Academic literature on the topic 'Hydrogen fuel blends'

In this study the performance, exhaust emission characteristics and combustion process of the engine fueled with hydrogen-diesel blends were compared to diesel fuel. Hydrogen was blended with diesel fuel at the volumetric ratios of 5%, 10% and 20%. AVL BOOST software was dedicated to simulate the performance and emission values for various blends of hydrogen with diesel fuel. The simulation results showed that hydrogen addition to diesel fuel improve both engine performance and exhaust emmisions.

Nowadays there is an increasing interest in carbon-free fuels such as ammonia and hydrogen. Those fuels, on one hand, allow to drastically reduce CO2 emissions, helping to comply with the increasingly stringent emission regulations, and, on the other hand, could lead to possible advantages in performances if blended with conventional fuels. In this regard, this work focuses on the 1D numerical study of an internal combustion engine supplied with different fuels: pure gasoline, and blends of methane-hydrogen and ammonia-hydrogen. The analyses are carried out with reference to a downsized turbocharged two-cylinder engine working in an operating point representative of engine operations along WLTC, namely 1800 rpm and 9.4 bar of BMEP. To evaluate the potential of methane-hydrogen and ammonia-hydrogen blends, a parametric study is performed. The varied parameters are air/fuel proportions (from 1 up to 2) and the hydrogen fraction over the total fuel. Hydrogen volume percentages up to 60% are considered both in the case of methane-hydrogen and ammonia-hydrogen blends. Model predictive capabilities are enhanced through a refined treatment of the laminar flame speed and chemistry of the end gas to improve the description of the combustion process and knock phenomenon, respectively. After the model validation under pure gasoline supply, numerical analyses allowed to estimate the benefits and drawbacks of considered alternative fuels in terms of efficiency, carbon monoxide, and pollutant emissions.

Abstract. Cheap renewable fuels are needed to replace fossil fuels to reduce greenhouse gas emissions that are causing global warming with the attendant negative consequences. The properties of blends of spent groundnut oil methyl ester (SGOME) and fossil diesel and the emissions from these blends as engine fuel were determined. Spent groundnut oil (SGO) was transesterified into SGOME using methanol and potassium hydroxide as catalyst. The SGOME was blended with fossil diesel and the properties determined and compared to fossil diesel (B0). The pure SGOME (B100) was blended with 90%, 80%, 70%, 60%, and 50% diesel to obtain the B10, B20, B30, B40, and B50 blends of biodiesel, respectively. The properties of the SGOME and the blends were determined according to ASTM and AOCS standards for biodiesel. The properties determined were flash point, carbon residue after combustion, pour and cloud points, kinematic and dynamic viscosities. The blends were used as fuel in a single cylinder 4-stroke water-cooled compression ignition engine that was coupled to a dynamometer from which the tail pipe emissions were measured using gas analyzers. The emissions were measured after the engine had reached a steady state at no load (0 kW) and 1 kW at 3 min interval for 15 min for each blend in 3 replicates. The greenhouse gas emissions measured were nitrogen oxide (NOx),hydrogen sulphide (H2S), particulate matter (PM), sulphur dioxide(SO2),and carbon monoxide (CO). The analysis of variance (ANOVA) at p = 0.05 was used to determine if there was significant difference in the amount of gas emitted from the various blend fuels. The F-LSD was used to separate the means where there was significant difference. The higher blends of the SGOME had better flash point, pour point, and dynamic viscosity than the lower blends. However, the lower blends had better cloud point. The carbon residue after combustion of the SGOME blends was better than that of the fossil diesel. The NOx, PM, SO2, and CO emissions were significantly different from the various blends of the SGOME. However, the H2S emission was not significantly different. Loading the engine did not significantly affect the NOx, H2S, SO2, and CO emissions but significantly affected the PM emission. The PM, CO, and SO2 emissions were highest from the fossil diesel and the lower blends (B10, B20, and B30) and lowest from the higher blends (B40, B50, and B100) at both engine loads. The NOx emission was lowest from the fossil diesel and the lower blends. The use of B20 increased the NOx emission by 10% at both engine loads. The H2S emission was the same for the fossil diesel, pure SGOME (B100), and the blends (B10–B50) at both engine loads. The SGOME fuel reduced tail pipe emission of PM, CO, and SO2 by 26%, 45%, and 78%, respectively. The higher blends had a considerably lower amount of toxic emissions at both engine loads. Keywords: Blends, Diesel, Emissions, Engine, Fuel, Properties, Spent groundnut oil methyl ester.

