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2018
MANSOUR, M. S., H. Pitsch, S. Kruse, M. F. Zayed, M. S. Senosy, M. Juddoo, J. Beeckmann, and A. R. Masri, A concentric flow slot burner for stabilizing turbulent partially premixed inhomogeneous flames of gaseous fuels, , vol. 91, pp. 214 - 229, 2018. AbstractWebsite

Combustion of turbulent inhomogeneous mixtures of air and fuel is common in many practical systems providing improved stability for both gaseous and liquid fuels. Understanding the structure and stability of turbulent flames in this mode has been the aim of many research groups who employed special burner designs to control the fuel and air mixing process. In this work, a modified design inspired by the Wolfhard-Parker slot burner was developed for planar turbulent flames with inlet conditions that are overall lean yet either compositionally inhomogeneous or partially premixed. The new burner is referred as the Concentric Flow Slot Burner (CFSB). The stability characteristics and flame structure are investigated for methane and natural gas fuels using planar laser induced fluorescence of C2Hx and high speed PLIF-OH. The effects of the jet equivalence ratio, the level of inhomogeneity, and the Reynolds number are investigated in this work. The data show that the flames with inhomogeneous mixture are more stable than fully premixed flames. Lean flames are stabilized in the CFSB burner. Stability is significantly improved by the use of a hollow truncated rectangular pyramid nozzle at the burner exit. The reaction zone structure varies significantly in the current burner from thin structures in rich flames to distributed with thick preheat zones in lean flames. The effect of the level of inhomogeneity on the reaction zone structure is presented and discussed. The new CFSB burner is able to generate a wide range of turbulent planar flames spanning the entire range from non-premixed to fully premixed flames. In addition, the high stability level of the burner allows for the study of highly turbulent flames of practical interest.

Elbaz, A. M., M. S. Senosy, M. F. Zayed, W. L. Roberts, and M. S. Mansour, Highly stabilized partially premixed flames of propane in a concentric flow conical nozzle burner with coflow, , 2018. AbstractWebsite

Partially premixed turbulent flames with non-homogeneous jet of propane were generated in a concentric flow conical nozzle burner in order to investigate the effect of the coflow on the stability and flame structure. The flame stability is first mapped and then high-speed stereoscopic particle image velocimetry, SPIV, plus OH planar laser-induced fluorescence, OH-PLIF, measurements were conducted on a subset of four flames. The jet equivalence ratio Φ = 2, Jet exit Reynolds number Re = 10,000, and degree of premixing are kept constant for the selected flames, while the coflow velocity, Uc, is progressively changed from 0 to 15 m/s. The results showed that the flame is stable between two extinction limits of mixture inhomogeneity, and the optimum stability is obtained at certain degree of mixture inhomogeneity. Increasing Φ, increases the span between these two extinction limits, while these limits converge to a single point (corresponding to optimum mixture inhomogeneity) with increasing Re. Regardless the value of Φ, increasing the coflow velocity improves the flame stability. The correlation between recessed distance of the burner tubes and the fluctuation of the mixture fraction, Δξ, shows that at Δξ around 40% of the flammability limits leads to optimum flame stability. The time averaged SPIV results show that the coflow induces a big annular recirculation zone surrounds the jet flames. The size and the location of this zone is seen to be sensitive to Uc. However, the instantaneous images show the existence of a small vortical structure close to the shear layer, where the flame resides there in the case of no-coflow. These small vertical structures are seen playing a vital role in the flame structure, and increasing the flame corrugation close to the nozzle exit. Increasing the coflow velocity expands the central jet at the expense of the jet velocity, and drags the flame in the early flame regions towards the recirculation zone, where the flame tracks and matches the spatial locations of low axial velocity fluctuations. At downstream, the flame is seen to conform to the passage of large scale structure. At Uc = 10 and 15 m/s, part of the primary reaction zone is rolled up towards upstream burner nozzle, anchoring the flame to the nozzle tip. This indicates that the stabilization of these flames in the presence of the coflow is controlled by the mutual interactions between the central jet and the coflow through the recirculation zone from one side, and the degree of the inhomogeneity of the central jet mixture from the other side.

