Truck & Off-Highway Engineering - April 2018 - 10

TECHNICAL INNOVATIONS

The dilution system, which provides
fresh air and/or nitrogen to the exhaust
gas stream, is used when the desired exhaust gas stream represents a lean-burn
combustion application. The dilution system provides a means for independent
control of O2 concentration and exhaust
gas temperature. The combination of
both the water-to-air heat exchanger and
the dilution system enable the ECTO-Lab
to independently control the temperature
of the exhaust gas stream and excess
oxygen for both conventional spark-ignited stoichiometric engines and compression-ignited lean-burn engines.

SwRI's newest
ECTO-Lab system is
capable of producing
exhaust streams with
flow rates of up to
3250 kg/hr.

One of the most recent advancements
on the ECTO-Lab system is the ability
to control the concentration as well as
speciation of HCs present in the exhaust
gas stream. This capability is of increasing interest for light-duty applications,
where HC emissions are as stringently
regulated as NOx emissions. The control
of the HC speciation profile is important
because HC components have varying
levels of reactivity depending on the
specific structure of the HC. To accurately quantify the performance of
emission control devices, it is imperative that the component or system be
tested in an exhaust gas stream that
represents the intended application.

The water-cooled ECTO-Lab system is capable of
simulating the lean and rich operating environment
encountered on light-duty applications which
utilize three-way catalysts and lean NOx traps.
10 April 2018

In a synthetic gas bench, the HC mixture is simplified to one or two components because of practical limitations.
For the engine test bench, the HC mixture is complex, but is typically constrained by the choice of engine hardware and/or operating condition. With
the ECTO-Lab system, complex HC mixtures are easily controlled so the impact
of these complex profiles on catalyst
performance can be quantified. The
techniques used allow for speciation
control with all HC fuels, including diesel and gasoline.
While these individual modules provide a significant level of capability for
exhaust gas composition, the system
would be of little use if these conditions
were not controlled accurately and precisely. A robust control strategy is required to replicate the complex and
highly transient emission profiles from
internal combustion engines. To solve
this challenge, SwRI engineers looked
to their successes in the control of internal combustion engines and development of model-based sliding mode
controllers for precise control of advanced combustion modes. Given the
similarities in the control requirements
for the ECTO-Lab system, this modelbased controller was adopted for this
purpose. The result is a highly transient,
highly reproducible system which can
replicate the exhaust gas conditions for
many different engines.

The greatest benefit of using the sliding mode control system is the ability to
replicate the emission profiles of engines
operated in highly transient drive cycles
like those encountered for the light-duty
and heavy-duty federal transient protocol (FTP-75 and HD-FTP). The transient
capability allows the ECTO-Lab to be
more than just a full-size synthetic gas
bench. With this transient capability, the
system can be used not just for fundamental full-size aftertreatment testing,
but also for the development of aftertreatment system controls.
One of the biggest challenges encountered with increasing stringency of
emission regulations is emission control
system cold-start strategy development. With a conventional enginebased test cell, the engine and aftertreatment system must be cold-soaked
for eight hours prior to a cold-start test.
With the ECTO-Lab system, there is no
engine, which means only the aftertreatment system must cool down.
SwRI has developed rapid cool-down
strategies, which allow for a cold-start
test to be conducted every hour. This
allows for an increase of calibration
throughput by a factor of eight, leading
to reduced development timelines and/
or improved controls.
Cary Henry, Ph.D., Assistant Director
of Diesel Engine and Emissions R&D at
Southwest Research Institute, wrote this
article for Truck & Off-Highway Engineering.
TRUCK & OFF-HIGHWAY ENGINEERING

BOTH IMAGES: SOUTHWEST RESEARCH INSTITUTE

HC speciation control a recent
development

Truck & Off-Highway Engineering - April 2018

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