It has little or nothing to do with emission law. American emission law is actually quite similar to European and Japanese law, and they converge a little closer with each revision.
DieselNet: Diesel Exhaust Emission Standards
From the manufacturer's perspective, it's more about simply reducing the number of engine options than it is about the type of engine. Have you noticed how many cars now have only one powertrain option available? This was unheard of a generation ago, when you could almost always select at least stick or automatic, and six, small-block v8 or big-block v8.
CAFE law biases the market much more than emission law. CAFE provides mileage credits for hybrid powertrains, extended-range electric vehicles and straight battery electric vehicles (in practice, achieving little more than a corporate welfare system for powertrain engineers) and vehicles which burn ethanol, (achieving little more than disbursing corporate welfare money to Archer Daniels Midland) but not for Diesel engines.
There are a few passenger cars available in the US with Diesel engines. Marketing people watch sales numbers closely. If Diesel-engined cars ever take off in the marketplace, you can be sure the Big 3 will begin offering them. But right now, they haven't, and I'm pretty sure it's not due to bad memories of the Oldsmobile Diesel.
Fuel Economy
Audi A3
Volkswagen Golf
Volkswagen Jetta
Volkswagen Jetta SportWagen
BMW 335d
BMW X5 xDrive35d
Mercedes-Benz ML350 Bluetec
Volkswagen Touareg
Mercedes-Benz R350 Bluetec
Audi Q7
Mercedes-Benz GL350 Bluetec
The bottom line is the bottom line. For most people, there's just no compelling reason to buy a Diesel engine. The pump price of fuel isn't high enough and most people don't drive enough to break even on the cost of a Diesel engine. Gasoline engines now routinely go 80,000 miles without a tune-up, 250,000 miles without engine work and most new-car buyers trade the car in before the odometer hits 100,000.
You can't even buy the ego gratification of clatter & smoke - new passenger-car Diesel engines don't clatter or smoke.
If you're a road warrior bent on the best possible fuel economy, you're going to go with a Prius. A Prius consumes 40% fewer gallons (50% fewer kilograms) of fuel than a Jetta tDi and the price of gasoline and Diesel fuel is now about the same.
Finally, there's little to be gained by promoting 60 mi/gal cars. Mi/gal gains are much more effective at the low end.
Quote:
We have done ourselves a distinct disadvantage by adopting "miles per gallon" as the standard measure of fuel economy instead of measuring fuel consumption - "gallons per mile", or as is common in the rest of the world, liters per 100 kilometers.
The net result is a distorted view of how fuel is really consumed and what's really the important element of policy aimed at reducing fuel consumption, petroleum imports and/or emissions.
In a grossly simplified example, consider a "fleet" consisting of one 10 mi/gal vehicle and one 50 mi/gal vehicle. What's the combined result?
Most Americans, particularly those educated before the New Math or in parochial schools, would say the combined fleet average fuel economy is 30 mi/gal - the linear (arithmetic) average of 10 and 50.
The actual average is 16.7 mi/gal.
Consider a year in which each vehicle is driven 10,000 miles. The 10-mi/gal vehicle consumes 1000 gallons; the 50-mi/gal vehicle consumes 200 gallons. At the end of the year, we have provided 20,000 miles of transportation utility and consumed 1200 gallons doing so. Divide 20,000 miles by 1200 gallons. The result is a 16.7 mi/gal fleet average.
If that's not intuitively obvious, calculate it again until it is.
By adopting miles per gallon instead of gallons per mile, we've made it into a non-linear problem. But if you want real results, you're not allowed to miscomprehend the problem just because it's hard.
Why do I bring this up?
We seem to be hung up on the nearly-mythical 50-plus mi/gal vehicle, when from a national policy perspective, there's a lot more to be gained by mandating seemingly modest gains from the bottom end of the fleet.
A 1 mi/gal bump in the fuel economy performance of the mid-size SUV fleet (Ford Explorer, Chevrolet Trailblazer, Dodge Durango) alone would reduce fuel consumption and emissions far more than each of the Big 3 automakers building a 50 mi/gal vehicle. Again, repeat the math if this isn't intuitively obvious.
Mandating fleet average fuel economy performance is (part of) the right way to go.
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