High speed imaging in fundamental and applied combustion research

This overview presents examples of applications of high frame rate imaging diagnostics in fundamental and applied combustion research. Progress in the performance of high frame rate digital cameras and high repetition rate lasers enabled the development of a range of new imaging diagnostics for measurements of velocities, concentrations and temperatures. Camera frame rates and storage capacities are now adequate to resolve and follow time scales spanning six orders of magnitude while camera chip size limitations restrict the spatial dynamic range to about three orders of magnitude. High-speed imaging studies of mixing processes, flame stabilization, ignition and extinction and the coupling of acoustic and chemical processes in turbulent flames and internal combustion engines have produced a wealth of new understanding, contributing also to the development of predictive models. Future progress in designing and operating cleaner and more efficient combustion device hinges on our ability to push operating conditions to leaner mixtures and often to higher pressures. There, small variations in boundary conditions, e. g. flow patterns or the formation of a fuel spray, might lead to combustion failures that can range from acoustic noise in a jet flame, a misfire in an automobile engine, to lean-blow-out of an aircraft gas turbine engine; from nuisance to catastrophe. High-speed imaging in turbulent flames and internal combustion engines allowed capturing and identifying detrimental conditions that might be rare in occurrence and defining in leading to failure. The examples presented in this review illustrate the status of diagnostic capabilities, show sample results, and examine some future directions. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.