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