Bioethanol characteristics can be used as an alternative fuel to spark-ignition (SI) engines to reduce emissions. This experiment evaluates the production of emissions for SI engines using hydrogen enrichment in the gasoline-bioethanol fuel blends. The fraction of bioethanol fuel blend was added to the gasoline fuel of 10% by volume and hydrogen fuel produced by the electrolysis process with a dry cell electrolyzer. The NaOH was used as an electrolyte which is dissolved in water of 5% by a mass fraction. The test is conducted using a single-cylinder 155cc gasoline engine with sensors and an interface connected to a computer to control loading and record all sensor variables in real-time. Hydrogen produced from the electrolysis reactor is injected through the intake manifold using two injectors, hydrogen injected simultaneously at a specific time with a gasoline-bioethanol fuel. The test was conducted with variations of engine speeds. The emission product of ethanol--H2 (BE10+H2) was an excellent candidate as a new alternative of fuel solution in the future. The engasolinerichment of hydrogen increased the flame speed and generated a stable combustion reaction. The hydrogen enrichment produced CO2 emission due to the unavailability of carbon content in hydrogen fuel. As a result, the C/H ratio is lower than for mixed fuels.

Abstract Petroleum is non-renewable supply of energy and also the diminution of natural fuel resources, leads to explore for various fuels for cars. The critical search for various fuels for compression ignition engines has been paying interest on fuels obtained from hydrogen and linseed oil plays a significant role in alternate fuel for C.I Engines. The aim of this research effort is to appraise the property of Linseed oil and Hydrogen as dual blend recital on a variable Compression ratio diesel engine. This really provides the discharge individualism of linseed oil amalgamated with gas and its blends with diesel and are taken up for study. Vertical, 4-stroke, water cooled VCR engine with Linseed oil blends for a extensive series of engine load conditions such as Diesel, B10, B20, B40 along with 5lpm, 10lpm and 15lpm of hydrogen were performed. The brake thermal competence of B20 is found nearly closer to diesel fuel with minimum vibrations and less emissions of CO, hydro carbons HC and slight increase in NOx when compared to fossil fuels. During the experiments, vibrations, performance uniqueness of the test engine was analysed and compared with the precise VCR diesel vibrations, fuel performance. The results obtained by using Python module and the best suited code is derived and found that the combined increase of compression ratio and injecting timing increases the brake thermal efficiency and reduces specific fuel consumption. This module helps and reduces each load variations and performances compared tp experimental. Diesel (25%) saved, will greatly meet the demand of fuel in automobiles.

The following paper presents thermodynamic and optical investigations of the natural flame and OH radical chemiluminescence of a hydrogen enriched methane combustion compared to natural gas combustion. The engine under investigation is a port-fueled unscavenged prechamber 4.8 L single cylinder large bore engine. The blends under consideration are 2%V, 5%V,10%V, and 40%V of hydrogen expected to be blended within existing natural gas grids in a short and mid-term timeline in order to store green energy from solar and wind. These fuel blends could be used for stabilization of the energy supply by reconverting the renewable fuel CH4/H2 in combined heat and power plants. As expected, admixture of hydrogen extends the ignition limits of the fuel mixture toward lean ranges up to an air-fuel equivalence ratio of almost 2. No negative effect on combustion is observed up to an admixture of 40%V hydrogen. At 40%V hydrogen, abnormal combustion like backfire occurs at an air-fuel equivalence ratio of 1.5. The higher mixtures exhibit increased nitrogen oxide emissions due to higher combustion chamber temperatures, while methane slip and CO emissions are reduced due to more complete combustion. The optical investigation of the natural flame and OH radical chemiluminescence are in good agreement with the thermodynamic results verifying the more intense combustion of the fuel blends by means of the chemiluminescence intensity. Further, lube oil combustion and a continuing luminescence after the thermodynamic end of combustion are observed.

