Model-Based Exhaust Gas Temperature Control to Reduce the Mixture Enrichment at High Loads

In this work an exhaust gas temperature and a piston damage model are coupled, with the aim to develop an innovative model-based strategy for the calibration of the lambda map and to actively control the spark advance (SA). In this way, the lambda value needed to reach a target exhaust gas temperature evaluated at the turbine inlet is determined. In the first part of the article, some empirical and semi-physical models for the calculation of the exhaust gas temperature, the combustion phase, the maximum in-cylinder pressure, and the knock intensity are developed and presented. A piston damage model previously developed by the authors determines the SA to reach a target piston erosion for the knock-limited operating conditions, increasing the combustion efficiency and lowering the temperature of the exhaust gases with respect to the standard spark timing map. The exhaust gas temperature model allows to estimate the lambda value that returns the maximum temperature at the turbine inlet, exploiting the gained combustion efficiency to extend the stoichiometric area of the engine operating field. In the last part of the work, the lambda map calibrated through the proposed algorithm is validated for both the transient and steady-state conditions, reproducing a real vehicle maneuver at the engine test bench. The results finally demonstrate that a combustion efficiency increase equal to 8% can be reached by managing the SA with a piston damage-based controller, and this number can be increased up to 16% by applying the recalibrated lambda map, with respect to the standard engine calibration.