[AT] Continuing "What to do"

[Stephen Offiler]

Cecil:

(By the way I loved that rant on concrete and culverts!  I'm a mechanical
engineer and I see similar "we've always done it this way" idiocy in my
world every day)

Different subject, see below...


On Wed, Jan 13, 2016 at 7:44 AM, Cecil R Bearden <crbearden at copper.net>
wrote:

> That is what I read also.  However, the result is a less reliable engine
> that uses more fuel.   How can you pollute less if the engine you are
> operating has all this crap on it but uses twice the mount of fuel?


Ask Volkswagen ;-)

Seriously, the answer lies in the definition of "pollution".  One pollutant
in particular is NOx.  A diesel engine inherently makes very high NOx
emissions.  The chemical reaction to form NOx happens at high temperature
and pressure, so, the more thermally efficient your diesel engine (the
better the engine at converting heat into motion) then the more NOx it will
emit.  The trick to emitting less NOx is to detune the engine, so it
operates at lower temperatures and pressures.  It uses more fuel because
you took away thermal efficiency.

And then there's yet another form of pollution called particulate matter,
PM.  Microscopic soot and ash, basically.  Modern diesels must be fitted
with traps to capture PM.  And the traps tend to fill up.  The way to clean
them is called a "regen" and it involves heating up the trap to a higher
temperature to burn the soot down.   The extra heat comes from extra fuel.
So there's another reason modern diesels use more fuel.


Steve O.