“If all we did was grab exhaust gas,
cool it and put it in the cylinder, we’d
need very large displacement engines, we’d need very high boost pressures, we’d need enormous peak
cylinder pressures and we wouldn’t
have a very realistic engine design.
“What we did was take air out of the
engine. Back in 1998, we had approximately a 28: 1 air/fuel ratio. In ’02/’04,
we had a reduction of 10 to 15% in
airflow and took it from 28: 1 to 24: 1
and the fuel system was the enabler
of that. We improved fuel system
capability — more pressure, more
controllability — which allowed us to
limit peak cylinder pressures, boost
pressures and heat rejection.
“For 2010, we’re taking more air out
of the engine than in 2007, down to
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about a 20: 1 air/fuel ratio. The quality
of the gases being recycled is, from an
emissions standpoint, higher and higher, as there’s less oxygen in it. It’s a virtuous circle that will reduce emission
and give us optimized fuel economy.”
While Cummins will continue to use
the Cummins Particulate Filter, designed and manufactured by Cummins
Emission Solutions, as its primary
aftertreatment system, there will also
be an addition of a close-coupled catalyst (CCC) mounted after the turbine
stage of the turbocharger. Similar in
concept to a unit used on Cummins
2008 Dodge Ram turbodiesel introduced earlier this year (see February
2007, Diesel Progress) it is used to
maintain proper thermal levels at various operating conditions. In situations where higher temperatures are
needed, a small amount of fuel is injected into the exhaust stream through
a dosing tube. As it is chemically oxidized by the CCC, it raises the temperature of the exhaust stream and
allows the downstream catalyst to
operate effectively.
“With lower NOx levels, we had to
change our regeneration strategy,”
noted Charlton. “In order to get the
maximum temperature to the oxidation
process, we do 50% of the oxidation
close to the engine and the other 50%
happens where it happens today — in
the diesel oxidation catalyst at the front
of the Cummins Particulate Filter.
“It’s really about getting the catalyst
light-off very quickly when we need to.
You can lose a lot of heat when you go
from the turbo to the aftertreatment. If
the aftertreatment is not on the back of
the cab, you can have a 12 or 15 ft.
run from the engine to the aftertreatment and it can cool down quite a bit.
“Because the CCC is within 10 in. of
the turbine exit, we already have very
high temperatures, and periodically we
will be able to put fuel into the exhaust
to maintain the proper temperatures.
We anticipate that it will not be a frequent occurence in most cases.”
As the final part of its 2010 strategy,
Cummins said it would expand its ISX
platform by adding two additional dis-
