Quantification of the Interactions between Flow and Laser-Induced Plasma

Abstract

Laser ignition is a new type of ignition system, operated by focusing a laser beam into one single point for igniting fuel. It is spotlighted with its high energy density and flexibility for optimizing timing and location of ignition. With the increasing demand of performance and emission control, this laser spark method is regarded as an alternative way of igniting fuel to the conventional electric spark-plug ignition system.

There is little research describing hydrodynamic effects between fuel droplet and laser spark. These interactions can affect severely to following flame propagation, which decides the quality of final combustion. Therefore, this study aims at characterizing the movement between gaseous flow and laser spark (so called, LIP, laser-induced plasma).

After creating LIP by focusing the laser beam, we took the time-resolved image by high-speed camera based on PIV technique. The velocity field before and after the creation of plasma could be measured by the adaptive correlation. Through virtual trajectory analysis, which is based on the interpolation of velocity fields from initial points, lets us deduce the position and angle of each trajectory affected by LIP.

Our study suggests a quantitative way to describe the interaction of LIP and flow. Velocity fields analysis of single and double-point LIP shows the statistics of LIP with the information of system’s characteristic time. Through the virtual trajectory analysis, we can trace the time-resolved trajectories with the information of position and angle at each point.

In conclusion, our study helps to understand the dynamic influence of LIP to gaseous flow. Based on velocity fields and virtual trajectory analysis, it is possible to characterize the system quantitatively with the knowledge of characteristic time, time-resolved local angle and position. This work can be extended with liquid fuel droplet, with higher inertial effect. Eventually, we hope this study to be the basic step to predict the hydrodynamics of flame generation in laser ignition.