The Garage 283

CONSTANT E
Meeting aftermarket requirements
Emission control Klarius Products 18
Most enthusiasts
will confirm
that you
can tell a classic
car or race
engine just from the smell
of the exhaust gas. Unlike
modern cars, older vehicles
featured simpler exhaust
systems that didn’t do much
for emission control. However,
the drive to improve air
quality has meant that exhaust
systems have changed
dramatically in design complexity
over the years.
Doug Bentley, Head of Research
and Development at
Klarius Products, the UK’s
largest manufacturer of aftermarket
exhausts, examines
major changes to the exhaust
system up to Euro 6,
and how this affects Klarius’
approach.
In Europe, the mandatory
use of catalytic converters
(CATs) and unleaded petrol
was introduced in the Euro
1 (EC93) standards of 1993,
ensuring a CAT was incorporated
on every new vehicle
design. Prior to this point
exhausts were designed to
provide some back pressure
for the engine to work
with, ensure cooled gases
exited quietly at the back of
the vehicle, and not much
else. The Euro 2 standard
of 1997 then made a differentiation
between petrol
and diesel vehicles, which
would continue through further
standards. However,
it would be the Euro 4 and
Euro 5 standards that would
most affect the diesel emissions
system.
Euro 4 of 2006 introduced
a limit of particulates and
NOx in diesel vehicles. Enter
the diesel particulate filter
(DPF). Located in closer
proximity to the manifold (to
use the higher temperatures
for regeneration), like a CAT,
the DPF reduces potentially
harmful combustion byproducts
from entering the
atmosphere.
Unlike a CAT though
(which is a flow-through
device), the DPF is a filter,
and collects soot from the
exhaust gas stream & stores
it to stop it escaping into the
atmosphere. During long
journeys, the vehicle’s ECU
triggers a burn-off process
to reduce the soot particles
to a fine ash, which is retained
within the device,
which stopped the visual
emission of black exhaust
smoke. By Euro 5 of 2011,
fitment of a DPF became
mandatory for all new diesel
vehicles. Some manufacturers
now combine CATs and
DPFs together as a single
unit, ensuring exhaust gases
are even cleaner to meet
Euro 6 standards that came
into force from 2015.
Closer proximity to the
manifold means that operating
temperatures are
reached sooner in the driving
cycle, which helps emissions
again, but complicates
the design of exhaust systems
even further. At the
hot end of an exhaust system,
what was once a round
pipe that fitted to a standard
flange on the exhaust manifold
has become a complex
fabrication with castings,
chambers, ceramic monoliths
(that are filters as well
as providing a catalysation
surface) and threaded sockets
for temperature and oxygen
sensors that provide the
feedback the engine needs
to successfully complete effective
burn-off / cleaning
cycles.
The latest change to the
diesel exhaust system also
introduced the process of
selective catalytic reduction
(SCR). Again, driven by the
more stringent Euro 6 standards,
SCR utilises a liquid
(AdBlue) added to the exhaust
system, which allows
NOx to be processed at much
lower exhaust temperatures.
Vehicle owners will typically
have to refill the fluid at service
intervals or during normal
use depending upon the
distance travelled. Again, for
a manufacturer this adds to
the complexity of what has
become an ‘emission control
system’, not just an exhaust.
18, 19 Opinion.indd 1 04/10/2018 11:23