Electric car idea.

[N80]

I'm sure there is some fatal flaw in this idea, and I know that I'm not the first or probably even the thousandth person to think about it, but why isn't anyone pursuing a diesel-electric car model based loosely on the concept of diesle-electric locomotives?

In other words, it seems to me you could put a tiny, high efficiency diesel engine in a car that would run at a constant ot near constant speed turning a small generator that in turn supplies electric drive motors. I would think that a small diesel optimized to run at a single constant speed would be very fuel efficient. And this would not be a 'hybrid' in the current sense of the word. The diesel would never provide power to the drive wheels.

Where is the flaw in this thinking? Is it just too much stuff to fit in a vehicle the size of a car? Would the fuel savings just not be sufficient to make it worth it?

 

[RobS]

The flaw is the "tiny, high efficiency engine" part. That will only give you "tiny" performance. To achieve acceptable performance (acceleration mostly), you need either a larger engine or some batteries to store some energy. Both add weight which is the enemy of economy. Locomotives are kind of like tractors: weight is good! They have much more hp than what they need to simply maintain cruising speed.

 

[N80]

The flaw is the "tiny, high efficiency engine" part. That will only give you "tiny" performance.

You're probably right, and my understanding of the electric requirements for car-sized electric motors is probably what I don't understand. However, I've seen some pretty small, very compact portable generators. And the APU's on aircraft (which are gas turbines, not diesels) are absolutely tiny.

It also seems that as lithium polymer battery technology improves that there will be weight savings there. Brushless electric motor technology should also allow for more powerful and efficient electric motors in small packages.

I guess, in the end, we just can't get enough electricity generated by small enough (or efficient enough) engine.

 

[SPYDERLK]

The flaw is the "tiny, high efficiency engine" part. That will only give you "tiny" performance. To achieve acceptable performance (acceleration mostly), you need either a larger engine or some batteries to store some energy. Both add weight which is the enemy of economy. Locomotives are kind of like tractors: weight is good! They have much more hp than what they need to simply maintain cruising speed.

Thats it. The mech to elec conversion has some losses, made up for by no real need for a transmission. This is perfect for a locomotive, but as said that diesel has the raw power to mechanically propel the locomotive up a grade at speed - with the proper gear transmission. Elec just decomplicates the transmitting of the high power over the speed range necessary.
larry

 

[SPYDERLK]

You're probably right, and my understanding of the electric requirements for car-sized electric motors is probably what I don't understand. However, I've seen some pretty small, very compact portable generators. And the APU's on aircraft (which are gas turbines, not diesels) are absolutely tiny.

It also seems that as lithium polymer battery technology improves that there will be weight savings there. Brushless electric motor technology should also allow for more powerful and efficient electric motors in small packages.

I guess, in the end, we just can't get enough electricity generated by small enough (or efficient enough) engine.

Its going to take about 10HP at the wheels to push a car thru the air at 60. That is level ground steady speed. With a little more and storage of the surplus you would be good to go if the storage didnt add much weight. The problem is the smaller the surplus the more storage you need to accelerate or go uphill at above a crawl. So it turns into a balancing act. Hopefully all the tricks are being looked at. Hopefully more will be discovered.
larry

 

[N80]

I'm guessing that in terms of diesel technology we are pretty close to the limits regarding power/size/efficiency. So the technology that will have to come together would be the efficiency of the electric motors and the weight of the batteries. Until then I suppose there won't be any significant step away from our current level of petroleum consumption.

 

[RobS]

I'm guessing that in terms of diesel technology we are pretty close to the limits regarding power/size/efficiency. So the technology that will have to come together would be the efficiency of the electric motors and the weight of the batteries. Until then I suppose there won't be any significant step away from our current level of petroleum consumption.

You are probably correct here. One improvements in today's hybrid and electric vehicles is regenerative braking. Regen is the recovery of all the lost braking energy into useable propulsion energy.

Getting back to your locomotive analogy, and something I recently learned, locomotives have what's called "dynamic brakes". Basically, they run the wheel motors and generators in reverse circuitry for braking. All that energy is converted to heat and disappated out the top of the loco (wasted).

 

[N80]

I think there are some cities that have had municipal buses that use that regen braking for a number of years.

 

[dmccarty]

I have read that the military is looking at running vehicles that are diesel/electric. Partly to lower fuel consumption as well as to quite the vehicle down when needed. I THOUGHT I had read that the car companies where looking at using diesel engines instead of gas.

Seems like one could take an electric car which has limited range, and put in a small diesel generator, roughly $3K, and add a small fuel tank. Yes it adds weight to the car but it would allow the batteries to recharge while the person is at work for 8-10 hours. Maybe extend the range while driving? Or do electric cars require a huge O amount of power to charge up?

Later,
Dan

 

[MrJimi]

How about a diesel engine made by Caterpillar like This one here
lots of uses for this little sweetheart

 

[RobS]

I do recall something about buses with regen some time back. Seems like they had a flywheel that would spin up during braking. Again, a weight issue for an economy minded car.

Regen in an electric car is relatively simple as the car already has the wheel motor and batteries.

For me, the optimal solution is similar to your original idea. A small (probably not tiny though) engine powering a generator powering wheel motors with the addition of batteries to handle peak demands. I'm not positive, but I think this is the layout of the Toyota Prius.

 

[N80]

I'm pretty sure the gasoline engine in the Prius is also used to drive the drive wheels. Electric motor kicks in only when done accelerating. Could be wrong.

I'm also intrigued by jet aircraft APUs. I saw a show years ago showing an electric car that used one of these along with batteries. They are basically simple gas turbines with like 2 moving parts at most. I'd guess the primary drawbacks would be noise and tremendous heat output. In the show I saw, it also seems like the turbine spun up a horizontally mounted flywheel that would continue to spin and generate power when the car was cruising or parked.

