High resolution global NOx sub-model for embedded system application with low calibration effort 2020-01-0246
The starting point is a global model of NOx formation for stoichiometric and lean combustion of hydrocarbons developed on the basis of a single non-linear algebraic equation. The latter is the analytical solution of a system of differential equations describing the main kinetic reaction schemes of NOx formation. These take into account the thermal (Zeldovich) and the N2O reaction paths.
The model has been validated in another study and proved to be suitable, on the one hand to be embedded in 1D and 3D simulation platforms, on the other hand for direct data evaluation and post-processing of engine testbench data. The non-linear algebraic equation for the calculation of the NOx concentration requires a numerical iterative solution method. This makes the model less attractive for a real-time application based on crank angle resolved information. However, its implementation on embedded systems for "in-situ" and "in memory" analysis of engine process data, or even its application as a virtual sensor, is of great importance due to its global nature and low calibration effort. Beside robustness, fast running times must also be ensured. The requirements for the latter are high and the time resolution for a crank angle resolved model on a dSpace Microautobox (MAB) is set to at least 1kHz.
The computationally most expensive steps have been identified and concern on the one hand the chemical equilibrium based on the minimization of the free Gibbs energy and on the other hand the iterative solution method of the non-linear algebraic equation for the determination of the actual NOx concentration. Approaches for both steps to reduce the computational time have been developed and tested on the dSpace MAB. The results are compared to the detailed model and show a very good agreement.
Georgios Bikas, Peter Weigand, Marina Brilz, Konstantinos Michos