# how high can mpg go??



## woodgeek (Aug 2, 2011)

Given the current discussion of CAFE standards and 60 mph hummers, I thought this was an interesting article....

http://www.energybulletin.net/stories/2011-08-01/100-mpg-gasoline-could-we-really

but then I'm a geek.

My one beef: I think we should use a gallons per mile (like the euro 'liters per 100 km') spec.  Going from 25 mpg to 50 mpg saves as much gas as going from 50 mpg to infinity mpg.  Not very intuitive.


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## begreen (Aug 2, 2011)

It all depends on how refined the design is and how you drive at to achieve high mileage. How about 282mpg?
http://www.treehugger.com/files/2008/07/vw-282-mpg-1-one-liter-car-production-2010.php

With ideal terrain and weather would you believe 11,516 mpg?
http://www.geekosystem.com/highest-mpg-car/


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## SolarAndWood (Aug 4, 2011)

Cool car but I'd be happy with the 69 mpg TDI hybrid Golf.


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## woodchip (Aug 4, 2011)

I could easily get 65mpg in my mini 25 years ago, but with modern things like electric windows (most people here cannot fathom out how to wind a window by hand these days), or air conditioning (we never get it very hot here, and a window down is fine for our summers), means that modern engine technology is spent powering all sorts of gadgets instead of actually moving you along......
The current VW Golf is a quarter on a ton heavier than the one that was introduced back in the 1970s.

But the easiest was to get a high mpg on my current car is the way I've always done it......

Leave the car on the drive and use the bicycle  ;-)


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## begreen (Aug 4, 2011)

Easy to do in relatively flat country, but a bike as primary transportation in an area of lots of hills and elevations from 0-2000 ft. makes for some wearisome bicycling. In spite of the adverse terrain and short trip driving (10 mi into town), we average 48.2mpg in the summer. On flat land it would be about 55-60mpg.


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## jimbom (Aug 4, 2011)

woodchip said:
			
		

> I could easily get 65mpg in my mini 25 years ago, but with modern things like electric windows (most people here cannot fathom out how to wind a window by hand these days), or air conditioning (we never get it very hot here, and a window down is fine for our summers), means that modern engine technology is spent powering all sorts of gadgets instead of actually moving you along......
> The current VW Golf is a quarter on a ton heavier than the one that was introduced back in the 1970s.
> 
> But the easiest was to get a high mpg on my current car is the way I've always done it......
> ...



And it is the best stress relief.  I had a nine mile commute in Hawaii that I took by bicycle.  It was perfect. Most aspects of living in Hawaii are perfect.  

The return trip took half the time because I was stressed from work.  By the time I got home and got a shower, I was mellow.


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## webbie (Aug 4, 2011)

I think the limit based on the current ideas is somewhere about 75 MPG. This means internal combustion as well as cars that weigh upwards of one ton. IC engines and the drive systems are inefficient - too much wasted heat and friction. I'm sure there are some engineers here, but it would be cool to know, for instance, how far the energy in one gallon of gasoline could push a 3000 lb (car w/2 passengers) down a relatively level road.....if the entire system were, say, 70% efficient. My understanding is that current cars are vastly less efficient. My quick guess says that a 40 MPG TDI has a total efficiency of less than 30% (engine and all systems combined). 

There is obviously an upper limit if a system if fuel based - that being the amount of energy in the fuel. A perfect fuel cell might be able to deliver 80% efficiency, and then electric motors might be able to deliver 80%, making a total of 64%. 

Of course, I have little idea of what I am talking about! I'm a generalist.


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## webbie (Aug 4, 2011)

Note the scale at:
http://www.smarterearth.org/content/transportation

A freight train is about 5X as efficient as even a 50 MPG car! The problem with cars (and planes, etc.) is that you have to move the vehicle itself as well as the fuel - in addition to the bodies! If we all sit on a train, the relative (vehicle) weight for each passenger is lower than one or two people in a 4000 lb car.