This study presents an experimental and analytical investigation on the effects of using methyl ester of linseed oil (MELO)-diesel blend of B10, B20, and B30 with hydrogen injection of 5%, 10%, and 15% in a VCR (Variable Compression Ratio) diesel engine, operated with the compression ratios (CRs) of 15, 16, 17, and 18 on DFM (duel fuel mode). This study also gives emphasis on the optimized emissions of CO, CO2 , NO, and smoke, when the engine was operated with MELO-diesel blends, and hydrogen injections with the variation in engine load, crank angle (CA), using response surface methodology (RSM) with the help of MINITAB programming. During the analysis it was observed that the emissions of CO, CO2 , O2 , NO, and smoke were found to be a function of biodiesel blends, compression ratios, load, and percentage of hydrogen injection. The research results report that, the dual fuel mode of diesel MELO 20% blend with hydrogen injection of about 10% gave optimized results in terms of performance and exhaust emissions, while the optimized CR was 17. The engine was smoothly operated with B20-H10-CR17 over lower emissions compared to diesel, throughout the load spectrum.

Hydrogen is largely considered as an attractive additive fuel for hydrocarbons and alcohol-fueled engines. Nevertheless, a complete understanding of the interactions between blended fuel mechanisms under oxidative conditions at low initial temperature is still lacking. This study is devoted to the numerical investigation of the laminar burning velocity of hydrogen–hydrocarbon and hydrogen–alcohol fuels under several compositions. Estimations were compared with experimental data reported in the current literature. Additionally, the effects of hydrogen addition on engine performance, NOX, and other pollutant emissions of the mentioned fuels have been thermodynamically analyzed. From the study, it has been observed that the laminar burning velocity of the fuel mixtures increased with increasing hydrogen fractions and the peak value shifted to richer conditions. Besides, hydrogen fraction was found to increase the adiabatic flame temperatures eventually favoring the NOX formation for all fuel blends except the acetylene–hydrogen–air mixture where hydrogen showed a reverse effect. Besides, hydrogen is also found to improve the engine performances and helps to surge thermal efficiency, improve the combustion rate, and lessen other pollutant emissions such as CO, CO2, and unburned hydrocarbons. The model predicted well and in good agreement with the experimental data reported in the recent literature.

Abstract Different fuel properties and chemical kinetics of two different fuels would make it challenging to predict the combustion parameters of a binary fuel. Understanding the effect of blending methane and hydrogen gas is the main focus of this paper. Utilizing a horizontal tube combustion rig, methane-hydrogen fuel blends were created using blending laws from past literature, over a range of equivalence ratios from 0.6 – 1.2 were studied, while keeping one combustion parameter constant, the theoretical laminar burning velocity. The selected theoretical laminar burning velocity for all the mixtures tested were kept constant at 0.6 ms−1. Different factors affected the flame propagation across the tube, including acoustic pressure oscillations, heat loss from the rig, and obvious difference in hydrogen percentage in the fuel blends. The average experimental laminar burning velocity of all the flames was 0.368 ms−1, compared to the expected value of 0.6 ms−1. In an attempt to keep the theoretical laminar burning velocity constant for different mixtures, it was discovered that this did not promise the same flame propagation behaviour for the tested mixtures. Further experimentation and analysis are required in order to better understand the underlying interaction of the fuel blends.

The development of hydrogen energetics is a possible way to reduce emissions of harmful substances into the atmosphere in the production of electricity. Its implementation requires the introduction of energy facilities capable of operating on environmentally safe fuel. At the same time, from a technological point of view, it is easier to implement a gradual shift to the use of hydrogen in power plants by burning methane–hydrogen blends. This paper presents the results of thermodynamic studies of the influence of the chemical composition of the methane–hydrogen blend on the performance of binary and trinary power units. It is shown that an increase in the hydrogen volume fraction in the fuel blend from 0 to 80% leads to a decrease in the Wobbe index by 16% and an increase in the power plant auxiliaries by almost 3.5 times. The use of a trinary CCGT unit with a single-circuit WHB and working fluid water condensation makes it possible to increase the net efficiency by 0.74% compared to a binary CCGT with a double-circuit WHB and a condensate gas heater.

