Simulation of Double-Front Detonation of Suspended Mixed Cyclotrimethylenetrinitramine and Aluminum Dust in Air

The two-phase detonation of suspended mixed cyclotrimethylenetrinitramine （i.e., RDX） and aluminum dust in air is simulated with a two-phase flow model. The parameters of the mixed RDX-AI dust detonation wave are obtained. The double-front detonation and steady state of detonation wave of the mixed dust are analyzed. For the dust mixed RDX with density of 0.565kg/m3 and radius of 10μm as well as aluminum with density of 0.145kg/m3 and radius of 4μm, the detonation wave will reach a steady state at 23m. The effects of the size of aluminum on the detonation are analyzed. For constant radius of RDX particles with radius of 10μm, as the radius of aluminum particles is larger than 2.0 μm, the double-front detonation can be observed due to the different ignition distances and reaction rates of RDX and aluminum particles. As the radius of aluminum particles is larger, the velocity, pressure and temperature of detonation wave will be slower. The pressure at the Chapman-Jouguet （CJ） point also becomes lower. Comparing the detonation with single RDX dust, the pressure and temperature in the flow field of detonation of mixed dust are higher.

Experimental and Numerical Study of the Effect of Fuel/Air Mixing Modes on NO_(x) and CO Emissions of MILD Combustion in a Boiler Burner

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emissions,stable combustion and low noise for various kinds of fuel,which has great potential in the industry.The aim of this study is to investigate the effect of fuel/air mixing modes on NO_(x) and CO emissions of MILD combustion in a boiler burner by experiments and numerical simulations.Three types of fuel/air mixing modes (premixing mode,diffusion mode and hybrid mode) have been considered in this study.The realizable k-ε turbulent model and the Eddy Dissipation Concept (EDC) combustion model were used in numerical simulations.In addition to the temperature near the burner head,the calculation results match very well with the axial temperature distribution at the furnace center.The flow pattern under different mixing modes is similar,while the hybrid mode has a higher OH concentration near the diffusive fuel nozzle than the premixing mode,and the corresponding position of the peak OH concentration is closer to the rear half of the furnace.The distribution of temperature is extremely uniform for the premixing mode in the main reactive zone,which is typical for MILD combustion.There is a distinct area where the reaction temperature is higher than 1600 K for the hybrid mode.Moreover,in the main reactive zone,the gas recirculation ratio is high enough to ensure flue gas recirculation,which is beneficial to achieve MILD combustion at local areas.At the location where the axial distance is greater than 0.2 m,the gas recirculation ratio of the premixing mode is larger than that of the hybrid mode,which strengthens the entrainment of hot flue gas into the recirculated gas.The experimental results show that when the thermal intensity is less than 1.67 MW·m^(-3),the NO_(x) emissions are less than 15× 10^(-6)@3.5%O_(2) in near stoichiometric ratio in the premixing mode,and the CO emissions are less than 10× 10^(-6)@3.5%O2 under the same conditions.In the diffusion mode,the NO_(x) emissions are less than 30×10^(-6)@3.5%O_(2).In order to keep NO_(x) and CO emissions low,the hybrid modes with optimized fuel distribution ratio are found under different thermal intensities.

Study on the effect of landfill leachate on nutrient removal from municipal wastewater

In this study, landfill leachate with and without pre-treatment was co-treated with municipal wastewater at different mixing ratios. The leachate pre-treatment was achieved by air stripping to removal ammonia. The objective of this study was to investigate the effect of landfill leachate on nutrient removal of the wastewater treatment process. It was demonstrated that when landfill leachate was co-treated with municipal wastewater, the high ammonia concentration in the leachate did not have a negative impact on the nitrification. The system was able to adapt to the environment and was able to improve nitrification capacity. The readily biodegradable portion of chemical oxygen demand（COD）in the leachate was utilized by the system to improve phosphorus and nitrate removal.However, this portion was small and majority of the COD ended up in the effluent thereby decreased the quality of the effluent. The study showed that the 2.5% mixing ratio of leachate with wastewater improved the overall biological nutrient removal process of the system without compromising the COD removal efficiency.

Numerical simulations of single and multi-staged injection of H_(2) in a supersonic scramjet combustor

Computational fuid dynamics(CFD)simulations of a single staged injection of H_(2) through a central wedge shaped strut and a multi staged injection through wall injectors are carried out by using Ansys CFX-12 code.Unstructured terahedral grids for narow channel and quarter geometries of the combustor are generated by using ICEM CFD.Steady three dimensional(3D)Reynods averaged Navier-stokes(RANS)simulations are carried out in the case of no H_(2) injection and compared with the simulations of single staged pilot and/or main H2 injections and multistage injection.Shear stuess transport(SST)based on k-ω turbulent model is adopted.Flow field visualization(omplex shock waves interactions)and static pressure distribution along the wall of the combustor are pradicted and compared with the experimental schlieren images and measured wall static pressures for validation.A good agreement is found between the CFD predicted results and the measured data.The narow and quarter geometries of the combustor give similar results with very small differences.Multi-staged injections of H_(2) enhance the turbulent H_(2)/air mixing by fomming vortices and additional shock waves(bow shocks).