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This study presents two new methods to rapidly analyze the ignition and combustion events recorded during in-cylinder high-speed imaging of homogeneous charge compression ignition (HCCI) and spark-assisted (SA) HCCI engine operation. Two categories of ignition have been observed during HCCI and SA HCCI: auto-ignition of parcels of fuel/air and ignition and propagation of reaction fronts. In this work, two methods of image analysis are developed which accommodate differences in the ignition and propagation events for the two categories. The methods are described by application to high speed imaging data acquired from an optically accessible engine operated in HCCI and SA HCCI modes using indolene fuel. Using method I, the projected area of reaction is identified in each frame, and a circle with a characteristic radius that yields the equivalent area is defined. The rate of area expansion is used to define the speed of reaction. Using method II, an edge-finding algorithm is used to identify the location of well-defined reaction fronts. The maximum dimensions of the reaction front in an x-y coordinate frame are measured. The projected area based on the average of these maximum dimensions is then determined. The change in the characteristic radius of the projected area is defined as the average propagation speed for the reaction front. The two analytical methods are applied to typical HCCI and SA HCCI image sequences. Outcomes of the image analysis indicate propagation speeds are typically between 2–5 m/s prior to volumetric ignition. Volumetric ignition is identified by propagation speeds greater than 20 m/s. The imaging data also identify times when reaction quenching occurred after spark ignition as times when negative propagation speeds are observed. When applied to the same imaging sequence, the two methods yield consistent results for propagation speeds; however, the method based on edge-finding exhibits larger variance.Copyright © 2010 by ASME

High-speed imaging combined with the optical access provided by a single-cylinder research engine offer the ability to directly study ignition and combustion phenomena. Such data provide valuable insight into the physical and chemical mechanisms important in advanced engine combustion strategies. In this study, crank-angle resolved chemiluminescence imaging data both orthogonal to and along the piston axis were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using indolene. This preliminary study focused on identifying how multi-axis imaging can contribute to understanding the effects of spark-assist on HCCI performance. Operating conditions of advanced spark ignition timing for extending the lean limits of bulk charge compression ignition were used. The experiments were performed at a fixed equivalence ratio of φ = 0.56, with fixed intake conditions (wide open throttle with air preheat). The multi-axis imaging provides a clear indication of the propagation of a reaction front from the spark kernel. The combination of orthogonal and axial views may provide valuable information spatially resolving volumetric heat release, thereby providing an indication of the fractional energy release due to the spark assist compared to the energy released by auto-ignition.Copyright © 2007 by ASME

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from φ = 0.77 to 0.27. The time-resolved imaging and pressure data show high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially-resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data.Copyright © 2006 by ASME