MEETING BIGGER
EMISSIONS CHALLENGES
One size definitely doesn’t fit all when it comes to SCR system technology on larger engines
For large engines equipped with SCR systems, special manifolds incorporating multiple injectors, such as this one developed by Emitec,
can be used to distribute the aqueous urea reductant and achieve a homogenous spray pattern in the exhaust stream.
BY RAIMUND MÜLLER
When it comes to emissions control, much of the focus for diesel and gaseous-
fuel engine manufacturers in recent
years has been on off-highway mobile
equipment, and the U.S. and Europe
have developed similar stringent NOx
and PM limits in emissions regulations
covering engines up to 750 hp. In
Europe, regulations for engines above
that range have not been implemented
while the U.S. has established require-
ments, though with less-stringent limit
values. There also are separate emis-
sions regulations covering locomotives,
marine vessels and stationary genera-
tor set engines.
Dr.-Ing. Raimund Müller is general manager, Technical Sales of the heavy-duty
truck and nonroad business at Emitec
GmbH, Lohmar, Germany The company’s
North American operation, Emitec USA, is
headquartered in Rochester Hills, Mich.,
and has a manufacturing facility in Fountain Inn, S.C.
As in the case of smaller engines,
selective catalytic reduction (SCR)
is expected to be the prime technology used to help larger engines
meet Tier 4 final emissions regulations. SCR has shown that emissions of nitrous oxides (NOx) can
be very efficiently reduced in the
presence of a specific catalyst with
the aid of a reducing agent, typically
an aqueous urea solution.
The reducing agent — typically
known as AdBlue or DEF (diesel
exhaust fluid) — is injected in small,
precise quantities calculated according to the momentary NOx mass flow
of the engine and the required NOx
reduction rate. The quantity of urea
solution is typically done by a metering pump or metering valve. Urea
dosing pumps and injectors are used
when compressed air is utilized for
atomization in the injection nozzle.
In case of a liquid-only solution
the atomization is done by liquid
pressure in a pulse width modulated
(PWM) injection valve mounted in
the exhaust stream upstream of the
SCR catalyst.
