EDC Model Research Articles

A comprehensive investigation of acoustic power level in a moderate or intense low oxygen dilution in a jet-in-hot-coflow under various working conditions

Reducing the level of noise emission is an important requirement in modern propulsion and power generation. This requires gaining a deeper understanding of the underlying physics and identifying the key parameters dominating noise generation in modern combustion technologies. Thus, this paper investigates the effect of several working parameters on moderate or intense low oxygen dilution (MILD) combustion noise. A finite volume solver, GRI-Mech 2.11 with 247 reactions and 49 species, k-ε RNG turbulence model as well as the EDC model are used to develop a computational model of the reactive flow, while the volume fraction and time scale constants are set to 3 and 1, respectively. After validating the numerical method by comparison with the experimental data, MILD combustion is simulated under various conditions to study the noise emission. The results show that modifying the inlet conditions such as changes in species mass fractions, inlet temperature, and inlet Reynolds number alter the acoustic power level through variations in heat release.

AN IMPLEMENTATION OF SOFTWARE EFFORT DURATION AND COST ESTIMATION WITH STATISTICAL AND MACHINE LEARNING APPROACHES

In software industry estimation of effort, cost (EDC) and duration is a troublesome procedure. The exertion itself is in charge of experiencing trouble in evaluating EDC. In any software estimation process, the preeminent advance is to characterize and comprehends the framework to be assessed. Software cost estimation algorithmic methods are estimating by analogy, expert judgment method, price to win method, topdown method, bottom-up method are developed by researchers in the field of software engineering. Any methods are not superior to the other methods. In fact, the qualities and shortcomings of those strategies are differentiating to one another. Presently there are two types of software EDC models to estimate the software those are statistical approaches and machine learning approaches. Many of the software cost estimation methods follows statistical approaches, which are not having the capability to present causes and strong or accurate results. Machine learning techniques are suitable in software engineering because it produces accurate results, which estimates by training rules and iterations. Machine learning techniques resolve the challenges like developing programs in a computer and to give the effective outputs by using the experience.

BLEVE fireball modeling using Fire Dynamics Simulator (FDS) in an Algerian gas industry

BLEVE is one of major accidents observed in gas industry causing severe damage to people and environment. Its effects are manifested in three ways: shock wave propagation, fireball radiation and fragments projection. To assess these effects, risk decision-makers often use Quantitative Risk Analysis (QRA). In most cases, QRA data are obtained from empirical correlations. However, these correlations are not very satisfactory because they generally overestimate BLEVE effects and do not take into account geometry effects. In order to overcome the limitations of these empirical approaches, CFD modeling appears as a powerful tool able to provide more accurate data to better realize QRA. In this paper, the objective is to develop a CFD methodology in order to predict BLEVE thermal effects. Numerical simulations are carried out using the CFD code FDS. A sensitivity analysis of numerical models is performed in order to choose the right parameters allowing to model the fireball dynamics. The models retained are based on a single-step combustion using EDC model coupled with a LES turbulence model. Predictions show good agreement in comparison with results issued from three large-scale experiments. Furthermore, a case study on a propane accumulator in an Algerian gas processing unit is carried out.

Dimensionally reduced modeling of nitric oxide formation for premixed methane-air flames with ammonia content

The paper presented an experimental and numerical study on a combustion process of ammonia doped methane flames with the NH3 content in the fuel from 1% up to 5%. Tests were performed with an atmospheric pressure axisymmetric burner for stoichiometric mixtures and fuel-lean conditions (φ = 0.63, 0.71, 0.83, 1.0) with the substrates preheating up to 573 K. Numerical modelling involved three reduced dimensionally combustion models (0D IdealGasReactor, 1D FreeFlame, 1D BurnerFlame) with four detailed reaction mechanisms for the hydrocarbons and nitrogen chemistry (GRI 3.0, SanDiego, Konnov 0.6 and Tian). Comparison of the 0D/1D calculations results with a complete burner geometry modelling (3D Ansys EDC) was performed for GRI 3.0.Experimental study shown that nitric oxide emission increased with the increase of NH3 content in the introduced fuel, however transition from NH3 to NO was incomplete and trend was not linear for the rising ammonia share. Doubling of the ammonia content in the fuel from 2.5% to 5% resulted in a rise of NO emission by only 55.5% (from 946 to 1471 ppmv) for the lean mixtures and by 48% (from 1451 to 2148 ppmv) for the stoichiometric conditions.The numerical analysis results were in a good agreement with the experimental results for the lean mixtures and ammonia content up to 1% for all investigated combustion models and the kinetic reaction mechanisms. Trends of the nitric oxide emission obtained with the stoichiometric flames were valid for 1D models. However overall values were over predicted for an adiabatic 1D FreeFlame calculations and under predicted for 1D BurnerFlame, which showed a sensitivity of the nitrogen chemistry to the process temperature. Analysis with the 3D Ansys EDC model and GRI 3.0 provided the most accurate results up to 2.5% of the NH3 share in the fuel with a maximum relative differences values to the experimental results from 10% up to 24% for the lean and the stoichiometric conditions respectively.

