The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- ti...The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- tion position, eddy dissipation concept （EDC） model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter. Simulation was conducted under six oxidant stream conditions with dif- ferent OjN2/CO2 molar ratios： 21/79/0, 30/70/0, 50/50/0, 21/0/79, 30/0/70 and 50/0/50. Results showed that 02 en- richment in the primary oxidant stream is in favor of combustion stabilization, acceleration of ignition and increase of maximum flame temperature, while the full substitution of N2 by CO2 in the oxidant stream delays ignition and decreases the maximum flame temperature. However, the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream. Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30% 02 and 70% CO2 in the oxidant stream, indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one. The swirl burner with a specially designed preheating chamber can increase flame temperature, accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion. Also, qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain 02 enrichment and oxy-coal combustion conditions against the air-coal combustion.展开更多
A suitable inductor modeling for power electronic DC-DC converters is presented in this paper. It is developed with the aim of improving inductor losses estimation achievable by averaged models, which inherently negle...A suitable inductor modeling for power electronic DC-DC converters is presented in this paper. It is developed with the aim of improving inductor losses estimation achievable by averaged models, which inherently neglect inductor current ripple. In order to account for its contribution to the overall inductor losses, an appropriate parallel resistance is thus enclosed into the inductor model, whose value should be chosen in accordance with the DC-DC converter operating conditions. This allows the development of improved averaged models of DC-DC converters, especially in terms of power losses estimation. The effectiveness of the proposed modeling approach has been validated through a simulation study, which refers to the case of a boost DC-DC converter and is performed by means of a suitable circuit simulator designed for rapid modelling of switching power systems （SIMetrix/SIMPLIS）.展开更多
Two TFs （transfer functions） are needed to analyze switching DC-DC converters in control-voltage mode： the duty-cycle to output-voltage （control to output） and the input-voltage to output-voltage （line to output...Two TFs （transfer functions） are needed to analyze switching DC-DC converters in control-voltage mode： the duty-cycle to output-voltage （control to output） and the input-voltage to output-voltage （line to output）. To obtain these TFs a small-signal analysis is required. The CCM （continuous conduction mode） and the DCM （discontinuous conduction mode） analysis are different. When a circuit includes the loss resistances of the components, the number of parameters increases considerably, making manual nodal-loop circuit analysis techniques impractical to obtain the TFs. Moreover, these circuits are bilinear （non-linear） and it is necessary to linearize the equations at a DC operating-point （approximate linearization）. Vorp6rian describes a PWM （pulse-width-modulated） switch model that includes all non-linear parts of the DC-DC switching converters. This model can be linearized and replaced on the switching converter schematic leading to a linear circuit. At this point it is possible to use symbolic analysis programs to obtain these TFs or to simply apply numerical values for either the Bode diagrams or the calculation of poles and zeros. Here we describe an application of Ekrem Cangeici＇s method on X DC-DC converter to obtain control to output and line to output TFs in CCM and DCM including loss resistances. The method presented in this paper is optimized to use in the online publishing platform OctaveRS. Also the control to output TF for PCC （peak current controlled） in CCM is obtained.展开更多
基金Supported by the Chinese Ministry of Science and Technology Project(2011DFA60390)The National High Technology Research and Development Program of China(2007AA05Z303)
文摘The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- tion position, eddy dissipation concept （EDC） model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter. Simulation was conducted under six oxidant stream conditions with dif- ferent OjN2/CO2 molar ratios： 21/79/0, 30/70/0, 50/50/0, 21/0/79, 30/0/70 and 50/0/50. Results showed that 02 en- richment in the primary oxidant stream is in favor of combustion stabilization, acceleration of ignition and increase of maximum flame temperature, while the full substitution of N2 by CO2 in the oxidant stream delays ignition and decreases the maximum flame temperature. However, the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream. Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30% 02 and 70% CO2 in the oxidant stream, indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one. The swirl burner with a specially designed preheating chamber can increase flame temperature, accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion. Also, qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain 02 enrichment and oxy-coal combustion conditions against the air-coal combustion.
文摘A suitable inductor modeling for power electronic DC-DC converters is presented in this paper. It is developed with the aim of improving inductor losses estimation achievable by averaged models, which inherently neglect inductor current ripple. In order to account for its contribution to the overall inductor losses, an appropriate parallel resistance is thus enclosed into the inductor model, whose value should be chosen in accordance with the DC-DC converter operating conditions. This allows the development of improved averaged models of DC-DC converters, especially in terms of power losses estimation. The effectiveness of the proposed modeling approach has been validated through a simulation study, which refers to the case of a boost DC-DC converter and is performed by means of a suitable circuit simulator designed for rapid modelling of switching power systems （SIMetrix/SIMPLIS）.
文摘Two TFs （transfer functions） are needed to analyze switching DC-DC converters in control-voltage mode： the duty-cycle to output-voltage （control to output） and the input-voltage to output-voltage （line to output）. To obtain these TFs a small-signal analysis is required. The CCM （continuous conduction mode） and the DCM （discontinuous conduction mode） analysis are different. When a circuit includes the loss resistances of the components, the number of parameters increases considerably, making manual nodal-loop circuit analysis techniques impractical to obtain the TFs. Moreover, these circuits are bilinear （non-linear） and it is necessary to linearize the equations at a DC operating-point （approximate linearization）. Vorp6rian describes a PWM （pulse-width-modulated） switch model that includes all non-linear parts of the DC-DC switching converters. This model can be linearized and replaced on the switching converter schematic leading to a linear circuit. At this point it is possible to use symbolic analysis programs to obtain these TFs or to simply apply numerical values for either the Bode diagrams or the calculation of poles and zeros. Here we describe an application of Ekrem Cangeici＇s method on X DC-DC converter to obtain control to output and line to output TFs in CCM and DCM including loss resistances. The method presented in this paper is optimized to use in the online publishing platform OctaveRS. Also the control to output TF for PCC （peak current controlled） in CCM is obtained.
