Malaczynski, G., Roth, G., and Johnson, D., "Ion-Sense-Based Real-Time Combustion Sensing for Closed Loop Engine Control," SAE Int. J. Engines 6(1):267-277, 2013, doi:10.4271/2013-01-0354.
The cycle-to-cycle and cylinder-to-cylinder variations that occur in a spark ignited engine create the opportunity for monitoring combustion in real time to provide useful benefits for engine control. Reduction of variation and operation of the engine at closer-to-optimum conditions is possible if real time feedback of the combustion process is available.An in-cylinder pressure sensor with pressure-based control algorithms is one method of monitoring the combustion process. However, such a solution presents new challenges of an additional cylinder penetration location, sensor packaging and added cost. A substitute for the in-cylinder pressure sensor is a device which measures the flame conductivity, commonly known as an ionization current sensor. It can be integrated with the spark plug in the case of SI engines, or with the glow plug in the case of compression ignition engines.This paper presents a methodology of data acquisition and processing which leads to the extraction, in real time, of the following parameters critical for closed loop engine control: combustion phasing, knock detection and combustion stability. The algorithms utilize a combination of various methods including crank-angle-aligned data extraction, digital filtering of the ion sense signal and neural-network-based ion signal interpretation. A Delphi Ion Sense Development Controller (ISDC) is used for high-speed data acquisition and subsequent real time combustion parameter computation.Our paper demonstrates key features and reports the performance of ionization-current-based combustion sensing using engine data. Key combustion parameters, generated by the ISDC on a combustion event basis, are sent to the engine controller via a Controller Area Network (CAN) for closed loop individual-cylinder combustion control.