DNS of swirling hydrogen–air premixed flames

Direct numerical simulation is employed to investigate the turbulent flow characteristics and their effect on local flames for mean reaction rate modelling in turbulent swirling premixed flames. Two swirl numbers having significant effects on the formation of a central recirculation zone in the combustor are considered. The large velocity gradients in the higher swirl number case produce high turbulence intensity in a relatively upstream region compared to the lower swirl number case. The conditional Probability Density Functions (PDFs) of the reaction rate and dissipation rates of turbulent kinetic energy and scalar fluctuations are also examined. The PDFs show correlations between the turbulence energy dissipation and reaction rates and between the scalar dissipation and reaction rates, suggesting that the heat and radicals from the hot products trapped in the recirculation zones are mixed with the reactants, not only through scalar dissipation rate (i.e. scalar gradient) but also by small-scale processes of turbulence relevant to turbulent kinetic energy dissipation rate. Therefore, both scalar and velocity gradients have a strong influence on the chemical reactions through mixing of cold reactant and hot products. A conventional flamelet and EDC models are used to estimate the mean reaction rate, and to study the balance between these two mixing mechanisms. Although both models show a qualitative agreement with the DNS results, these models compensate their limitations each other, depending on the local turbulence and thermochemical conditions. A simple approach is proposed to exploit the advantages of these two models by considering the balance of two mixing mechanisms based on the chemical and turbulence time scales. The estimated mean reaction rate using the proposed model is significantly improved for the higher swirl number case, although the estimated value slightly shifts away from the DNS results for the lower swirl number case. The improved modelling estimate and the balance of turbulence and chemical time scales suggest that the locations of intense reaction zones are strongly related to the dissipation rates of both scalar and turbulent kinetic energy.

Numerical study of flame structure in the mild combustion regime

In this paper, turbulent non-premixed CH4+H2 jet flame issuing into a hot and diluted co-flow air is studied numerically. This flame is under condition of the moderate or intense low-oxygen dilution (MILD) combustion regime and related to published experimental data. The modelling is carried out using the EDC model to describe turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. The flame structure for various O2 levels and jet Reynolds numbers are investigated. The results show that the flame entrainment increases by a decrease in O2 concentration at air side or jet Reynolds number. Local extinction is seen in the upstream and close to the fuel injection nozzle at the shear layer. It leads to the higher flame entertainment in MILD regime. The turbulence kinetic energy decay at centre line of jet decreases by an increase in O2 concentration at hot Co-flow. Also, increase in jet Reynolds or O2 level increases the mixing rate and rate of reactions.

Simulation study on spray combustion mechanism of diesel–gasoline blend fuels

In order to reveal the spray combustion mechanism of blend fuels, a combustion model was established using EDC model based on previous experimental research. The simulation results show that under lower co-flow temperature, the auto-ignition of n-heptane (represent diesel) occurred earlier than gasoline (represent gasoline), as a result of the combined effect of slower vaporization rate and lower activation energy required for the initial dehydrogenation reaction. On the contrary, under high co-flow temperature condition, iso-octane began to ignite before n-heptane, because the chemical reaction of both n-heptane and iso-octane occurs rapidly due to the rapider vaporization so that the auto-ignition delay is most determined by the vaporization and diffusion rate of fuel. The simultaneous auto-ignition temperature “Ts” was defined in previous work to represent the co-flow temperature, at which diesel and gasoline ignited spontaneously. Further simulation research results show that, the increment of injection pressure and background pressure will increase Ts, and the impact of injection pressure on Ts is much less than that of background pressure.