2017
ElRashedy, R., H. Imam, K. Elsayed, and M. Mansour, "Spectroscopic investigation of plasma evolution induced by double pulse laser in distilled water", Journal of Plasma Physics, vol. 83, issue 4: Cambridge University Press, pp. 905830406, 2017. AbstractWebsite

Considerable interest has been paid to laser-induced breakdown in liquid because of its wide application to medical issues of the eye and environmental monitoring. Therefore, the present work aims to study the phenomena of LIB in bulk distilled water generated in laser-induced breakdown spectroscopy (LIBS) experiment. The effect of experimental parameters such as inter-pulse delay between the two lasers, laser pulse energy and detection time window have been studied to examine the temporal growth of the laser-induced plasma in bulk water. Electron density and plasma temperature have been determined. The Stark broadening profile has been utilized for the electron density determination where the hydrogen lines

$H_{\unicode[STIX]{x1D6FC}}$

and

$H_{\unicode[STIX]{x1D6FD}}$

have been used. A deviation between electron density values from the broadening of both lines has been observed and discussed. The electron density values are varied between

$10\text{E}+18$

and

$10\text{E}+17~\text{cm}^{-3}$

corresponding to the timing experimental parameters. The plasma temperature is varied over a range 16 000 

$\text{K}$

to 10 700 

$\text{K}$

due to the plasma’s temporal behaviour with experimental parameters.

Mansour, M. S., A. M. Elbaz, W. L. Roberts, M. S. Senosy, M. F. Zayed, M. Juddoo, and A. R. Masri, "Effect of the Mixing Fields on the Stability and Structure of Turbulent Partially Premixed Flames in a Concentric Flow Conical Nozzle Burner", Combustion and Flame, vol. Volume 175, issue January 2017, pp. 180-200, 2017.
2016
MANSOUR, M. S., "Classification of the Mixing Field of Partially Premixed Flames Using Regime Diagram", Combustion Science and TechnologyCombustion Science and Technology, vol. 188, issue 4-5: Taylor & Francis, pp. 667 - 683, 2016. AbstractWebsite

ABSTRACTPartially premixed combustion is one of the common combustion modes for many practical combustion systems where the mixture is classified as nonhomogeneous. The available experimental data show that the nature of mixing affects significantly the flame stability and structure of partially premixed flames at the same level of turbulence and local stoichiometry. Quantitative description of the mixing field is not yet available in order to discuss and analyze the effect of mixing on the flame structure and stability. The broad range of fluctuations in mixture fraction space within this mode requires proper classification into sub-ranges with common characteristics. This classification should be applicable for both laminar and turbulent flames. Accordingly a new diagram classifying the mixing field of partially premixed combustion into eight regimes within and partially within the flammability limits is proposed. The local mean and range of mixture fraction fluctuations are used to construct this diagram. One of those regimes covers the triple flames where the fluctuations lie within the flammability limits. The link between the stability and the proposed regimes is investigated using quantitative experimental data of turbulent flames. The data show promising correlation between stability and location of the flames within the diagram. The proposed regime diagram can be used as a platform for the classification of the mixing field of partially premixed flames.

Elbaz, A. M., M. F. Zayed, M. Samy, W. L. Roberts, and M. S. Mansour, "The flow field structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner with coflow", Special issue on Ninth Mediterranean Combustion Symposium, vol. 73, pp. 2 - 9, 2016. AbstractWebsite

