Esmail M. A. Mokheimer - Academia.edu (original) (raw)
Papers by Esmail M. A. Mokheimer
Arabian Journal for Science and Engineering, Nov 22, 2023
Heat and Mass Transfer, 2020
In hot and humid climates, the evaporative cooling system not works effectively. To reduce the re... more In hot and humid climates, the evaporative cooling system not works effectively. To reduce the relative humidity of inlet air, the reciprocating desiccant mesh (RDM) is introduced before the cooling tower. The cooling tower is fabricated as per the Merkel's theory and RDM is placed before the cooling tower. Experiments have been conducted to compare the performance of normal and RDM cooling towers at different operating conditions. The results of this study indicate that the most favorable velocity and water flow rate of the RDM cooling tower are 1.8 m/s and 17.3 L/min, respectively. At this condition, the cooling effect of the RDM cooling tower is 1.6°C greater than the normal cooling tower. Further, the maximum effectiveness of normal and RDM cooling tower are 0.72 and 0.82, respectively. At last, this study recommends that the RDM cooling tower reduces water consumption as compared to the normal cooling tower due to the lower temperature of cold water.
![Research paper thumbnail of Erratum to “Fuel flexibility, stability and emissions in premixed hydrogen-rich gas turbine combustion: Technology, fundamentals, and numerical simulations” [Appl Energy 154 (2015) 1020–1047]](https://attachments.academia-assets.com/115384899/thumbnails/1.jpg)
](Applied Energy, Jun 1, 2018
Erratum Erratum to "Fuel flexibility, stability and emissions in premixed hydrogenrich gas turbin... more Erratum Erratum to "Fuel flexibility, stability and emissions in premixed hydrogenrich gas turbine combustion: Technology, fundamentals, and numerical simulations" [Appl Energy 154 (2015) 1020-1047]
Energy Conversion and Management, May 1, 2019
The present study focuses on energy and exergy analyses of the trigeneration system consisting of... more The present study focuses on energy and exergy analyses of the trigeneration system consisting of heliostat field, organic Rankine cycle with the heat exchanger, and ejector-absorption chiller which has the merits of refrigerating a thermal load of below than 0°C with solar energy more efficiently along with the generation of process heat and electric power in an eco-friendly manner. A parametric study is carried out to investigate the effect of varying the influencing operating variables on trigeneration system output, and its energy and exergy efficiencies. It is found that the exergetic output of isobutane operated system increases from 2562 kW to 4314 kW while for propane operated system it is raised from 1203 kW to 2028 kW when the direct normal irradiations are increased from 600 to 1000 W/m 2. Results of energy and exergy utilization show that for isobutane ORC fluid, out of 100% solar energy supplied to the system 65.42% can be produced as energetic output and rest 34.58% is lost via thermal exhaust to ambient. On the other hand, out of 100% solar exergy supplied only 13.98% is the produced exergy, 84. 89% is the exergy destroyed due to irreversibilities, and rest 1.13% is the exergy loss.
Applied Energy, Sep 1, 2015
The objective of this paper is to review the progress made in understanding the effects of fuel c... more The objective of this paper is to review the progress made in understanding the effects of fuel composition on premixed gas turbine combustion, with a special emphasis on system stability and emissions, for hydrogen-rich synthetic gas (syngas) mixtures. This is driven by the rising interest in the use of hydrogen blends and syngas in combined cycle power plants, as an alternative to standard natural gas. Typical applications where such mixtures are used include the recycling of hydrogen by-product from industry as well as promising pre-combustion carbon capture methods like fuel reforming or gasification integrated with gas turbine combined cycle plants. Syngas is mainly a mixture of H2, CO and CH4; its composition can vary due to fluctuations in the process’s conditions but can also dramatically change if the feedstock is modified like coal or biomass grades in gasification. Due to the substantially different chemical, transport and thermal properties that distinguish the syngas components, especially H2, when compared with conventional hydrocarbon fuels, these non-standard fuels pose several challenges in premixed combustion. These challenges are reviewed in this paper along with the combustion fundamentals of these fuels. A survey of available technologies able to handle syngas and hydrogen-rich fuel in general is provided reflecting the difficulties encountered while using these fuels in real large scale commercial applications. We find that a limited number of options exist today for fully premixed combustion, but promising designs are under development. Finally, the ever growing use of numerical simulation to cost-effectively study full scale combustion systems—with Large Eddy Simulations (LES) being at the forefront as a compromise between accuracy and computational cost—justifies the simultaneous review of the different numerical attempts to simulate hydrogen-containing fuel mixtures and syngas in premixed combustion. Challenges specific to performing LES calculations for these reacting flows are highlighted. We find that, while the literature on premixed LES methane combustion is abundant, LES of premixed syngas and hydrogen-rich fuels combustion is comparatively scarce. Only few attempts were made so far showing the need for more research effort in this area to help tackle the challenges presented by these fuels.