Assessment of Turbulence-Chemistry Interaction Models in MILD Combustion Regime

The present paper reports on the assessment of different turbulence-chemistry interaction closures for modeling turbulent combustion in the Moderate and Intense Low oxygen Dilution combustion regime. 2D RANS simulations have been carried out to model flames issuing from two burners DJHC burner and Adelaide JHC burner which imitate the MILD combustion. In order to model these flames, two different approaches of turbulence-chemistry interaction models are considered; while in the PDF based modeling, two different variants are invoked to understand the applicability of the PDF based models in the MILD regime: one is based on presumed shape PDF approach and the other one is transported PDF approach. A comprehensive study has been carried out by comparing the results obtained from these different models. For the DJHC burner, the computations are carried out for a jet speed corresponding to Reynolds numbers of Re=4100, whereas the Adelaide JHC burner computations are performed for a jet speed corresponding to Reynolds number of Re=10000. The effects of molecular diffusion on the flame characteristics are also studied by using different micro-mixing models. In the case of DJHC burner, it has been observed that the mean axial velocity and the turbulent kinetic energy profiles are in good agreement with the measurements. However, the temperature profiles are over-predicted in the downstream region by both EDC and the PDF based models. In the context of Adelaide JHC burner, the profiles of the temperature and the mass fraction of major species (CH4, H2, O2, H2O, CO2) obtained using LPDF approach are in better agreement with the measurements compared to those obtained using EDC model; although, both the solution approaches fail to capture CO and OH radical profiles.

Analysis of Nitrogen Oxides Formation in CH<sub>4</sub>/Air Laminar Premixed Flame

Many combustion processes seriously pollute the environment because of producing nitrogen oxides emission, which abstracts wide attention from researchers. How to reduce nitrogen oxides emission is important to protect the environment. At the present work, a reduction mechanism based on a detailed chemical reaction kinetics mechanism, Gri_Mech3.0 was adopted to analyze nitrogen oxides formation in a CH4/air laminar premixed and turbulent diffusion flames, a two dimensional turbulent diffusion flame was simulated with the EDC model. Parameters were obtained, including flame temperature, burning velocity and mass fraction of nitrogen oxides. The results of laminar premixed flame show that nitrogen oxides emission mainly comes from the thermal and prompt NO mechanisms. A large amount of free radicals O, H and OH produced by combustion processes provide reactants for the reactions of nitrogen oxides formation. Mole fraction of nitrogen oxides increases with the increasing of both flame temperature and chemical equivalence ratios. By contrast, there is a lower mass fraction of nitrogen oxides formation for the fuel-lean flame.

Numerical study of the effect of turbulence on rate of reactions in the MILD combustion regime

In this paper, the importance of fluctuations in flow field parameters is studied under MILD combustion conditions. In this way, a turbulent non-premixed CH4+H2 jet flame issuing into a hot and deficient co-flow air is modeled using the RANS Axisymmetric equations. The modeling is carried out using the EDC model to describe the turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. Results illustrate that although the fluctuations in temperature field are small and the reaction zone volume are large in the MILD regime, the fluctuations in temperature and species concentrations are still effective on the flow field. Also, inappropriate dealing with the turbulence effect on chemistry leads to errors in prediction of temperature up to 15% in the present flame. By decreasing of O2 concentration of hot co-flow air, the effect of fluctuations in flow field parameters on flame characteristics are still significant and its effect on species reaction rates does not decrease. On the other hand, although decreasing of jet inlet Reynolds number at constant inlet turbulence intensity addresses to smaller fluctuations in flow filed, it does not lead to lower the effect of turbulence on species distribution and temperature field under MILD combustion conditions.

