TY - JOUR
T1 - Study of ignition chemistry on turbulent premixed flames of n-heptane/air by using a reactor assisted turbulent slot burner
AU - Windom, Bret
AU - Won, Sang Hee
AU - Reuter, Christopher B.
AU - Jiang, Bo
AU - Ju, Yiguang
AU - Hammack, Stephen
AU - Ombrello, Timothy
AU - Carter, Campbell
N1 - Funding Information:
This work was supported by the AFOSR Research Grant FA9550-12-1-0140 and by the Air Force Research Laboratory, Aerospace Systems Directorate. BJ was supported by the China Scholarship Council. The authors sincerely thank Prof. Tonghun Lee (University of Illinois at Urbana Champaign) for help with kHz PLIF measurements.
Publisher Copyright:
© 2016 The Combustion Institute.
PY - 2016/7/1
Y1 - 2016/7/1
N2 - The changes in flame structure and burning velocity of premixed n-heptane/air flames associated with ignition chemistry have been investigated in a reactor-assisted turbulent slot (RATS) burner. Two distinct turbulent flame regimes are identified by varying the flow residence time and reactor temperature. A chemically frozen (CF) regime is observed at a reactor temperature of 450K and a low-temperature ignition (LTI) regime is identified at 650K. At a reactor temperature of 450K, the measured turbulent burning velocities (ST) exhibit a monotonic trend, proportional only to the turbulent intensity and laminar flame speed (SL) calculated with the initial fuel/air mixture. At a reactor temperature of 650K, ST initially decreases with increasing flow residence times (decreasing turbulent intensity) but then increases once the reactor flow residence time exceeds the LTI delay. Furthermore, ST in the LTI regime exhibits a strong correlation with the extent of low-temperature reactivity (defined by CH2O concentration). The species distributions at the exit of the RATS burner after the onset of LTI are quantified by gas sampling-chromatography and used to compute the changes in SL and mixture Lewis number (Le), which are shown to substantially change after the onset of LTI. Damköhler's scaling analysis indicates that the increase in ST in the LTI regime originates from an increase in SL, a decrease in Le, and an increase in turbulence intensity due to the heat release from the low-temperature chemistry. To examine the role of ignition chemistry on flame stability, flame flashback measurements have been performed by varying mean jet velocities and n-heptane/air mixture equivalence ratios for reactor temperatures of 450 and 650K. Measurements at 650K imply the strong influence of high-temperature ignition on flame stability phenomena.
AB - The changes in flame structure and burning velocity of premixed n-heptane/air flames associated with ignition chemistry have been investigated in a reactor-assisted turbulent slot (RATS) burner. Two distinct turbulent flame regimes are identified by varying the flow residence time and reactor temperature. A chemically frozen (CF) regime is observed at a reactor temperature of 450K and a low-temperature ignition (LTI) regime is identified at 650K. At a reactor temperature of 450K, the measured turbulent burning velocities (ST) exhibit a monotonic trend, proportional only to the turbulent intensity and laminar flame speed (SL) calculated with the initial fuel/air mixture. At a reactor temperature of 650K, ST initially decreases with increasing flow residence times (decreasing turbulent intensity) but then increases once the reactor flow residence time exceeds the LTI delay. Furthermore, ST in the LTI regime exhibits a strong correlation with the extent of low-temperature reactivity (defined by CH2O concentration). The species distributions at the exit of the RATS burner after the onset of LTI are quantified by gas sampling-chromatography and used to compute the changes in SL and mixture Lewis number (Le), which are shown to substantially change after the onset of LTI. Damköhler's scaling analysis indicates that the increase in ST in the LTI regime originates from an increase in SL, a decrease in Le, and an increase in turbulence intensity due to the heat release from the low-temperature chemistry. To examine the role of ignition chemistry on flame stability, flame flashback measurements have been performed by varying mean jet velocities and n-heptane/air mixture equivalence ratios for reactor temperatures of 450 and 650K. Measurements at 650K imply the strong influence of high-temperature ignition on flame stability phenomena.
KW - Flashback
KW - KHz LIF diagnostic
KW - Low temperature ignition
KW - N-Heptane
KW - Turbulent burning velocity
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U2 - 10.1016/j.combustflame.2016.02.031
DO - 10.1016/j.combustflame.2016.02.031
M3 - Article
AN - SCOPUS:84964948320
SN - 0010-2180
VL - 169
SP - 19
EP - 29
JO - Combustion and Flame
JF - Combustion and Flame
ER -