| dc.description.abstract | This study quantitatively measures the laminar and turbulent burning velocities (ST and SL) of premixed hydrogen/carbon monoxide syngas flames over an initial pressure range of p = 0.1 ~ 1.0 MPa. A series of centrally-ignited laminar and turbulent combustion experiment are performed, using a high-pressure, fan-stirred, large-scale, turbulent combustion system. This turbulent combustion system included an inner chamber and an outer chamber, as a double-chamber design. The inner chamber applies the same design of the cruciform burner previously used at National Central University led by Professor Shy, which is constructed by two mutually crossing cylindrical vessels, a horizontal vessel and vertical vessel, forming a cruciform shape. Using two identical frequency-controlled counter-rotating fans equipped at two ends of the horizontal vessel, a near-isotropic turbulent flow field can be generated in the central region of the inner chamber. In it the maximum value of turbulent fluctuating velocities u’’ can be up to 8.4 m/s. Furthermore, four sensitive pressure-releasing valves placed symmetrically around the vertical vessel of the inner chamber are applied. These valves are immediately activated when the pressure inside the inner chamber is 25 kPa greater than that of the outer chamber during explosion. Thus, outwardly propagating premixed flames interacting with isotropic turbulence can be obtained under nearly constant pressure condition. Besides, the outer chamber is large enough to absorb pressure releasing from the inner chamber, assuring the safety of experiments. Flame visualizations are carried out via optical-accessed quartz windows of both chambers using high-speed, high-resolution CMOS cameras. After the image processing, the flame burning velocities can thus be obtained. In this study, we select the syngas derived from entrained-flow gasifier with a fuel composition 65%CO/35%H2 at two different equivalence ratios of ? = 0.5 and 0.7 to measure laminar and turbulent velocity. Besides, in order to investigate effect of different syngas fuel composition for laminar and turbulent burning velocities, we also select two different syngas fuel composition 50%CO/50%H2 and 95%CO/5%H2, at the same ? = 0.7 to measure the laminar and turbulent burning velocities. Results show that lean syngas laminar and turbulent flames at elevated pressure are highly unstable resulting in cellular structures all over the expanding flame front surface. It is also found the laminar burning velocities all decrease with increasing pressure in a minus exponential manner for different equivalence ratios and syngas fuel composition, by which SL ~ p-n where the values of n range from 0.10 to 0.20. This trend is more modest than the same effect of pressure on lean methane laminar flame (SL ~ p-0.41). Contrarily, at a fixed u? ≈ 1.4 m/s, values of lean syngas ST increase with increasing pressure, by which ST ~ pm where the values of m range from 0.10 to 0.22. It is also found that, at any given pressure condition varying from p = 0.1 ~ 1.0 MPa, increasing hydrogen or equivalence ratios of syngas increases values of SL and ST. Moreover, in order to further investigate effect of turbulence on ST, we measures the changes of ST with different turbulent intensities at two different initial pressure 0.1 MPa and 0.5 MPa. Results show that increasing turbulent intensity is still a way much more effective in increasing value of ST/SL than increasing pressure, but the increments of ST/SL with u?/SL is getting smaller and smaller, revealing the bending effect. Moreover, this bending effect also exist at high pressure condition and pressure elevation seems to be able to delay bending effect. The present result should be of help in the direct application of syngas for gas turbines and internal combustion engines.
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