Towards Plasma-Assisted Combustion Using a Continuous Optical Discharge

Abstract

The following contribution investigates the use of a laser-initiated continuous optical discharge (COD) for applications related to plasma-assisted combustion. The COD proposed here is initiated using a fs-LASER pulse in high-pressure H2-O2 mixtures (T0=300K, p0=30 bar). Subsequently, a high-power continuous wave (CW) laser is employed to add energy into the pre-ionized gas. The preliminary studies presented here focus on the use of a 1-D axis-symmetric CFD model to better understand the CW laser intensity required to heat, and, ultimately, ignite the combustible mixture. Simulation results suggest that the heated kernel generated by a femtosecond plasma filament (ne=1x1017 cm-3, T=600 K) can be maintained by overlapping a CW laser at ILASER=1x104 W/cm2 due to the laser-induced inverse bremsstrahlung energy absorption. Further increasing the laser intensity leads to significant gas heating. For example, we report a maximum kernel temperature of T=2540 K at ILASER=1x106 W/cm2. Successful combustion was also achieved using a laser intensity of 1x104 W/cm2 with an ignition delay of 330 μs. The ability to sustain and tailor the plasma properties using a CW plasma can have a broad range of applications for combustion including ignition, flame stabilization, flame holding and reduction of emissions. The goal of the present study is to provide evidence of COD gas heating and quantify the required laser intensities to aid in sizing the CW laser system required for experimental testing.