Application of independent component analysis for the study of flame dynamics and cyclic variation in spark ignition

This article reports on the application of independent component analysis (ICA) to line-of-sight, cycle-resolved images of luminosity during combustion, acquired in an optically accessible engine. The experiments are conducted on a port fuel injection spark ignition (PFI SI) engine. The analysis identifies the independent components related to the underlying phenomena of the combustion process. The components, along with their corresponding time dependent coefficients, are used to characterize the morphological evolution of the luminous combustion during a single cycle and over a number of cycles. When ICA is applied to a single cycle, independent structures are identified, clearly separated in time, and related to the spatial distribution in the highluminosity zone. The corresponding coefficients correlate well with the integral flame luminosity, and characterize the time evolution of the combustion morphological pattern in the chamber. The analysis over several cycles shows that independent components contain information about the dominant luminosity shapes of the cyclic variations. Mutual correlation of the corresponding components for successive cycles is found to be relatively low as expected, due to the high spatial variability of the combustion process in spark ignition engines. This is mainly due to the combustion of fuel pockets segregating in the combustion chamber as a consequence of the erratic behavior of the port-fuel injection process. The procedure is applied to more than one sequence of cycles under different experimental conditions. The method proves to be a relatively fast and detailed new means of non-intrusive analysis of the complex combustion processes taking place in the engine.