Diesel Engine Combustion Sensing Methodology Based on Vibration Analysis

The increasing request for pollutant emissions reduction spawned a great deal of research in the field of combustion control and monitoring. As a matter of fact, newly developed low temperature combustion strategies for diesel engines allow obtaining a significant reduction both in particulate matter and NOx emissions, combining the use of high EGR rates with a proper injection strategy. Unfortunately, due to their nature, these innovative combustion strategies are very sensitive to in-cylinder thermal conditions. Therefore, in order to obtain a stable combustion, a closed-loop combustion control methodology is needed. Many works demonstrate that a closed-loop combustion control strategy can be based on real-time analysis of in-cylinder pressure trace that provides important information about the combustion process, such as start of combustion, center of combustion and torque delivered by each cylinder. Nevertheless, cylinder pressure sensors on-board installation is still uncommon, due to problems related to unsatisfactory measurement long term reliability and cost. This paper presents a newly developed approach that allows extracting information about combustion effectiveness through the analysis of engine vibrations. In particular, the developed methodology can be used to obtain an accurate estimation of the indicated quantities of interest combining the information provided by engine speed fluctuations measurement and by the signals coming from acceleration transducers mounted on the engine. This paper also reports the results obtained applying the whole methodology to a light-duty turbocharged common rail diesel engine.