Igor Novosselov

Experimental and Numerical Study of NOx Formation From the Lean Premixed Combustion of CH4 Mixed With CO2 and N2

This paper describes an experimental and numerical study of the emission of nitrogen oxides (NO x ) from the lean premixed (LPM) combustion of gaseous fuel alternatives to typical pipeline natural gas in a high intensity, single-jet, stirred reactor (JSR). In this study, CH 4 is mixed with varying levels CO 2 and N 2 . NO x measurements are taken at a nominal combustion temperature of 1800K, atmospheric pressure, and a reactor residence time of 3 ms. The experimental results show the following trends for NO x emissions as a function of fuel dilution: (1) more NO x is produced per kg of C H 4 consumed with the addition of a diluent, (2) the degree of increase in emission index is dependent on the chosen diluent; N 2 dilution increases NO x production more effectively than equivalent CO 2 dilution. Chemical kinetic modeling suggests that NO x production is less effective for the mixture diluted with CO 2 due to both a decrease in N 2 concentration and the ability of CO 2 to deplete the radicals taking part in NO x formation chemistry. In order to gain insight on flame structure within the JSR, three dimensional computational fluid dynamic (CFD) simulations are carried out for LPM CH 4 combustion. A global CH 4 combustion mechanism is used to model the chemistry. While it does not predict intermediate radicals, it does predict CH 4 and CO oxidation quite well. The CFD model illustrates the flow field, temperature variation, and flame structure within the JSR. A 3-element chemical reactor network (CRN), including detailed chemistry, is constricted using insight from spatial measurements of the reactor, the results of CFD simulations, and classical fluid dynamic correlations. GRI 3.0 is used in the CRN to model the NO x emissions for all fuel blends. The experimental and modeling results are in good agreement and suggest the underlying chemical kinetic reasons for the trends.

Chemical Reactor Network Application to Emissions Prediction for Industial DLE Gas Turbine

A chemical reactor network (CRN) is developed and applied to a dry low emissions (DLE) industrial gas turbine combustor with the purpose of predicting exhaust emissions. The development of the CRN model is guided by reacting flow computational fluid dynamics (CFD) using the University of Washington (UW) eight-step global mechanism. The network consists of 31 chemical reactor elements representing the different flow and reaction zones of the combustor. The CRN is exercised for full load operating conditions with variable pilot flows ranging from 35% to 200% of the neutral pilot. The NOpilot. The NOx and the CO emissions are predicted using the full GRI 3.0 chemical kinetic mechanism in the CRN. The CRN results closely match the actual engine test rig emissions output. Additional work is ongoing and the results from this ongoing research will be presented in future publications.Copyright

NOx Behavior for Lean-Premixed Combustion of Alternative Gaseous Fuels

Gaseous fuels other than pipeline natural gas are of interest in high-intensity premixed combustors (e.g., lean-premixed gas turbine combustors) as a means of broadening the range of potential fuel resources and increasing the utilization of alternative fuel gases. An area of key interest is the change in emissions that accompanies the replacement of a fuel. The work reported here is an experimental and modeling effort aimed at determining the changes in NOx emission that accompany the use of alternative fuels. Controlling oxides of nitrogen (NOx) from combustion sources is essential in non-attainment areas. Lean-premixed combustion eliminates most of the thermal NOx emission, but is still subject to small, though significant amounts of NOx formed by the complexities of free radical chemistry in the turbulent flames of most combustion systems. Understanding these small amounts of NOx, and how their formation is altered by fuel composition, is the objective of this paper. We explore how NOx is formed in high-intensity, lean-premixed flames of alternative gaseous fuels. This is based on laboratory experiments and interpretation by chemical reactor modeling. Methane is used as the reference fuel. Combustion temperature is maintained the same for all fuels so that the effect of fuel composition on NOx can be studied without the complicating influence of changing temperature. Also, the combustion reactor residence time is maintained nearly constant. When methane containing nitrogen and carbon dioxide (e.g., landfill gas) is burned, NOx increases since the fuel/air ratio is enriched in order to maintain combustion temperature. When fuels of increasing C/H ratio are burned leading to higher levels of carbon monoxide (CO) in the flame, or when the fuel contains CO, the free radicals made as the CO oxidizes cause the NOx to increase. In these cases, the change from high-methane natural gas to alternative gaseous fuel causes the NOx to increase. However, when hydrogen is added to the methane, the NOx may increase or decrease, depending on the combustor wall heat loss. In our work, in which combustor wall heat loss is present, hydrogen addition deceases the NOx. This observation is compared to the literature. Additionally, minimum NOx emission is examined by comparing the present results to the findings of Leonard and Stegmaier.Copyright

