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Fuzzy Math
“Green” Europe Fudging Car Emissions Numbers

Europeans sip gasoline while Americans guzzle it, or at least that’s how the story goes. But as the Economist reports, once you look under the hood, Europe’s fuel efficiency emissions standards are a little suspect:

Europe’s procedure is out of date and open to abuse. Carmakers send prototypes for testing. They are engineered to be as frugal as possible. Weighty extras such as the sound system and even wing mirrors are routinely jettisoned. Special lubricants make the engines run more smoothly. Tape on the cracks around panels and doors reduces drag. Low-resistance tyres filled with special gas add to the miles covered.

The cars are driven to a preset routine of gentle accelerations and low speeds, run at the highest permitted temperature of 29ºC (engines are more efficient in the heat). Modern electronics can even detect the pattern of the start of the test and switch into a special “economy mode” that makes for even lower emissions.

Contrast that with the U.S., which, under President Obama, has enacted some very strong fuel efficiency standards that are putting a sizable dent in our nation’s carbon footprint, even without the kinds of test fudging seen across the Atlantic. Europe likes to think itself a paragon of green policies, but with electricity costs spiraling and coal consumption rising, it looks like it’s having to resort to some fuzzy math to defend its eco-friendly status.

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  • dankingbooks

    Hmmm. I don’t believe that engines are more efficient in the heat. Thermodynamics says that the maximum efficiency of an engine is given by (Th – Tc)/Tc, where Th is the temperature of the hottest part of the engine cycle, and Tc is the coldest part. The temperatures have to be given in absolute values, i.e., in Kelvin or Rankine. The difference between hot and cold determines the energy you get from your engine. By that reasoning, you want the hot to be as hot as possible, and the cold to be as cold as possible. The cold temperature of your car engine is approximately the temp of the muffler. That will be colder on a cold day than a hot one.

    So by all accounts you should get better gas mileage on a cold winter day, assuming your engine is warmed up.

    Tell me where I’m wrong. I’m a chemist, not an engineer.

    • Andrew Allison

      The catalytic converter is heated by the exhaust gases and gets hot enough to, e.g., ignite dry grass. The increased heat loss due to Newton’s Law of Cooling on a cold day versus a warm one is probably negligible, and in any case wouldn’t affect the temperature of the engine exhaust. Just the thoughts of a non-chemist and -mechanical engineer.

      • dankingbooks

        Then what is the muffler for? It is a heat exchanger, and the reason you need a heat exchanger is to throw away heat to create a cold temperature heat sink. The catalytic converter is placed before the muffler, or so I believe.

        • dankingbooks

          Also, the catalytic converter is a net drain on engine efficiency, not a benefit.

          • Andrew Allison

            True, but what does that have to do with Tc?

        • Andrew Allison

          Let me once again emphasize that it’s been 50-plus years since I was taught anything about thermodynamics, and I know nothing about internal combustion engines. That said, the purpose of the muffler is, surprise [/grin], to muffle the sound of the exhaust, not to exchange heat (that’s why people who want their vehicles to “rumble” stick broomsticks through the muffler). Thermodynamically, it appears to me that the engine doesn’t detect anything beyond it’s exhaust temperature, which is essentially independent of ambient temperature.

          • dankingbooks

            Can’t be true. An engine that worked that way would have no power. The muffler plays an important role. People who use broomsticks forfeit significant gas mileage.

          • Andrew Allison

            Your argument was, “Thermodynamics says that the maximum efficiency of an engine is given by
            (Th – Tc)/Tc, where Th is the temperature of the hottest part of the
            engine cycle, and Tc is the coldest part.” What, pray tell, do the catalytic converter or muffler have to do with the temperature of the engine cycle? Furthermore, for modern engines, the factory muffler reduces mileage (

          • dankingbooks

            The original steam engine used steam as the working fluid. It was heated and cooled in the same container, which means Th and Tc both happened within the working cylinder.

            The genius of the internal combustion engine was 1) to use air as the working fluid, and 2) instead of putting the entire cycle in the cylinder, instead the working fluid is moved from one place to another. Thus the hot part of the cycle takes place in the cylinder, but then the working fluid is expelled and rapidly cooled in the muffler (or, in your version, instantaneously and miraculously just outside the cylinder).

            Somewhere in any engine there has to be a cold sink. Otherwise the engine can’t function. That’s why power plants are almost always placed by rivers. Or they need big, ultra-efficient cooling towers, analogous to a car’s muffler.

            For a good description of the old-fashioned steam engine, look up the Newcomen engine on Wikipedia. For a very readable and accessible account of the history and workings of engines, read John Sandfort’s excellent book, Heat Engines. For a somewhat tendentious riff on the whole story, read my post, here:

    • MartyH

      My guess is that the reason to run the test in the higher temperature is aerodynamic drag, not engine efficiency. Air density at 29 degrees C is ~95% that of air at 15 degrees C (Assuming same pressure and dew point). Air density is linearly related to the drag force, so I’m guessing the the air temp could affect results by a MPG or more, depending on the amount of other energy losses-rolling resistance, engine heat, engine friction, etc.

      • dankingbooks

        I think this is probably the correct answer.

    • SDN

      Remember that both engine and transmission are lubricated by fluids that drop in viscosity as the temperature increases. Lower viscosity = easier for a given amount of fuel to push down the piston, thus increasing fuel economy. That’s also why you change oil with a warm engine: the lower viscosity means more of the old oil drains out.

      Also, both gasoline and diesel vaporize more completely at higher temps, improving combustion and again fuel economy.

      • dankingbooks

        No, I don’t buy this. Engine oil viscosity depends on the engine temperature, i.e., Th. That is much higher than the outside temp once the engine is warmed up. Likewise, fuel vaporizes in the cylinder, which is at a very high temperature. So this can’t be a factor.

        Transmission fluid viscosity might be a factor.

  • Fat_Man

    So what? The EPA’s numbers for CAFE purposes are fudged.

    “Of course, CAFE is measured more generously than the numbers on the window sticker—a Honda Accord with a 31-mpg-combined label is rated at 40.8 mpg for CAFE—but that has long been the case.”

  • FriendlyGoat

    Glad to know TAI approves of Obama on this. That’s the gist of the last paragraph, isn’t it?

  • Corlyss

    “But as the Economist reports, once you look under the hood, Europe’s fuel efficiency emissions standards are a little suspect:”

    The Europeans lie about a lot of stats. Their crime stats have been bogus for so long they wouldn’t know how to report the facts. Only very very rarely is it reported by any publication, much less a flagship publication like Economist. I’m perfectly happy for the EU to screw themselves over with tough and useless emissions standards in pursuit of a junkscience goal. I am not sanguine about the chances that the incoming administration in 2017 will be able to undo the damage done to the US economy by Doofus and the jackbooted shakedown artists in EPA in pursuit of the same goal.

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