[Big Dave]

I like to think of myself as being smarter than the average bear on the subject of diesels. My first job out of high school in 1969 was at a factory that made diesel-electric locomotives. I've driven a diesel vehicle continuously since 1983.

That said, I am not a bit sanguine about diesels ever doing well in the US.

Two reasons drive that opinion.

First it US regulatory excess. The EPA's Tier II requirement for diesels is considerably more stringent the the Euro 5 spec used across the pond. Under current technological constraints meeting Tier II requires EGR, a barrier filter and in some cases selective noncatalytic reduction.

Any engine subjected to these will not get very good MPG and it will suffer from poor reliability. Already the diesels avaialble on three-quarter ton and up pickup trucks are in trouble. The EGRs cause reduced engine efficiency and excessive cylinder pressures resulting in cylinder head gasket failures. The barrier filter undermines efficiency in two ways. First of all, any barrier filter imposes back pressure and increases pumping power requirements on the engine. It is like running with an exhaust brake constantly on. Secondly the filter occasionally has to "regenerate." This means an auxiliary burner comes on and oxidizes the captured graphite into carbon dioxide. That entials even more fuel burn.

Now M-B is going to import their "Blue-Tec" technology into the US. To make this work you have to fill a small tank with urea periodically and another with tap water. Tap water and urea react to make a dilute ammonia solution that (if the temperatures are right) reacts the NOx into nitrogen and water vapor. If it works. selective non-catlytic reduction is a very tempermental pollution control technology. If the temperature is not within a fairly narrow band, the reaction does not go to completion and the tailpipe emits not only unreacted oxides of nitrogen but also noxious ammonia - a vapor the human nose easily detects in very low concentrations. This technology has a very checkered past in stationary applications with constant monitoring and maintenance by professionals. Just how reliable do you think it will be in a mobile application subjected to the rigors of the road?

Diesels are necessarily more expensive than gas engines of equal power output. No with all these (dubious) pollution control add-ons it may very well be that a diesel vehicle will require a $10,000 cost premium over an equivalent gas engined vehicle. A $10,000 price premium on a small car is a deal-killer.

The other big reason that diesels will not fly in the US is that Americans prefer automatic transmissions and diesels' torque characteristics tend to destroy automatics. As much as I love them I just don't think americans will want relaible and efficient manual transmissions. They are too busy talking on their cell phones. Yes there are some automatics that are designed for diesel service. The transmission offered on GM pickups (a value-engineered Allison 1000) has some problems and still commands a $4,000 premium over the mass-produced gas-engine automatics.

Thanks to regulatory excess, todays diesels will be unreliable, possibly noxious to be around, very costly and just not efficient enough to to justify all the deficiencies.

A lot of work and governmental compromise will be needed to make the diesel popular.