US NAVY'S - Incat

Improving exhaust emissions and fuel consumption
involves the engine builder’s grasp of combustion
and thus goes to the very heart of the matter.
“Combustion is obviously the central science of
combustion engines and MAN Diesel has special
advantages,” he continues. “Unique among
builders of medium speed engines, as well as
designing, developing and producing the engine
itself we have a great fund of knowledge and
experience with strategic components and systems
like turbochargers, fuel injection equipment,
electronic hardware and engine control software.
Using this expertise, we were able to reduce the
specific fuel consumption of the 28/33D by some 5
to 7% without affecting NOx emissions, compared
with its immediate predecessor, the RK 270.”
The reference to electronics is important since
advanced digital engine management is the
enabling technology of increasingly accurate and
flexible control of parameters affecting combustion.
“Fuel injection, turbocharging, valve timing and
thermal engine management are the primary
measures we use to enhance fuel efficiency and
lower exhaust emissions ’at source’ i.e. in the
combustion chamber,” Koch states. “The electronic
hardware and software we use on the 28/33D
will continue to give us scope for improvements.
With all our in-house expertise in the key engine
technologies at MAN Diesel, the software we write
ourselves includes very accurate mathematical
models of engine processes and thus gives very
precise control.”
Continuous Development
The 28/33D already offers market leading values
for emissions and fuel consumption, but technical
milestones which will bring further improvements are
pre-programmed into the MAN Diesel continuous
development process. Already under preparation,
and due for introduction later in 2008, for example,
is the next step in electronic engine management,
MAN Diesel’s advanced “SaCoSone” system. The
acronym stands for “Safety and Control System”
and the suffix for “on engine, since the system
is very compact and mounted entirely on the
structure of the 28/33D.
Together with the 28/33D’s fuel injection system with
solenoid valve controlled injectors, SaCoSone will allow
very precise “shaping” of the rate and timing of fuel
injection and hence greater control over combustion.
“This technology will be an important aspect in
undercutting IMO Tier 2 NOx emissions limits,” Koch
states.
Early Closing for Miller Light
Further plans to reduce NOx emissions and fuel
consumption on the 28/33D include a package of
modifications to enable the so-called “Miller” process.
Named after its inventor, the Miller process involves
closing the inlet valve early so that air entering the
cylinder expands and cools to reduce combustion
temperature peaks. In fact, over 90% of NOx is formed
due to temperature peaks during combustion and
an elegant way to eliminate the peaks is to cool
the combustion air entering the cylinders. “One well
established method is the charge air cooler (a.k.a.
intercooler or aftercooler), another the Miller process,”
Koch observes. “On the 28/33D we achieve a “light”
Miller process using a revised inlet cam profile to close
the inlet valve slightly earlier. Plans call for this to be
complemented by a turbocharger that delivers air
to the cylinders at higher pressure. This ensures we
still get the same amount of air into the cylinders in
spite of shorter valve opening, to the benefit of both
performance and fuel consumption.
No Smoking
Concluding, Koch notes that the sum of all these steps
will help the 28/33D diesel engine maintain its market
leading fuel consumption values and achieve emissions
levels decisively below the limits of IMO Tier 2 - ahead
of its implementation.
Finally, he points to a very vital aspect for INCAT.
“On passenger vessels it is especially important to
achieve visibly clean combustion with minimal fouling.
The measures we aim to introduce on the 28/33D
will promote smoke-free exhaust gases under all the
operating conditions the 28/33D engine will meet on
an INCAT catamaran.”
20 Incat THE Magazine Issue 36