Pressure Analysis of the Initial Process of Diffusion Combustion Surge in a 350 kW Gas Boiler

In order to meet the increasingly stringent requirements for nitrogen oxides(NOx)emissions from gas boilers,flue gas recirculation(FGR)technology is commonly used to achieve ultra-low NOx emissions.However,under some ultra-low NOx combustion conditions with FGR,a surge phenomenon occurs in the boiler,which causes a flameout and should be avoided.In this study,the diffusion combustion surge of gas boiler with a rated power of 350 k W and equipped with FGR device was investigated.Pressure characteristic analysis results of the initial process of combustion surge showed that the high-frequency component of pressure is closely related to combustion stability and its change can provide reference for the occurrence of surge.Besides,the initial process of surge was analyzed by wavelet packet entropy method.Results indicated that the wavelet packet entropy of pressure signals could effectively reflect the stability of combustion in the furnace,and it could also be used to study the occurrence of surge.

Features of Combustion of a Mixture of a Hydrogen Microjet with Various Gases

The objective of the present study is an experimental investigation of diffusion combustion of round microjets,i.e.,mixtures of hydrogen with methane,helium,and nitrogen.It is found that the evolution of burning microjets is associated with generation of a“bottleneck flame region”close to the nozzle exit,as it was observed earlier during hydrogen combustion.Combustion of a mixture of hydrogen and methane with increasing flow velocity occurs with the transformation of the torch.At first,a torch stabilized on the nozzle is observed,then it is divided into a stabilized part in contact with the nozzle and into a raised part of the torch.The combustion process occurs in two areas.A further increase in velocity promotes the breakdown of the raised torch,but maintains combustion in the nozzle area.The results on hydrogen/methane combustion are obtained in a smaller range of the microjet velocity than those of a hydrogen microjet.Somewhat similar data are derived for other gas additives.To make combustion of gas mixtures more stable with increasing microjet velocity,one has to increase the portion of hydrogen in the gas mixture or reduce the fractions of other gas additives.

Numerical Investigation of Effect of Porosity and Fuel Inlet Velocity on Diffusion Filtration Combustion

Methane-air diffusion filtration combustion in a radiative round-jet burner was numerically investigated in this work.The purpose of this study was focused on the effects of porous media porosity and gas velocity on temperature distribution and CO and NO_(x)emissions.Reduced chemical kinetics was used where air and methane were assumed to be at their stoichiometric ratio,while thermo-physical properties were varied per the solid matrix porosity variation.Combustion characteristics were evaluated based on conduction and radiation as the two primary heat transfer modes within the solid matrix.Numerical simulations were carried out based on a packed bed with 3 mm alumina pellets.Results show that combustion temperature increases while the temperature gradient decreases with the increase in porosity,yielding higher NO_(x),and lower CO emissions.Furthermore,the combustion temperature is the lowest and most uniformly distributed with 1 m/s and 3 m/s gas velocities,wherewith 3 m/s gas velocity,combustion occurs outside of the porous zone.The corresponding NO_(x)and CO emissions are the lowest with 1 m/s gas velocity and increase with the increase in gas velocity from 1 m/s to 10m/s.