碩士
長庚大學
機械工程研究所
97
This study is aimed at the laminar flame speed and combustion characteristics of hydrogen blended fuels such as hydrogen-natural gas (methane), hydrogen-primary reference fuels (propane), and synthesis gases (hydrogen-carbon monoxide). The laminar flame speeds of the blended fuels are computed and compared with a model of 1-D free-propagation premixed flames, which is analyzed theoretically with detailed chemical kinetics and thermal and transport properties. The effects of the mixture equivalence ratio, the amount of hydrogen and dilution gases (CO2, H2O, N2) are discussed at various atmospheric pressure and mixture temperature. The results showed that the laminar flame speeds of hydrogen blended fuels are increasing with increasing hydrogen percentage, and the synthesis gases mixtures (H2-CO) are affected the most. Besides, the maximum flame temperature of synthesis gases mixtures and the amount of exhaust gases (CO, CO2, NOX) are decreasing with increasing hydrogen percentage. The effects of dilution gases added in hydrogen blended fuels showed the laminar flame speeds are decreasing most with CO2 dilution, and least with N2 dilution. The laminar flame speeds of hydrogen blended fuels and the amount of exhaust nitrogen oxide are increased at higher temperature. However, at higher atmospheric pressure, the laminar flame speeds of hydrogen blended fuels are decreased, especially for hydrogen-natural gas (methane) mixture, but the amount of exhaust nitrogen oxide are increased.

