Simple Way to Reduce Foreign Oil Use, But Not Mentioned ...

<div class='quotetop'>QUOTE(JackDodge @ Jul 2 2006, 08:02 PM) [snapback]280294[/snapback]</div>

Hey,

Who said I was driving on a road???????

I race at the track and have not had a speeding ticket since 1990 and I do not own a fuzzbuster, do not have a speedometer, and my wife always complains that I drive too slow.

In regards to gas guzzlers, most cars will achieve that status when compared with a Prius. I'm pretty happy to get 28mpg with a 383 stroker and Moser 12 bolt rear with a 700R4 transmission.

The gas guzzlers are where we can make the most immediate improvement in fuel economy while cleaning up the air. If every old gas guzzler had new plug wires, new coil, headers, and cold air intake, plus a computer tune we could improve fuel economy by 10% across the entire existing fleet of gas guzzling cars, and if we actually took the time to teach out average drivers how to drive we could make it 20%. Now that would make a very significant different in our reliance upon foreign oil, and with fuel being burned more completely we would be producing less greenhouse gasses.

When Montana was forced to establish speed limits back in the 1970's, the accident rate went up. The Autobahn has a better safety record than any US highway.

If we look out of the box at the big picture which is reducing emissions, increasing mile per gallon performance, and preparing for our species to survive the inevitable warming due to whatever factors, in my opinion we do not have time to "push an agenda" of legislation that will delay our efforts.

Just my two cents.

 

<div class='quotetop'>QUOTE(Iria @ Jul 1 2006, 06:59 PM) [snapback]279815[/snapback]</div>

... in a world where time has no value.

Time has real value in my world. If a driver now drives 10,000 highway miles a year at 70 mph, this costs 143 hours a year of the driver's (and any passengers') time. If that driver slows down to 55 mph, this travel time cost rises to 182 hours. The difference is 39 hours, or nearly a week of full time paid work. How much money could you make in the additional time you'd spend driving? I'd say the cost of slowing down to 55 mph is closer to a week's paycheck than it is to a dime.

What other things could you do for the environment with this time? How many trees could you plant? How much time and/or money could you contribute to your favorite charity? Whan energy saving improvements could you make to your house? How much could you replace short drives with biking? How many children could you teach about conservation? How many miles of driving (together with fuel consumption, emissions, and traffic congestion) could you eliminate by spending the extra time required to carpool or use public transit?

 

typo

 

<div class='quotetop'>QUOTE(tnthub @ Jul 3 2006, 08:31 AM) [snapback]280509[/snapback]</div>

For the Autobahn and many other foreign roads speed is not a factor in most accidents because they all follow "rules". If you are going slower, get over to the right. Don't use your car as a weapon or to make a statement about how you feel about other drivers. Less distractions and more attention on the task of driving.

You can ask for a lower speed limit but without enforcement it is meaningless. I agree that time is definitely of greater value as well. We need to work on infrastructure of roadways, alternative fuel availability, and ongoing research and development of fuel efficient/alternative fuel vehicles.

 

<div class='quotetop'>QUOTE(darelldd @ Jul 2 2006, 11:46 PM) [snapback]280374[/snapback]</div>

Well I'm not an expert, so perhaps you're right, but it seems something is being left out. Air resistance is only one factor. Other relevant factors are weight of the vehicle, shape, gearing, etc. What is the terminal velocity of an average car (ie: the point at which air resistance would not allow it to go any faster). Of course this varies by shape, but it seems it might be 1000-3000 mph. As a result, how relevant is air resistance at 80 mph, when taking into account other factors. As I said, if the engine runs for a shorter period of time without much extra effort (because the car was designed well), it seems it could get better mileage at 80 than at 55 mph. If the shorter running time more than offsets the increased engine effort, the car gets better mileage at the faster speed.

For example, following your logic, a car would get better mileage driving for 50 hours at 2 mph than if it drove at 50 mph for 2 hours. I don't think that's correct, especially if hills are involved. Why is 55 the magic number? It's not. If air resistance it not highly relevant relative to other factors, as is wouldn't be with a well designed car, then the car could very well get better mileage at speeds higher than 55 mph.

 

For me, the theoretical possibility the fuel efficiency rises at speeds over 55 mph basically boils down to if engine efficiency at heavier engine loads at higher speeds can rise faster than air resistance which rises with the cube of speed. Perhaps in a Ferrari or other aerodynamic overpowered supercar? As much as theoretical discussion appeals to a theorist like myself, this really seems to be an empirical question.

