Exhaust-Aftertreatment Integrated, DoE-based Calibration 2012-01-1303

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 NO_X-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), DeNO_X-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 NO_X emissions forces manufacturers to find an optimal solution, especially with regard to increasing fuel prices.

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 conversion rate.

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 NO_X 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 configured ones.

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 over lifetime.

Overall, this tool allows the integrated optimization of the whole calibration process instead of calibrations based on individually optimized parts.