Fluid dynamics modeling of a stratified disk burner in swirl co-flow

The work describes Large Eddy Simulations of an unconfined partially premixed propane-air burner with swirl. A premixing section consisting of two axisymmetric cavities, formed along three concentric disks, supplies the afterbody disk recirculation with a radial equivalence ratio gradient. Flame stabilization is established there supported by a swirling co-flow of air. Lean and ultra-lean conditions are examined by regulating the fuel-air stratification and the swirl. An implicit finite-volume LES method is applied, employing the dynamic Smagorinsky model and the Eddy Dissipation Concept. Propane combustion and NOx production are modelled with an eleven-step scheme. The LES reveals intrinsic features of the flame front anchoring close to the burner rim under the influence of inlet mixture stratification and reproduces large and small scale features of the primary vortex flame stabilization and its interaction with the downstream vortex breakdown zone. Comparisons with measurements indicate a satisfactory agreement in the mean and turbulent velocity fields, while the impact of combustion and heat release on the wake development is reproduced well by the model. Deviations in the mean and fluctuating fields increase in the vicinity of the interaction of the twin vortex system. Preliminary comparisons between simulations and global species measurements suggest that the turbulence-chemistry model represents satisfactorily the experimental trends. ▸ Large Eddy Simulations of stratified disk burner are performed. ▸ Combustion is stabilized on a cavity premixer/disk burner under the action of swirl. ▸ Turbulent reactions were treated with the EDC model with eleven-step chemistry. ▸ Simulations represented satisfactorily both large and small scale burner characteristics. ▸ Intrinsic features of stratified flame stabilization in the primary vortex are exposed.

LES of a Meso Combustion Chamber with a Detailed Chemistry Model: Comparison between the Flamelet and EDC Models

The goal of this paper is to contribute to the design of high-performance mesocombustors, a field currently under rapid development, in particular for propulsion, e.g., for UAVs, and micro/meso-electrical power generators. This study is focused on a cylindrical combustor of 29 cm3, fuelled by methane and air, which provides 2 kW of thermal power. The device was entirely designed and built at the Sapienza University of Rome and coupled with an ultra-micro turbine. Two 3D LES simulations with detailed chemistry are presented. They differ only for the combustion models, so that a model comparison can be carried out. The calculated maximum temperature inside the chamber, the gas exhaust temperature and the combustion efficiency are compared and discussed. The results, reported at two different physical times, show the effects of the different combustion models, which predict different temperature and species concentration maps, but similar values for the combustion efficiency. Thermal, chemical and kinematic maps show that the Eddy Dissipation Concept allows for a more accurate estimatation of the performance parameters for application to first-order design procedures.

Numerical and Experimental Characterization of a Natural Gas Engine With Partially Stratified Charge Spark Ignition

This paper outlines the development of a comprehensive numerical framework for the partially stratified charge (PSC) lean-burn natural gas engine. A 3D model of the engine was implemented to represent fluid motion and combustion. The spark ignition model was based on the works of Herweg and Maly (1992, “A Fundamental Model for Flame Kernel Formation in SI Engines,” SAE Technical Publication, Paper No. 922243) and Tan and Reitz (2006, “An Ignition and Combustion Model Based on the Level-Set Method for Spark Ignition Engine Multidimensional Modeling,” Combust. Flame, 145, pp. 1–15). The EDC model (Ertesvåg and Magnussen, 2000, “The Eddy Dissipation Turbulence Energy Cascade Model,” Combust. Sci. Technol., 159, pp. 213–235) with a two-step mechanism was used to model natural gas turbulent combustion process. An open geometry simulation strategy was adopted to account for intake-exhaust gas and valve movements. Each simulation was executed for multiple cycles to produce a representative residual gas fraction. The numerical results were compared with the experimental data obtained on the Ricardo Hydra single cylinder research engine for both homogeneous and PSC cases and they were found to be in excellent agreement in pressure trace and heat release rate. The detailed investigation of the numerical data showed the development of an ignitable mixture under PSC cases, allowing stable kernel growth well beyond the lean misfire limit of the bulk mixture. Furthermore, limits on successful ignition can be identified using the ignition model, which exhibited self-similar behavior in terms of flame speed and turbulent fluctuation. It can also be shown that, at ultralean air-fuel ratios, the PSC plume helps replicate the ignition conditions that can be found under stoichiometric operation.