The stability limits, the stabilization mechanism, and the flow field structure of highly stabilized partially premixed methane flames in a concentric flow conical nozzle burner with air co-flow have been investigated and presented in this work. The stability map of partial premixed flames illustrates that the flames are stable between two extinction limits. A low extinction limit when partial premixed flames approach non-premixed flame conditions, and a high extinction limit, with the partial premixed flames approach fully premixed flame conditions. These two limits showed that the most stable flame conditions are achieved at a certain degree of partial premixed. The stability is improved by adding air co-flow. As the air co-flow velocity increases the most stable flames are those that approach fully premixed. The turbulent flow field of three flames at 0, 5, 10m/s co-flow velocity are investigated using Stereo Particle Image Velocimetry (SPIV) in order to explore the improvement of the flame stability due to the use of air co-flow. The three flames are all at a jet equivalence ratio (Φj) of 2, fixed level of partial premixing and jet Reynolds number (Rej) of 10,000. The use of co-flow results in the formation of two vortices at the cone exit. These vortices act like stabilization anchors for the flames to the nozzle tip. With these vortices in the flow field, the reaction zone shifts toward the reduced turbulence intensity at the nozzle rim of the cone. Interesting information about the structure of the flow field with and without co-flow are identified and reported in this work.

2015
Mansour, M., Description of the Mixing Status of Partially Premixed Flames Using Regime Diagram, , 2015/06/07. Abstract

Partially premixed combustion is one of the common modes for many practical combustion systems where the mixture is not homogenous and characterized by fluctuations in mixture fraction. This mode covers a wide range between fully premixed and non-premixed combustion modes. Quantitative description of the several regimes in partially premixed mode is essential for understanding and modeling the flame structure. In this work a new regime diagram describing the mixing status for partially premixed environment is proposed in order to be used for the characterization of partially premixed flames. The mixing regime diagram describes different regimes within the partially premixed mode. The limits of mixture fraction and its mean value within the mixture fraction field are used to classify those regimes. In addition, the range of flammability limits and its mean are used for normalization of the diagram axes. The diagram describes the nature of the regimes within the partially premixed conditions and thus provides quantitative tool for the analysis and discussion of partially premixed flames. It classifies the partially premixed modes into eight well defined regimes. In general, partially premixed mode is defined as non-homogenous mixture with pockets at different stoichiometric values. The limits of partially premixed regimes of different fuels are listed in this work. The link between the flame stability and its mixing status within the proposed diagram is discussed using mixture fraction measurements.Several partially premixed turbulent flames of methane and propane are selected in order to be located within the proposed diagram. The relation between the flame stability and its location within the diagram is then discussed. The data show that the location of the flames in the regime diagram is related to its stability characteristics. The proposed mixing regime diagram can thus be used as an initial step for the design of stable partially premixed flames based on its mixing characteristics.

Mansour, M., M. Abd Azim, A. Elbaz, and N. Solouma, Partially Premixed Flames in a Concentric Flow Conical Nozzle Burner with Turbulence Generator, , 2015/06/07. Abstract

This work presents experimental investigation of turbulent partially premixed flames (PPF’s) stabilized within a concentric flow conical nozzle (CFCN) burner with a turbulence generator. The burner stability limit is investigated. In addition, the flow and temperature fields are measured above the conical nozzle exit using 2D PIV and fine wire thermocouple, respectively. The turbulence generator is used to increase the turbulence level as compared to previous measurements. Six turbulent partially premixed natural gas (NG) flames are investigated to study the effect of the level of partial premixing, jet equivalence ratio and Reynolds number. The Reynolds numbers varies between 5.9×103 and 8.9×103 while the jet equivalence ratio varies between 3 and 4.5. The effects of heat release on the flow structure are investigated. The results show that the change of turbulence level has a limited effect on the flame stability. However, the turbulence affects the mixing and hence the best stabilization is achieved at smaller mixing length as compared to the original burner. The flow field shows flow divergence that leads to high flame stability. The centerline axial velocity increases in reactive case by a factor of 1.5-4 higher than that of the non-reactive case. Moreover, the reactive case reaches a reduction in the local Reynolds number by a factor of 4-5.5. The centerline normalized standard deviation increases in the reactive case by a factor of 2-9 higher than that of the nonreactive case.

