Spatio-temporal effect of the breakdown zone in the laser-initiated ignition of atomized ethyl alcohol-air mixture

Abstract

Laser initiated ignition would play a vital role in future gas turbine combustors. Two lasers of 270 μJ and 50 mJ pulse energy are used to study the laser-induced spark ignition of atomized ethyl alcohol-air mixture. With the low-energy pulse of 270 μJ energy, no display of ignition is observed even though it fulfills the threshold conditions to create breakdown. However, with the high-energy pulse of 50 mJ energy, ignition is observed if the plasma kernel was following certain conditions after the occurrence of the breakdown. It is observed that breakdown created by the low-energy pulse was unable to ignite the atomized ethanol-air mixture because the lifetime of the plasma kernel was very small (in microseconds). While performing the study with high-energy pulse, it is observed that the breakdown becomes a sufficient condition for ignition only when the lifetime of the kernel is couple of milliseconds. Additionally, the spatial location of the laser spark is found to play a vital role in successful ignition of the mixture. This work also discusses the spray formation process with its effect on ignition and the role of the third lobe on rapid development of the plasma kernel. The process of laser energy deposition to full scale combustion is categorized into three events. Finally, based on the experimental observations, this work has proposed some favourable conditions for initiating ignition with a laser spark. Knowledge of the proposed conditions can play a vital role for designing a practical laser ignition system.