Medhat A. Nemitallah

Bio: Medhat A. Nemitallah is an academic researcher from King Fahd University of Petroleum and Minerals. The author has contributed to research in topics: Combustion & Combustor. The author has an hindex of 23, co-authored 109 publications receiving 1371 citations. Previous affiliations of Medhat A. Nemitallah include Massachusetts Institute of Technology & Alexandria University.

Experimental investigations of ignition delay period and performance of a diesel engine operated with Jatropha oil biodiesel

Abstract: Jatropha-curcas as a non-edible methyl ester biodiesel fuel source is used to run single cylinder, variable compression ratio, and four-stroke diesel engine. Combustion characteristics as well as engine performance are measured for different biodiesel – diesel blends. It has been shown that B50 (50% of biodiesel in a mixture of biodiesel and diesel fuel) gives the highest peak pressure at 1750 rpm, while B10 gives the highest peak pressure at low speed, 1000 rpm. B50 shows upper brake torque, while B0 shows the highest volumetric efficiency. B50 shows also, the highest BSFC by about (12.5–25%) compared with diesel fuel. B10 gives the highest brake thermal efficiency. B50 to B30 show nearly the lowest CO concentration, besides CO concentration is the highest at both idle and high running speeds. Exhaust temperature and NO x are maximum for B50. Delay period is measured and correlated for different blends. Modified empirical formulae are obtained for each blend. The delay period is found to be decreased with the increase of cylinder pressure, temperature and equivalence ratio.

Experimental and numerical investigations of an atmospheric diffusion oxy-combustion flame in a gas turbine model combustor

Abstract: An atmospheric diffusion oxy-combustion flame in a gas turbine model combustor has been investigated experimentally and numerically. Oxy-combustion and emission characterization, flame stabilization and oxy-combustion model validation analyses are the main goals of the present research work. The combustor is fuelled with CH4 and a mixture of CO2 and O2 as oxidizer. A modified two-step oxy-combustion reaction kinetics model for methane–oxygen combustion has been used in order to predict accurately the oxy-combustion characteristics. The conducted experimental results were used to validate the numerical model. Wide ranges of different operating parameters have been considered including equivalence ratio, percentage of O2/CO2 in the oxidizer mixture and fuel volume flow rate. The stability of the oxy-combustion diffusion flame is also investigated both experimentally and numerically. The experimental and numerical results showed that the stability of the oxy-combustion flame is affected when the operating percentage of oxygen in the oxidizer mixture is reduced below 25%. In all cases, flame was extinct for conditions of less than 21% oxygen in the oxidizer mixture. Flame visualization over a wide range of operating parameters has been carried out experimentally and comparisons with the numerical results have been conducted. The flames have been characterized in detail by measuring the exhaust gas temperatures and emissions and comparing them with those from the numerical model. The combustion was found to be improved with increasing the percentage of O2 at inlet however there is a limitation in temperature. Both experimental and numerical results are in good agreement. The modified two step reaction kinetics model was found to be capable of capturing the trends of temperature and the overall flame shape of the experimental data. Flame zone is also characterized in details by plotting the axial and radial temperatures, species concentrations and flow velocities using the numerical model.

Recent Development in Oxy-Combustion Technology and Its Applications to Gas Turbine Combustors and ITM Reactors

Abstract: For decreasing greenhouse gas (mainly CO2) emissions, several approaches have been evaluated and reviewed for capturing CO2 in the utility industry, namely, carbon capture and storage technology (CCS), including precombustion capture, oxy-fuel combustion, and postcombustion capture. As a promising CCS technology, oxy-fuel combustion can be used to existing and new power plants. In oxy-combustion, a fuel is oxidized in a nearly nitrogen-free, diluted mixture such that the products consist mainly of CO2 and water vapor, enabling a relatively simple and inexpensive condensation separation process, and then, CO2 could be captured easily. There are two main approaches available to utilize the oxy-combustion technology, one of them is through the use of air separation units to separate O2, which will be used in the combustion process, and the other application is the ion transport membrane (ITM) reactor technology. This membrane separates oxygen from oxygen containing upstream (typically air). The oxygen transp...

Oxy-fuel combustion technology: current status, applications, and trends

Abstract: Summary The increased level of emissions of carbon dioxide into the atmosphere due to burning of fossil fuels represents one of the main barriers toward the reduction of greenhouse gases and the control of global warming. In the last decades, the use of renewable and clean sources of energies such as solar and wind energies has been increased extensively. However, due to the tremendously increasing world energy demand, fossil fuels would continue in use for decades which necessitates the integration of carbon capture technologies (CCTs) in power plants. These technologies include oxycombustion, pre-combustion, and post-combustion carbon capture. Oxycombustion technology is one of the most promising carbon capture technologies as it can be applied with slight modifications to existing power plants or to new power plants. In this technology, fuel is burned using an oxidizer mixture of pure oxygen plus recycled exhaust gases (consists mainly of CO2). The oxycombustion process results in highly CO2-concentrated exhaust gases, which facilitates the capture process of CO2 after H2O condensation. The captured CO2 can be used for industrial applications or can be sequestrated. The current work reviews the current status of oxycombustion technology and its applications in existing conventional combustion systems (including gas turbines and boilers) and novel oxygen transport reactors (OTRs). The review starts with an introduction to the available CCTs with emphasis on their different applications and limitations of use, followed by a review on oxycombustion applications in different combustion systems utilizing gaseous, liquid, and coal fuels. The current status and technology readiness level of oxycombustion technology is discussed. The novel application of oxycombustion technology in OTRs is analyzed in some details. The analyses of OTRs include oxygen permeation technique, fabrication of oxygen transport membranes (OTMs), calculation of oxygen permeation flux, and coupling between oxygen separation and oxycombustion of fuel within the same unit called OTR. The oxycombustion process inside OTR is analyzed considering coal and gaseous fuels. The future trends of oxycombustion technology are itemized and discussed in details in the present study including: (i) ITMs for syngas production; (ii) combustion utilizing liquid fuels in OTRs; (iii) oxy-combustion integrated power plants and (iv) third generation technologies for CO2 capture. Techno-economic analysis of oxycombustion integrated systems is also discussed trying to assess the future prospects of this technology. Copyright © 2017 John Wiley & Sons, Ltd.

