I've written a few posts on my search for a new car including evaluating options for an efficient clean, green car and comparing high mileage vehicles. Well, I finally made the decision and I went with the 2012 VW Jetta TDI.
My car is mainly a work vehicle, shuttling me and my energy efficiency equipment (mainly LED light fixtures, parking deck retrofit kits, light meter, watt meter, etc.) to appointments in the southeast, so I needed something that was dependable, gets great mileage, and could help me avoid the semi-trucks hurtling down the Atlanta interstates. It's tough to find the combination of zip and mileage, but with the Jetta turbo-diesel, I think I've found it.
On Friday I had an appointment about 50 miles from my house that included 1 mile of city driving, 45 miles of highway driving (65 mph) and about 5 miles of back road driving (50 mph). I got a combined 44 mpg there!
Way back in 2008, Popular Mechanics had a great article on Clean Diesel Advantages. The article opens up with:
I'm behind the wheel of a preproduction 2009 Volkswagen Jetta, which is powered by a 2.0-liter turbo-charged, direct-injected diesel engine that, even as I leave the speed limit in tatters, is averaging nearly 50 mpg. Equally important, what's coming out of the tailpipe is no dirtier than the emissions from the 35-mpg econoboxes I can now see in my rearview mirror.
The article also mentions why diesel has cleaned up its act, by getting help from low sulfur fuel:
However, in response to EPA mandates that went into effect in late 2006, oil refineries are now producing what's called ultra-low-sulfur diesel (ULSD). By definition, this "clean diesel" has sulfur concentrations of no more than 15 parts per million (ppm). That's 98.5 percent cleaner than the sludge that coursed through the fuel delivery systems in those disco-era rides, and 97 percent less sulfur than was allowed under a 500-ppm standÂard instituted in 1993.
And explaining why it gets so much better gas mileage compared to gasoline powered cars:
Meanwhile, diesel's core virtues remain unchanged. The fuel contains more energy per unit volume than gasoline, and diesel engines operate at higher compression ratios than gasoline engines--typically 14:1 to 25:1, compared to 8:1 to 12:1. (The compression ratio is the relationship between the volume of the cylinder when the piston is at the bottom of its stroke and the volume when it's at the top.) The higher the compression ratio, the more mechanical energy an engine can squeeze from its fuel/air mixture. So each time the mixture in a diesel engine's cylinder ignites, the car gets a slightly bigger push than it would in a gasoline engine. That means it takes less fuel to move the car down the road. It also means that the engine generates a lot of power even when it isn't cycling fast--and that's the source of the beefy low-end torque these vehicles are famous for.
The high compression ratios also explain why diesel engines tend to last so long. "Diesel engines need to be built stronger," explains Tony Molla, author of Chilton's Diesel Engine Service Manual. "The crankshaft and connecting rods are quite a bit heavier than those in gasoline engines." And because diesel has a low coefficient of friction, it also happens to be a good lubricant that provides protection to the cylinder walls. The result? It's not unusual to see diesel engines still chugging along at 250,000 miles.
That great performance at high mileage means that my resale value will be higher with a diesel than with a gasoline powered car. I just wasn't so sure that a gasoline hybrid would still perform well at high mileage. Hopefully I can use biodiesel in the car one day when someone comes out with a conversion kit for the 2011/12 TDI engine.
My next car will still probably be a plug-in hybrid, but a high mileage clean diesel is a great gap car!
Green Tech Media has a great article on the Diesel Engine Renaissance.