Numerical study of influence of molecular diffusion in the Mild combustion regime

In this paper, the importance of molecular diffusion versus turbulent transport in the moderate or intense low-oxygen dilution (Mild) combustion mode has been numerically studied. The experimental conditions of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154] were used for modelling. The EDC model was used to describe the turbulence–chemistry interaction. The DRM-22 reduced mechanism and the GRI 2.11 full mechanism were used to represent the chemical reactions of an H2/methane jet flame. The importance of molecular diffusion for various O2 levels, jet Reynolds numbers and H2 fuel contents was investigated. Results show that the molecular diffusion in Mild combustion cannot be ignored in comparison with the turbulent transport. Also, the method of inclusion of molecular diffusion in combustion modelling has a considerable effect on the accuracy of numerical modelling of Mild combustion. By decreasing the jet Reynolds number, decreasing the oxygen concentration in the airflow or increasing H2 in the fuel mixture, the influence of molecular diffusion on Mild combustion increases.

Effect of hydrogen on hydrogen–methane turbulent non-premixed flame under MILD condition

Energy crises and the preservation of the global environment are placed man in a dilemma. To deal with these problems, finding new sources of fuel and developing efficient and environmentally friendly energy utilization technologies are essential. Hydrogen containing fuels and combustion under condition of the moderate or intense low-oxygen dilution (MILD) are good choices to replace the traditional ones. In this numerical study, the turbulent non-premixed CH 4+H 2 jet flame issuing into a hot and diluted co-flow air is considered to emulate the combustion of hydrogen containing fuels under MILD conditions. This flame is related to the experimental condition of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154]. In general, the modelling is carried out using the EDC model, to describe turbulence–chemistry interaction, and the DRM-22 reduced mechanism and the GRI2.11 full mechanism to represent the chemical reactions of H 2/methane jet flame. The effect of hydrogen content of fuel on flame structure for two co-flow oxygen levels is studied by considering three fuel mixtures, 5%H 2+95%CH 4, 10%H 2+90%CH 4 and 20% H 2+80%CH 4(by mass). In this study, distribution of species concentrations, mixture fraction, strain rate, flame entrainment, turbulent kinetic energy decay and temperature are investigated. Results show that the hydrogen addition to methane leads to improve mixing, increase in turbulent kinetic energy decay along the flame axis, increase in flame entrainment, higher reaction intensities and increase in mixture ignitability and rate of heat release.

Turbulent diffusion combustion model using chemical equilibrium combined with the eddy dissipation concept for reducing detailed chemical mechanisms: An application of H2‐air turbulent diffusion flame

AbstractThis research aims at building a turbulent diffusion combustion model based on chemical equilibrium and kinetics for simplifying a complex chemical mechanism. This paper presents the combustion model based on chemical equilibrium combined with an eddy dissipation concept model (CE‐EDC); the model is validated by simulating a H2‐air turbulent diffusion flame. In the CE‐EDC model, the reaction rate of fuels and intermediate species are estimated by using the equations of the EDC model. Then, the reacted fuels and intermediate species are assumed to be in chemical equilibrium; the amounts of the other species are determined by the Gibbs free energy minimization method by using the amounts of the reacted fuels, intermediate species, and air as reactants. An advantage of the CE‐EDC model is that the amounts of the combustion products can be determined without using detailed chemical mechanisms. Moreover, it can also predict the amounts of the intermediate species. The obtained results are compared with Takagi's experimental data and the data computed by the EDC model, which uses the complex chemical mechanisms. The mole fractions of H2, O2, H2O, temperature, and velocity obtained by using our CE‐EDC model were in good agreement with the reference data without taking into account the chemical reaction rates of the O2 and H2O. Furthermore, the mole fractions of OH and H are in good agreement with the results of the EDC model at high temperatures. On the other hand, the chemical equations involving OH and H were used for predicting the mole fractions of OH and H, which were similar to those obtained from the EDC model at low temperatures. Using the present CE‐EDC model, amounts of combustion products can be calculated by using a reduced chemical mechanism and the Gibbs free energy minimization theory. The accuracy of this model is in the same order as that of the EDC model. The CE‐EDC model uses reduced chemical mechanism concerning selected species, while the result of the chemical equilibrium calculation was employed to the other species; further, the accuracy of the CE‐EDC model is the same as that of the EDC model as to major species, T, U, and k. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20296

Effect of the combustion model and kinetic mechanism on the MILD combustion in an industrial burner fed with hydrogen enriched fuels