I think our cars will be moving toward all electric in the future - even if gasoline is used to generate the electric (fuel cells, hybrids, etc.) it is still a better way.  It would seem possible, in the end, to build great fleets of electric vehicles for less money than IC cars. Maybe I should buy some Tesla stock while it is down today?


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## woodchip (Aug 5, 2011)

Webmaster said:
			
		

> A freight train is about 5X as efficient as even a 50 MPG car! The problem with cars (and planes, etc.) is that you have to move the vehicle itself as well as the fuel



Trains have the advantage of smooth acceleration and planned smooth braking over a distance of miles, friction from metal wheel to metal track is also a lot less than rubber to road.

However, it's worth looking at this hyperdriving stite to see what you could do on a quiet road, not always easy for the busy rush hour freeway drive  ;-) 

http://www.hypermiling.com/car-mpg.html


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## woodgeek (Aug 5, 2011)

Nice.  The article I linked showed that for cars at highway speeds, air resistance clearly dominates--for trains the rolling resistance should be lower, and the air resistance per unit of cargo should be much lower if not negligible (being related to the frontal area).

High diesel prices will kill long haul trucking--cargo will move by boat and trains (diesel or electric), with trucks only as the short last leg.


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## ironpony (Aug 5, 2011)

what everyone is partially missing is
the oil companys need x dollars to survive
so if they sell half the gas the price will double
hence no savings tot the end user
also the govt loses huge tax income
half the gas half the taxes collected
tax is per gallon not per dollar
save a little oil
pay the same out of pocket
further bankrupt govt.
JMO


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## begreen (Aug 5, 2011)

Unfortunately that is not so. Our refined petroleum products bring a high premium in some foreign markets. China and Dubai for example are serious diesel importers. They are glad to buy our diesel. This keeps our prices higher.


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## midwestcoast (Aug 5, 2011)

ironpony said:
			
		

> what everyone is partially missing is
> the oil companys need x dollars to survive
> so if they sell half the gas the price will double
> hence no savings tot the end user
> ...



I must have missed a day in Econ class where they explained how reduced demand increases price...
So if we all burn & buy more oil the price will drop? Even though there's a finite supply? I don't think so.


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## benjamin (Aug 8, 2011)

Efficiency with regard to automobile transortation is entirely relative.  In physics there is no "work" done in transportation unless the elevation is changed, so driving from coast to coast has no intrinsic energy consumption.  Last I heard, dividing by zero gives you a meaningless answer.


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## Highbeam (Aug 8, 2011)

benjamin said:
			
		

> Efficiency with regard to automobile transortation is entirely relative.  In physics there is no "work" done in transportation unless the elevation is changed, so driving from coast to coast has no intrinsic energy consumption.  Last I heard, dividing by zero gives you a meaningless answer.



In the low level physics classes you assume many things are zero if they are too hard to calculate. It is a way to simplify the math. Wind resistance and friction for example are actual forces, that when applied over a distance become work. That work is wasted as heat to the environment. 

You can't dumb down real life.


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## Highbeam (Aug 8, 2011)

midwestcoast said:
			
		

> ironpony said:
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All of my economics classes assumed things like free market. When you have a monopoly such as OPEC, the normal supply and demand rules do NOT apply. I also believe that if international consumption goes down, prices per gallon must go up in order to maintain the income stream to those OPEC nations. 

It actually happens with utilities too. Water for example, if conserved means the utility purveryor must increase rates to replace the lost income. It happens all the time. When water consumption goes up, rates do not go down.


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## semipro (Aug 8, 2011)

ironpony said:
			
		

> what everyone is partially missing is
> the oil companys need x dollars to survive
> so if they sell half the gas the price will double
> hence no savings tot the end user
> ...



Oil companies are going to have to starting thinking more in terms of being "energy" companies.  There's nothing to stop them from investing their not-so-insignificant resources in alternative energy.  

The federal government will make money in taxes for whatever replaces oil.  Road taxes will be charged on miles traveled and will be independent of fuel sales.


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## Highbeam (Aug 8, 2011)

BP has been running commercials about how they are investimg in alternative energy sources. Maybe PR maybe they actually give a rip. 

