A numerical study is conducted to grasp the flame structure and NO emissions for a wide range of oxy-fuel combustion (covering from air-blown combustion to pure oxygen combustion) and various mole fractions of recirculated CO 2 in a CH 4 -O 2 /N 2 /CO 2 counterflow diffusion flame. Special concern is given to the difference of the flame structure and NO emissions between air-blown combustion and oxy-fuel combustion w/o recirculated CO 2 and is also focused on chemical effects of recirculated CO 2 . Air-blown combustion and oxy-fuel combustion without recirculated CO 2 are shown to be considerably different in the flame structure and NO emissions. Modified fuel oxidation reaction pathways in oxy-fuel combustion are provided in detail compared to those in air-blown combustion without recirculated CO 2 . The formation and destruction of NO through Fenimore and thermal mechanisms are also compared for air-blown combustion and oxy-fuel combustion without recirculated CO 2 , and the role of the recirculated CO 2 and its chemical effects are discussed. Importantly contributing reaction steps to the formation and destruction of NO are also estimated in oxy-fuel combustion in comparison to air-blown combustion.

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SUMMARYIn order to understand the e!ect of coal type on coal gasi"cation process at 15 atmospheric pressure of pressurized drop tube furnace (PDTF), a numerical study was conducted. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the solid phase. Turbulence is modelled using the standard k} model. The turbulent gas-phase combustion model incorporates the eddy dissipation model. One-step two-reaction model is employed for the devolatilization.E!ect of coal type on carbon conversion at the same coal feed rate and gas #ow rate cannot be veri"ed due to the variation of equivalence ratio according to coal composition. Therefore, the same equivalence ratio is chosen to evaluate the e!ect of coal type on gasi"cation. It is found that the volatile release based on experimental results should be taken in computations to predict accurate carbon conversion, especially in coal gasi"cation due to the low gasi"cation reaction. Even at over 1500 K and 15 atmospheric pressure, at which reactions are primarily di!usion-controlled, the exit carbon conversion varies with the coal type. The temperature gradient in near-burner region becomes gentle with increasing proximate volatile and moisture contents, but the volatiles released can make the temperature gradient steep by means of the fast reaction with oxygen.

SUMMARYHydrogen-blending effects in flame structure and NO emission behaviour are numerically studied with detailed chemistry in methane-air counterflow diffusion flames. The composition of fuel is systematically changed from pure methane to the blending fuel of methane-hydrogen through H 2 molar addition up to 30%. Flame structure, which can be described representatively as a fuel consumption layer and a H 2 -CO consumption layer, is shown to be changed considerably in hydrogen-blending methane flames, compared to pure methane flames. The differences are displayed through maximum flame temperature, the overlap of fuel and oxygen, and the behaviours of the production rates of major species. Hydrogen-blending into hydrocarbon fuel can be a promising technology to reduce both the CO and CO 2 emissions supposing that NO x emission should be reduced through some technologies in industrial burners. These drastic changes of flame structure affect NO emission behaviour considerably. The changes of thermal NO and prompt NO are also provided according to hydrogen-blending. Importantly contributing reaction steps to prompt NO are addressed in pure methane and hydrogen-blending methane flames.