Mansour, M. A., H. b f Imam, K. A. c e Elsayed, A. M. d g Elbaz, and W. b Abbass, "Quantitative mixture fraction measurements in combustion system via laser induced breakdown spectroscopy", Optics and Laser Technology, vol. 65: Elsevier Ltd, pp. 43-49, 2015. AbstractWebsite

Laser induced breakdown spectroscopy (LIBS) technique has been applied to quantitative mixture fraction measurements in flames. The measured spectra of different mixtures of natural gas and air are used to obtain the calibration parameters for local elemental mass fraction measurements and hence calculate the mixture fraction. The results are compared with the mixture fraction calculations based on the ratios of the spectral lines of H/N elements, H/O elements and C/(N+O) and they show good agreement within the reaction zone of the flames. Some deviations are observed outside the reaction zone. The ability of LIBS technique as a tool for quantitative mixture fraction as well as elemental fraction measurements in reacting and non-reacting of turbulent flames is feasible. © 2014 Elsevier Ltd. All rights reserved.

2014
Selçuk, N. a, F. b Beretta, M. S. c Mansour, and A. d D'Anna, "Eighth Mediterranean Combustion Symposium", Experimental Thermal and Fluid Science, vol. 56: Elsevier Inc., pp. 1, 2014. AbstractWebsite
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Mansour, M. S. a, A. M. b c Elbaz, and M. F. a Zayed, "Flame kernel generation and propagation in turbulent partially premixed hydrocarbon jet", Combustion Science and Technology, vol. 186, no. 4-5: Taylor and Francis Inc., pp. 698-711, 2014. AbstractWebsite

Flame development, propagation, stability, combustion efficiency, pollution formation, and overall system efficiency are affected by the early stage of flame generation defined as flame kernel. Studying the effects of turbulence and chemistry on the flame kernel propagation is the main aim of this work for natural gas (NG) and liquid petroleum gas (LPG). In addition the minimum ignition laser energy (MILE) has been investigated for both fuels. Moreover, the flame stability maps for both fuels are also investigated and analyzed. The flame kernels are generated using Nd:YAG pulsed laser and propagated in a partially premixed turbulent jet. The flow field is measured using 2-D PIV technique. Five cases have been selected for each fuel covering different values of Reynolds number within a range of 6100-14400, at a mean equivalence ratio of 2 and a certain level of partial premixing. The MILE increases by increasing the equivalence ratio. Near stoichiometric the energy density is independent on the jet velocity while in rich conditions it increases by increasing the jet velocity. The stability curves show four distinct regions as lifted, attached, blowout, and a fourth region either an attached flame if ignition occurs near the nozzle or lifted if ignition occurs downstream. LPG flames are more stable than NG flames. This is consistent with the higher values of the laminar flame speed of LPG. The flame kernel propagation speed is affected by both turbulence and chemistry. However, at low turbulence level chemistry effects are more pronounced while at high turbulence level the turbulence becomes dominant. LPG flame kernels propagate faster than those for NG flame. In addition, flame kernel extinguished faster in LPG fuel as compared to NG fuel. The propagation speed is likely to be consistent with the local mean equivalence ratio and its corresponding laminar flame speed. Copyright © Taylor & Francis Group, LLC.

Selçuk, N. a, F. b Beretta, M. S. c Mansour, and A. d Danna, "Preface: Eighth mediterranean combustion symposium", Combustion Science and Technology, vol. 186, no. 4-5: Taylor and Francis Inc., pp. 387-388, 2014. AbstractWebsite
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2013
Baudoin, E. a, X. S. a Bai, B. a b Yan, C. a b Liu, R. a Yu, A. c Lantz, S. M. a Hosseini, B. c Li, A. d Elbaz, M. e Sami, et al., "Effect of partial premixing on stabilization and local extinction of turbulent methane/air flames", Flow, Turbulence and Combustion, vol. 90, no. 2, pp. 269-284, 2013. AbstractWebsite

The stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime, significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study. © 2012 Springer Science+Business Media B.V.

