EuroCombi - Haldex

While SCR technology is costly in terms of loading capacity, it does have its advantages in terms of consumption.
converts nitrogen oxide contained in
exhaust gases into harmless water vapour
and nitrogen. EGR combats the production
of nitrogen oxides at the source: Using this
method, burning temperatures inside the
engine are reduced so as to produce very
little NOx.
Both processes have their pros and cons:
SCR technology implicates significantly
heavier dead load (hence less usable load)
and forces transporters to always provide
sufficient top-up space for the reducing
agent AdBlue. For its part, EGR is relatively
lightweight and its purchase price is more
appealing. In terms of usage, however, the
process tends to come with its share of
disadvantages.
Engines have now become impressively
clean: Euro 4 did bring about an 80%
reduction in particulate emissions, while
Euro 5 (mandatory as of 2008) brought
about a further reduction in nitrogen oxide,
that is to say an 80% reduction compared
with Euro 3.
Measures are still expected to become
somewhat tougher. The EU is considering a
wide spectrum of possibilities for Euro 6.
Engine manufacturers are already drawing
attention to the fact that politicians are
shooting beyond the target. This would
result in extremely high development costs.
And in order to comply with new limit
values, tomorrow’s trucks would have to
incorporate changes that would only be
feasible in the long term. In practical terms
this could mean the following: trucks would
have to trail with them a substantial
arsenal of exhaust treatment apparatus
(wall-flow particle filters, NOx storage
devices/reduction catalysts and downstream
oxy catalysts) and, because of high exhaust
gas recirculation rates, would also have to
generate a refrigerating capacity that would
be extremely difficult to achieve with
current vehicle concepts.
Whatever the outcome of Euro 6,
tomorrow’s engine will probably be
equipped with both SCR and EGR
technology.
Measured against the potentially very high
technological expenditure incurred by
particulate limit values at the very least,
environmental benefits would be relatively
small, as only a fraction of fine dust
pollution is attributed to heavy goods traffic
(even in traffic-heavy Germany, it only
accounts for about 10 percent). The same
cannot be said for the effectiveness of
tougher limit values on nitrogen oxide,
which would significantly alleviate
environmental pollution.
Whatever decision the politicians reach,
time is running out: the EU is planning to
introduce Euro 6 for 2012/2013 and in the
interim period, engine manufacturers are
sitting on hot coals: “If new exhaust gas
limit values are not determined soon,” says
Iveco Engine Manager Rudolf Ellensohn, “it
will be impossible to develop a proactive
solution before 2009.”
Such a solution must be found as a matter
of urgency if tomorrow’s conveyers are to
continue to enjoy the same toll benefits that
they currently have with Euro 5 heavy
goods vehicles.
Control mechanism
In the form of the Varivent system,
Haldex offers an intelligent solution
that supports variable exhaust gas
recirculation control, while at the same
time obviating the need for an exhaust
gas pumping mechanism. A pivotal
role in the Varivent system is played by
the Venturi preformed part, built into
the intake manifold. It functions like
the wing of an aeroplane, speeds up
the air flowing over the curved surface,
whereby static air pressure changes
along the length of the structure. It
reaches a minimum at the narrowest
section of the preformed part. And it is
right here that the circulating exhaust
gases are allowed to gently enter the
otherwise overpowering flow of turbocharged
fresh air. At the narrowest
section, pressure can be varied almost
at will and therefore the quantity of
circulated exhaust gas can also vary
through a change in position of the
Venturi element.
Haldex Magazine - Spring 2007
11