In recent years, electrochemical capacitors have emerged as devices with the potential to enable major advances in electrical energy storage. Electrochemical capacitors (ECs) are akin to conventional capacitors but employ higher surface-area electrodes and thinner dielectrics to achieve larger capacitances. This helps ECs to attain energy densities greater than those of conventional capacitors and power densities greater than those of batteries. Akin to conventional capacitors, ECs also have high cycle-lives and can be charged and discharged rapidly. But ECs are yet to match the energy densities of mid to high-end batteries and fuel cells. On the basis of mechanism involved in the charge-storage process, ECs are classified as electrical double-layer capacitors (EDLCs) or pseudocapacitors. Charge storage in EDLCs and pseudocapacitors is brought about by non-faradaic and faradaic processes, respectively. Faradaic process, such as an oxidation-reduction reaction, involves the transfer of charge between electrode and electrolyte. By contrast, a non-faradaic process does not use a chemical mechanism and charges are distributed on surfaces by physical processes that do not involve any chemical reaction. ECs employ both aqueous and non-aqueous electrolytes in either liquid or solid form, the latter providing the advantages of freedom from leakage of any liquid component, compactness, reliability and large operating potential-window. In the literature, polymer electrolytes are the most widely studied solid electrolytes. Complexation of functional-groups of certain polymers with cations results in the formation of polymer-cation complexes commonly referred to as solid-polymer electrolytes (SPEs). Mixing a polymer with an alkali metal salt dissolved in an organic solvent result in the formation of a polymer gel electrolyte. Organic solvents with low molecular-weights, such as ethylene carbonate and propylene carbonate, employed in polymer gel electrolytes are commonly referred to as plasticizers. When water is used as a plasticizer, the polymer electrolyte is called a polymer hydrogel electrolyte. Part I of the thesis is directed to studies pertaining to Polymer Hydrogel Electrolytes for Electrochemical Capacitors and comprises four sections. After a brief survey of literature on polymer hydrogel electrolytes employed in ECs in Section I.1, Section I.2 of Part I describes the studies on electrochemical capacitors employing cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration. Acidic poly (vinyl alcohol) hydrogel membrane electrolytes (PHMEs) with different perchloric acid concentrations are prepared by cross-linking poly (vinyl alcohol) with glutaraldehyde in the presence of a protonic acid acting as a catalyst under ambient conditions. PHMEs are characterized by scanning electron microscopy and temperature-modulated differential scanning calorimetry in conjunction with relevant electrochemical techniques. An optimised electrochemical capacitor assembled employing PHME in conjunction with black pearl carbon (BPC) electrodes yields a maximum specific capacitance value of about 96 F g-1, phase angle value of about 79o and a discharge capacitance value of about 88 F g-1. Section I.3 of Part I describes the studies on cross-linked poly (vinyl alcohol)/ploy (acrylic acid) blend hydrogel electrolytes for electrochemical capacitors. Acidic poly (vinyl alcohol)/poly (acrylic acid) blend hydrogel electrolytes (BHEs) have been prepared by cross-linking poly (vinyl alcohol)/poly (acrylic acid) blend with glutaraldehyde in presence of perchloric acid. These acidic BHEs have been treated suitably to realize alkaline and neutral BHEs. Thermal characteristics and glass-transition behavior of BHEs have been followed by differential scanning calorimetry. Ionic conduction in acidic BHEs has been found to take place by Grötthus-type mechanism while polymer segmental motion mechanism is predominantly responsible for ion motion in alkaline and neutral BHEs. Ionic conductivity of BHEs has been found to range between 10-3 and 10-2 S cm-1 at 298 K. Electrochemical capacitors assembled with acidic PVA hydrogel electrolyte yield a maximum specific capacitance of about 60 and 1000 F g-1 with BPC and RuOx.xH2O/C electrodes, respectively. Section I.4 of Part I describes the studies on gelatin hydrogel electrolytes and their application to electrochemical capacitors. Gelatin hydrogel electrolytes (GHEs) with varying NaCl concentrations have been prepared by cross-linking an aqueous solution of gelatin with aqueous glutaraldehyde under ambient conditions, and characterized by scanning electron microscopy, temperature-modulated differential scanning calorimetry, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic chronopotentiometry. Glass transition temperatures for GHEs range between 340 and 377 K depending on the dopant concentration. Ionic conductivity behavior of GHEs is studied with varying concentrations of gelatin, glutaraldehyde and NaCl, and conductivity values are found to vary between 10-3 and 10-1 S cm-1 under ambient conditions. GHEs have a potential window of about 1 V with BPC electrodes. The ionic conductivity of pristine and 0.25 N NaCl-doped GHEs follows Arrhenius behavior with activation energy values of 1.9×10-4 and 1.8×10-4 eV, respectively. Electrochemical capacitors employing GHEs in conjunction with black pearl carbon electrodes are assembled and studied. Optimal values for capacitance, phase angle, and relaxation time constant of about 81 F g-1, 75o, and 0.03 s are obtained for 3 M NaCl-doped GHE, respectively. EC with pristine GHE exhibits continuous cycle life for about 4.3 h as against 4.7 h for the electrochemical capacitor with 3 M NaCl-doped GHE. Unlike electrochemical capacitors, fuel cells do not store the charge internally but instead use a continuous supply of fuel from an external storage tank. Thus, fuel cells have the potential to solve the most challenging problem associated with the electrochemical capacitors, namely their limited energy-density. A fuel cell is an electrochemical power source with advantages of both the combustion engine and the battery. Like a combustion engine, a fuel cell will run as long as it is provided with fuel; and like a battery, fuel cells convert chemical energy directly to electrical energy. As an electrochemical power source, fuel cells are not subjected to the Carnot limitations of combustion (heat) engines. A fuel cell operates quietly and efficiently and, when hydrogen is used as a fuel, it generates only power and potable water. Thus, a fuel cell is a so called ‘zero-emission engine’. In the past, several fuel cell concepts have been tested in various laboratories but the systems that are being potentially considered for commercial developments are: (i) Alkaline Fuel Cells (AFCs), (ii) Phosphoric Acid Fuel Cells (PAFCs), (iii) Polymer Electrolyte Fuel Cells (PEFCs), (iv) Solid-Polymer-Electrolyte-Direct Methanol Fuel Cells (SPE-DMFCs), (v) Molten Carbonate Fuel Cells (MCFCs) and (vi) Solid Oxide Fuel Cells (SOFCs). Among the aforesaid systems, PEFCs that employ hydrogen as fuel are considered attractive power systems for quick start-up and ambient-temperature operations. Ironically, however, hydrogen as fuel is not available freely in the nature. Accordingly, it has to be generated from a readily available hydrogen carrying fuel such as natural gas, which needs to be reformed. But, such a process leads to generation of hydrogen with some content of carbon monoxide, which even at minuscule level is detrimental to the fuel cell performance. Pure hydrogen can be generated through water electrolysis but hydrogen thus generated needs to be stored as compressed / liquefied gas, which is cost-intensive. Therefore, certain hydrogen carrying organic fuels such as methanol, ethanol, propanol, ethylene glycol, and diethyl ether have been considered for fuelling PEFCs directly. Among these, methanol with a hydrogen content of about 13 wt. % (specific energy = 6.1 kWh kg-1) is the most attractive organic liquid. PEFCs using methanol directly as fuel are referred to as SPE-DMFCs. But SPE-DMFCs suffer from methanol crossover across the polymer electrolyte membrane, which affects the cathode performance and hence the cell performance during its operation. SPE-DMFCs also have inherent limitations of low open-circuit-potential and low electrochemical-activity. An obvious solution to the aforesaid problems is to explore other promising hydrogen carrying fuels such as sodium borohydride, which has a hydrogen content of about 11 wt. %. Such fuel cells are called direct borohydride fuel cells (DBFCs). Part II of the thesis includes studies on direct borohydride fuel cells and comprises three sections. After a brief introduction to DBFCs in section II.1, Section II.2 describes studies on an alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant. A peak power density of about 150 mW cm-2 at a cell voltage of 540 mV could be achieved from the optimized DBFC operating at 70oC. Section II.3 describes studies on poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells. This DBFC employs a poly (vinyl alcohol) hydrogel membrane as electrolyte, an AB5 Misch metal alloy as anode, and a gold-plated stainless steel mesh as cathode in conjunction with aqueous alkaline solution of sodium borohydride as fuel and aqueous acidified solution of hydrogen peroxide as oxidant. The performance of the PHME-based DBFC in respect of peak power outputs, ex-situ cross-over of oxidant, fuel, anolyte and catholyte across the membrane electrolytes, utilization efficiencies of fuel and oxidant as also cell performance durability under ambient conditions are compared with a similar DBFC employing a Nafion®-117 membrane electrolyte (NME). Peak power densities of about 30 and 40 mW cm-2 are observed for the DBFCs with PHME and NME, respectively. The PHME and NME-based DBFCs exhibit cell potentials of about 1.2 and 1.4 V, respectively, at a load current density of 10 mA cm-2 for 100 h. Publications of Nurul Alam Choudhury 1. Gelatin hydrogel electrolytes and their application to electrochemical supercapacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Electrochem. Soc., 155 (2008) A74. 2. Cross-linked polymer hydrogel electrolytes for electrochemical capacitors, N. A. Choudhury, A. K. Shukla, S. Sampath, and S. Pitchumani, J. Electrochem. Soc., 153 (2006) A614. 3. Hydrogel-polymer electrolytes for electrochemical capacitors: an overview, N. A. Choudhury, S. Sampath, and A. K. Shukla, Energy and Environmental Science (In Press). 4. Cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration and their application to electrochemical capacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Chem. Sc. (Submitted) 5. An alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant, N. A. Choudhury, R. K. Raman, S. Sampath, and A. K. Shukla, J. Power Sources, 143 (2005) 1. 6. Poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells, N. A. Choudhury, S. K. Prashant, S. Pitchumani, P. Sridhar, and A. K. Shukla, J. Chem. Sc. (Submitted). 7. A phenyl-sulfonic acid anchored carbon-supported platinum catalyst for polymer electrolyte fuel cell electrodes, G. Selvarani, A. K. Sahu, N. A. Choudhury, P. Sridhar, S. Pitchumani, and A. K. Shukla, Electrochim. Acta, 52 (2007) 4871. 8. A high-output voltage direct borohydride fuel cell, R. K. Raman, N. A. Choudhury, and A. K. Shukla, Electrochem. Solid-State Lett., 7 (2004) A 488. 9. Carbon-supported Pt-Fe alloy as a methanol-resistant oxygen-reduction catalyst for direct methanol fuel cells, A. K. Shukla, R. K. Raman, N. A. Choudhury, K. R. Priolkar, P. R. Sarode, S. Emura, and R. Kumashiro, J. Electroanal. Chem., 563 (2004) 181.

