Single-laser-shot femtosecond coherent anti-Stokes Raman scattering temperature measurements at 5 kHz in a jet diffusion flame
Abstract
The objective of this research is to apply recently developed femtosecond (fs) coherent anti-Stokes Raman scattering (CARS) spectroscopy diagnostic techniques on an unsteady jet diffusion flame. With the advantage of using a 5kHz repetition rate laser system, higher data rates can be achieved which will provide information of transient processes occurring in the diffusion flame which occur on time scales smaller than those measurable using current nanosecond CARS techniques. In the experiment pump and Stokes pulses arrive at the probe volume simultaneously while the probe pulse is chirped using a 30 cm glass rod. The glass rod introduces a chirp in the probe pulse which forces the different frequency components of the pulse to leave the glass rod at different times due to their interaction with different indices of refraction. The pump and Stokes pulses excites the Raman transition and while the transitions first oscillate in phase they degenerate to their own natural frequencies which causes interference and Raman coherence decay. The chirped probe pulse interacts with this coherence to create the CARS signal while mapping the coherence decay to the frequency of the CARS signal. CARS spectra is recorded in a near adiabatic Hencken burner and used as reference temperature spectra. Spectra is then recorded in an unsteady jet diffusion flame over various different radial positions at three different heights above the nozzle, x/d = 0.6, 2.0, and 15.0. The spectra recorded as a reference is input into an already developed spectral fitting code to calculate various laser parameters while holding the temperature constant. The laser parameters are then used to fit experiment spectra recorded in the jet flame to determine the temperature. Temperatures are detected in the jet flame from 400-2500 K while using laser parameters which provide low error levels when fitting to shots in those temperature ranges.
Degree
M.S.M.E.
Advisors
Lucht, Purdue University.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.