Energy Procedia, Dec 1, 2017
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Energy Conversion and Management, Dec 1, 2021
Energy Conversion and Management, Aug 1, 2017
In this work, a parametric study on a b-type Stirling engine with no regenerator was conducted nu... more In this work, a parametric study on a b-type Stirling engine with no regenerator was conducted numerically using ANSYS fluent 14.5 software. The three parameters that were studied are; initial charge pressure, thermal boundary condition; and three different types of working fluids (Air, He and H 2). Variable thermal properties of these gases were adopted to get more realistic results. The results include a comparison of the amount of heat transfer, power output, and thermal efficiency. It was found that the best engine performance is achieved when H 2 gas is used as working fluid. Moreover, results revealed that each of the power output and the efficiency has different optimum charge pressure. Additionally, it was found that there is a small variation in the pressure across the engine chambers, which results in miss matching between the net heat transfer rates and power output calculated from PV-diagram. This error is higher when the air is used as working fluid, especially at high charge pressure.
Combustion and Flame, 2016
Abstract In this paper, we report results from an experimental investigation on transitions in th... more Abstract In this paper, we report results from an experimental investigation on transitions in the average flame shape (or microstructure) under acoustically coupled and uncoupled conditions in a 50 kW swirl stabilized combustor. The combustor burns CH4/H2 mixtures at atmospheric pressure and temperature for a fixed Reynolds number of 20,000 and fixed swirl angle. For both cases, essentially four different flame shapes are observed, with the transition between flame shapes occurring at the same equivalence ratio (for the same fuel mixture) irrespective of whether the combustor is acoustically coupled or uncoupled. The transition equivalence ratio depends on the fuel mixture. For the baseline case of pure methane, the combustor is stable close to the blowoff limit and the average flame in this case is stabilized inside the inner recirculation zone. As the equivalence ratio is raised, the combustor transitions to periodic oscillations at a critical equivalence ratio of ϕ = 0.65 . If hydrogen is added to the mixture, the same transition occurs at lower equivalence ratios. For all cases that we investigated, flame shapes captured using chemiluminescence imaging show that the transition to harmonic oscillations in the acoustically coupled cases is preceded by the appearance of the flame in the outer recirculation zone. We examine the mechanism associated with the transition of the flame between different shapes and, ultimately, the propagation of the flame into the outer recirculation zone as the equivalence ratio is raised. Using the extinction strain rates for each mixture at different equivalence ratios, we show that these transitions in the flame shape and in the instability (in the coupled case) for different fuel mixtures collapse as a function of a normalized strain rate : κ e x t D U ∞ . We show that the results as consistent with a mechanism in which the flame must overcome higher strains prevailing in the outer recirculation zone, in order to stabilize there.
Energy Conversion and Management, Sep 1, 2017
Solar energy is an abundant resource in many countries in the Sunbelt, especially in the middle e... more Solar energy is an abundant resource in many countries in the Sunbelt, especially in the middle east, countries, where recent expansion in the utilization of natural gas for electricity generation has created a significant base for introducing integrated solar-natural gas power plants (ISGPP) as an optimal solution for electricity generation in these countries. ISGPP reduces the need for thermal energy storage in traditional concentrated solar thermal plants and results in dispatchable power on demand at lower cost than stand-alone concentrated thermal power and much cheaper than photovoltaic plants. Moreover, integrating concentrated solar power (CSP) with conventional fossil fuel based thermal power plants is quite suitable for large-scale central electric power generation plants and it can be implemented in the design of new installed plants or during retrofitting of existing plants. The main objective of the present work is to investigate the possible modifications of an existing gas turbine cogeneration plant, which has a gas turbine of 150 MWe electricity generation capacity and produces steam at a rate of 81.4 at 394°C and 45.88 bars for an industrial process, via integrating it with concentrated solar power system. In this regard, many simulations have been carried out using Thermoflow software to explore the thermoeconomic performance of the gas turbine cogeneration plant integrated with LFR concentrated solar power field. Different electricity generating capacities of the gas turbine and different areas of solar collectors have been examined. Thermoflow software simulation results have been used to identify the optimal configuration and sizing of the gas turbine and the solar field of the integrated solar gas turbine cogeneration plant (ISGCPP) required to achieve the required steam generation with the minimum cost and environmental impact. The study revealed that ISGCPP can reduce the levelized electricity cost by 76-85% relative to the fully-solar-powered LFR power plant. Moreover, the study identified the configuration of ISGCPP with a gas turbine size of 50 MWe capacity and 93 ha of LFR solar field as the optimally integrated plant. It reduces the annual CO 2 emission by 100 k Tonne (18%) in comparison with that emitted by the corresponding conventional plant with 50 MWe and 400 k tonne (43.75%) compared with that emitted by the original conventional plant with a gas turbine if 150 MWe power generation capacity. The study revealed also that integrating the LFR technology with a gas turbine cogeneration power plant in locations with high solar insolation was proved to have more economic feasibility than CO 2 capturing technology. Under Dhahran weather conditions, the LEC of about 5 USȻ/kW h is obtained using the proposed optimally configured ISGCPP compared with about 7.5 USȻ/kW h obtained by the corresponding conventional cycle integrated with carbon capture technology. In other words, the ISGCPP reduces the LEC by 50% while achieving the same reduction of CO 2 emission by an equivalent conventional plant integrated with carbon capture technology.
