I understand that next year, all diesel fuel sold in the US will have to be low sulfur to reduce emissions. Will this mean more diesels (ie for Midsized SUVs), or will upcoming tighter emissions rules still limit diesels to bigger trucks?

Lord_Grey_Boots: Yep, that is the way I see it. AQMD in Los Angeles Calif, has been making noises for cleaner diesel fuel for a number of years now because they can't mandate more stringent deisel air pollution rules because of the high sulfur content of the fuel. Now with the new fuel that will all change.

Yes, we will get the better engines in lighter vehicles.  The problem with sulfur is the after treatment of exhaust gas.  With sulfur, running this through the oxidative catalyst makes sulfuric acid which will rapidly wash the catalyst metals from the ceramic.

Diesels already make the emissions requirements for all but NOx and particulate emissions.  Oxidation catalysts are needed for the latter while reduction catalysts are needed for the NOx.  And that sulfuric acid plays havoc with the reducing catalyst.

Imagine a 1/2 ton truck with a 3.5 liter diesel getting 30 MPG.  Not impossible.  How about a full sized passenger car getting 40 MPG?  These vehicles are every bit as quick as comparable gasoline-fueled engines but offer much better drivability since the torque comes on fast.  As such, small diesel engines feel like much bigger engines than they are.

Now if we see more direct injected gasoline engines, the diesel will lose its advantages.  DI gasoline engines have injectors like a diesel but also a sparkplug.  Ignition happens before top dead center so much higher compression ratios can be used, increasing the thermodynamic efficiency.  Since the "burn" is protracted, the cycle mimics diesel in power output but at the expense of complexity.

I'll take a diesel any day.  

Expect BMW and Mercedes to bring diesels into the country.

You mean bring them BACK into this country.  The engine used in the Jeep Liberty (sorry, all sold out) is a Daimler.

Now an Audi A6 Avant quattro with a 2.5 liter PDI would be a hoot!

Nissan's Pathfinder has  2.5 Liter turbodiesel over in Europe. 30 mpg(imperial), about 26-27 mpg (US).  Big time torque.

That would be ideal for the Xterra.

Toyota makes some amazing diesel SUVs and pickups overseas.

Quoted: I understand that next year, all diesel fuel sold in the US will have to be low sulfur to reduce emissions. Will this mean more diesels (ie for Midsized SUVs), or will upcoming tighter emissions rules still limit diesels to bigger trucks?

What it likely means is that diesel will be $3.50 or so a gallon or $0.50-$0.75 a gallon higher than regular unleaded.

Get ready to bend over and pay out the arse for it at the pumps.

BigDozer66

Quoted: Quoted: I understand that next year, all diesel fuel sold in the US will have to be low sulfur to reduce emissions. Will this mean more diesels (ie for Midsized SUVs), or will upcoming tighter emissions rules still limit diesels to bigger trucks? What it likely means is that diesel will be $3.50 or so a gallon or $0.50-$0.75 a gallon higher than regular unleaded. Get ready to bend over and pay out the arse for it at the pumps. BigDozer66

Not so.  Bp has already switched over and produces ULS diesel.  Other refiners who cannot meet this requirement will take a hit, selling their #2 distillate for off-road and heating use.  There still is a big market in marine, power generation and heating oil.

Off road diesel asulfur limits have been cut back in 2002.  They will eventually be the same as ULS but phased in over time.

All of the profits from recent time are already spent for fuel reformulation.