Rectangular Slit Atmospheric Pressure Aerodynamic Lens Aerosol Concentrator

A rectangular slit micro-aerodynamic-lens (μADL) aerosol concentrator operating at atmospheric pressure has been developed. A single stage version has shown concentration ratios of up to 40:1 for 1 μm aerosol particles while particles larger than 2 μm can be concentrated by more than 100:1 in a single stage. The design of this device has been guided by unsteady 3D CFD modeling using detached eddy simulations (DES), and has been validated experimentally using polystyrene spheres and salt crystals of known aerodynamic diameters. The pressure drop in the device does not exceed 1.5 kPa in the major flow and 0.3 kPa in the minor flow at a total flow of 10 slpm. Copyright 2014 American Association for Aerosol Research

Removal Rates of Explosive Particles From a Surface by Impingement of a Gas Jet

The rate of particle removal from a surface by air jet impingement has been evaluated for 3 different types of trace explosives. Samples of research development explosive (cyclotrimethylenetrinitramine), trinitrotoluene, and C-4 were each transferred to glass surfaces and then subjected to a short burst of air from a jet with varying diameter, standoff distance, and backpressure to achieve a range of shear stresses at the surface. TNT was observed to be easiest to remove, while C-4 required the greatest shear force to resuspend. An analytical model has been developed to predict removal of spherical particles as a function of particle diameter and nondimensionalized downstream distance from a gas jet. This model was fitted to experimental data from the removal of ceramic microspheres of various sizes. The removal rate of these ceramic microspheres was observed to be much greater than that of the 3 types of explosive particles, despite the particles’ similar sizes. Copyright 2012 American Association for Aerosol Research

Development and Application of an Eight-Step Global Mechanism for CFD and CRN Simulations of Lean-Premixed Combustors

In this paper, the development of an eight-step global chemical kinetic mechanism for methane oxidation with nitric oxide formation in lean-premixed combustion at elevated pressures is described and applied. In particular, the mechanism has been developed for use in computational fluid dynamics (CFD) and chemical reactor network (CRN) simulations of combustion in lean-premixed gas turbine engines. Special attention is focused on the ability of the mechanism to predict NOx and CO exhaust emissions. Applications of the eight-step mechanism are reported in the paper, all for high-pressure, lean-premixed, methane-air (or natural gas-air) combustion. The eight steps of the mechanism are as follows: 1. Oxidation of the methane fuel to CO and H2 O. 2. Oxidation of the CO to CO2 . 3. Dissociation of the CO2 to CO. 4. Flame NO formation by the Zeldovich and nitrous oxide mechanisms. 5. Flame NO formation by the prompt and NNH mechanisms. 6. Post-flame NO formation by equilibrium H-atom attack on equilibrium N2 O. 7. Post-flame NO formation by equilibrium O-atom attack on equilibrium N2 O. 8. Post-flame Zeldovich NO formation by equilibrium O-atom attack on N2 .Copyright

Design and Performance of a Low-Cost Micro-Channel Aerosol Collector

Aerosol sampling and identification is vital for assessment and control of particulate matter pollution, airborne pathogens, allergens and toxins, and their effect on air quality, human health, and climate change. Assays capable of accurate identification and quantification of chemical and biological airborne components of aerosol provide very limited sampling time resolution and relatively dilute samples. A low-cost micro-channel collector (μCC) which offers fine temporal and spatial resolution, high collection efficiency, and delivers highly concentrated samples in very small liquid volumes was developed and tested. The design and optimization of this μCC was guided by computational fluid dynamics (CFD) modeling. Collection efficiency tests of the sampler were performed in a well-mixed aerosol chamber using aerosolized fluorescent microspheres in the 0.5–6 μm diameter range. Samples were collected in the μCC and eluted into 100 μL liquid aliquots; bulk fluorescence measurements were used to determine the performance of the collector. Typical collection efficiencies were above 50% for 0.5 μm particles and 90% for particles larger than 1 μm. The experimental results agreed with the CFD modeling for particles larger than 2 μm, but smaller particles were captured more efficiently than predicted by the CFD modeling. Nondimensional analysis of capture efficiencies showed good agreement for a specific geometry but suggested that the effect of channel curvature needs to be further investigated. Copyright 2014 American Association for Aerosol Research

Characterizing the Mechanism of Lean Blowout for a Recirculation-Stabilized Premixed Hydrogen Flame

