| Syngas, derived from coal, biomass and organic waste gasification, is considered to be a more attractive fuel due to the cleanness and high efficiency. Compared with direct combustion of solid fuel, syngas (basis CO/H2/CH4/CO2/N2/O2) can not only enhance energy utilization efficiency but also reduce the toxic emission, which is very potential for further energy conversion and utilization. However, the complex gas composition, much lower low calorific value (LCV) and combustion instability of syngas as well as the shortage of combustion mechanism research, the practical application of syngas is faced with huge challenge. Therefore, it is necessary to investigate the combustion characteristic in depth, and efficiently and cleanly utilize the LCV syngas.Laser diagnostics in combustion is a kind of ideal instrument for combustion mechanism investigation due to the noninterference for flow field and nice applicability for the abominable combustion environment. Premixed laminar and turbulent combustion characteristic of syngas and combustion enhancement of O3were investigated using advanced laser diagnostics technology and formed a relative comprehensive and systemic syngas combustion theory, which not only provide groundwork and guidance for the development and optimize of new combustion equipment, but also have great meaning for future combustion science and engineering design.First, laminar flame temperatures of lean premixed bituminous coal gasification syngas were measured quantitatively using Rayleigh scattering and the results of thermocouple and CHEMKIN calculation were also carried out to compare with the experimental results; then adiabatic laminar flame speeds of two typical syngases:5%H2-95%CO and20%H2-20%CO-60%N2were accurately measured using improved Heat Flux method and thermographic phosphor. Three chemical kinetic mechanisms:GRI-Mech3.0, USC Mech Ⅱ and Davis’H2/CO were adopted to calculate and evaluate the experimental data. Results show that N2dilution restrain the flame speed of syngas while higher preheat temperature accelerate the flame speed. The smallest measurement uncertainty of the flame speed using heat flux method in present measurement was±0.5975cm/s. The Davis’H2/CO mechanism gives the best prediction among all the three models.Then, lean premixed turbulent flame characteristics of several typical coal/biomass gasification syngases were investigated using OH planar laser induced fluorescence (PLIF) technology, including turbulent flame structure, flame front and turbulent flame speed etc. The syngases were prepared according to the actual gas composition of syngas. Results show that equivalence ratio, H2content, LCV and turbulence intensity are the most effective factors influencing the OH radical intensity distribution, thickness of OH reaction layer, flame length, flame front and turbulent flame speed. The bituminous coal gasification syngas has the fastest turbulent flame speed and tends to burn out easily. Through changes in thickness of the OH layers and signal intensities, the reaction layer can be compressed by intensifying turbulence and thereby the combustion processes of syngas.In the end, the adiabatic laminar flame speeds of premixed methane/air flames with/without O3additive were accurately measured using the Heat Flux method, and the effect of O3on the enhancement of flame speed was investigated. An improved new16-step O3kinetic mechanism were proposed and adopted in the PREMIX module of CHEMKIN to calculate and validate the experimental results, including the premixed flame temperature, main radical distribution, sensitivity analysis of10key reactions and flame speed. The crucial reactions for the combustion enhancement by ozone additive were confirmed and the enhancement mechanism of ozone was investigated. Results show that Extra O radicals contributed by O3molecules in the pre-heat zone initiate and accelerate the chain-branching reactions and consequently increase the burning velocity. |
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