Integrating concentrated solar thermal energy into fossil-fuels for the production of power/clean fuels is receiving growing attention as the combination of the two energy sources can provide lower emissions of carbon and other pollutants, lower cost, and continuous supply. Various types of hybrid concepts have been proposed. However, all of these concepts employ stand-alone solar receivers and standalone combustors. The University of Adelaide has developed an alternative approach with which to fully integrate a combustor into a solar cavity receiver. This offers the potential for significant savings from reduced infrastructure investment and reduced start-up and shut-down losses. In addition, this hybrid also results in the direct interaction between concentrated solar radiation and a flame, which is theoretically known to be coupled. However, the influence of concentrated solar radiation (CSR) on the flame has not been experimentally investigated. Hence this thesis aims at filling this gap. High flux solar simulators, comprising an array of high-intensity-discharge lamps coupled with elliptical reflectors, have been widely employed to study concentrated solar thermal energy systems. The use of electrical solar simulators holds the advantage over natural solar radiation in providing repeatable performance without the variability of the solar resource. Reliable models which predict the heat flux generated by a solar simulator are desirable because they enable efficient and systematic optimization of the system to meet the required trade-off between cost and performance. To this end, a concentric multilayer model of the light source is developed in this study to accurately predict the spatial distribution of the heat flux at the focus using a commercial Monte Carlo ray-tracing code. These simulations were validated with measurements of both the radiant intensity of the light source and the distribution of the concentrated heat flux. Further to that, on the experimentally validated ray tracing model, the geometry and surface reflectance of the additional concentrators were also assessed of two high flux solar simulators: one employs a single lamp, the other uses a seven-lamp array. In addition, the time-resolved spectra of solar simulators employing a metal halide and a xenon arc lamp are also measured, which provides the first experimental results of this kind that acquired from the same spectrometer to allow for direct comparison. This thesis also reports the first set of measurements of the influence of concentrated solar radiation on the soot volume fraction and temperature in a laminar sooty flame. Detailed laser diagnostics was performed on a laminar sooty flame with and without the irradiance of CSR, because laser diagnostics are demonstrated to hold the advantages of being non-intrusive, lower interferences and of being applicable to environments with high flux radiation. The current measurement using laser induced incandescence shows that the soot volume within the laminar flame was increased by 55% by CSR. In addition, the measurement of temperature using two-line atomic fluorescence shows that the flame temperature was increased by around 8% under CSR. In addition to the detailed laser diagnostics, an assessment of the influence of soot volume fraction on the global performance of the flames was also performed through a systematic study of flames using fuels of different soot propensities, which is achieved by blending hydrogen into hydrocarbon fuels, with hydrogen volume fraction ranging from 0 to 100%. Results show that flames with higher soot volume fraction have higher radiant fraction and lower NOx emissions. The principle contribution of the thesis is that the first measurement of the influence of concentrated solar radiation on the soot volume fraction and temperature of a flame was performed, which pushed forward the existing understanding of the interaction between broadband solar radiation and combustion. Its second major contribution is establishing an experimentally validated ray-tracing model that accurately predicts the concentrated heat flux from the solar simulator, and on this model, new design and optimization of solar simulators were performed. While this ray-tracing model is developed for metal halide lamps, the methodology is applicable more generally to solar simulators employing other types of discharge arc lamps.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2016

