[mikestew]

The EPA standard is the strictest in the world, and they have successfully ruined many diesel powered devices.

One thought, then, is that diesels are not suited to the task. If that particular type of engine can't move things down the road without filling the air with pollution, perhaps it's time we moved on to something else. I mean, what tasks require a diesel? Commercial vehicles, okay. Consumer cars? Not if they spew crap into the air just to save a few MPG. Small farm equipment? See below, totally unnecessary, IMO. Class A motorhomes? Please. The fact that it's designation has "recreational" in the name tells you that kittens won't die if we don't have anymore of them.

An extreme stance? I dunno, maybe. Just like getting rid of lead in our fuel was probably an extreme proposition at one time. But we knew lead was bad, we knew it for decades. But profits uber alles, eh? I just don't know how one would justify to future generations, "sorry 'bout the smog, but Daddy needed to run his garden tractor on diesel, and wanted to save a few bucks on fuel."

I could see an exception for commercial vehicles, but I can't see a good argument for consumer diesels if we can't produce ones that don't choke the air with particulates and NOx.

Personally, the two major things I want to do with a tractor are run a large snowblower and maintain our horse pasture.

Not to pick on you personally, but those tasks don't require a diesel. PTO, plowing a small field, running a bush hog or deck mower, pick your poison, it can all be done just fine with a gas engine. And the gas engine will start when it's -20F and that driveway needs plowed. I grew up in farm country, and the only ones running diesel where the ones with farm equipment the size of your house. I refuse to accept that we'll back off on EPA regulations because some dude feels like he needs a diesel to maintain his five acre play farm. (Again, not directed at you; I have no idea how many acres you have.)

[danjayh]

Prior to the current (Tier 4) standards, the Tier 3 standards had already reduced NOx and particulate emissions to the the point that it's misleading to characterize those engines as "filling the air with pollution". Now that CO2 has been declared as pollution, the improved thermal efficiency of diesels over gasoline engines probably means that they were already "better" than gas under some operating conditions. Even ignoring their superior thermal efficiency, Tier 3 diesels achieved similar results to gasoline engines when both were operated at high load (Say, running down the highway at 80mph). This was accomplished with technologies that, while they added complexity and cost to the engine (such as direct injection, EGR, DOC, VVT, advanced FIE, improved combustion chamber design, increased compression ratio, advances in turbochargers), did not compromise the utility and safety of the device using the engine.

As you have suggested, many manufacturers will probably move back to gasoline engines in some of the smaller applications ... but they will moved to air-cooled V-Twins for many of these, which fall into the same power range as the diesels they replace (~20-40HP). Air-cooled gasoline engines are not clean beasts, and this move will probably actually end up being a net environmental loss.

Have a look at the chart on page 2 of this: http://www.mtu-online.com/uploads/tx_templavoila/WhitePaper_...

The additional NOx reductions achieved by tier 4 are extremely small compared to the cost & trouble caused by the technologies used to achieve them ... the previous tech (up to Tier 3) was fairly reliable & had already achieved most of that was had in the overall journey from unregulated -> Tier 4.

Also, almost none of the garden tractors sold are diesel, because in that application it doesn't make sense - those engines aren't run at high load for long periods of time. However, for a compact tractor that may well be run all day long in high heat with a demanding attachment, a diesel actually does make a lot of sense - there is a large environmental cost to dumping a machine with 5-600 hours on it because the engine gave out prematurely (which happens to entirely too many of the garbage lawn & garden tractors sold at box stores, despite their relatively easy lives).

FWIW, I let my lawn die in the summer and probably mow it fewer times in an entire season than many folks do in a month ... living in the sticks with nobody to judge me has its benefits :) You did get reasonably close on the size, though. My dad and I live close enough together to share a tractor, and we have 26 acres, a goat, five horses, and sundry other critters between the two of us (and our wives, of course).