Influence of Pressure on Near Nozzle Flow Field and Soot Formation in Laminar Co-Flow Diffusion Flames

Soot formation from combustion devices, which tend to operate at high pressure, is a health and environmental concern, thus investigating the effect of pressure on soot formation is important. While most fundamental studies have utilized the coflow laminar diffusion flame configuration to study the effect of pressure on soot, there is a lack of investigations into the effect of pressure on the flow field of diffusion flames and the resultant influence on soot formation. A recent work has displayed that recirculation zones can form along the centreline of atmospheric pressure diffusion flames. This present work seeks to investigate whether these zones can form due to higher pressure as well, which has never been explored experimentally or numerically. The CoFlame code, which models co-flow laminar, sooting, diffusion flames, is validated for the prediction of recirculation zones using experimental flow field data for a set of atmospheric pressure flames. The code is subsequently utilized to model ethane-air diffusion flames from 2 to 33 atm. Above 10 atm, recirculation zones are predicted to form. The reason for the formation of the zones is determined to be due to increasing shear between the air and fuel steams, with the air stream having higher velocities in the vicinity of the fuel tube tip than the fuel stream. This increase in shear is shown to be the cause of the recirculation zones formed in previously investigated atmospheric flames as well. Finally, the recirculation zone is determined as a probable cause of the experimentally observed formation of a large mass of soot covering the entire fuel tube exit for an ethane diffusion flame at 36.5 atm. Previously, no adequate explanation for the formation of the large mass of soot existed.

Influence of Pressure on Near Nozzle Flow Field and Soot Formation in Laminar Co-Flow Diffusion Flames

Soot formation from combustion devices, which tend to operate at high pressure, is a health and environmental concern, thus investigating the effect of pressure on soot formation is important. While most fundamental studies have utilized the coflow laminar diffusion flame configuration to study the effect of pressure on soot, there is a lack of investigations into the effect of pressure on the flow field of diffusion flames and the resultant influence on soot formation. A recent work has displayed that recirculation zones can form along the centreline of atmospheric pressure diffusion flames. This present work seeks to investigate whether these zones can form due to higher pressure as well, which has never been explored experimentally or numerically. The CoFlame code, which models co-flow laminar, sooting, diffusion flames, is validated for the prediction of recirculation zones using experimental flow field data for a set of atmospheric pressure flames. The code is subsequently utilized to model ethane-air diffusion flames from 2 to 33 atm. Above 10 atm, recirculation zones are predicted to form. The reason for the formation of the zones is determined to be due to increasing shear between the air and fuel steams, with the air stream having higher velocities in the vicinity of the fuel tube tip than the fuel stream. This increase in shear is shown to be the cause of the recirculation zones formed in previously investigated atmospheric flames as well. Finally, the recirculation zone is determined as a probable cause of the experimentally observed formation of a large mass of soot covering the entire fuel tube exit for an ethane diffusion flame at 36.5 atm. Previously, no adequate explanation for the formation of the large mass of soot existed.

CORE DESIGN OF BREED & BURN MOLTEN SALT FAST REACTOR

Previous designs of once-through solid-fuelled breed-and-burn (B&B) reactor and the conventional molten salt reactor (MSR) concepts suffer from material limitation of neutron irradiation damage and chemical corrosion. A novel breed-and-burn molten salt reactor (BBMSR) concept uses separate molten salt fuel and coolant in a linear assembly core configuration. Similar to Moltex Energy Stable Salt Reactor (SSR) design, the configuration with fuel salt contained in fuel tubes and coolant salt in pool type reactor vessel has been previously studied. The study confirmed that breed-and-burn operation is feasible in principle, however with a low neutronic margin. The objective of this paper was to seek improvements of the neutronic margin with a metallic natural uranium blanket design. A parametric study was performed for the natural uranium blanket design. BBMSR neutronic performance simulation was modelled using Serpent, a Monte Carlo reactor physics code, with a single 3D hexagonal channel containing a single fuel tube in an infinite lattice with reflective radial and vacuum axial boundary conditions. The addition of a metallic natural uranium blanket inside the fuel tube, which increases the natural uranium metal to fuel salt ratio (ϒ) of the BBMSR, was shown to significantly increase the neutronic performance of the BBMSR.

Safety Analysis of Gas Pressure in a Subcritical Assembly for Molybdenum-99 Production System

The Subcritical Assembly for Molybdenum-99 Production system is a subcritical system fueled by uranium nitrate, which utilizes the Kartini reactor’s beam port as the neutron source. One of the problems in using uranium nitrate fuel involves the radiolysis reactions and gaseous fission products that form in the cavity above the Subcritical Assembly for Molybdenum-99 Production fuel tube, resulting in a buildup of pressure. To address this issue, this study examined the total accumulated gas pressure in each Subcritical Assembly for Molybdenum-99 Production tube contributed by gaseous fission products and water radiolysis by neutron and gamma radiation during 7 days of operation. Examinations were performed by combining the Subcritical Assembly for Molybdenum-99 Production and Kartini reactor geometry to obtain the burnup power using a tally within the Monte Carlo N-Particle eXtended code. Subcritical Assembly for Molybdenum-99 Production system was then simulated for 7 days with the obtained burnup power with the same code. Outputs from the code were then calculated and analyzed to determine the total accumulated pressure on each fuel tube from each of the pressure contributors. This research showed that the maximum accumulated pressures were 0.45 atm and 0.5 atm for Kartini reactor’s power of 100 kW and 110 kW, respectively. These pressures are lower than the atmospheric pressure; hence, the current Subcritical Assembly for Molybdenum-99 Production system can be operated safely for 7 days.

Computational Fluid Dynamic Analysis of Compressible Flow across a Complex Geometry Carburettor Venturi

A commercial computational fluid dynamics package could be used to develop a three dimensional, fully turbulent model of the compressible flow across a complex geometry venturi, such as those found in small engine carburettors. The results of the CFD simulation can be used to understand the effect of the different obstacles in the flow on the mass flow rate and the static pressure at the tip of the fuel tube. This would be helpful to analyze the pressure loss in the throat area. Analysis would be performed to study airflow across carburettor venturi by locating fuel tube at the diverging nozzle of the venturi and for various positions of throttle valve in the present paper, fuel tube and throttle plate would be modelled and analyze in order to have better understanding of the flow in complex venturi. The results of this study necessitate for modification throttle valve design. The carburettor body is remodelled with two throttle bodies replacing conventional throttle. Analysis has been performed to study flow field with modified design and results have been discussed.

Flow Behaviour Analysis of Injection Mixer for CNG Engines using Computational Fluid Dynamics

Use of gaseous fuels for fuelling the engines reduces reactive hydrocarbons and do not pose the problem of vaporization as with the liquid fuels. One of the problems of gaseous mixers is the ability to prepare a homogeneous mixing of air and fuel at a specific air-fuel ratio prior to entering the engine resulting high exhaust emissions. The objective of this project is to carry out three dimensional CFD analysis of CNG injection mixer to understand the flow behaviour of air fuel mixture and to optimize the design of injection mixer. The analysis was carried out by varying the injection position and injection inclination. The results of the CFD simulation could be used to understand the effect of position of fuel tube, injection inclination in the mixing of air and fuel. Further the results of the study would also be considered for the design modification.