Journal of Energy Resources Technology-transactions of The Asme, Jun 12, 2018
Cooling the air before entering the compressor of a gas turbine of combined cycle power plants is... more Cooling the air before entering the compressor of a gas turbine of combined cycle power plants is an effective method to boost the output power of the combined cycles in hot regions. This paper presents a comparative analysis for the effect of different air cooling technologies on increasing the output power of a combined cycle. It also presents a novel system of cooling the gas turbine inlet air using a solar-assisted absorption chiller. The effect of ambient air temperature and relative humidity on the output power is investigated and reported. The study revealed that at the design hour under the hot weather conditions, the total net power output of the plant drops from 268 MW to 226 MW at 48 °C (15.5% drop). The increase in the power output using fogging and evaporative cooling is less than that obtained with chillers since their ability to cool down the air is limited by the wet-bulb temperature. Integrating conventional and solar-assisted absorption chillers increased the net power output of the combined cycle by about 35 MW and 38 MW, respectively. Average and hourly performance during typical days have been conducted and presented. The plants without air inlet cooling system show higher carbon emissions (0.73 kg CO2/kWh) compared to the plant integrated with conventional and solar-assisted absorption chillers (0.509 kg CO2/kWh) and (0.508 kg CO2/kWh), respectively. Also, integrating a conventional absorption chiller shows the lowest capital cost and levelized electricity cost (LEC).
Journal of Applied Mechanical Engineering, 2015
Solar Cooling Technologies Classification Solar Cooling technologies can be classified in three m... more Solar Cooling Technologies Classification Solar Cooling technologies can be classified in three main categories: solar electrical, thermal and combined power/cooling cycles as illustrated in Figure 1. Solar Cooling System and Application Temperature Ranges The solar cooling system can be divided into three major components; solar energy collecting element, refrigeration cycles, and the application at different temperature ranges. The proper cycle for each application mainly can be selected based
Energy, Dec 1, 2018
The energetic and exergetic performance of a solar thermal power and ejector-absorption refrigera... more The energetic and exergetic performance of a solar thermal power and ejector-absorption refrigeration system is investigated. R141b, R600a, R290, R717 and R143a were employed as the working fluids for ORC and NH 3-LiNO 3 was utilized in the ejector-absorption cycle for cooling production. The energetic and exergetic output of PTC driven combined power and refrigeration cycle were evaluated along with the calculation of thermodynamic irreversibility. The distribution of solar exergy input to the cycle in term of exergy produced, destroyed due to irreversibility, and loss due to thermal exhaust to the ambient was computed and compared with the traditional energy distribution. The maximum exergy was destroyed in the PTC where it amounts to 79.61% of the overall exergy destruction. The conversion of solar exergy input to the cycle exergy output was best (14.6%) for R141b fluid and worst (3.9%) for R143a fluid. Parametric analysis of the results reveals that Solar beam radiation (SBR), turbine inlet pressure (TIP), ORC pump inlet temperature, heat transfer fluid (HTF) temperature at the inlet of PTC, and the selection of ORC working fluid have the significant effect on the energetic and exergetic outputs of solar thermal power and ejector-absorption cooling system.
Journal of Energy Resources Technology, 2017
A large amount of the operating costs in a building is determined by the energy requirements of i... more A large amount of the operating costs in a building is determined by the energy requirements of its air conditioning system. The demand for more energy efficient units desired by both manufacturers and the consumers results in a dire necessity to have air conditioning units that are more energy efficient than the existing ones. In order to achieve the abovementioned features, a tool must be designed to simulate the thermal behavior of the air conditioners. In this work, a mathematical model is developed for air conditioning units and coded into a computer program to estimate the overall performance, as indicated by the unit energy efficiency ratio (EER). The main objective is to maximize the unit EER by proposing modifications or enhancements in the existing unit and to study the economics of these modifications based on the measured terms such as the energy savings and the operating cost. Finally, the effect of the proposed design modifications on the economy and environment at the...
Stratified Flames have gained prominence in the combustion research applications due to its impro... more Stratified Flames have gained prominence in the combustion research applications due to its improved stability and lower emission characteristics. In the present study, stratified jet flames are studied in a dual annular combustor. The static stability and the flame macrostructure have been presented and discussed. Stratification by making the inner annulus mixture rich was found to significantly improve the static stability limits. Furthermore, stratification by making the inner annulus rich was found to lead to attached flame at lower equivalence ratios of 0.22-0.38. Thus, stratification is more helpful at lower equivalence ratios.
ACS omega, Sep 2, 2022
Reynolds averaged Navier Stokes technique was used to develop a validated numerical model for str... more Reynolds averaged Navier Stokes technique was used to develop a validated numerical model for stratified flames. The validation was carried out with the experimental data of the non-swirl flames of the Cambridge dual annulus swirl burner. The RNG k–ε turbulence model along with the SG-35 skeletal chemical mechanism was found to give a good prediction of scalar and vector quantities while resulting in the reduction of computational time by 99.75% in comparison with that required for large eddy simulation techniques used in the literature. The effect of stratification at a constant input power, global equivalence ratio, and Reynolds number was examined. At stratification ratios (SRs = ϕin/ϕout) 1 and 2, intense burning, marked by the higher OH concentration, was observed close to the bluff body. Beyond SR = 2, the region of intense burning shifts downstream away from the bluff body. This is a result of the high equivalence ratio in the inner annulus, which is beyond the rich flammability limit of methane–air flames, and as a result, the primary flame region is shifted downstream after the mixtures from inner and outer annulus have mixed properly to produce a mixture with the equivalence ratio in the flammability limit. The maximum temperature was found to increase by 24.1% when the SR is increased from 1 to 2 and the combustion efficiency was found to significantly improve by 267%. The highest maximum temperature of 2249 K is observed for the mildly stratified flame at SR = 2. Beyond SR = 2, the maximum temperature decreases, while the combustion efficiency increases slightly.
