Single-shot CARS imaging of near-wall turbulent reacting flows

Single-shot CARS imaging of near-wall turbulent reacting flows

El Sioufy, Karim (TU Delft Aerospace Engineering)

Bohlin, Alexis (mentor)

Delft University of Technology

Aerospace Engineering

2020-04-09

This master thesis investigates the assessment of Flame-Wall Interaction using 1D broadband RCARS thermometry. Flame-Wall Interactions (FWI) have been shown to adversely effect combustion processes in terms of both efficiency and maximum performance. Heat and momentum losses cause incomplete combustion and allow for unburnt hydrocarbons (UHCs) and unoxidised radicals such as carbon monoxide to leave a combustion engine. This is not accurately represented within presently used combustion models, which raises the need for accurate data on essential combustion parameters, such as temperature, during a FWI. In order to assess thermal energy losses, CARS thermometry has been found to be an accurate, non-intrusive temperature measuring technique which can be used for in situ probing of combustion processes. Due to increasing power densities of newly developed combustion engines as well as continuously increasing aerial traffic, the adverse effects of FWI on combustion affect the efficiency and environmental impact of aircraft engines only increases. By curbing the losses induced by maintaining combustion in a confined space, depleting fuel reserves are better conserved and adverse environmental effects curbed. This study focuses on the evaluation of temperature data obtained by broadband RCARS thermometry of a turbulent FWI as well as the delay of the probe pulse with respect to the pump/Stokes beams. Since the dephasing of the excited rotational states is not constant across the rotational states, the measured relative population of each state changes with increasing delay. In order to compensate for the resulting spectral heating issue, the pulse delay needs to be accounted for when generating the spectral libraries used to obtain temperature information from the spectral data captured by the camera. The integrity of these spectral libraries has been investigated by performing a spectral fitting routine of ideal CARS spectra computed by a Matlab code. The spectral libraries consist of Nitrogen CARS spectra ranging from 200K to 2400K in steps of 100K. The probe pulse delays investigated range from 50 ps to 450 ps. The temperature error measured in this study reduces with an increase in temperature and alternates between overestimating and underestimating the actual temperature of the investigated spectrum.

CARS thermometry
turbulen combustion
FWI

http://resolver.tudelft.nl/uuid:cb6f3320-702b-44a2-b31c-b126dc19f3ae

Student theses

master thesis

© 2020 Karim El Sioufy