 

[BigE_]

Seems like one could take an electric car which has limited range, and put in a small diesel generator, roughly $3K, and add a small fuel tank. Yes it adds weight to the car but it would allow the batteries to recharge while the person is at work for 8-10 hours. Maybe extend the range while driving? Or do electric cars require a huge O amount of power to charge up?

I've seen what looks like a modified golf cart around town. It has license plates, so it must be road legal. Its got a generator strapped into the back. The generator is one of those Honda inverter type, so it is probably fairly efficient.

 

[N80]

I've seen what looks like a modified golf cart around town. It has license plates, so it must be road legal. Its got a generator strapped into the back. The generator is one of those Honda inverter type, so it is probably fairly efficient.

That's the idea I'm talking about!

 

[RobS]

I'm pretty sure the gasoline engine in the Prius is also used to drive the drive wheels. Electric motor kicks in only when done accelerating. Could be wrong.

I'm also intrigued by jet aircraft APUs. I saw a show years ago showing an electric car that used one of these along with batteries. They are basically simple gas turbines with like 2 moving parts at most. I'd guess the primary drawbacks would be noise and tremendous heat output. In the show I saw, it also seems like the turbine spun up a horizontally mounted flywheel that would continue to spin and generate power when the car was cruising or parked.

One of the big downsides to a gas turbine is the speed at which they have to spin to operate. The high speed requires a lot of gearing to get to a more useful rpm and all that gearing adds inefficiencies (not to mention cost and weight).

Any heat engine (gas, diesel, turbine etc.) is inherently inefficient as a good amount of the energy potential of the fuel is lost to heat generation. This is where fuel cells and such have an advantage.

Ultimately, it takes a certain amount of energy to propel a vehicle and it's contents. That energy comes from some source and in the case of a vehicle, must be transportable. The more efficient the conversion of the energy source to propulsion the better, and the less energy loss to braking, aerodynamics, road friction etc. the better.

Side note, saw the famous turbine powered Indy car at the 500 museum over Christmas. Still an impressive machine, after all these years.

 

[Tig]

The energy storage piece of the puzzle may be solved by supercapacitors. Supercapacitor - Wikipedia, the free encyclopedia

 

[Wayne County Hose]

There are basically 2 things which keep this theory from happening. Cost and weight. I was a tech on computerized high end forklifts before opening my shop. The forklift industry has about mastered electric propulsion. With the AC motor technology, regenerative braking, and the motor controllers currently available, I could make an electric car that would out accelerate most gas cars. Problem is, batteries won't last. Install a generator, now we have a weight issue. I've made 8,000 lb.+ forklifts absolutely bake the drive tires.

If you make a generator powerful enough to not need a battery, it would suck up too much fuel. It would be counter productive as you would burn more fuel to generate the electricity than you would have just using the IC engine to propel the vehicle. Remember now, energy can be neither created or destroyed, only transferred. Everytime you transfer energy, there are power losses. Onboard generating would create heat and sound energy. Both result in power losses. Now if you add batteries as an energy reserve, weight is an issue. And, you have to recharge those batteries somehow, and energy isn't free.

These electric drive systems are also pretty expensive. The entire drive system of a forklift, dealer cost, is probably in excess of $4,000. Add a generator, batteries, and the rest of the car and it quickly becomes cost prohibitive. It wouldn't be able to compete with the current automobiles and wouldn't sell.

You may be thinking, "What about the hybrids currently in production?" Well, they are made very light and underpowered. Try putting their drivetrains in a mini-van. The automotive industry is light years behind in electric propulsion. The systems are out there, but with the costs, they never really worked much on them as they couldn't sell and make a profit.

 

[RobS]

Well put WCH. Just curious, can you comment on the weight and lifespan of forklift batteries, as a data point for our study here?

An interesing aside to the gas/diesel hybrid is the solar powered car. If you have ever seen one they are very light, thin, sleek and flimsy. They are remarkable in their capabilities, but only in full sun. There are college level competitions for solar cars and they basically shut down with cloud cover. The answer for everyday use? Batteries, engine or fuel cell. Each adds a lot of weight and we're back to the bane of efficient vehicles.

 

[texbaylea]

One of the big downsides to a gas turbine is the speed at which they have to spin to operate. The high speed requires a lot of gearing to get to a more useful rpm and all that gearing adds inefficiencies (not to mention cost and weight).

Any heat engine (gas, diesel, turbine etc.) is inherently inefficient as a good amount of the energy potential of the fuel is lost to heat generation. This is where fuel cells and such have an advantage.

Ultimately, it takes a certain amount of energy to propel a vehicle and it's contents. That energy comes from some source and in the case of a vehicle, must be transportable. The more efficient the conversion of the energy source to propulsion the better, and the less energy loss to braking, aerodynamics, road friction etc. the better.

Side note, saw the famous turbine powered Indy car at the 500 museum over Christmas. Still an impressive machine, after all these years.

Chrysler put a turbine powered car on the streets back in the 50s or early 60s. Cities were unhappy since the exhaust melted the asphalt paving. Also you did not want to walk close to the rear or you would get burn't feet

I saw one on the streets of Houston but only briefly. I do not know how they handled the transmission of power.

Vernon

 

[N80]

These electric drive systems are also pretty expensive.

I'm sure they are. I used to race RC nitro powered trucks. Brushless electric motors are just now breaking onto that scene and they can outperform the nitro powered trucks, but at a cost. A basic brushless for an RC monster truck can run over $300 with speed control. Larger ones run much higher.

But here's the thing. When gas hits $10 a gallon and there is a market for millions of these units, prices come down, just like anything else...... except gasoline of course.