For on- and off-highway applications in 2012/2014 new
legislative emissions requirements will be applied for both
European (EURO 6/stage 4) and US (US 2010/Tier4 final) standards.
Specifically the NOX-emission limit will be lowered down to 0.46
g/kWh (net power ≻ 56 kW (EU)/130 kW (US) - 560 kW). While for the
previous emissions legislation various ways could be used to stay
within the emissions limits (engine internal and aftertreatment
measures), DeNOX-aftertreatment systems will be mandatory to
reach future limits.
In these kinds of applications fuel consumption of the engines
is a very decisive selling argument for customers. Total cost of
ownership needs to be as low as possible. The trade-off between
fuel consumption and NOX emissions forces manufacturers to find
an optimal solution, especially with regard to increasing fuel
In state-of-the-art calibration processes the aftertreatment
system is considered separately from the calibration of the
thermodynamics. The thermodynamic engineers find the best fuel
consumption in steady state engine operating points and most
efficient combustion with regard to engine-out emissions which
might be converted by an aftertreatment system with an assumed
The problem associated with this approach is that the transient
and therefore the heat-up behavior of the aftertreatment system are
not being considered. The heat-up behavior becomes more and more
important in particular for test procedures including a
cold-started cycle such as WHTC or NRTC. To overcome these problems
a second mode for the heating of the exhaust aftertreatment system
(EATS) and sometimes a third mode with low NOX emissions will be
calibrated separately. The optimization of the operation strategy
with all modes is mostly done at the test bench. The optimization
is always done in a serial way when using this approach. This does
not consider all calibration parameters at the same time.
Therefore, the overall fuel consumption or the total cost of
ownership does not reach the optimum.
A new approach developed by FEV GmbH and the Institute for
Combustion Engines RWTH Aachen University (VKA) takes into account
the aftertreatment system and all engine calibration parameters
from the first calibration step. VKA and FEV have developed a tool
(SimEx) which is capable of simulating a freely configurable
aftertreatment system. The integrated global engine DoE and an
automatic optimizer will calibrate all engine and EATS parameters.
The target of the optimization is an optimal solution for fuel
consumption/total cost of ownership with regard to the transient
tail-pipe emissions. The engineering target for the emissions in
the homologation cycle is typically the constraint. Along with the
reduction of fuel consumption in the certification cycles the fuel
consumption of the specific application can also be taken into
account during the calibration process through the use of
customer-defined cycles. The total cost of ownership can be
effectively minimized through this process.
The parameters for optimization can be chosen completely freely,
e.g., injection and air path parameters for different engine modes,
operation strategy, EATS parameters like size and position.
Furthermore different models can be included, such as ECU models
for the operation strategy, catalyst-aging models, and newly
If use of the tool is begun in a state where the exhaust
aftertreatment is not fixed, there is the opportunity to design and
optimize the aftertreatment system for the lowest total cost of
ownership including the prices for precious metal and consumed fuel
Overall, this tool allows the integrated optimization of the
whole calibration process instead of calibrations based on
individually optimized parts.