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Automotive News & Views MPG Ratings Will Drop Under EPA Proposal
375 messages, Last post on Oct 02, 2008 at 9:08 PM
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See this Edmunds.com article! EPA Overhauls Fuel Economy Estimates for 2008 - As the 2008 model-year cars hit the lot, shoppers will notice a big difference — the EPA has changed its fuel economy testing methods to produce mileage estimates that reflect "real world" driving habits. - (more)
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Replying to: explorerx4 (Sep 26, 2008 2:55 pm) Actually, no. Having a battery has nothing to do with it. AT PZEV: Advanced Technology PZEVs AT PZEVs meet the PZEV requirements and have additional "ZEV-like" characteristics. A dedicated compressed natural gas vehicle, or a hybrid vehicle with engine emissions that meet the PZEV standards would be an AT PZEV. And: AT PZEV—Advanced Technology PZEV Compressed natural-gas or hybrid vehicles that meet SULEV standards for tailpipe emissions, have a 15-year/150,000-mile warranty, zero evaporative emissions, as well as include advanced technology components. There are no gasoline-only cars which are AT-PZEV. This is as clean as you can get without being ZEV.
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Replying to: jeffyscott (Sep 27, 2008 4:45 am) Light-duty vehicles and light-duty trucks must calculate and report the weighted mass of each relevant pollutant, i.e., THC, CO, THCE, NMHC, NMHCE, CH4, NOX, and CO2in grams per vehicle mile. Title 40: Code of Federal Regulations (the regulations governing the EPA measurements of automotive exhaust emissions) Part of what makes all this so confusing and maddening is that the EPA really does not measure miles per gallon, at least not in the way that we might commonly think about measuring MPG. They measure emissions. They measure the byproducts of combustion. This is in keeping with the EPA's charge to protect the environment. The data reflects how efficiently a fuel has been burned, and does not reflect how far a car traveled while burning that fuel. They take that data and calculate estimated MPG. It is a convoluted and complex process that ultimately estimates MPG rather than measuring MPG. We have known since the beginning that the calculation produced a high result, and even under the new test it still does. So, those results of that calculation is further massaged to get to the numbers you and I see on those window stickers. Some may claim that this process is erroneous, but it is a highly controlled process intended to get at least somewhat consistent results. Despite the controls, the assumptions, stipulations, simulations, predictions, and other factors are susceptible to outside political influence. We have been arguing about all that since the beginning. You and me and most of the automotive press usually employ a much simpler method. Fill up the car, drive for a while, fill up again. Divide the number of miles driven by the amount of fuel consumed. Voila. Not nearly as controlled, ends up with a wide variety of results, but a whole lot simpler.
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Replying to: mattandi (Sep 29, 2008 8:10 am) The EPA determines fuel used based on measuring the carbon in the exhaust, which is then used to calculate the amount of fuel burned during the test. I don't see any problem with that, the carbon in the exhaust will be equal to the carbon in the fuel and from that the gallons of fuel used can be calculated. I would guess that they do this because it is more precise than trying to measure the volume of fuel used in a 10 mile highway run (for example). They drive the cars on a dynamometer so that all cars are tested under controlled conditions. Not sure what else they could do, if consistent test conditions are desired. http://www.fueleconomy.gov/feg/how_tested.shtml
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Replying to: jeffyscott (Sep 29, 2008 9:16 am) The fueleconomy.gov site distills the process down to something that is more easily digested by someone without a chemical engineering degree. One look at the Code of Federal Regulations reveals it is much more complicated than simply dividing the number of miles by the amount of fuel consumed. Lots of weighting of the various factors at play takes place. This doesn't work so well in a brochure: (h)(1) For gasoline-fueled automobiles tested on test fuel specified in §86.113–04(a), the fuel economy in miles per gallon is to be calculated using the following equation: mpg = (5174 × 104 × C × CWF × SG)/[((CWF × HC) + (0.429 × CO) + (0.273 × CO2)) × ((0.6 × SG × NHV) + 5471)] Where: HC = Grams/mile HC as obtained in paragraph (g) of this section. CO = Grams/mile CO as obtained in paragraph (g) of this section. CO2= Grams/mile CO2as obtained in paragraph (g) of this section. CWF = Carbon weight fraction of test fuel as obtained in paragraph (g) of this section. NHV = Net heating value by mass of test fuel as obtained in paragraph (g) of this section. SG = Specific gravity of test fuel as obtained in paragraph (g) of this section. In essence it is weight per mile that is then converted to distance per gallon. Hey, it produces the result it produces. It is consistently high. It gets adjusted. We live with it.
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Replying to: larsb (Sep 29, 2008 4:27 am) the only cng vehicle for sale i know of is the civc gx. go down to the local dealer and try to buy one. |
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Replying to: mattandi (Sep 29, 2008 10:26 am) Not really, it's complicated because they calculate fuel used based on carbon in the emissions. A complicated formula does not mean that the the concept has to be complicated. The concept for determining fuel use is a mass balance on carbon. The carbon in the exhaust comes from the carbon in the fuel and the fuel contains a certain percentage carbon, from all this you can determine the amount of fuel that was used. In essence it is weight per mile that is then converted to distance per gallon. Not sure why you think that is a problem. Once the weight of fuel per mile is determined, you would just take the inverse and multiply by the density of the fuel.
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Replying to: jeffyscott (Oct 01, 2008 6:12 pm) Not sure why you think that is a problem. Well, it's just a conflict that occurs when the test protocols, procedures, and estimates run into reality. The tests and resulting estimates are intended to provide consumers with a means to compare different cars. That is all well and good until the consumer actually buys a car. Then those tests and estimates are transformed in the new owner's mind into a prediction of the MPG they will actually get with their new car. Not at all what the government intends. When there is a difference, and there almost invariably is a difference, the owner concludes that the EPA test sucks and the EPA testers are idiots. Now the test doesn't suck and the testers are not idiots. Just a misunderstanding, or mistaken assumption, of what the test actually tells us. There is only passing resemblance between the test and reality. You and I don't drive on a dynamometer. We drive on streets. We don't control and repeatedly test the fuel we put in our cars. We buy what the local station has available. We don't give weight to the various components that make up the fuel and figure that into our actual MPG. We choose regular or premium and maybe try to avoid ethanol. We don't have precision instruments connected to our cars picking up minute bits of info as we drive them around. We have a fuel gauge and an odometer. We don't follow a carefully controlled set of protocols and driving sequences. We sit in traffic jams while we take the kids to dance class. We don't measure emission from our exhaust and extrapolate the data to a class of cars for comparison. We fill up our tank and wonder what the price will be the next time we need to fill up. Carefully controlled tests and consistent results and calculated estimates run into the chaotic and uncontrolled reality of fickle, irrational, unpredictable, and emotional drivers. Not sure I would characterize it as a problem really. It is what it is. There just is no way that test can possibly tell us what so many of us want that test to tell us. |
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Well it got porked up. Every Senator with a pet amendment figured this is a must do bill, so why not tack on a tax break or two. I am sure we all agree that a tax break to rum producers in Puerto Rico will solve the credit crisis. Anyway, amongst the fat is an interesting tidbit, Transportation and Domestic Fuel Security Provisions. Included a tax credit for plug-in electric drive vehicles, like the Chevy Volt. Minimum $2500 plus $417 for each kWh battery capacity above 4 kWh. Limits set by weight. Most passenger vehicles will probably get the $7500 limit on vehicles with a GVWR of 10,000 pounds. Limit is higher for larger vehicles. |
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