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Gas Mileage
StuDent   1/24/2012 2:00:54 PM
"True" gas mileage is meaningless in this discussion.  The mileage being discussed is really an index obtained by driving the vehicle on a dynamometer over the well-defined speed, load, acceleration and deceleration cycles used by the EPA. The key advantage is that these cycles are repeatable.  They were originally designed to mimic real city and highway driving patterns, but time and technology change, so they are really an approximation. 

I measure my "true" mileage every time I fill the tank—how far I have driven divided by how many gallons it took to fill up.  For my 2006 Honda Civic Si, it ranges from a worst of 21 mpg for consistent short drives to a best of 36 mph for a round trip for the weekend from Sacramento to north Lake Tahoe.

One of the great variables is the driver. Some drivers constantly accelerate and decelerate, others keep reasonably close to a constant speed. This driving difference can make a subcompact have the "true" mpg of an SUV and almost vice versa.

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Tragedy of the Commons
RobLewis   1/24/2012 1:27:30 PM
This is a classic Tragedy of the Commons, and it's disheartening how many people choose to view it through the lens of "personal liberty." 

You do not, repeat DO NOT, have the right to contribute to the destruction of my earth's climate because you insist on burning a ridiculous amount of gasoline to drag two tons of steel with you to the 7-11 to pick up beer and chips. 

I'm not sure there's any hope of saving the planet even with 54.5 mpg, or 60 mpg. But I KNOW there's no hope if we don't make big changes. 

bob from maine
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Maximizing MPG
bob from maine   1/24/2012 1:06:19 PM
First, everyone back to school. Knowing how to make a car move does not mean you can maximize fuel economy. Give an exise tax or other break for everyone who attends and passes an approved "drive safely and economically" school. Make the course meaningful and charge for big $$ for it.

Second: CVTs allow engines to run at optimum speed independent of wheel speed. Making engines capable of consuming enough fuel to accelerate yet using only enough fuel to maintain steady speed compromises economy. Design an engine to run at a steady speed when on the highway, then add energy storage to provide surge power for acceleration (sounds like a hybrid).

Third: Design and manufacture purpose-built vehicles. If you drive 80% highway, buy a highway vehicle that can achieve 60 or more MPG on the highway, understanding that in the city mileage will drop to 40 or less. If you drive 80% city, an electric with a charging motor of small (<10 or 15KW) capacity. When battery voltage drops below 40% reduce available power for acceleration to half or less. Electric range is largely a function of driver behavior, if you drive like it's a sports car, you will be parking early and often.

Fourth: Develope road-trains with electronic controls. When you are on the highway, understand you will be travelling at a fixed speed controlled by a highway smart-grid. Once part of the train, your only options will be to exit or stay in the train.

My 1000cc motorcycle routinely gets 53MPG with 2 people on it. The air-conditoner and heater work in the wrong seasons, the windshield wiper is a function of speed and I find it very hard to text or talk on my phone while driving. But, it does get 53mpg! It is obviously a compromise I consciously made to do without many "necessities" but it sure is fun to drive!  I am uncomfortable with the government setting a goal that demands I compromise things I don't want to. So part of the issue is whether I will accept a government mandated economy-mobile no matter how much research whent into its development or whether I will buy a 15mpg pick-up out of spite.

Christian Jorde
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Cars with 58 mpg are quite realistic
Christian Jorde   1/24/2012 12:52:48 PM
In Europe we do not understand your arguments.  We do have some cars with 4 liters per 100 km wich equals  58.8 miles per gallon.  This cars are available and the number is growing.  They are mostly running on diesel but this does not mean they are slow or tiny cars.  The key is to think on fuel consum for many parts and in all phases of design.
What is really consuming energy?  The accelaration (multiplied by weight) all kind of friction ( motor, gear, tires, bearings, etc) and the resistance of air for higher speed ( c - value).  If you recuperate then a part of kinetic enercy will be get back during braking.

To achieve a much higher efficency on engines is not possible but to save the waste seems a question of priority of design goals.



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Re: How to engineer 54.5MPG cars?
PatrickH.   1/24/2012 11:42:46 AM
Seems like somewhere along the way people lost focus on the topic.  Everyone seems to be discussing how to improve real world on the road fuel economy.  An important subject, but not the focus of the article which was asking how to improve CAFE.