Fuel Processing Technology, Sep 1, 2023
The study to improve the characteristics in terms of performance, emission and combustion aspects... more The study to improve the characteristics in terms of performance, emission and combustion aspects without any modification to a direct injection compression ignition engine using pine oil blend and additive addition was executed. Biofuels known for their reduction in emission also degrades the engine's performance value. To overcome this, pine oil mixture was used with an additive (1,4-dioxane). Pine oil taken at two different concentrations (P20, P40) and the additive at two varying proportions (5 ml, 10 ml) were utilized. In total, six pine oil mixtures were prepared and analyzed for the emission, performance and combustion aspects of the test engine and compared with diesel values. The result evidenced the rise of 3.88% and 5.57% for brake thermal efficiency and fuel consumption, respectively, for P20-10 ml blend compared with diesel. Contemplating the emission aspects, considerable decrease in pollutants (22.41% CO, 29.19% HC and 22.80% smoke) excluding NOx and CO 2 at peak load conditions was depicted. NOx and CO 2 increase about 7.23% and 25.41%, respectively. Combustion parameters like heat release rate and peak pressure of pine oil mixture exhibited inferior values compared with diesel. Only P20 blend with 10 ml additive exhibited values very close (a drop of 2.8% HRR and 2.4% CP) to that of diesel value. To conclude, out of half-dozen blends when compared with diesel, P20 with 10 ml additive proves as the best blend, providing much capable outcomes.
Fuel, Sep 1, 2020
High production cost, inefficient energy utilization, high water requirement, and environmental p... more High production cost, inefficient energy utilization, high water requirement, and environmental pollution are the major challenges to heavy oil production through the conventional steam injection method. Thermochemical fluid injection is a novel and environmentally benign technology for in-situ generation of heat and nitrogen from the exothermic reaction of certain chemicals. Thermochemical stimulation offers several advantages including minimal heat loss and reduced emission of CO 2 compared with steam injection. This study aims at harnessing the potential of injecting thermochemical fluids (TCF) to preheat the reservoir for improved in-situ combustion of bitumen (TCF-ISC). Bitumen sample was preheated using TCF (ratio: 10 ml TCF: 5 g bitumen) or steam. Thermogravimetric Analysis (TGA) was conducted to compare the combustion characteristics of original bitumen sample (B 0), those pre-treated using steam (B 1) and TCF (B 2). In addition, numerical simulation studies were performed to evaluate the performance of the proposed process. The thermochemical reaction produced temperature and pressure of 67°C and 1600 psi, respectively, and ΔH = 370 KJmol −1. The SEM-EDX analysis show that TCF treatment created open cavities on the matrix of the bitumen sample (B 2) which strongly supports potential to increase thermal communication during the ISC process. The thermogravimetric analysis (TGA) show that the TCF treatment of bitumen sample improve combustion performance with higher exothermicity and reactivity. These results revealed higher combustion reactivity and higher potential for combustion front propagation with TCF. Moreover, numerical simulation confirms higher cumulative oil production (m 3), oil recovery factor (%), and lower heat loss (GJ/m 3) using TCF preheating before the ISC.
International Journal of Energy Research, Jan 15, 2016
The demand for gas turbines that accept a variety of fuels has continuously increased over the la... more The demand for gas turbines that accept a variety of fuels has continuously increased over the last decade. Understanding the effects of varying fuel compositions on combustion characteristics and emissions is critical to designing fuel-flexible combustors. In this study, the combustion characteristics and emissions of methane and hydrogen-enriched methane were both experimentally and numerically investigated under ultra-lean conditions (Ø ≤ 0.5). This study was performed using global mechanisms with a one-step mechanism by Westbrook and Dryer and a two-step mechanism with an irreversible and reversible CO/CO 2 step (2sCM1 and 2sCM2). Results show that the 2sCM2 mechanism under-predicted the temperature, major species, and NO x by more than 100% under ultra-lean conditions; thus, we proposed a modified-2sCM2 mechanism to better simulate the combustion characteristics. The mechanisms of Westbrook, 2sCM1, and modified 2sCM2 predicted the temperature and the CO 2 emission with an average deviation of about 5% from the experimental values. Westbrook and 2sCM1, however, over-predicted the NO x emission by approximately 81% and 152%, respectively, as compared with an average under-prediction of 11% by the modified-2sCM2 mechanism. The numerical results using the proposed modified-2sCM2 mechanism shows that the presence of hydrogen in the fuel mixture inhibits the oxidation of methane that led to the formation of unburned hydrocarbons in the flame. We also showed that for any given fuel compositions of H 2 /CH 4 , there is an optimum equivalence ratio at which the pollutant emissions (CO and NO x) from the combustor are minimal. Zero CO and 5 ppm NO x emissions were observed at the optimal equivalence ratio of 0.45 for a fuel mixture containing 30% H 2. The present study provides a basis for ultra-lean combustion toward achieving zero emissions from a fuel-flexible combustor.