Here is a graph comparing the fuel efficiency of 8 fuel efficient German market cars at speeds from 50 mph up to 155 mph or their own top speed.
http://bioage.typepad.com/.shared/image.ht...d/autobild1.png
Note that while there are no overpowered supercars, the fuel efficiency of all 8 falls with speeds over 50 mph.

Here is an english summary
http://www.greencarcongress.com/2006/05/fuel_consumptio.html
of the german auto-magzine article
http://www.autobild.de/test/neuwagen/artik...rtikel_id=11378

To see what PriusChatters have already said about this article, look here:
http://priuschat.com/index.php?showtopic=19900&hl=german

 

<div class='quotetop'>QUOTE(theorist @ Jul 4 2006, 09:59 AM) [snapback]280962[/snapback]</div>

As shown in the formula below, air resistance increases at the square of the speed, not the cube.

Air resistance = A/2 × Cd × D × V^2

with

A being the frontal area of the car in m2,
Cd being the drag coefficient,
D being the density of air (1.29 kg/m3) and
V being the velocity in m/sec.

Perhaps I'm totally off base on this, but it seems that if you worked with the factors above (ie: minimize frontal area and drag coefficient), you could lower air resistance enough, so that the additional power needed to move the car faster would be more than offset by the shorter running time.

The study you provided seems to indicate otherwise. But I wonder if our national speed limit was 80mph, would we find ways to design cars that get optimal mileage at that speed.

Also, the study you note seems incorrect. It says the Prius gets 36 mpg at 60mph and 30 mpg at 80 mph. I drive between Boston and NY frequently. I'm usually in the left lane driving with traffic, which is often moving at 70 to as high as 90 mph. I've never gotten less than 40 mpg on this trip, even in the winter when the fuel composition gives lower mileage than in the summer. In the summer, I regularly get 45 mpg or higher.

 

It seems to me that you'd have to intentionally make the car less efficient at 55 mph for it to be more efficient at 80 mph. It takes more energy to push the air out of the way at 80 mph so unless you designed the car badly I don't see how it could be more efficient in that environment.

 

<div class='quotetop'>QUOTE(tripp @ Jul 4 2006, 06:22 PM) [snapback]281131[/snapback]</div>

I think the issue has to do with when air resistance becomes relevant. For example, since air resistance is lower at 2 mph than at 50 mph, would you get better mileaage driving at 2 mph? I doubt it.

At the extreme, if the car was shaped like a narrow needle with a tapered rear (ie: very low air resistance), the extra power needed to drive the car at 80mph instead of 55mph, might be low, because incremental air resistance would be low. If the motor was running for a shorter period of time at only a small amout of extra effort, isn't it possible that the car gets better mileage at the higher speed.

Air resistance is not the only relevant factor. It seems more than that needs to be taken into account.

I'm not an engineer, so maybe I'm not getting it. This is all theoretical anyway. One thing for sure though, the speed at which cars get the best mpg varies car to car. It can't be the same for all cars. And it's can't be 55 mph for all cars.

 

I know from experience at the dragstrip that aerodynamics really do not matter much until speeds go over a hundred miles per hour in any way that can be quantified by hundredths of seconds.

 

<div class='quotetop'>QUOTE(tnthub @ Jul 4 2006, 09:04 PM) [snapback]281175[/snapback]</div>

Hi tnthub,

I cannot dispute that - expecially since the drag race time is what under 15 seconds? But when a vehicle is operating at speed for an 1/2 hour a day, aerodynamic improvements even at much lower speeds make a difference in a yearly gas consumption.

A Prius is at .6058 CdA (m^2) with a car with a .36 Cd (2001 Honda Civic) of the same frontal area is going to have a CdA .8389. That means that .8389/.6058 = 1.38 times the energy is needed at speeds above which rolling resistance is small. Or about 70 mph. This is the difference between 45 mpg in the Prius and 32.6 mpg in the hypothetical car, assuming that the the engine efficiency is the same at the two power level.

In a 12,607 mile year at 70 mph this saves 106.5 gallons, or $330. ($3.10 a gallon here this weekend).

 

<div class='quotetop'>QUOTE(tnthub @ Jul 4 2006, 05:04 PM) [snapback]281175[/snapback]</div>

At a steady-state speed, it takes almost twice the power to move a car like the Rav4EV at 70mph as it does at 45mph. Add it up over the time of your trip, and it is pretty clear that faster = more energy required.

While air resistance does increase as the square of speed, the energy required to overcome the air resistances increases with the cube of speed. Air resistance is a huge deal at our regular (under 100mph) freeway speeds.