2012
Elsayed, K. A., H. b Imam, A. b Harfoosh, Y. d Hassebo, Y. b Elbaz, M. b Aziz, and M. c Mansour, "Design and construction of Q-switched Nd:YAG laser system for LIBS measurements", Optics and Laser Technology, vol. 44, no. 1, pp. 130-135, 2012. AbstractWebsite

A passive, Q-switched pulsed, Nd:YAG laser system was designed and built, which can provide a potential compact robust laser source for portable laser induced breakdown spectroscopy systems. The developed laser system operates at 1064 nm. Each laser shot contains a train of pulses having maximum total output energy of 170 mJ. The number of pulses varies from 16 pulses in each laser shot depending on the pump energy. The pulse width of each pulse ranges from 20 to 30 ns. The total duration of the output pulse train is within 300 μs. The multi-pulse nature of the laser shots was employed to enhance the LIBS signal. To validate the system, LIBS measurements and analysis were performed on ancient ceramic samples collected from Al-Fustat excavation in Old Cairo. The samples belong to different Islamic periods in Egypt history. The results obtained are highly indicative that useful information can be provided to archeologists for use in restoring and repairing of precious archeological objects. © 2011 Elsevier Ltd. All rights reserved.

Soliman, A. M. a, M. S. b Mansour, N. c Peters, and M. H. d Morsy, "Dissipation element analysis of scalar field in turbulent jet flow", Experimental Thermal and Fluid Science, vol. 37, pp. 57-64, 2012. AbstractWebsite

For better understanding of turbulence, the geometry of turbulent structures in turbulent jet flow should be analyzed. The aim of the present work was to experimentally verify the dissipation element theory on highly resolved two-dimensional measurements turbulent jets using Rayleigh scattering technique. The statistical analysis of the characteristic parameters of dissipation elements; namely the linear length connecting the extremal points and the absolute value of the scalar difference at these points, respectively was also investigated. Rayleigh scattering was used to topographically produce 2D images of turbulent mixing to obtain the concentration distribution of two gases in a turbulent shear flow. The scalar field obtained was subdivided into numerous finite size regions. In each of these regions local extremal points of the fluctuating scalar are determined via gradient trajectory method. Gradient trajectories starting from any point in the scalar field φ(x, y) in the directions of ascending and descending scalar gradients will always reach a minimum and a maximum point where ∇ φ=0. The dissipation element has two extremal points (one maximal and one minimal) and two saddle points at the boundaries. © 2011 Elsevier Inc.

Selçuk, N. a, F. b Beretta, M. S. c Mansour, and A. d D'Anna, "Seventh Mediterranean Combustion Symposium", Experimental Thermal and Fluid Science, vol. 43, pp. 1, 2012. AbstractWebsite
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Mansour, M. S. a, A. M. b Elbaz, and M. c Samy, "The stabilization mechanism of highly stabilized partially premixed flames in a concentric flow conical nozzle burner", Experimental Thermal and Fluid Science, vol. 43, pp. 55-62, 2012. AbstractWebsite

Many practical combustion systems are based on the mode of partially premixed flames where the interaction between lean and rich pockets improves the flame stability. In our recent work a highly stabilized concentric flow conical nozzle burner has been designed and developed for partially premixed flames. Flow field, temperature and OH radical measurements were conducted outside the cone. The early region of the flame within the cone affects the stability of the flame. So, the aim of the present work is to study the stabilization mechanism inside the cone based on two dimensional measurements of the flow field and temperature field. Five turbulent partially premixed flames have been investigated at Reynolds numbers range between 8.3×10 3 and 14.5×10 3 and equivalence ratio ranges between 2.5 and 4. The turbulent flow field inside and outside the conical quartz nozzle were obtained using a three-dimensional PIV system. The flow filed at the near region inside the cone shows a recirculation zone suggesting air entrainment along the cone wall. This stream of air is likely to be heated by the flame and thus improves the flame stability. Thus, the stabilization mechanism of the conical nozzle burner is mainly affected by the flow pattern inside the cone. This flow field structure improves the stability significantly as compared to similar partially premixed flames without cone. The mean temperature field indicated two distinctive regions at early axial distances, the first of a lower central flame temperature and a second region of a higher flame temperature, which located at a shifted radial distances. These two regions are associated with four distinctive regions of temperature fluctuations. The jet equivalence ratio has a limited effect on flow fields and has relatively milder effect on the temperature field. © 2012 Elsevier Inc.