Applied Surface Science, Oct 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Arabian Journal for Science and Engineering, Nov 22, 2023
Heat and Mass Transfer, 2020
In hot and humid climates, the evaporative cooling system not works effectively. To reduce the re... more In hot and humid climates, the evaporative cooling system not works effectively. To reduce the relative humidity of inlet air, the reciprocating desiccant mesh (RDM) is introduced before the cooling tower. The cooling tower is fabricated as per the Merkel's theory and RDM is placed before the cooling tower. Experiments have been conducted to compare the performance of normal and RDM cooling towers at different operating conditions. The results of this study indicate that the most favorable velocity and water flow rate of the RDM cooling tower are 1.8 m/s and 17.3 L/min, respectively. At this condition, the cooling effect of the RDM cooling tower is 1.6°C greater than the normal cooling tower. Further, the maximum effectiveness of normal and RDM cooling tower are 0.72 and 0.82, respectively. At last, this study recommends that the RDM cooling tower reduces water consumption as compared to the normal cooling tower due to the lower temperature of cold water.
Applied Energy, Jun 1, 2018
Erratum Erratum to "Fuel flexibility, stability and emissions in premixed hydrogenrich gas turbin... more Erratum Erratum to "Fuel flexibility, stability and emissions in premixed hydrogenrich gas turbine combustion: Technology, fundamentals, and numerical simulations" [Appl Energy 154 (2015) 1020-1047]
Energy Conversion and Management, May 1, 2019
The present study focuses on energy and exergy analyses of the trigeneration system consisting of... more The present study focuses on energy and exergy analyses of the trigeneration system consisting of heliostat field, organic Rankine cycle with the heat exchanger, and ejector-absorption chiller which has the merits of refrigerating a thermal load of below than 0°C with solar energy more efficiently along with the generation of process heat and electric power in an eco-friendly manner. A parametric study is carried out to investigate the effect of varying the influencing operating variables on trigeneration system output, and its energy and exergy efficiencies. It is found that the exergetic output of isobutane operated system increases from 2562 kW to 4314 kW while for propane operated system it is raised from 1203 kW to 2028 kW when the direct normal irradiations are increased from 600 to 1000 W/m 2. Results of energy and exergy utilization show that for isobutane ORC fluid, out of 100% solar energy supplied to the system 65.42% can be produced as energetic output and rest 34.58% is lost via thermal exhaust to ambient. On the other hand, out of 100% solar exergy supplied only 13.98% is the produced exergy, 84. 89% is the exergy destroyed due to irreversibilities, and rest 1.13% is the exergy loss.
Applied Energy, Sep 1, 2015
The objective of this paper is to review the progress made in understanding the effects of fuel c... more The objective of this paper is to review the progress made in understanding the effects of fuel composition on premixed gas turbine combustion, with a special emphasis on system stability and emissions, for hydrogen-rich synthetic gas (syngas) mixtures. This is driven by the rising interest in the use of hydrogen blends and syngas in combined cycle power plants, as an alternative to standard natural gas. Typical applications where such mixtures are used include the recycling of hydrogen by-product from industry as well as promising pre-combustion carbon capture methods like fuel reforming or gasification integrated with gas turbine combined cycle plants. Syngas is mainly a mixture of H2, CO and CH4; its composition can vary due to fluctuations in the process’s conditions but can also dramatically change if the feedstock is modified like coal or biomass grades in gasification. Due to the substantially different chemical, transport and thermal properties that distinguish the syngas components, especially H2, when compared with conventional hydrocarbon fuels, these non-standard fuels pose several challenges in premixed combustion. These challenges are reviewed in this paper along with the combustion fundamentals of these fuels. A survey of available technologies able to handle syngas and hydrogen-rich fuel in general is provided reflecting the difficulties encountered while using these fuels in real large scale commercial applications. We find that a limited number of options exist today for fully premixed combustion, but promising designs are under development. Finally, the ever growing use of numerical simulation to cost-effectively study full scale combustion systems—with Large Eddy Simulations (LES) being at the forefront as a compromise between accuracy and computational cost—justifies the simultaneous review of the different numerical attempts to simulate hydrogen-containing fuel mixtures and syngas in premixed combustion. Challenges specific to performing LES calculations for these reacting flows are highlighted. We find that, while the literature on premixed LES methane combustion is abundant, LES of premixed syngas and hydrogen-rich fuels combustion is comparatively scarce. Only few attempts were made so far showing the need for more research effort in this area to help tackle the challenges presented by these fuels.
Energy Procedia, Dec 1, 2017
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Energy Conversion and Management, Dec 1, 2021
Energy Conversion and Management, Aug 1, 2017
In this work, a parametric study on a b-type Stirling engine with no regenerator was conducted nu... more In this work, a parametric study on a b-type Stirling engine with no regenerator was conducted numerically using ANSYS fluent 14.5 software. The three parameters that were studied are; initial charge pressure, thermal boundary condition; and three different types of working fluids (Air, He and H 2). Variable thermal properties of these gases were adopted to get more realistic results. The results include a comparison of the amount of heat transfer, power output, and thermal efficiency. It was found that the best engine performance is achieved when H 2 gas is used as working fluid. Moreover, results revealed that each of the power output and the efficiency has different optimum charge pressure. Additionally, it was found that there is a small variation in the pressure across the engine chambers, which results in miss matching between the net heat transfer rates and power output calculated from PV-diagram. This error is higher when the air is used as working fluid, especially at high charge pressure.
