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| 2. |
- Wang, Shixing, et al.
(författare)
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Experimental study and kinetic analysis of the laminar burning velocity of NH3/syngas/air, NH3/CO/air and NH3/H2/air premixed flames at elevated pressures
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 221, s. 270-287
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Tidskriftsartikel (refereegranskat)abstract
- Mixing ammonia with syngas can be a promising way to overcome the low reactivity of ammonia, allowing it to find usage in IGCC (Integrated Gasification Combined Cycle) systems and gas turbines for power generation. However, fundamental experimental data on laminar burning velocity of NH3/syngas/air are rather scarce, especially at elevated pressures. This information is critical for the development and validation of reaction mechanisms and advances in combustor design. In the present work, measurements of the laminar burning velocities (SL) of NH3/syngas/air, NH3/CO/air, and NH3/H2/air premixed flames were performed by the heat flux method at pressures up to 5 atm, equivalence ratios ranging from 0.7 to 1.6, ammonia mole fractions in the fuel mixture from 0.2 to 1.0 in the NH3/syngas/air mixtures and 0.03–1.0 in the NH3/CO/air mixtures. Several recently published ammonia oxidation mechanisms were tested against the present experimental data. The measurements and predictions of SL exhibit discrepancies especially for NH3/H2/air flames at elevated pressures. The pressure exponent factors, β, characterizing burning velocity at elevated pressure via empirical power-law correlation SL/SL0 = (P/P0)β are extracted from the measured SL and compared with the numerical results. The thermal, diffusion, and chemical effects of blending syngas with ammonia on SL of the mixtures are distinguished, and the dominant role of the adiabatic flame temperature on the variation of the pressure exponent β is discussed. Kinetic modeling and sensitivity analyses showed that reactions of NHi to N2Hi (i = 0–4) species affect the predicted SL under rich conditions. At elevated pressures, these reactions also affect the NO formation via third-body collision reactions and NHi + NO reactions. Even for rich flames, the ammonia consumption is favored with the addition of syngas which also promotes NO formation by enriching the H and OH radical pools and increasing the flame temperature. The addition of hydrogen or carbon monoxide has equally promoting effect on the ammonia decomposition and NOx formation although their flame speed differs a lot.
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| 3. |
- Yu, Sen Bin, et al.
(författare)
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非预混旋流火焰中部熄火及重新稳燃机理研究
- 2021
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Ingår i: Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics. - 0253-231X. ; 42:12, s. 3312-3319
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Tidskriftsartikel (refereegranskat)abstract
- The effects of quarl on the non-premixed swirling flames were studied by performing simultaneous OH-PLIF/PIV measurements experimentally and coupling LES with PDF combustion model numerically. The results showed that LES-PDF method can successfully capture the swirl flow fields and flame structures even including local extinction and re-stabilization. Compared to the no quarl case, the quarl plays a significant role on the expansion of the recirculation zone thus influencing the attached flame and the following extinction, though it affects the re-stabilization height rarely. With the high scalar dissipation rate, local extinction occurs due to the strong heat loss caused by the central fuel jet. In addition, fuel and air are partially premixed accompanied with some partial oxidation reactions producing CH2O, which provides preferential conditions for the stabilization of the non-premixed swirling flame. Moreover, the reaction rate term of OH is at least 10 times larger than its diffusion term, indicating that the reaction front dominates the re-ignition process for the flame re-stabilization downstream. It is thus concluded that the partially premixed flame propagation plays a dominant role in controlling the re-stabilization of this flame.
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| 4. |
- Yu, S., et al.
(författare)
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LES/PDF modeling of swirl-stabilized non-premixed methane/air flames with local extinction and re-ignition
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 219, s. 102-119
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent non-premixed flames with local extinction and re-ignition exhibit multiple combustion modes including ignition waves, diffusion flames, partially premixed flames, and ignition-assisted partially premixed flames. The mechanisms of local extinction and re-ignition are not well understood and numerical modeling of multi-mode combustion is a challenging task. In this work, a specially designed swirl-burner was used to study local extinction and re-ignition of non-premixed turbulent methane/air flames. High speed Particle Image Velocimetry (PIV) and laser induced fluorescence of OH radicals (OH-PLIF) measurements along with Large Eddy Simulation (LES) were carried out to investigate the mechanisms of extinction and re-ignition processes in the burner. LES is based on a transported probability density function model within the framework of Eulerian Stochastic Fields (PDF-ESF). It is found that local extinction occurs when the scalar dissipation rate around the stoichiometric mixture fraction is high. The characteristic time scale for local extinction and re-ignition in the present flames is an order of magnitude longer than the characteristic time scale of diffusion/extinction of laminar flamelets. There are two mechanisms for flame hole re-ignition in the present flames. First, under low degree of local extinction conditions (i.e., for small flame holes surrounded by flames) the flame hole re-ignition is due to the mechanism of turbulent flame folding. Second, under high degree of extinction conditions (i.e., with large regions of extinction and lifted flames), re-ignition of the locally extinguished flame is due to the mechanism of ignition assisted partially premixed flame propagation. The results show that the PDF-ESF model is capable of simulating the quenching and re-ignition process found in the experiments.
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