2010
Beretta, F. a, N. b Selçuk, M. S. c Mansour, and A. d Danna, "Sixth mediterranean combustion symposium", Combustion Science and Technology, vol. 182, no. 4-6, pp. 331-332, 2010. AbstractWebsite
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Selçuk, N. a, F. b Beretta, M. S. c Mansour, and A. d D'Anna, "Sixth Mediterranean Combustion Symposium", Experimental Thermal and Fluid Science, vol. 34, no. 3, pp. 257, 2010. AbstractWebsite
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b Yan, B. a, B. c Li, E. b Baudoin, C. a b Liu, Z. W. c Sun, Z. S. c Li, X. S. b Bai, M. c Aldén, G. a Chen, and M. S. d Mansour, "Structures and stabilization of low calorific value gas turbulent partially premixed flames in a conical burner", Experimental Thermal and Fluid Science, vol. 34, no. 3, pp. 412-419, 2010. AbstractWebsite

Experiments are carried out on partially premixed turbulent flames stabilized in a conical burner. The investigated gaseous fuels are methane, methane diluted with nitrogen, and mixtures of CH4, CO, CO2, H2 and N2, simulating typical products from gasification of biomass, and co-firing of gasification gas with methane. The fuel and air are partially premixed in concentric tubes. Flame stabilization behavior is investigated and significantly different stabilization characteristics are observed in flames with and without the cone. Planar laser induced fluorescence (LIF) imaging of a fuel-tracer species, acetone, and OH radicals is carried out to characterize the flame structures. Large eddy simulations of the conical flames are carried out to gain further understanding of the flame/flow interaction in the cone. The data show that the flames with the cone are more stable than those without the cone. Without the cone (i.e. jet burner) the critical jet velocities for blowoff and liftoff of biomass derived gases are higher than that for methane/nitrogen mixture with the same heating values, indicating the enhanced flame stabilization by hydrogen in the mixture. With the cone the stability of flames is not sensitive to the compositions of the fuels, owing to the different flame stabilization mechanism in the conical flames than that in the jet flames. From the PLIF images it is shown that in the conical burner, the flame is stabilized by the cone at nearly the same position for different fuels. From large eddy simulations, the flames are shown to be controlled by the recirculation flows inside cone, which depends on the cone angle, but less sensitive to the fuel compositions and flow speed. The flames tend to be hold in the recirculation zones even at very high flow speed. Flame blowoff occurs when significant local extinction in the main body of the flame appears at high turbulence intensities. © 2009 Elsevier Inc. All rights reserved.

2009
Li, B. a, E. b Baudoin, R. b Yu, Z. W. a Sun, Z. S. a Li, X. S. b Bai, M. a Aldén, and M. S. c Mansour, "Experimental and numerical study of a conical turbulent partially premixed flame", Proceedings of the Combustion Institute, vol. 32 II, Montreal, QC, pp. 1811-1818, 2009. AbstractWebsite