Combustion and Flame, 2016
Abstract In this paper, we report results from an experimental investigation on transitions in th... more Abstract In this paper, we report results from an experimental investigation on transitions in the average flame shape (or microstructure) under acoustically coupled and uncoupled conditions in a 50 kW swirl stabilized combustor. The combustor burns CH4/H2 mixtures at atmospheric pressure and temperature for a fixed Reynolds number of 20,000 and fixed swirl angle. For both cases, essentially four different flame shapes are observed, with the transition between flame shapes occurring at the same equivalence ratio (for the same fuel mixture) irrespective of whether the combustor is acoustically coupled or uncoupled. The transition equivalence ratio depends on the fuel mixture. For the baseline case of pure methane, the combustor is stable close to the blowoff limit and the average flame in this case is stabilized inside the inner recirculation zone. As the equivalence ratio is raised, the combustor transitions to periodic oscillations at a critical equivalence ratio of ϕ = 0.65 . If hydrogen is added to the mixture, the same transition occurs at lower equivalence ratios. For all cases that we investigated, flame shapes captured using chemiluminescence imaging show that the transition to harmonic oscillations in the acoustically coupled cases is preceded by the appearance of the flame in the outer recirculation zone. We examine the mechanism associated with the transition of the flame between different shapes and, ultimately, the propagation of the flame into the outer recirculation zone as the equivalence ratio is raised. Using the extinction strain rates for each mixture at different equivalence ratios, we show that these transitions in the flame shape and in the instability (in the coupled case) for different fuel mixtures collapse as a function of a normalized strain rate : κ e x t D U ∞ . We show that the results as consistent with a mechanism in which the flame must overcome higher strains prevailing in the outer recirculation zone, in order to stabilize there.
Energy Conversion and Management, Sep 1, 2017
Solar energy is an abundant resource in many countries in the Sunbelt, especially in the middle e... more Solar energy is an abundant resource in many countries in the Sunbelt, especially in the middle east, countries, where recent expansion in the utilization of natural gas for electricity generation has created a significant base for introducing integrated solar-natural gas power plants (ISGPP) as an optimal solution for electricity generation in these countries. ISGPP reduces the need for thermal energy storage in traditional concentrated solar thermal plants and results in dispatchable power on demand at lower cost than stand-alone concentrated thermal power and much cheaper than photovoltaic plants. Moreover, integrating concentrated solar power (CSP) with conventional fossil fuel based thermal power plants is quite suitable for large-scale central electric power generation plants and it can be implemented in the design of new installed plants or during retrofitting of existing plants. The main objective of the present work is to investigate the possible modifications of an existing gas turbine cogeneration plant, which has a gas turbine of 150 MWe electricity generation capacity and produces steam at a rate of 81.4 at 394°C and 45.88 bars for an industrial process, via integrating it with concentrated solar power system. In this regard, many simulations have been carried out using Thermoflow software to explore the thermoeconomic performance of the gas turbine cogeneration plant integrated with LFR concentrated solar power field. Different electricity generating capacities of the gas turbine and different areas of solar collectors have been examined. Thermoflow software simulation results have been used to identify the optimal configuration and sizing of the gas turbine and the solar field of the integrated solar gas turbine cogeneration plant (ISGCPP) required to achieve the required steam generation with the minimum cost and environmental impact. The study revealed that ISGCPP can reduce the levelized electricity cost by 76-85% relative to the fully-solar-powered LFR power plant. Moreover, the study identified the configuration of ISGCPP with a gas turbine size of 50 MWe capacity and 93 ha of LFR solar field as the optimally integrated plant. It reduces the annual CO 2 emission by 100 k Tonne (18%) in comparison with that emitted by the corresponding conventional plant with 50 MWe and 400 k tonne (43.75%) compared with that emitted by the original conventional plant with a gas turbine if 150 MWe power generation capacity. The study revealed also that integrating the LFR technology with a gas turbine cogeneration power plant in locations with high solar insolation was proved to have more economic feasibility than CO 2 capturing technology. Under Dhahran weather conditions, the LEC of about 5 USȻ/kW h is obtained using the proposed optimally configured ISGCPP compared with about 7.5 USȻ/kW h obtained by the corresponding conventional cycle integrated with carbon capture technology. In other words, the ISGCPP reduces the LEC by 50% while achieving the same reduction of CO 2 emission by an equivalent conventional plant integrated with carbon capture technology.
