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May 06, 2006



113mpg (UK) = 94mpg (USA). UK gallons are bigger and better :)
Calculator here (see bottom line).


Has anyone ever seen an estimate of what kind of MPG would be available in a diesel hybrid? I can't think of anything that would mean a diesel hybrid would have less kinetic energy to recover than a gasoline hybrid. Can you not shut off a diesel engine as easily as a gasoline one? The math shows that if you go from a fleet average of 20 MPG to 100 MPG you cut gasoline use by 80%, which (if implemented all at once) would cut US oil use by 7.5 MMBD. The 250 MPG hybrid from AFS would 92% reduction. Now overnight this isn't going to happen, and I'm looking forward to the results for the next Prius . . . but I'm wondering if the guys at VW did a hybrid, would they hit 100 MPG on the first shot?


I'm not sure that a diesel hybrid would be more efficient than a gas hybrid.

I've heard that diesel engines are (like electric motors) more efficient than gasoline engines at slow, start-and-stop driving; but that highway driving might favor gasoline engines. If you take make a diesel hybrid, therefore, you're running an electric motor rather than diesel engine at the speeds where you get diesel efficiency, and then running diesel instead of gasoline at high speeds where you would get the gasoline efficiency.

But I'm not sure if this is correct. What do you all think?


As the owner of two diesel VWs, I can speak to that. I consistently get 40-50 mpg. 42-44 around town and 50 on the highway. And the Jetta is not a light car. The gas version only gets about 25 to 30 mpg. Diesel engines are much more efficient than gas engines in all conditions and applications, especially on the highway. And, since all the electricity to run a hybrid comes from the engine, directly or indirectly, the efficiency of the diesel should pay off. If a gas hybrid can get 50mpg , the diesel should get 70mpg. The downside is that using a diesel engine will further add to the cost of the vehicle, as diesel engines cost more initially. But, they cost no more to maintain and last longer.


Actually, after posting that I remember a study I read about a year ago, by the DOT on combinations of gasoline and diesel engines with a hydraulic hybrid. On their experimental hybrid, instead of little generators at each wheel, they had pumps which stored up high pressure hydraulic fluid in a tank. The energy stored in the form of high pressure fluid was then used to help power the vehicle during acceleration. I have not heard of anyone going further with that technology, but it did work, according to the study. I will link it if I can find it.

Anyway, the best mileage was with the combination diesel/hybrid vehicles. Gas hybrid and diesel only were about the same and gas only was the worst.


I'm curious if Hyundai chairman Chung Mong-Koo made the statement about moving towards hybrids instead of fuel cells before or after he was arrested for embezzlement.



Scroll down here for more info:



Actually, there appears to be a lot of activity on hydraulic hybrids




The reason that I thought that gas-electric hybrid would be more efficient than diesel-electric hybrids were these two articles:

1) Mostly this one:

2) Somewhat this one:


I am suspicious of the numbers he cites. The diesel engine is always more efficient than a comparable gasoline engine. That is true whether they are mated to a hybrid system or not. Note that the CO2 emissions for the diesel engine are lower. It can't have lower CO2 emissions if it is burning more fuel. Less CO2 means less fuel burned. Something there doesn't add up.


Found this in the Technology Review archive . . . diesel hybrids in France.


Answers my own original question I guess.


Oops, follow the link in my user ID, not the link I pasted.

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Batteries/Hybrid Vehicles