TY - JOUR
T1 - A numerical study of the pyrolysis effect on autoignited laminar lifted dimethyl ether jet flames in heated coflow air
AU - Jung, Ki Sung
AU - Jung, Ba Reum
AU - Kang, Sang Hun
AU - Chung, Suk Ho
AU - Yoo, Chun Sang
N1 - KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2018R1A2A2A05018901). SHC was supported by KAUST. This research used the resources of the KAUST Supercomputing Laboratory and UNIST Supercomputing Center. We would like to thank Prof. T. Lu at the University of Connecticut for valuable discussions.
PY - 2019/8/9
Y1 - 2019/8/9
N2 - The liftoff, autoignition, and stabilization characteristics of autoignited laminar lifted dimethyl ether (DME) jet flames in heated coflow air are numerically investigated by varying the fuel jet velocity, U0. The detailed numerical simulations are performed using the laminarSMOKE code with a 55-species detailed kinetic mechanism of DME oxidation. An unusual U-shaped liftoff height, HL, behavior under MILD combustion condition is observed from the simulations, which is qualitatively consistent with previous experimental results. From additional numerical simulations with modified mass diffusivity of hydrogen, it is verified that the decreasing HL trend of the lifted flames under relatively-low U0 conditions is mainly attributed to the fast diffusion of hydrogen generated from the DME pyrolysis. The species transport and displacement speed analyses verify that the differential diffusion effect renders the lifted flames to be leaner at the center of the jet, ultimately leading to the change of their stabilization mechanism from the autoignition to the autoignition-assisted flame propagation mode with increasing U0. The chemical explosive mode analysis (CEMA) identifies important variables and reactions contributing to the autoignition of the DME jet flames, through which the fast diffusion rates of small species are found to cause the deviation of 2-D autoignition characteristics from that of 0-D homogeneous ignition. The effects of DME pyrolysis on the characteristics of the autoignited laminar DME jet flames are further investigated by varying the fuel tube length, Lres. HL shows a non-monotonic behavior with increasing Lres because the flame structure changes from a MILD combustion to a tribrachial edge flame and to an attached flame while the stabilization mechanism also changes from the autoignition to the autoignition-assisted flame propagation mode as the degree of the DME pyrolysis increases.
AB - The liftoff, autoignition, and stabilization characteristics of autoignited laminar lifted dimethyl ether (DME) jet flames in heated coflow air are numerically investigated by varying the fuel jet velocity, U0. The detailed numerical simulations are performed using the laminarSMOKE code with a 55-species detailed kinetic mechanism of DME oxidation. An unusual U-shaped liftoff height, HL, behavior under MILD combustion condition is observed from the simulations, which is qualitatively consistent with previous experimental results. From additional numerical simulations with modified mass diffusivity of hydrogen, it is verified that the decreasing HL trend of the lifted flames under relatively-low U0 conditions is mainly attributed to the fast diffusion of hydrogen generated from the DME pyrolysis. The species transport and displacement speed analyses verify that the differential diffusion effect renders the lifted flames to be leaner at the center of the jet, ultimately leading to the change of their stabilization mechanism from the autoignition to the autoignition-assisted flame propagation mode with increasing U0. The chemical explosive mode analysis (CEMA) identifies important variables and reactions contributing to the autoignition of the DME jet flames, through which the fast diffusion rates of small species are found to cause the deviation of 2-D autoignition characteristics from that of 0-D homogeneous ignition. The effects of DME pyrolysis on the characteristics of the autoignited laminar DME jet flames are further investigated by varying the fuel tube length, Lres. HL shows a non-monotonic behavior with increasing Lres because the flame structure changes from a MILD combustion to a tribrachial edge flame and to an attached flame while the stabilization mechanism also changes from the autoignition to the autoignition-assisted flame propagation mode as the degree of the DME pyrolysis increases.
UR - http://hdl.handle.net/10754/656775
UR - https://linkinghub.elsevier.com/retrieve/pii/S0010218019303529
UR - http://www.scopus.com/inward/record.url?scp=85070199467&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2019.07.042
DO - 10.1016/j.combustflame.2019.07.042
M3 - Article
SN - 0010-2180
VL - 209
SP - 225
EP - 238
JO - Combustion and Flame
JF - Combustion and Flame
ER -