Portable In-cylinder Pressure Measurement and Signal Processing System for Real-time Combustion Analysis and Engine Control 2020-01-1144
To meet ever strict emissions regulations, cycle-to-cycle combustion control based on statistical processing and model-based prediction has attracted considerable attention from academia and industry. Feedback combustion control typically adjusts ignition-related parameters (spark advance, injection timing, cam timing, etc.) in a cycle-by-cycle manner based on the combustion characteristics measured from previous events. Cycle-to-cycle control guarantees a tight control at steady state and fast response during transients, enforcing an optimal combustion process over a wide variety of engine speed/load conditions. However, these control strategies are constrained by the combustion cycle duration, usually in the order of tens of milliseconds. Therefore, high-speed data acquisition and real-time processing is required. This paper describes a portable in-cylinder pressure measurement and processing system (P-BOT) that enables such a feedback control application to be used on an engine control unit (ECU). This system measures high-speed cylinder pressure signals and engine position, performs real-time heat release analysis, and sends the combustion results to the ECU for engine control at the end of each combustion event. This system is implemented on a Xilinx Zynq processor, which integrates an FPGA processor and dual-core ARM CPUs in a single integrated circuit (IC) chip. This feature reduces system size, power consumption, and allows ultra-fast data communication between the FPGA and the ARM CPUs. The high-speed data acquisition is done by the FPGA module. A tracking algorithm was implemented to measure engine position and cam phasing from the stock sensors on cam- and crank-shaft tooth wheels. It also increased position tracking resolution from 6 crank angle degree (CAD), limited by the stock 60 tooth wheel, to 15/16 CAD, to achieve the accuracy required by combustion analysis. Additionally, it measures high-speed voltage signals from the in-cylinder pressure sensors in the crank-angle domain and buffers for the entire combustion cycle. The ARM module performs the signal processing using user-defined algorithms developed in MATLAB/Simulink. Results from the analysis are transmitted over Ethernet to the ECU where the engine control strategy is executed. The P-BOT system has been integrated with a cycle-to-cycle controller and tested on a 1.6 L Ford EcoBoost engine in a test cell. Experimental results demonstrated that the P-BOT system fulfills the speed and accuracy requirements for cycle-to-cycle combustion control algorithms. Additionally, the system is designed to be portable, low cost, high performance, and is compatible for in-vehicle applications. Future applications of such systems can enable more sophisticated combustion control strategies such as inter-cycle control, statistical predictive control, and machine-learning-based control to be implemented on an existing ECU.
Yilun Luo, Bryan Maldonado, Siying Liu, Charles Solbrig, Devon Adair, Anna Stefanopoulou
Southwest Research Institute, University of Michigan