The stability of hydrogen combustion under lean premixed conditions in a back-mixed jet-stirred reactor (JSR), is experimentally and numerically investigated. The goal is to understand the mechanism of flame extinction in this recirculation-stabilized flame environment. Extinction is achieved by holding the air flow rate constant and gradually decreasing the flow rate of the hydrogen fuel until a blowout event occurs. In order to gain insight on the mechanism controlling blowout, two dimensional computational fluid dynamic (CFD) simulations are carried out for the lean premixed combustion (LPM) of hydrogen as the fuel flow rate is reduced. The CFD model illustrates the evolution of the flow-field, temperature profiles, and flame structure within the JSR as blowout is approached. A single element chemical reactor network (CRN) consisting of a plug flow reactor (PFR) with recirculation is constructed based on the results of the CFD simulations, and its prediction of blowout is in good agreement with the experimental results. The chemical mechanism of Li et al. is used in both the CFD and CRN models, and GRI is used in the CRN for comparison. The modeling suggests that lean blowout does not occur with the flame in a spatially homogeneous condition, but rather under a zonal structure. Specifically, the flame is stabilized by the entrainment of combustion products from the re-circulation zone into the base of the reactant jet. The mixture of hot products and incoming premixed reactants proceeds through an ignition induction period followed by an ignition event. As the fuel flow decreases, the induction period increases and the ignition event is pushed further around the recirculation zone. Eventually, the induction period becomes so long that the ignition is incomplete at the point where the recirculating gas is entrained into the jet. This threshold leads to overall flame extinction.Copyright

Design and evaluation of an aerodynamic focusing micro-well aerosol collector

ABSTRACT Aerosol sampling and identification is vital for the assessment and control of particulate matter pollution, airborne pathogens, allergens, and toxins and their effect on air quality, human health, and climate change. In situ analysis of chemical and biological airborne components of aerosols on a conventional filter is challenging due to dilute samples in a large collection region. We present the design and evaluation of a micro-well (µ-well) aerosol collector for the assessment of airborne particulate matter (PM) in the 0.5–3 µm size range. The design minimizes particle collection areas allowing for in situ optical analysis and provides an increased limit of detection for liquid-based assays due to the high concentrations of analytes in the elution/analysis volume. The design of the collector is guided by computational fluid dynamics (CFD) modeling; it combines an aerodynamic concentrator inlet that focuses the aspirated aerosol into a narrow beam and a µ-well collector that limits the particle collection area to the µ-well volume. The optimization of the collector geometry and the operational conditions result in high concentrations of collected PM in the submillimeter region inside the µ-well. Collection efficiency experiments are performed in the aerosol chamber using fluorescent polystyrene microspheres to determine the performance of the collector as a function of particle size and sampling flow rate. The collector has the maximum collection efficiency of about 75% for 1 µm particles for the flow rate of 1 slpm. Particles bigger than 1 µm have lower collection efficiencies because of particle bounce and particle loss in the aerodynamic focusing inlet. Collected samples can be eluted from the device using standard pipettes, with an elution volume of 10–20 µL. The transparent collection substrate and the distinct collection region, independent of particle size, allows for in situ optical analysis of the collected PM.

Design and Optimization of a Compact Low-Cost Optical Particle Sizer

Direct measurements of time- and size-resolved particulate matter (PM) concentrations are of major importance in air quality studies and pollution monitoring. Low-cost, compact optical particle counters (OPCs), which provide accurate PM measurements independent of the particle complex index of refraction (CRI), can be useful in personal exposure monitoring and distributed sensor network studies applications. A methodology is presented for the optimization of the sensor design and operation parameter space aimed at reducing the effect of the CRI on particle sizing errors. The Monte Carlo numerical simulation, which utilizes Mie scattering calculations, is used to determine the optimal detector angle for the specific set of constraints described by the weighting coefficients. The optimized detector position (θ = 48°) has the lowest dependency on CRI over the entire particle size range of 0.5-10 microns. The near-forward, optimized, and perpendicular detector angles are compared experimentally using monodisperse 2 μm and 4 μm particles of silica, PSL, and alumina; the light collection cone angle is set at α = 20° in all experiments. The data agree well with the numerical results for all tested scenarios. Overall, the perpendicular detector location has the best precision and worst accuracy related to the CRI variations. The optimized detector position has the best accuracy for both silica and alumina particles. The use of low-cost components, such as laser diodes, photodiodes, miniaturized integrated electronics, and simple component layouts allows for the development of compact OPCs capable of accurately sizing PM. The number of sizing bins, sizing accuracy and precision, and other parameters of interest can be used as an input to an optimization algorithm.