School of Aerospace Engineering, Huazhong University of Science and Technology

Low total temperature at takeover flight speeds, long ignition delay times for hydrocarbon fuels, incomplete fuel-air mixing, and limited fuel residence time due to high flow speeds make reliable ignition in supersonic combustion chambers extremely challenging. Larger initial flame kernels, intense non-spherical inward flow, higher flame kernel propagation velocities, and more flexible ignition position control prompt the laser technology to have much better ignition advantages under the lean fuel conditions. The selection of laser energy is important in the ignition process. Extensive studies are carried out on laser ignition of gaseous fuels, including parametric studies of ignition at different laser energies. But the laser ignition processes of liquid are few reported and presents significant difference from the gaseous fuels. In particular, cavitation bubble is induced when the laser is focussed on a liquid medium. Therefore, it is necessary to first study the influence of laser energy on the evolution of cavitation bubbles. The dynamic properties of cavitation bubbles induced by pulsed laser deposited in water with different energies from 5 mJ to 60 mJ are analyzed in the experiments. It is found two different patterns of the cavitation bubble evaluation due to the laser energy. The multiple cavitation bubbles are observed at high laser energy conditions, and their interaction has a dominant effect on the evolution of bubble. The variations of the parameters, such as maximum radius, compression wave intensity and the interacting section, are detailed discussed.