Review of Novel Combustion Techniques for Clean Power Production in Gas Turbines

Abstract: The tremendous increase in energy demand due to increased population and rapid economics results in an increased level of atmospheric pollutants and global warming. The global shift to the use of renewable clean energies still has some restrictions in terms of the availability of the advanced reliable technologies and the cost of application compared to conventional fossil fuels. Until we can have this full conversion to renewables, the development of novel techniques for clean combustion of fossil fuels is appreciated. Forced by the simultaneous increased pressure of strict emissions regulations and the target of limiting the global warming to 2 °C, gas turbine manufacturers developed novel combustion techniques for clean power production in gas turbines as per the present review study. These novel techniques depend either on modification in the existing combustion system or developing novel burners for clean power production. In this review, different clean combustion techniques are presented including ...

Applied Combustion Diagnostics

Abstract: The editors have assembled a world-class group of contributors who address the questions the combustion diagnostic community faces. They are chemists who identify the species to be measured and the interfering substances that may be present; physicists, who push the limits of laser spectroscopy and laser devices and who conceive suitable measuremen

Oxyfuel combustion for CO2 capture in power plants

Abstract: Oxyfuel combustion is one of the leading technologies considered for capturing CO2 from power plants with CCS. This involves the process of burning the fuel with nearly pure oxygen instead of air. In order to control the flame temperature, some part of the flue gas are recycled back into the furnace/boiler. Since the publication of the Special Report on CO2 Capture and Storage by the International Panel for Climate Change (IPCC, 2005), the development of oxyfuel combustion technology has progressed significantly and could be considered at par in terms of technology maturity as compared to other leading CO2 capture technologies. This paper presents an overview to the current state-of-the-art technology on the development of oxyfuel combustion applied to (a) PC and CFB coal fired power plants and (b) gas turbine based power plant. It should be noted that it is not the intention of this paper to provide a comprehensive review but to present what have been achieved in the past 10 years of RD&D efforts. For coal fired power plant using oxyfuel combustion, this paper primarily presents the different development aspects of the burners and boilers (combustion and heat transfer), emissions, operation of the plant (i.e. start-up and turndown) and its integration to the ASU and CPU. For gas turbine based power plant using oxyfuel combustion, the different GT cycles are described, looking at the different aspects in combustion, emissions, cycle efficiency and development of the turbomachineries. Also presented in this paper is a snapshot to what we have learned from the operation of the different large-scale pilot plants and development of large scale demonstration projects worldwide. The paper concludes by presenting the potential of this technology and highlighting the importance of realizing large scale demonstration plant as a necessary step to achieve its ultimate goal of technology commercialization.

Unit Operations Of Chemical Engineering

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Performance, emission and combustion characteristics of a diesel engine using Carbon Nanotubes blended Jatropha Methyl Ester Emulsions

Abstract: An experimental investigation was conducted in a single cylinder constant speed diesel engine to establish the effects of Carbon Nanotubes (CNT) with the Jatropha Methyl Esters (JME) emulsion fuel. The JME was produced from the Jatropha oil by transesterification process, and subsequently the JME emulsion fuel was prepared in the proportion of 93% of JME, 5% of water and 2% of surfactants (by volume) with a hydrophilic–lipophilic balance of 10. The Carbon Nanotubes are blended with the JME emulsion fuel in the various dosages systematically. The whole investigation was conducted in the diesel engine using the following fuels: neat JME, neat JME emulsion fuel and CNT blended JME emulsion fuels accordingly. The experimental results revealed an appreciable enhancement in the brake thermal efficiency for the CNT blended JME emulsion fuels compared to that of neat JME and neat JME emulsion fuel. At the full load, the brake thermal efficiency for the JME fuel observed was 24.80%, whereas it was 26.34% and 28.45% for the JME2S5W and JME2S5W100CNT fuels respectively. Further, due to the combined effects of micro-explosion and secondary atomization phenomena associated with the CNT blended JME emulsion fuels, the level of harmful pollutants in the exhaust gases (such as NOx and smoke) was drastically reduced when compared to that of neat JME. At the full load, the magnitude of NOx and smoke opacity for the neat JME was 1282 ppm and 69%, whereas it was 910 ppm and 49% for the JME2S5W100CNT fuel respectively.