lbhskier37 said:
Trucks doing worse or breaking even with the new emissions regulations because their regulations are still loose enough that they can use conventional techniques like EGR and retarded injection timing to pass emissions, all which cause a big drop in efficiency. This is the big reason the PD lost efficiency to the older motors, they needed to use these efficiency robbing techniques.
This is true to most extents, but advancements in other areas (e.g. improved injection systems, combustion development, thermal management and friction reduction) blunted the effects and in some cases continued to improve the fuel economy overall. In a large number of cases, worsened fuel economy cannot be traced solely to these emissions measures, but to larger and heavier vehicles as these same models evolved over time.
With exhaust aftertreatment (which btw will be required on big trucks in the next round of emissions) they can lean the mixture back down to pre-emissions regulation levels and get much more efficient combustion, then let the aftertreatment deal with the NOx after the fact. This is much like SI engine cars of today can be far more efficient than say in the 70s because the 3-way catalyst lets them run stoiciometric creating efficient combustion and deal with the pollution afterwards where as before the 3-way cat most engines had to run rich to pass emissions, giving us the horrible gas hog sub-200hp V8s of the 70s.
No, this is not entirely true, and was already stated in another thread. NOx aftertreatment for Diesel engines require the use of an active reductant, whether it be hydrocarbons from additional injected fuel or urea-type additive.
Especially with these new aftertreatment schemes,
you DON'T have the freedom to calibrate the engine to run at its most efficient point, emissions be damned, and let the aftertreatment deal with it after the fact. The amount of reductant consumed is directly proportional to the amount of engine-out NOx that needs to be converted, and the consumer will not accept having to refill the urea tank too frequently, or in the case of non-urea-based NOx treatment, accept the large hit in fuel economy.
Also, when dealing with such stringent regulations that amount to mere parts-per-million NOx in the exhaust stream, and where the warming-up phase of a driving cycle -- while the catalysts are still ineffectual -- produces the bulk of the emissions in a tiny fraction of the driven distance, it is NOT acceptable to let the engine produce as much emissions to run most efficiently; the exhaust must be as clean as possible right out of the get-go.
That's why despite the advancements in aftertreatment technology, this has not removed the intense spotlight from combustion development and internal measures to minimize engine-out emissions.