Ignition and Extinction Behavior of Fuels in a Microcombustor
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Direct numerical simulation of micro combustion in a narrow circular channel with a detailed kinetic mechanism
Abstract Direct Numerical Simulation (DNS) of micro combustion in a narrow circular channel is conducted for a methane–air mixture. The narrow circular channel with a radius of 0.5 mm is supposed to have a wall temperature gradient in the streamwise direction. To represent the methane–air reaction, a detailed kinetic mechanism (GRI-Mech 3.0) including 53 species and 325 elementary reactions is adopted. Four series of DNS are conducted with different inflow temperature and wall temperature gradient to investigate the unsteady phenomena in micro combustion. Similar to the previously reported experiment, unsteady behaviors of the flame such as the oscillating flame and the flame repetitive extinction and ignition (FREI) are obtained depending on the inflow temperature and the wall temperature gradient. To investigate the FREI mechanism, the total heat transfer rate through the wall of the mixture is introduced and evaluated in one cycle of both FREI and oscillating flame. It has been shown that FREI possesses the negative phase in the total heat transfer rate through the wall. Therefore it suggests that the definition of the origin of FREI is given by this total heat transfer rate. It is also presented that the amplitude and period of FREI exhibit linear relationships with the wall thermal thickness based on the wall temperature gradient when they are scaled by the inflow mass flux of the mixture and the thermal thickness of the steady flame at the same inflow and outflow temperature conditions.
Morphological and molecular evidence for a new species of the genus Raphidascaris (Nematoda: Anisakidae) from marine fishes from the South China Sea
A new anisakid nematode, Raphidascaris (Ichthyascaris) longispicula sp. nov., is described from the intestine and stomach of the marine fish Uroconger lepturus (Richardson) (Anguilliformes: Congridae) from the South China Sea (Guangdong and Hainan Province, respectively). The new species differs from all congeners in the subgenus Ichthyascaris by the short ventricular appendix (0.36–0.49 mm long), the number and arrangement of caudal papillae (25–28 pairs of preanal, 1–2 pairs of paranal, and 6–8 pairs of postanal), and the very long spicules (1.13–1.32 mm long, representing 9.34–10.3% of body length). The sequences of the internal transcribed spacer of ribosomal DNA of R. (I.) longispicula sp. nov. are analyzed and compared with the closely related nematode sequences. Molecular analyses seem to support the validity of this new nematode species based on morphological observation.