Ammonia, when blended with hydro carbon fuels, can be used as a composite fuel to power existing IC engines. Such blends, similar to ethanol and gasoline fuel blends, can be used to commercialize ammonia as an alternative fuel. Feasibility of developing ammonia gasoline liquid fuel blends and the use of ethanol as an emulsifier to enhance the solubility of ammonia in gasoline were studied using a small thermostated vapor liquid equilibrium (VLE) high pressure cell in this research. A larger VLE cell was used to develop identified fuel blends in sufficient quantities for engine dynamo-meter tests. A engine dynamometer equipped with a 2.4L gasoline engine was used to benchmark performance of ammonia fuel blends against standard fuels. Solubility test results proved that ethanol free gasoline is capable of dissolving 4.5% of ammonia on volume basis (23 g/l on mass basis) at 50 psi [344.7 kPa] pressure and 286.65 K temperature in liquid phase. Solubility levels are increased with the use of ethanol. Gasoline with 30% ethanol can retain 18% of ammonia in the liquid phase by volume basis (105 g/l by mass basis) at the same pressure and temperature. Dynamometer results show the ability of new composite fuel blends to produce the same amount of torque and power in the lower rpm limits. At higher rpm levels ammonia rich fuels result in an increased torque and power. Thus it can be concluded that hydrogen energy can be stored as ammonia-gasoline fuel blends and recovered back successfully without any strenuous modification to the existing infrastructure and end user equipment or behavior.

Producer gas, any of a variety of gases generated from biomass gasification, is a renewable gaseous fuel that can be burned in gas engines for power production. Producer gas consists primarily of methane, hydrogen, carbon monoxide, carbon dioxide, and nitrogen. These gas blends can be problematic as a fuel for natural gas engines due to widely varying composition and significantly different fuel properties than natural gas. Characterization of combustion properties of different producer gas compositions is critical if the gas engine is to be operated reliably and at the greatest efficiency possible. A sample space of 35 producer gas blends consisting of distinct percentages of combustible gases (methane, hydrogen, and carbon monoxide) and diluent (carbon dioxide and nitrogen) is created to provide a basis for methane number testing. A test cell is established to mix producer gas blends of desired constituent makeup for consumption in a Waukesha F2 Cooperative Fuel Research (CFR) engine to directly measure methane number for each blend. Additional measurements include combustion pressure statistics, fuel consumption, and power output. Methane number is correlated to combustion pressure statistics and producer gas properties. Methane number measurements are compared with predictions using the software AVL Methane, often employed by engine manufacturers to characterize gaseous fuels. Measured methane number shows a strong correlation to 0–10% and 10–90% burn durations. The predicted methane number values from AVL Methane are significantly different than measured methane number in many cases. The error in the prediction is strongly dependent on the amount of carbon monoxide and hydrogen in the producer gas.

