Careful now... per gallon or per mile driven?
i dont think there is much argument against (in general) diesels get better mileage.
diesel itself produces higher BTU that gasoline. thus for a given vehicle will use less fuel to move.
I think much of the disconnect with diesels is the confusion about emissions and "global warming." Diesel has a higher carbon dioxide output per mile than gasoline. (22lbs per gallon vs 19.5 roughly) That argument doesnt hold up to me, as i see i dont burn gallons per commute, rather i drive miles per commute. If i was to drive a 60 mile commute in my diesel i would produce something shy of 30 lbs of carbon dioxide, whereas in a comparable(performance and option/size etc)gasser i would probably produce closer to 40lbs.
however the two thought trains are generally not combine. Hyper-milers almost never break there mileage down by carbon units/mile, while the "save the earth" community frequently point to the fact that a gallon of diesel produces a larger carbon footprint as compared to a gallon of gasoline.
but to digress back to the main topic, porsche's demographic is likely not concerned with emission, mileage, or their personal carbon footprint. and a 1.9 liter diesel engine will never produce the same kind of power that a 1.9 liter gasser will, and thus it is not suitable for most sports cars in the eyes of the vast majority.
Ben dur's post makes real sense, and it deserves reiteration to emphasize the importance of the distinction:
The amount of Carbon dioxide emitted per volume of fuel (diesel versus gasoline) is different. One correct way to state the difference:
The complete combustion of gasoline (no Carbon Monoxide-
complete oxidation to CO2 and water) results in 12.6% less carbon dioxide production. Here are data from
one source-
CO2 emissions from a gallon of gasoline = 2,421 grams x 0.99 x (44/12) = 8,788 grams = 8.8 kg/gallon = 19.4 pounds/gallon
CO2 emissions from a gallon of diesel = 2,778 grams x 0.99 x (44/12) = 10,084 grams = 10.1 kg/gallon = 22.2 pounds/gallon
So, 19.9 is 12.6% less than 22.2 (that much is a simple fact). Can you hear the spin? ... "diesel engines produce more greenhouse gas than gasoline engines"
But, there are two additional things to consider.
1. The first and simplest is that Diesel engines generally produce greater than 12.6% more DISTANCE or miles per gallon (liters/km) than gasoline engines. In fact, if you believe some of the claims around here.. OK, we won't go there
But apples to apples comparisons (cars with similar displacement) reveal that diesel cars get anywhere from 20 to 25% farther per gallon (point made by Ben dur, and others). You can start arguing about torque versus horse power now if you want to, but...
The point is that the actual amount of CO2 emissions is at worse, on parity, but more likely to be lower in real world cause and effect... "driving from here to there" Diesel vehicles contribute less carbon dioxide to the atmosphere than gasoline vehicles.
2. The second thing to consider, which is less important than the first additional consideration, is the question of how efficient (or complete) is the combustion in the engine? That is, how much additional combustion is completed by the catalyst (which is essentially there to take CO to CO2). The answer to this is how diesel engines are inherently more efficient than gasoline engines, and isn't important to the about facts.
But Porsche buyers are not Volkswagen buyers. Porsche is now bona fide boutique, and Money is often seeking prestige AND raw power. Faster gasoline engines beat not faster Turbo diesel in a straight line. But diesel has advantages mid corner due to tractable stable torque that does NOT spin out. I pass V8s handily everyday, with high confidence, in my li'l Volkswagen.