Feedforward Control Approach for Digital Combustion Rate Shaping Realizing Predefined Combustion Processes 2015-01-0876

The aim of this research collaboration focuses on the realization of a novel Diesel combustion control strategy, known as Digital Combustion Rate Shaping (DiCoRS) for transient engine operation. Therefore, this paper presents an initial, 3D-CFD simulation based evaluation of a physical model-based feedforward controller, considered as a fundamental tool to apply real-time capable combustion rate shaping to a future engine test campaign.

DiCoRS is a promising concept to improve noise, soot and HC/CO emissions in parallel, without generating drawbacks in NOx emission and combustion efficiency. Instead of controlling distinct combustion characteristics, DiCoRS aims at controlling the full combustion process and therefore represents the highest possible degree of freedom for combustion control. The manipulated variable is the full injection profile, generally consisting of multiple injection events. So far, however, DiCoRS was only realized by feedback-based iterative learning control, lacking sufficient control speed. Thus, an additional feedforward control unit is required to transfer the benefits of DiCoRS also to the dominating transient engine operation condition in passenger car applications.

Therefore, a new model-based feedforward control concept is developed and initially investigated in this paper. Desired combustion rates and therefore the desired in-cylinder gas state traces are formulated based on energy- and mass conservation equations. An inverse 0-D heat release model calculates the required injection profile, taking into account hardware related boundaries of the fuel injection system. Each submodule of the feedforward controller, such as the ignition delay model, is calibrated offline via steady-state engine test cell data. The overall functionality of the feedforward control concept is finally demonstrated based on a 3D-CFD combustion simulation study.