A numerical and experimental investigation of a burner operating in MILD combustion regime and fed with methane and methane-hydrogen mixtures (with hydrogen content up to 20% by wt.) is presented. Numerical simulations are performed with two different combustion models, i.e. the ED/FR and EDC models, and three kinetic mechanisms, i.e. global, DRM-19 and GRI-3.0. Moreover, the influence of molecular diffusion on the predictions is assessed. Results evidence the need of a detailed chemistry approach, especially with H 2, to capture the volumetric features of MILD combustion. The inclusion of molecular diffusion influences the prediction of H 2 distribution; however, the effects on the temperature field and on the major species are negligible for the present MILD combustion system. A simple NO formation mechanism based on the thermal and prompt routes is found to provide NO emissions in relatively good agreement with experimental observations only when applied on temperature fields obtained with the EDC model and detailed chemistry.

2207 反応速度論を取り入れた平衡法によるCO-H_2-air乱流拡散火炎の数値解析(G06-4 熱工学(4) 燃焼(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The aim of our research is to build a model which can evaluate the amount of combustion products by using the chemical equilibrium method with a few chemical reactions. This paper presents a eddy dissipation concept/chemical equilibrium model (EDC/CE) and validates it by simulating CO-H_2 air turbulent diffusion flame. The obtained results were compared to the Correa's experimental data, Gran's computational data. An advantage of the EDC/CE model that any combustion products are obtained without using detailed chemical mechanisms. The results obtained by the EDC/CE model are in good agreement with these reference data. With the combustion model built in this paper, the combustion products can be calculated without detail chemical mechanisms, and the accuracy present model is in same order of the EDC model.

Study of the behaviour of a flame resulting from the combustion of pine needles in a cylindrical basket

This experimental and numerical study examines the behaviour of a flame resulting from the combustion of pine needles. The objective of this work is to evaluate the performances of two models of combustion, the validity of these being discussed by comparing the results with experimental measurements. An apparatus was designed to simulate and study in laboratory conditions the flame and the near-field plume stemming from the combustion of an isolated shrub. The burner was made of a cylindrical wire mesh basket filled with pine needles ignited at the lower circumference of the basket. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) were used to characterize the velocity field in the proximity of the fuel and to identify the propagation of the flame. A set of time-dependent equations is obtained for each phase and the coupling between the gas phases is rendered through exchange terms of mass, momentum and energy. Turbulence is approached by using a k – ε statistical model constructed from the Favre averaging method. The chemical kinetics is assumed as infinitely fast compared with other characteristics of the flow. Two models of turbulent combustion are tested. The first is the EDC model, which considers an immediate reaction and the direct transformation of fuel into water and carbon dioxide. The second is the β-PDF model, which is based on an instantaneous thermodynamic equilibrium at any point. The solution is performed numerically by a finite-volume method. The numerical results obtained are presented and compared to experimental measurements.

Synchrotron radiation photoemission studies of core level excitation effects

The recent availability of intense polarized radiation tuneable over the range 20–150 eV enables several core levels to be excited. Several remarkable effects have recently been reported when core excitation thresholds have been reached. For example, an increase in yield of 50% was observed in GaSe at the Se 3d threshold ( h ̵ ω = 57 eV) . A considerable increase in photoemission intensity at 6 eV binding energy has been reported by Guillot et al. for Ni at the 3p threshold. We have made a very careful study using the CIS, CFS and EDC models of photoemission spectroscopy of core threshold effects in Ni, Pr and GaSe. We find a modulation of the Ni Fermi edge emission as a function of photon energy which we attribute to a configuration interaction between 3p 5 3d 10 4s and 3p 6 3d 8 4s ef. Similar effects occur in Pt at the 4f threshold involving the configurations 4f 13 5d 10 6s and 4f 14 5d 8 6s. Further, the lineshapes of the Pt and Ni upper valence band CIS's resemble those obtained by electron loss (ELS) and photoabsorption, all of which can be fitted theoretically to a Fano model. Emission from levels lying well below the Fermi level often has superimposed contributions due to incoherent effects which complicate the interpretation. In cases in which core levels are excited well above threshold, the CIS technique may be used to examine final states. Of particular interest is the possible consequent determination of adsorbate site geometry. We present data 2p emission from a c(2 × 2) Na overlayer on Ni(001).