Effect mechanism of nitrogen injection into fire-sealed-zone on residual-coal re-ignition under stress in goaf

Coal is the one of foundations of energy and economic structure in China,while the unsealing of coal mine fres would cause a great risk of coal re-ignition.In order to explore the infuence of pressure-bearing state on the re-ignition characteristics for residual coal,the uniaxial compression equipped with a temperature-programmed device was built.The scanning electron microscope,synchronous thermal analyzer and Fourier transform infrared absorption spectrometer was applied to investigate the microscopic structure and thermal efect of the coal samples.Moreover,the microscopic efect of uniaxial stress on coal re-ignition is revealed,and the re-ignition mechanism is also obtained.As the uniaxial stress increasing,the number,depth and length of the fractures of the pre-treated coal increases.The application of uniaxial stress causes the thermal conductivity to change periodically,enhances the inhibition of injecting nitrogen on heat transfer and prolonges the duration of oxidation exothermic.The content of oxygen-containing functional groups has a high correlation with apparent activation energy,and coal samples at 6 MPa is more probability to re-ignite while the fre zone is unsealed.Uniaxial stress could control the re-ignition mechanism by changing the structure of fractures and pores.The side chains and functional groups of coal structure are easier to be broken by thermal-stress coupling.The higher the·OH content,the more difcult coal samples would be re-ignited.The research results would lay a solid theoretical foundation for the safe unsealing of closed fre-areas underground,tighten the common bond between the actual industry and the experimental theory in closed fre-areas underground,and provide the theoretical guidance for coal re-ignition preventing.

Theoretical Study of Combustion Processes in Aero Gas Turbines for Air Craft Engines

Combustion process involves various physical and chemical processes which govern and control flames initiation in aero gas turbine engines. During certain flying conditions, at full load, unexpected critical situation may take place in such engines called blow off conditions, which leads to flames diminishing in the combustion chamber of such engines. Gas motion, flow velocity and turbulence kinetic energy are the most important parameters in ensuring flame stabilities. These parameters play a tremendous role and effects on this phenomenon. In gas turbines, the flame exists within a high velocity, non-uniform and intensely turbulent flow field, therefore careful temperature control is vital. Another important factor which must be considered to avoid blow off conditions, is mixture strength. Nearly, all modern gas turbines, due to emissions restrictions, operate on lean mixture conditions which are hard to ignite and lower flame temperatures and thus more risk to reach blow off conditions which leads to a complete flame extinction. These conditions may exist in an air craft engines due to sharp changes in loading parameters, (θL): pressure (Pu), temperature (Tu), mass flow rate (), and cross sectional area (Au). At present there is no detailed theory of gas turbine combustion. Therefore, we must resort to simple models and experimental correlations. This paper investigates the blow-off phenomena in aero gas turbine engines, its causes and estimation of required energy to ensure recovery (re-ignition) again inside the combustion chamber. Identifying the conditions at which blow-off takes place and associated loading parameters (θL) which are a function of (A, T, P, and ). The paper also, quantify the recovery conditions (required energy to re-ignition, change in loading parameter (Δq) Power, Required VHRR: (Volumetric Heat Release Rate) and changes in other loading variables (ρ: density, T: Temperature, P: Pressure, and : mass flow rate) tarts with discussing causes of blow off along with effecting operating conditions.

Numerical Study on the Morphology of a Re-Ignited Laminar Partially Premixed Flame with a Co-Axial Pilot Flame

Re-ignited partially premixed flame(PPF)is a quite extensive flame type in real applications,which is directly relevant to the local and global extinction and re-ignition phenomenon.The authors designed a model burner to establish laminar re-ignited PPFs.Numerical simulations were carried out to reveal the morphology of laminar re-ignited PPF.Based on the distributions of temperature,heat release and radicals,the morphologies of re-ignited flames were explored.W-shaped flames were formed under pilot-lean conditions.Line-shaped and y-shaped flames were formed under pilot-rich conditions.Both w-shaped and y-shaped flames had a triple-flame structure.The re-ignited flames can stand beyond the rich flammability limit.Additionally,OH distributions indicated both pilot flame and re-ignited flame well as it rapidly increased near the flame front.OH concentration did not increase visibly while CH2O concentration mildly increased during the mild re-ignition process in the pre-zone of the re-ignited PPF.According to the results of 0-D simulations using closed homogeneous reactor,both OH and CH2O reduced ignition time significantly.The results of this work are helpful for understanding re-ignited PPF more closely.