FPGA Implementation of In-Cycle Closed-Loop Combustion Control Methods

This paper investigates the FPGA resources for the implementation of in-cycle closed-loop combustion control algorithms. Closed-loop combustion control obtains feedback from fast in-cylinder pressure measurements for accurate and reliable information about the combustion progress, synchronized with the flywheel encoder. In-cycle combustion control requires accurate and fast computations for their real-time execution. A compromise between accuracy and computation complexity must be selected for an effective combustion control. The requirements on the signal processing (evaluation rate and digital resolution) are investigated. A common practice for the combustion supervision is to monitor the heat release rate. For its calculation, different methods for the computation of the cylinder volume and heat capacity ratio are compared. Combustion feedback requires of virtual sensors for the misfire detection, burnt fuel mass and pressure prediction. Different alternatives proposed in the literature are compared based on their accuracy and implementation requirements. In-cycle closed-loop combustion controllers were previously investigated by the authors. A National Instruments Xilinx Virtex-5 platform was used as a case study for the quantification of the total necessary resources. The resources for the implementation of the different modules and control strategies are studied to determine the hardware requirements. The results show that the total number of slices is the main limiting factor on the consumed FPGA resources. The quantification of the required hardware provides guidance on how to select an FPGA to implement the different in-cycle combustion control alternatives. This permits to evaluate the total cost of the system as a trade-off between the increased efficiency by the closed-loop combustion control and the cost for its implementation.