TY - JOUR
TI - Characterization of critical stretch rate using outwardly propagating spherical flames
AU - De La Rosa-urbalejo Daniel
AU - Martínez-Martínez Simón
AU - Sánchez-Cruz Fausto A
JN - Thermal Science
PY - 2019
VL - 23
IS - 2
SP - 561
EP - 571
PT - Article
AB - Outwardly propagating spherical flames within a constant volume combustion  chamber (CVCC) are studied to analyse the non-linear relationship between  flame stretch and flame speed, enabling a critical appraisal of a methodology  proposed for characterizing the critical stretch rate. Four fuels, namely  methane, propane, methanol and ethanol in air, are chosen to investigate the  correlation between maximum critical stretch rate and the flame extinction  across a range of equivalence ratios at various ambient conditions in  under-driven flames, and to compare the hypothesis against data from the  traditional counter-flowing flame technique. Flame propagation is recorded  via high-speed Schlieren photography, and low ignition energies are achieved  via a variable capacitive-discharge supply, enabling the critical early  stages of flame propagation, critical stretch rate and the sensitivity of the  non-linear methodology to ignition energy to be systematically analysed. The  non-linear methodology shows partial agreement with extinction stretch rate  from counter flowing flames, particularly in the case of gaseous fuels.  Although the fuel vapour data lies between previous extinction stretch rate  measurements using the counter-flowing flame methodology, and predictions  from chemical kinetic schemes, a 40% deviation is observed. A mathematical  expression was produced to determine the critical stretch at the specific  conditions of the present work.