1st - we should note that the CAFE numbers are not what we see on the window sticker of every car.  CAFE numbers (if I remember correctly) would be closer to the old consumer fuel economy numbers before the revamp that occurred several years ago.  So a Toyota Prius likely already meets 54.5MPG CAFE today.

Lighter weight, less drag, smaller engines.

More advanced engines (direct injection with very lean a/f ratios, direct control over valve timing & lift to reduce pumping losses through elimination of the throttle plate).

Hybridization (stop-start functionality at the very least with the ability to reclaim some energy through regen)

Any other novel ideas that can be packaged for mass-manufacturing.  What happened with BMW's turbosteamer?  Any advance with TEGs on the exhaust?  Exhaust driven generators to provide electricity for a hybrid system?  (I'd suspect that yes, financial and manufacturing complications keep these out of the vehicle).

William K.
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How to engineer 54.5MPG cars?
William K.   1/24/2012 10:39:45 AM
Several things can be changed to increase the miles per gallon quite a bit. Changing the traffic controls and roadways is one area that would not need any engineering breakthroughs, although it will probably be by far the most difficult to implement.

REducing the drag and rolling resistance can certainly reduce fuel consumption, but while most of the ways to do this have been figured out by racing teams already, adding them to most passenger cars would be a challenge indeed.

The stop-restart engine scheme could certainly be a large contributor to urban driving efficiency, but it will require a major upgrade in engine cranking systems, since the current starter motor arrangement is neither quik enough nor durable enough to be suitable for that kind of driving. In addition, to gain the very most from the stop-start mode,  there would need to be a means to disengage the drive wheels so that coasting would have the minimum drag effect. Coasting would be a major contributor for the reason that almost half of urban driving involves deceleration. An effective de-clutch and shutoff system could allow a skilled driver to obtain a large reduction in fuel consumption. Providing a similar degree of reduction with an automated system is probably well beyond tha capabilities of any and all automotive software development teams. Probably a satisfactory control algorithm for adding the shutoff and coast-down mode will remain unavailable for the near and distant future, but providing a manual means for the skilled drivers would still be worth the effort. Yes, I am asserting that a large number of drivers lack the capability of anything more than driving a car down the road using other than an automatic transmission.

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Re: go back to the pre-OEM past and then to the future
jemeils   1/24/2012 10:12:32 AM
I agree with the idea of reducing the number of stops one has to make in any given driving situation.  Where I live the stop lights are designed to stop traffic for non-existant traffic.  And I don't mean 1 or 2 cars. I mean NO cars!  In England most intersections are round-abouts where noone stops and everyone gets where they are going. They also don't have the EPA emissions requirements we have and are already getting 50-60mpg(American) with both diesel and gas engines (most have manual transmissions). Take a car that gets better than 45 mpg and reduce the emissions requirements (slightly) due to the extreme efficiency of the vehicle. In environmental impact terms, an extremely efficient vehicle will put out less pollution than a regulated gas-guzzler.

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Cars of the 19-teens
John   1/24/2012 10:01:05 AM
Some automobiles in the 19-teens did it.  Wouldn't think it's impossible, but they didn't have many electric lights, A/C, power steering, may or may not have starter, water pump, alternator, or even an oil pump, wooden frame, minnimal glass and top speed is probably 45 mph.  Which that should be more than adequate for any in town driving.  Probably average 35mph in town anyhow when considering time at a stop.  I guess your new car won't be getting a tri-coat paint job any time soon though.  Too heavy.  Forget slicker paint job.  Too much time sanding. 

I seriously doubt we will be going back to the above, but be interesting to see how it's pulled off.  Honestly, I always thought it would be diesel, like the rest of the world.  There's way too much sitting in traffic for gasoline.  With that said, anyone doing anything to improve efficiency of the roadways other than add another lane to it.

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54 mpg
wade   1/24/2012 9:53:05 AM
diesel needs to be part of the solution.  i'm not sure why we haven't embraced this technology in the US pass car market, but we are behind the rest of the world.  could have something to do with the current N/A refining capacity for diesel and the periodic gap between the gasoline and diesel pricing.

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Re: mpg in Europe,and only sold there!!!
Gusman   1/24/2012 9:41:08 AM
Oh really?  Last time I was there (June) fuel was sold by the liter.  In any case, my own calculations yielded 50+ MP(American) gallon every time with the various diesel cars I rented.

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