Abstract

Laser ignition of kerosene droplets and sprays was investigated experimentally in a lab-scale flow channel under well-defined boundary conditions. The work was performed in the context of research in the field of altitude relight of aero engines and covered fundamental aspects of the transition from an ignition plasma to a flame kernel. Optical diagnostics based on schlieren imaging, shadowgraphy, light scattering and spectral analysis were applied with high temporal resolution. A particular aspect of the study was the effect of the blast wave on nearby droplets. The physical and chemical processes during the transition from a plasma to a flame were analyzed by the measurement of the temporal development of the optical emissions. While in the first few hundred nanoseconds after breakdown broadband emissions from bremsstrahlung and lines from ionic species dominated the spectrum, atomic and molecular species contributed after approximately 1 μs. Finally, the appearance of CH chemiluminescence indicated the onset of combustion within about 100 μs after the laser pulse. The experimental results gave insights into details of the complex transient processes during ignition and present a data base for the validation of numerical simulations.

© 2015 Optical Society of America