gas vs. diesel (emissions)

You don't have to wonder. Just look for EPA rating labels, like SULEV & PZEV.

The cleaner diesel does make those levels of clean realistic, but whether or not an automaker will actually deliver vehicles that achieve them is an entirely different matter.

Regardless, an engine-only automatic diesel still cannot compete with a "full" hybrid in mixed driving conditions when it comes to efficiency. The real-world data clearly confirms that.

There's a big fight going on just now about this over here:

http://www.greenhybrid.com/discuss/hybrid-diesel-the-mercury-meta-one.1245.html

My pro-diesel stance took a battering!

You can pick up a lot of the diesel pros/cons from that, and there is a link to a .pdf with all the Tiers/Bins/SULEV/PZEV etc requirements.

There's also the problem of particulate emission to be taken into account. Particulates are one of the problems in diesel engines (remember the black smoke coming from tailpipes?). Modern diesel engines are much better but there's one snag: Emissions are measured in mass (i.e. µg of particles/m3 of air). New engines emit a higher number of particles, but with a much smaller diameter. As mass decreases with the 3rd power of diameter, you can reduce the mass even when the number increases. The big question now is: what causes health problems? Is it the particle mass, the surface or the number???? This is still much debated in the scientific community.
I guess what should really drive this discussion is not just the fuel efficiency, but the emissions. And not just the gaseous emissions (NOx, CO, etc.) but also particulates. I guess the Prius is doing better here than most diesels.

mgaelli said:

And not just the gaseous emissions (NOx, CO, etc.) but also particulates.

Click to expand...

PM (particulate matter) is part of the SULEV & PZEV emission ratings.

Anyway, where does the saving come? Less time in a refinery for the same original product?

john1701a said:

mgaelli said:

And not just the gaseous emissions (NOx, CO, etc.) but also particulates.

Click to expand...

PM (particulate matter) is part of the SULEV & PZEV emission ratings.

Click to expand...

But as I mentioed earlier, PM is mass based, so it can still be an issue.