Journal of Energy Resources Technology-transactions of The Asme, Jun 12, 2018
Cooling the air before entering the compressor of a gas turbine of combined cycle power plants is... more Cooling the air before entering the compressor of a gas turbine of combined cycle power plants is an effective method to boost the output power of the combined cycles in hot regions. This paper presents a comparative analysis for the effect of different air cooling technologies on increasing the output power of a combined cycle. It also presents a novel system of cooling the gas turbine inlet air using a solar-assisted absorption chiller. The effect of ambient air temperature and relative humidity on the output power is investigated and reported. The study revealed that at the design hour under the hot weather conditions, the total net power output of the plant drops from 268 MW to 226 MW at 48 °C (15.5% drop). The increase in the power output using fogging and evaporative cooling is less than that obtained with chillers since their ability to cool down the air is limited by the wet-bulb temperature. Integrating conventional and solar-assisted absorption chillers increased the net power output of the combined cycle by about 35 MW and 38 MW, respectively. Average and hourly performance during typical days have been conducted and presented. The plants without air inlet cooling system show higher carbon emissions (0.73 kg CO2/kWh) compared to the plant integrated with conventional and solar-assisted absorption chillers (0.509 kg CO2/kWh) and (0.508 kg CO2/kWh), respectively. Also, integrating a conventional absorption chiller shows the lowest capital cost and levelized electricity cost (LEC).
Journal of Applied Mechanical Engineering, 2015
Solar Cooling Technologies Classification Solar Cooling technologies can be classified in three m... more Solar Cooling Technologies Classification Solar Cooling technologies can be classified in three main categories: solar electrical, thermal and combined power/cooling cycles as illustrated in Figure 1. Solar Cooling System and Application Temperature Ranges The solar cooling system can be divided into three major components; solar energy collecting element, refrigeration cycles, and the application at different temperature ranges. The proper cycle for each application mainly can be selected based
Energy, Dec 1, 2018
The energetic and exergetic performance of a solar thermal power and ejector-absorption refrigera... more The energetic and exergetic performance of a solar thermal power and ejector-absorption refrigeration system is investigated. R141b, R600a, R290, R717 and R143a were employed as the working fluids for ORC and NH 3-LiNO 3 was utilized in the ejector-absorption cycle for cooling production. The energetic and exergetic output of PTC driven combined power and refrigeration cycle were evaluated along with the calculation of thermodynamic irreversibility. The distribution of solar exergy input to the cycle in term of exergy produced, destroyed due to irreversibility, and loss due to thermal exhaust to the ambient was computed and compared with the traditional energy distribution. The maximum exergy was destroyed in the PTC where it amounts to 79.61% of the overall exergy destruction. The conversion of solar exergy input to the cycle exergy output was best (14.6%) for R141b fluid and worst (3.9%) for R143a fluid. Parametric analysis of the results reveals that Solar beam radiation (SBR), turbine inlet pressure (TIP), ORC pump inlet temperature, heat transfer fluid (HTF) temperature at the inlet of PTC, and the selection of ORC working fluid have the significant effect on the energetic and exergetic outputs of solar thermal power and ejector-absorption cooling system.
Journal of Energy Resources Technology, 2017
A large amount of the operating costs in a building is determined by the energy requirements of i... more A large amount of the operating costs in a building is determined by the energy requirements of its air conditioning system. The demand for more energy efficient units desired by both manufacturers and the consumers results in a dire necessity to have air conditioning units that are more energy efficient than the existing ones. In order to achieve the abovementioned features, a tool must be designed to simulate the thermal behavior of the air conditioners. In this work, a mathematical model is developed for air conditioning units and coded into a computer program to estimate the overall performance, as indicated by the unit energy efficiency ratio (EER). The main objective is to maximize the unit EER by proposing modifications or enhancements in the existing unit and to study the economics of these modifications based on the measured terms such as the energy savings and the operating cost. Finally, the effect of the proposed design modifications on the economy and environment at the...
Stratified Flames have gained prominence in the combustion research applications due to its impro... more Stratified Flames have gained prominence in the combustion research applications due to its improved stability and lower emission characteristics. In the present study, stratified jet flames are studied in a dual annular combustor. The static stability and the flame macrostructure have been presented and discussed. Stratification by making the inner annulus mixture rich was found to significantly improve the static stability limits. Furthermore, stratification by making the inner annulus rich was found to lead to attached flame at lower equivalence ratios of 0.22-0.38. Thus, stratification is more helpful at lower equivalence ratios.
ACS omega, Sep 2, 2022
Reynolds averaged Navier Stokes technique was used to develop a validated numerical model for str... more Reynolds averaged Navier Stokes technique was used to develop a validated numerical model for stratified flames. The validation was carried out with the experimental data of the non-swirl flames of the Cambridge dual annulus swirl burner. The RNG k–ε turbulence model along with the SG-35 skeletal chemical mechanism was found to give a good prediction of scalar and vector quantities while resulting in the reduction of computational time by 99.75% in comparison with that required for large eddy simulation techniques used in the literature. The effect of stratification at a constant input power, global equivalence ratio, and Reynolds number was examined. At stratification ratios (SRs = ϕin/ϕout) 1 and 2, intense burning, marked by the higher OH concentration, was observed close to the bluff body. Beyond SR = 2, the region of intense burning shifts downstream away from the bluff body. This is a result of the high equivalence ratio in the inner annulus, which is beyond the rich flammability limit of methane–air flames, and as a result, the primary flame region is shifted downstream after the mixtures from inner and outer annulus have mixed properly to produce a mixture with the equivalence ratio in the flammability limit. The maximum temperature was found to increase by 24.1% when the SR is increased from 1 to 2 and the combustion efficiency was found to significantly improve by 267%. The highest maximum temperature of 2249 K is observed for the mildly stratified flame at SR = 2. Beyond SR = 2, the maximum temperature decreases, while the combustion efficiency increases slightly.
