just read your recent column on automotive emissions. You didnít
mention diesel particulate emissions, and I wish you had. It seems
hard to find info on the current performance of diesels. I hear talk
of "clean diesel" but donít know if that just means
low-sulfur. I donít much like the idea of tiny particles burying
themselves in my lungs and would like to educate myself as to
whether this is an irrational fear or not.
question, Bill. "Clean diesel" generally refers to diesel
engines built since 2007 that use ultra-low-sulfur diesel fuel and
employ additional technologies to enhance engine efficiency and
reduce exhaust emissions.
diesel, or ULSD, has sulfur concentrations of 15 particles per
million or less, which is about 97 percent cleaner than the previous
1993 standard. Besides greatly reducing emissions of sulfur dioxide,
which can combine with water to produce acid rain, ULSD allows the
use of a diesel particulate filter and selective catalytic
I should also
mention modern diesel engines typically employ common rail direct
fuel injection, which also improves performance, allows quicker
starts and reduces emissions and noise, compared to earlier methods.
"Common rail" means all of the engineís fuel injectors
have fuel pressure available at all times and are electronically
operated, allowing precise and highly atomized fuel delivery. The
engine management system employs a variety of sensors to allow very
smart fuel delivery functions.
to the exhaust: An oxidation catalyst cleans up carbon monoxide and
hydrocarbons. Next is the diesel particulate filter, which collects
and stores soot. The engine management system can tell when itís
time to clean the filter and adds fuel to add heat/burn off the
urea-based solution called AdBlue or DEF (domestic diesel exhaust
fluid) is sprayed into the exhaust just ahead of the selective
catalytic reduction unit. Exhaust heat converts the urea to ammonia,
which reacts with oxides of nitrogen inside the unit, transforming
it into nitrogen gas and water vapor.
selective catalytic reduction have a 5- to 7-gallon DEF tank, which
needs to be refilled approximately at each oil change. High-mileage
cars may go further; the DEF is metered at about 2-6 percent of fuel
used. DEF varies wildly in price, from about $3 per gallon in bulk
to about $5 at Wal-Mart ó a great price ó up to about $30 per
gallon at a luxury car dealer. The cost of the DEF is largely offset
by greater engine efficiency, compared to a system that doesnít
use this system.
line: Modern diesels run cleanly and smoothly, and are surprisingly
quiet. Iíve had a chance to drive some of the European passenger
car models. With the exception of exhilarating low-end torque, a
lower-than-usual tachometer red line, and great mileage, you might
not realize it wasnít a gasoline engine.