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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 2:34 pm) And the Prius is technically rated as AT-PZEV, which is a slightly different classification than regular PZEV. This is a certification given to just a handful of vehicles and stands for Advanced Technology Partial Zero Emissions Vehicle. What all that means is that the car gives off 70 percent less smog-forming emissions than the average car. This also means that there are almost no fuel leaks or fuel vapors escaping from the fuel system. The AT-PZEV certification requires the SULEV exhaust standard linked with the ability to meet a zero-fuel-evaporative standard, a 150,000-mile durability demonstration, extended emissions system warranty, and technology deemed by the California Air Resources Board (CARB) to advance future fuel cell vehicles. There are no gasoline engine cars which have achieved an AT-PZEV rating. The EPA test system is not setup for electric cars. They do not use diesel or gasoline by the gallon, so cannot be assigned a "miles per gallon" figure. The could be assigned a "cost per mile" which could then be correlated to gasoline equivalents. |
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Replying to: larsb (Sep 26, 2008 2:45 pm) i think you are making conclusions based on the way you think things work.
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Replying to: larsb (Sep 26, 2008 2:45 pm) That is because the mnemonic was derived for the hybrids. Just so we are clear here. A PZEV rated car getting 40 MPG actual will be just as clean in every way as an AT-PZEV rated hybrid getting 40 MPG actual. Don't be confused by the erroneous EPA ratings game.  CO2 emission is directly related to the amount of fuel used. Not some number on a window sticker.
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Replying to: gagrice (Sep 26, 2008 3:18 pm) This is true. However, the CAFE standards were not created in order to limit CO2 emissions. CO2 is not regulated by the EPA as a pollutant at all. The emission standards of cars are for pollutants such as NOx, hydrocarbons and CO. http://www.fueleconomy.gov/feg/airpoll.shtml While greater fuel efficiency would likely be related to lower emissions of HC and CO as those are products of incomplete combustion, this is not the case for NOx. In fact for NOx, it tends to be the opposite, optimising for low NOx would tend to make a less efficient engine. The EPA standards currently are met by equipping cars, no matter how fuel efficient they are, with catalytic converters not by designing an engine capable of meeting the standards without add on controls. While there may be some connections, CAFE standards were not created for purposes of controlling NOx, HC, or CO. There are explicit standards, expressed in grams per mile, that must be met for these pollutants.
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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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