The structure and dynamics of a turbulent partially premixed methane/air flame in a conical burner were investigated using laser diagnostics and large-eddy simulations (LES). The flame structure inside the cone was characterized in detail using LES based on a two-scalar flamelet model, with the mixture fraction for the mixing field and level-set G-function for the partially premixed flame front propagation. In addition, planar laser induced florescence (PLIF) of CH and chemiluminescence imaging with high speed video were performed through a glass cone. CH and CH2O PLIF were also used to examine the flame structures above the cone. It is shown that in the entire flame the CH layer remains very thin, whereas the CH2O layer is rather thick. The flame is stabilized inside the cone a short distance above the nozzle. The stabilization of the flame can be simulated by the triple-flame model but not the flamelet-quenching model. The results show that flame stabilization in the cone is a result of premixed flame front propagation and flow reversal near the wall of the cone which is deemed to be dependent on the cone angle. Flamelet based LES is shown to capture the measured CH structures whereas the predicted CH2O structure is somewhat thinner than the experiments. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Mansour, M. S. a, H. b Imam, K. A. c Elsayed, and W. b Abbass, "Local equivalence ratio measurements in turbulent partially premixed flames using laser-induced breakdown spectroscopy", Spectrochimica Acta - Part B Atomic Spectroscopy, vol. 64, no. 10, pp. 1079-1084, 2009. AbstractWebsite

One of the most recently applied laser-based techniques in combustion environment is the laser-induced breakdown spectroscopy (LIBS). The technique has been extensively and successfully applied to elemental concentration measurements in solids and liquids. The LIBS signal is much weaker in gases and hence more work is required for quantitative measurements in flames. In the present work we used two orthogonal Nd:YAG lasers that operate at the fundamental wavelength with laser pulse energy of about 100 mJ/pulse. A Princeton-Instruments IMAX ICCD camera attached to a PI-Echelle spectrometer was used for signal detection. The lasers are focused using two 5-cm lenses. Several calibration points have been collected in well defined and homogeneous mixtures of air and fuel in order to be used as references for the measurements in turbulent partially premixed flames. This work shows that the application of the LIBS technique in a turbulent combustion environment is feasible and signal is enhanced by applying an orthogonal dual-pulse arrangement for air-fuel. © 2009 Elsevier B.V. All rights reserved.

Hemdan, M. a, J. a El-Azab, A. b El-Meliegy, M. c Mansour, and A. c El-Nadi, "A study of the synchronization recovery time of chaotic semiconductor laser", 6th International Symposium on High Capacity Optical Networks and Enabling Technologies, HONET '09, Alexandria, pp. 267-273, 2009. Abstract

The chaotic optical communication systems are based on the synchronization between the transmitting and receiving chaotic laser diodes. The performance of the system is determined by the bit error rate which can result from either the synchronization deviation or the desynchronization bursts. The time required for resynchronization results in loss of bits. The synchronization recovery time is studied for the different chaotic synchronization schemes. Also, the effect of the parameters mismatch between the transmitting and receiving laser diodes on the recovery time is investigated. ©2009 IEEE.

2008
Salem, H. G. a, M. S. b Mansour, Y. b Badr, and W. A. b Abbas, "CW Nd:YAG laser cutting of ultra low carbon steel thin sheets using O2 assist gas", Journal of Materials Processing Technology, vol. 196, no. 1-3, pp. 64-72, 2008. AbstractWebsite

There are many non-linear interaction factors responsible for the performance of the laser cutting process. Identification of the dominant factors that significantly affect the cut quality is important. The present research aims to evaluate the CW ND:YAG laser cutting parameters (the gas pressure, laser power, and scanning speed) for 1.2 mm thick ultra-low carbon steel sheets. The effect of the cutting parameters on the cut quality was then investigated, by monitoring the variation in hardness, oxide layer width and microstructural changes within the heat affected zone (HAZ). Results revealed that good quality cuts can be produced in ultra low carbon steel thin sheets, at a window of laser scanning speed of 1100-1500 mm/min and at a minimum heat input of 337 W under an assisting O2 gas pressure of 5 bar. Higher laser power resulted in either strengthening or softening in the HAZ surrounding the cut kerfs. The oxide layer width is not affected by the energy density input, but is affected by the O2 gas pressure due to exothermal reaction. © 2007.

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