Fuel Processing Technology, Sep 1, 2023
The study to improve the characteristics in terms of performance, emission and combustion aspects... more The study to improve the characteristics in terms of performance, emission and combustion aspects without any modification to a direct injection compression ignition engine using pine oil blend and additive addition was executed. Biofuels known for their reduction in emission also degrades the engine's performance value. To overcome this, pine oil mixture was used with an additive (1,4-dioxane). Pine oil taken at two different concentrations (P20, P40) and the additive at two varying proportions (5 ml, 10 ml) were utilized. In total, six pine oil mixtures were prepared and analyzed for the emission, performance and combustion aspects of the test engine and compared with diesel values. The result evidenced the rise of 3.88% and 5.57% for brake thermal efficiency and fuel consumption, respectively, for P20-10 ml blend compared with diesel. Contemplating the emission aspects, considerable decrease in pollutants (22.41% CO, 29.19% HC and 22.80% smoke) excluding NOx and CO 2 at peak load conditions was depicted. NOx and CO 2 increase about 7.23% and 25.41%, respectively. Combustion parameters like heat release rate and peak pressure of pine oil mixture exhibited inferior values compared with diesel. Only P20 blend with 10 ml additive exhibited values very close (a drop of 2.8% HRR and 2.4% CP) to that of diesel value. To conclude, out of half-dozen blends when compared with diesel, P20 with 10 ml additive proves as the best blend, providing much capable outcomes.
Fuel, Sep 1, 2020
High production cost, inefficient energy utilization, high water requirement, and environmental p... more High production cost, inefficient energy utilization, high water requirement, and environmental pollution are the major challenges to heavy oil production through the conventional steam injection method. Thermochemical fluid injection is a novel and environmentally benign technology for in-situ generation of heat and nitrogen from the exothermic reaction of certain chemicals. Thermochemical stimulation offers several advantages including minimal heat loss and reduced emission of CO 2 compared with steam injection. This study aims at harnessing the potential of injecting thermochemical fluids (TCF) to preheat the reservoir for improved in-situ combustion of bitumen (TCF-ISC). Bitumen sample was preheated using TCF (ratio: 10 ml TCF: 5 g bitumen) or steam. Thermogravimetric Analysis (TGA) was conducted to compare the combustion characteristics of original bitumen sample (B 0), those pre-treated using steam (B 1) and TCF (B 2). In addition, numerical simulation studies were performed to evaluate the performance of the proposed process. The thermochemical reaction produced temperature and pressure of 67°C and 1600 psi, respectively, and ΔH = 370 KJmol −1. The SEM-EDX analysis show that TCF treatment created open cavities on the matrix of the bitumen sample (B 2) which strongly supports potential to increase thermal communication during the ISC process. The thermogravimetric analysis (TGA) show that the TCF treatment of bitumen sample improve combustion performance with higher exothermicity and reactivity. These results revealed higher combustion reactivity and higher potential for combustion front propagation with TCF. Moreover, numerical simulation confirms higher cumulative oil production (m 3), oil recovery factor (%), and lower heat loss (GJ/m 3) using TCF preheating before the ISC.
International Journal of Energy Research, Jan 15, 2016
The demand for gas turbines that accept a variety of fuels has continuously increased over the la... more The demand for gas turbines that accept a variety of fuels has continuously increased over the last decade. Understanding the effects of varying fuel compositions on combustion characteristics and emissions is critical to designing fuel-flexible combustors. In this study, the combustion characteristics and emissions of methane and hydrogen-enriched methane were both experimentally and numerically investigated under ultra-lean conditions (Ø ≤ 0.5). This study was performed using global mechanisms with a one-step mechanism by Westbrook and Dryer and a two-step mechanism with an irreversible and reversible CO/CO 2 step (2sCM1 and 2sCM2). Results show that the 2sCM2 mechanism under-predicted the temperature, major species, and NO x by more than 100% under ultra-lean conditions; thus, we proposed a modified-2sCM2 mechanism to better simulate the combustion characteristics. The mechanisms of Westbrook, 2sCM1, and modified 2sCM2 predicted the temperature and the CO 2 emission with an average deviation of about 5% from the experimental values. Westbrook and 2sCM1, however, over-predicted the NO x emission by approximately 81% and 152%, respectively, as compared with an average under-prediction of 11% by the modified-2sCM2 mechanism. The numerical results using the proposed modified-2sCM2 mechanism shows that the presence of hydrogen in the fuel mixture inhibits the oxidation of methane that led to the formation of unburned hydrocarbons in the flame. We also showed that for any given fuel compositions of H 2 /CH 4 , there is an optimum equivalence ratio at which the pollutant emissions (CO and NO x) from the combustor are minimal. Zero CO and 5 ppm NO x emissions were observed at the optimal equivalence ratio of 0.45 for a fuel mixture containing 30% H 2. The present study provides a basis for ultra-lean combustion toward achieving zero emissions from a fuel-flexible combustor.
Applied Surface Science, Oct 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.