need to have a power output high enough to make sure that you can power the vehicle and charge it at the same time.

So if you had a worst case scenario of utilizing a 100 amp draw on the system you would still kill off the power with a generator you have if its max output was only 80 amp.

Possible yes, but it would definitely take some homework to get it done.

Ian F wrote: In reply to Graefin10: Yep. This is basically how the Volt works - using a gasoline generator. Your idea is also exactly how the Top Gear crew built their hybrid.

I guess the only real difference in Rutan's idea and the Volt is that his would use a turbo diesel instead of gasoline. It should be more fuel effiecient.

Here's how I see it...

Any time you change states of energy (fuel to HP, HP to electricity, electricity to HP, etc) you lose a significant amount. I don't understand the value (other than placating an uneducated mass of consumers) of these vehicles.

The bottom line is, if you need to get X hp to the ground the most efficient way of doing it is with the least amount of changes of energy; fewer direction changes like in a rear axle, less friction, fewer energy conversions.

The Volt goes like this:
- uses energy in fuel, converts it to kinetic energy (hp) with an engine. That step alone can only hope to be about 30% efficient. The rest of the energy is wasted as sound, heat, friction, and light.
- uses the engine's hp to drive a generator and make a different kind of kinetic energy; electricity. That process can only be about 80% efficient. The rest is lost as heat and friction.
- uses the electric energy to turn motors, again about 80% efficient.

So, its releasing stored energy in fuel to convert to kinetic energy, then to electricity, then back to kinetic energy. How can that possibly be more efficient? That's like plugging an inverter into your 12v outlet so you can plug in a 110v phone charger which converts back to 12v anyway. Or its like putting a windmill on an electric car; you will spend more energy pushing the windmill through the air than you will get in return from the spinning windmill.

As an amateur engineer, I think the smartest way is the least complicated. Either find ways to generate or store greater electrical capacity so the engine isn't needed, or just put a diesel in it

curtis73 wrote: Here's how I see it... Any time you change states of energy (fuel to HP, HP to electricity, electricity to HP, etc) you lose a significant amount. I don't understand the value (other than placating an uneducated mass of consumers) of these vehicles. The bottom line is, if you need to get X hp to the ground the most efficient way of doing it is with the least amount of changes of energy; fewer direction changes like in a rear axle, less friction, fewer energy conversions.

I think the advantage in this type of system is that the internal combustion engine operates in a very narrow, efficient RPM range. The theory being that this offsets some of the other losses.

Don't know if it's exactly what you're looking for, but this vw concept is a plug-in diesel hybrid:

(Quick Google):

http://www.autoweek.com/article/20110125/CARNEWS/110129931

In reply to jamscal: I think I recall a news headline about that car but those are the first pictures I've seen.

Thinkkker wrote: Diesel Locomotives?

Or making it a whole lot bigger- all modern cruise ships run that way. Massive diesels drive generators that then drive various electric powered propellers in various layouts (some internal thrusters, some single direction push, some azepods, etc). Pretty amazing stuff.

No reason why it won't work, but probably GM's reason to not choose a diesel is system cost. The car is already really expensive with all the parts you have. Diesel adds a lot of cost, and even more so the emissions hardware. Depending how well an ICE engine is optimized for it's best settigns, the cost of the difference vs the advantage becomes a big issue.

Thinking about it is always a good thing.

Aren't gas turbines more efficient than piston engines. I seem to remember some of them in the 90% range. Using one of them to drive the generator should help reduce the waste.

That appears to have been part of Jaguar's thinking. From C/D here:

"The C-X75 is at heart a research project designed to fuse aerospace and automotive technologies. The car was developed over a nine-month span and paid for by Jag, while the powertrain springs from a joint project with the British government–sponsored Technology Strategy Board. On the most basic level, the car’s complex powertrain is a range-extending hybrid that operates roughly like the Chevrolet Volt's. In the Jag, a 19-kWh, 330-pound cache of lithium-ion batteries provides up to 68 miles of pure-electric AWD propulsion from four 195-hp electric motors. Mounted inboard, each drives a single wheel through a 3:1 gear reduction, and together create a claimed 1180 lb-ft of torque. (Four electric motors? Maybe Jaguar should have called it the XJ440.)

When the battery pack is exhausted, two miniature gas turbines weighing 77 pounds each and making 94 hp at 80,000 rpm provide recharging power and also can boost the electric-motor output when high performance is required. The turbines, made by the English company Bladon Jets and housed in a box behind the two seats with inlet air channeled through ducts around the occupant’s heads, extend the range to 560 miles."

Graefin10 wrote: I guess the only real difference in Rutan's idea and the Volt is that his would use a turbo diesel instead of gasoline. It should be more fuel effiecient.

For something that's not going to see much use (hopefully) I'm happier with reasonably efficient and fewer bits to go wrong. For something where it's running all (or most of) the time, that's a different story.

curtis73 wrote: Here's how I see it... Any time you change states of energy (fuel to HP, HP to electricity, electricity to HP, etc) you lose a significant amount. I don't understand the value (other than placating an uneducated mass of consumers) of these vehicles. The bottom line is, if you need to get X hp to the ground the most efficient way of doing it is with the least amount of changes of energy; fewer direction changes like in a rear axle, less friction, fewer energy conversions. The Volt goes like this: - uses energy in fuel, converts it to kinetic energy (hp) with an engine. That step alone can only hope to be about 30% efficient. The rest of the energy is wasted as sound, heat, friction, and light. - uses the engine's hp to drive a generator and make a different kind of kinetic energy; electricity. That process can only be about 80% efficient. The rest is lost as heat and friction. - uses the electric energy to turn motors, again about 80% efficient. So, its releasing stored energy in fuel to convert to kinetic energy, then to electricity, then back to kinetic energy. How can that possibly be more efficient? That's like plugging an inverter into your 12v outlet so you can plug in a 110v phone charger which converts back to 12v anyway. Or its like putting a windmill on an electric car; you will spend more energy pushing the windmill through the air than you will get in return from the spinning windmill. As an amateur engineer, I think the smartest way is the least complicated. Either find ways to generate or store greater electrical capacity so the engine isn't needed, or just put a diesel in it

Yes, but....

You're not giving the generators and motors enough credit. They should easily do 90%, and potentially more.

Also - an engine that only has to run at a set RPM / Load can be MUCH more efficient than one that needs to operate over a range of RPMs / Loads.

The Volt's engine can and does directly drive the wheels as far as I know. It doesn't just drive a generator to recharge the batteries, eventhough that's how it was touted. I may be wrong here, but I'm pretty sure we beat this one to death a few months back. Some people cried bat and switch and others said what's the big deal?

GM already did it... the "EV1 Series Hybrid" coupled a small gas-turbine APU to charge the batteries. According to Wikipedia it would get 60 - 100 mpg in hybrid mode, depending upon conditions.

Gas-turbines can be designed to be very efficient at a single (or narrow) band of speeds.

http://en.wikipedia.org/wiki/General_Motors_EV1#EV1_series_hybrid