Road taxes should have always been based on miles and tonnage. That's what tears up roads.


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## begreen (Aug 8, 2011)

That and cold weather. Snowplows, studded tires and frost heaves cause a lot of wear and tear.


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## woodchip (Aug 9, 2011)

Highbeam said:
			
		

> BP has been running commercials about how they are investimg in alternative energy sources. Maybe PR maybe they actually give a rip.
> 
> Road taxes should have always been based on miles and tonnage. That's what tears up roads.



I suspect fuel companies want to provide people with the alternative fuel, which does pose the question, if they are showing an interest, is it possible alternatives could be just round the corner and they don't want to be left out!

And I agree about road taxes, most road damage round here comes from over weight trucks coming from Europe which rarely get stopped, most of our roads would be described as quaint by your standards, and old roads built in the days of horses and carts really are struggling to take lorries of 44 tons nose to tail.


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## benjamin (Aug 9, 2011)

Highbeam said:
			
		

> benjamin said:
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It's ridiculous to say that a car is x percent efficient, that 60% of the energy is wasted by the engine, more by the transmission, rolling resistance, wind resistance etc. This leaves you with nothing to divide by. It is just as valid to say that all of the energy is wasted as heat (or all of the energy is put to use to move the car).  

My point is there is no limit on MPG, because there is no intrinsic work being done. 

Just like there is (practically???) no limit on home heating and cooling efficiency, because there is no inherent work that needs to be done to maintain a steady state.


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## woodgeek (Aug 9, 2011)

There is indeed no classical 'work' being done, but there are clear physical limits to mpg for specific transportation tasks, like moving a family of four and a little cargo 100 km in one hour.  Limited to gasoline powered heat engines with conventional (read affordable) materials, the wind resistance of a near optimum shape sets a limit not far from 80 mpg.

Of course, that is 75% less energy consumption than many/most vehicles on the road today.  If/when gas is $10/gal there will be plenty of vehicles closer to 80 mpg.


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## woodchip (Aug 9, 2011)

woodgeek said:
			
		

> If/when gas is $10/gal there will be plenty of vehicles closer to 80 mpg.



If you can't wait for it, come to England where we already have gas at $10 a gallon in our local garages. 

Still waiting for affordable cars that do 80mpg  ;-)


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## CTYank (Aug 9, 2011)

woodchip said:
			
		

> Webmaster said:
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Methinks you're a little crossed up there. In order:
Trains accelerate much more slowly than cars, at full power. Smoothness is only a matter of transitioning in switchgear. Zero impact on efficiency.
Train braking can impact efficiency if it's regenerative. Haven't heard of any yet.
True, metal-metal coefficient of friction is much lower than rubber-road, but meaningless here. The rolling resistance is MUCH lower; this is the BIG difference.

Trains also generally operate on much lower grades than cars/trucks. Where there are significant grades, synthetic AC technology enables use of much fewer diesel locomotive units, reducing fuel consumption greatly.

Electric trains are seldom preferable over diesel-electric in the US because of the density & type of traffic. Counter-example: NE Corridor. France, Germany, Switzerland, Sweden, etc. profit from electric propulsion.


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## ironpony (Aug 9, 2011)

Highbeam said:
			
		

> midwestcoast said:
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thank you, some thing just are not taught in school...............


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## ironpony (Aug 9, 2011)

Highbeam said:
			
		

> BP has been running commercials about how they are investimg in alternative energy sources. Maybe PR maybe they actually give a rip.
> 
> Road taxes should have always been based on miles and tonnage. That's what tears up roads.




the last higher up oil exec I heard said.....
we are in the OIL business we are NOT in the alternative energy business......


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## SolarAndWood (Aug 9, 2011)

CTYank said:
			
		

> Electric trains are seldom preferable over diesel-electric in the US because of the density & type of traffic.



That is the problem I have with most of the new tech cars.  Our hybrid doesn't do much better than the gas version on the highway where the majority of our miles are driven.  A low speed low range plug in is even less relevant.  Diesel-electric optimized for 75, now we're talking.


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