...When you consider that my 200 hp Passat gets better official consumption on the highway than the 115 hp 99 Jetta (6.8 vs 7.0), that's quite remarkable given the size and performance difference.
Mike - didn't really mean to rain on your, or anyone else’s, 2.0T parade. If you're happy with your Passat 2.0T, that's all that really matters.
My beef is with Ford’s assertion that “an EcoBoost engine comes close to matching the efficiency of a diesel”. I guess it depends on what is meant by “close” and what “diesel” is being considered (there are a few examples of this being true). However, it doesn’t appear to me that the assertion is true in general, and I’ve supported (and further supporting below) my reasons for doubting Ford’s assertion.
The examples of “downsized turbo GDI” vehicles compared to diesel vehicles of essentially the same performance in my earlier post was the ABSOLUTE difference based on CO2 emissions in the NEDC combined test cycle. If you incorporate the higher volumetric energy density of diesel fuel vs. gasoline, the “fuel mileage” is correspondingly higher.
The best “apples-to-apples” comparison that I’ve run across is the latest versions of BMW’s I6 diesel and turbo GDI gasoline engines. Both are 3.0 liters in static displacement and both are rated at 225 kW (see
http://www.greencarcongress.com/2009/06/bmw-tech-20090625.html#more ). The turbo GDI version features the latest in “twin-scroll” turbocharger technology.
According to specs directly from BMW (pages 28 and 34 respectively of the “BMW Technology Day 2009. EfficientDynamics.” publication), the 3.0 liter “TwinPower” turbo GDI has a minimum brake specific fuel consumption (BSFC) of 245 g/kWh. The latest version of the 3.0 liter diesel (i.e., incorporating the 2000 bar CR injection system and VGT on the “smaller” turbocharger) has a minimum BSFC of 197 g/kWh. 245 ÷ 197 = 1.244 or 24.4% greater efficiency.
According to Argonne National Laboratory, ULS gasoline (26 ppm sulfur) has a slightly higher energy content
per unit mass than ULS diesel (11 ppm sulfur) (41.18 BTU/gram vs. 40.39 BTU/gram). 1.244 X (41.18/40.39) = 1.268 or 26.8% greater efficiency for the diesel based on BSFC and assuming European gasoline and diesel fuel specs are equivalent to U.S. fuel. Again, this is absolute energy efficiency, and doesn’t take the higher volumetric (e.g., per gallon) energy density of diesel fuel into account.
Assuming ANL’s values of 129,488 BTU/gallon for ULS diesel fuel and 116,090 BTU/gallon for ULS gasoline, based on BSFC, a BMW vehicle with the 3.0 liter diesel should get about 41.4% better fuel mileage than the same vehicle with the turbo GDI engine. From what I’ve been able to gather, these newest engines are both used currently in three BMW vehicle lines in Europe (the 5 series, the 7 series, and the X5). According to official fuel consumption data (
http://www.vcacarfueldata.org.uk/search/index.asp ), the 535d gets 6.1 liters/100 km or 46.3 mpg (imperial) in the combined NEDC, the 535i gets 8.4 l/100 km or 33.6 mpg. 46.3 ÷ 33.6 = 1.378 or 37.8% better fuel mileage for the 535d. According to BMW, the 535d out-accelerates the 535i (0-100 km/hr), 5.7 seconds to 6.1 seconds. In the 7-series, the 740d has a combined 40.9 mpg vs. 28.5 for the 740i, a 43.5% advantage for the diesel. In this case however, the 740i has better performance statistics, 0-100 km/hr in 5.9 sec vs. 6.3 sec for the 740d. Lastly, in the X5, the X5 40d has a combined 37.7 mpg vs. a combined 28.0 for the X5 40i, a 34.7% advantage for the diesel. In this case, according to BMW, the X5 40d has a slight advantage in 0-100 km/hr performance (6.6 sec vs 6.8 sec). It appears, when taking performance differences into account, the relative efficiency advantage of the diesel correlates quite well with the official fuel consumption values from VCA. Also notice that the fuel consumption data include the diesel with DPF.
The specs on the Ecoboost are very similar to the specs on the BMW GDI gas engine. From info I’ve obtained from various tech documents from Ford, the Ecoboost has a compression ratio of 10.0:1, 12 psi max turbo boost, 200 bar max injection pressure, and fully variable valve timing. The BMW TwinPower GDI (BMW’s specs) has 10.2:1 compression ratio, 10.7 psi (0.7 bar) max turbo boost, 200 bar max fuel injection pressure, and fully variable valve timing (“VALVETRONIC”). There doesn’t appear to be any immediate reason to believe that Ford’s turbo GDI technology would be significantly more efficient than BMW’s turbo GDI technology.
As I’ve mentioned, I acknowledge that there are economic factors that are working against LD diesel vehicles here and, since my expertise isn’t mechanical engineering, maybe I’m missing something with respect to the “downsized turbo GDI vs. diesel” efficiency comparison. Any critical or clarifying comments welcomed.