<div class='quotetop'>QUOTE(nyprius @ Jul 4 2006, 03:58 PM) [snapback]281148[/snapback]</div>

The answer is yes - in an electric vehicle. An ICE is terribly inefficient at low speeds not because of air resistance but because an ICE is only relatively efficient in a very narrow operational band. At 2mph, I could drive my EV over 200 miles. At 55mph, I could drive it 100 miles. And this is purely because of air resistance.


<div class='quotetop'>QUOTE(tripp @ Jul 4 2006, 03:22 PM) [snapback]281131[/snapback]</div>

Yup.

 

<div class='quotetop'>QUOTE(Iria @ Jul 1 2006, 07:59 PM) [snapback]279815[/snapback]</div>

Hi Iria,

The main problem with slowing roads down, here at least, is capacity. The metropolitan highway systems are truely networks. You have so much traffic entering the network at any time of day and everything works in that the the traffic clears off the network quickly enough not to cause a jam. How many cars a road can handle is proportional to the car speed. 10 miles of road at 70 mph takes .143 hours. 10 miles at 55 mph takes .182 hours. So, in .182 hours 1 car makes it down the road while 1.3 cars can make it through at 70 mph. This is a complete guestimate, and things are more complicated. An aquantance of mine was privvy to a research engineering study done on a large Chicagoland expressway. They plotted throughput versus speed. They found that 62 mph was the optimum throughput speed for this road, which had lots of short on and off ramps. Above that speed accident rate reduced throughput and below that speed the concept above reduced throughput. This particular road is one of the highest density roads in the Chicagoland area and thus the money was available for the study. The road has a 55 mph speed limit, but people do not get pulled over doing up to 62 mph any more is my understanding. The issue is if the road jams, the engine efficiency difference from 55 mph to stop in go is so much worse than the car efficiency reduction between 55 mph and 70 mph, that as a community we use less gas keeping the flow going, rather than risk a jam with an enforced 55 mph limit.

If government could provide the extra resource to support the commute traffic at 55 mph, then your suggestion would work. But ....

Here in Chicagoland I can guess that things are about maxed out. So, to drop the average speed from say 55 mpg to 45 mpg (typical peak travel speeds of 75 to 55 respectively - pure guess) would require 55/45 times as much road. Or about 3 lanes for every 4 lane road (can do that with reversable lanes) or adding 4 lanes to every 6 lane expressway.

At a 1/2 a billion a mile for road construnction, this is probably not economically practical.

 

<div class='quotetop'>QUOTE(nyprius @ Jul 4 2006, 11:15 AM) [snapback]280982[/snapback]</div>

Thank you, nyprius. Yes, while the energy lost to aerodynamic drag increases proportionately with the cube of the velocity, the force rises with the square of the velocity according to the formula you quote. In other terms, the losses per unit of time rise with the square of the speed while the losses per unit distance rise with the square of the speed. I'm sorry for being sloppy earlier and not clarifying what I meant. Thank you for helping.

In hindsight talking about energy per mile, and so the square of speed being proportional to aerodynamic losses, is useful since this relates better to L / 100km or gallons per mile. Don't get me started on my feelings about the idiocy of mpg.

Is it just me or is this topic sounding more and more like a religious debate between people who came into it knowing their truth? Later.

 

<div class='quotetop'>QUOTE(darelldd @ Jul 4 2006, 06:50 PM) [snapback]281191[/snapback]</div>

Damn, you beat me to it.

 

I'm not arguing with the logic. However time slips are calculated to the thousandth on the regular printouts. We keep detail records of track temperature, tire pressures, engine and transmission temperatures, shift points, incremental times and mph figures, cloud cover or sun, humidity, temperature, density altitude, barometric pressure, to the point where we do our best to estimate performance to within .01 every time.

I do know that on a windy day it is more difficult to estimate a boxy vehicle like an old Nova or a truck than it is a Corvette or a dragster.

Ram air systems do not seem to have much impact either until over 100.

 

Well, driving slower doesn't seem to be very popular. I suppose the suggestion of driving *less* would be met with howls of derision?

 

<div class='quotetop'>QUOTE(hyo silver @ Jul 5 2006, 12:15 PM) [snapback]281444[/snapback]</div>

Driving less and more efficiently makes a whole lot of sense to me.

 

<div class='quotetop'>QUOTE(theorist @ Jul 4 2006, 09:26 PM) [snapback]281253[/snapback]</div>

My thoughts, exactly.