Abstract Stakeholders in the aviation industry committed to a goal of 50% reduction in carbon emissions by the year 2050, to be achieved by reducing emissions 1.5% each year from 2020 onwards. There are multiple pathways to achieve this goal however; with, the most promising technology being Sustainable Aviation Fuels (SAF), which are biofuels blended with kerosene. As the industry shifts towards SAF, it is important to evaluate these fuels in terms of their long-term sustainability, and this is the objective of the current study. Sixteen types of fuels were assessed which include fossil, natural gas, electric, and SAF. A Multi Criterion Decision Making methodology was adopted which considers three categories, namely environmental, economic, and social aspects which in turn are broken up into 8 indicators in all (such as ecological footprints, cost of transportation, investment cost, operating costs, employment generation, and health & safety). A Monte Carlo analysis was also performed to analyze sensitivity of the results to the weights attributed to the three categories. The most sustainable fuel was found to be Hydrogen, with a score of 0.91 out of 1.0. The least sustainable were determined to be the military kerosene-based fuels (with the experimental fuel JP-8 + 100LT being the poorest with a normalized score of 0.50).

Kerosene-type fuels are the most common aviation fuel, and an understanding of their combustion properties is essential for achieving optimized gas turbine operation. Presently, however, there is lack of experimental flame speed data available by which to validate the chemical kinetic mechanisms necessary for effective computational studies. In this study, premixed jet fuel surrogate blends and commercial kerosene are studied using particle image velocimetry in a stagnation flame geometry. Numerical simulations of each experiment are obtained using the CHEMKIN-PRO software package and the JetSurF 2.0 mechanism. The neat hydrocarbon surrogates investigated include n-decane, methylcyclohexane, and toluene, which represent the alkane, cycloalkane, and aromatic components of conventional aviation fuel, respectively. Two blends are studied in this paper. The first is a binary blend formulated to reproduce the laminar flame speed of aviation fuel using a mixing rule based on the laminar flame speed and adiabatic flame temperature of the hydrocarbon components, weighted by their respective mixture mole fractions. The second blend is a tertiary blend formulated to emulate the hydrogen to carbon ratio of the kerosene studied. All of the considered fuels and blends are studied at three equivalence ratios, corresponding to lean, stoichiometric, and rich conditions, and at several stretch rates. The centreline axial velocity profiles from numerical simulations are directly compared to the measured velocity profiles to validate the mechanism at each condition. The difference between the experimental and simulated reference flame speed is used to infer the true unstretched laminar flame speed of the mixture. These results allow the effectiveness of the different blending methodologies to be assessed.

Requirement of significantly reducing NOx and particulate emissions while maintaining combustor performance is one of the main drivers for combustion research. Fuel blending represents a very promising approach for reducing both NOx and particulate emissions from flames. This paper reports an investigation on the effects of using hydrogen blending with different fuels on pollutants emission in counterflow flames. The fuels investigated include methane and n-heptane. Methane-hydrogen flame is computed using the GRI-3.0 mechanism, while n-heptane-hydrogen flame is computed by combining the Held’s oxidation mechanism with the Li and Williams’ NOx mechanism. Results indicate that in methane/hydrogen blends, emission of NOx is increases with hydrogen addition, but the effect is not significant. However, emission of CO and C2H2 (which is a very important soot precursor) are affected significantly by the addition of hydrogen. First, addition of hydrogen decreases the carbon content in the fuel for the same strain rate. Second, the chemistry of combustion also changes due to higher reactivity and higher concentration of H, O and OH radicals produced due to hydrogen addition. In heptane/hydrogen blends, all the three pollutant species investigated (NO, CO and C2H2) are found to be affected significantly by hydrogen addition. The effect of pressure on pollutants emission has also been investigated.

Abstract New ignition delay time (IDT) measurements for two natural gas (NG) blends composed of C1 – C7 n-alkanes, NG6 (C1:60.625%, C2:20%, C3:10%, C4:5%, nC5:2.5%, nC6:1.25%, nC7:0.625%) and NG7 (C1:72.635%, C2:10%, C3:6.667%, C4:4.444%, nC5:2.965%, nC6:1.976%, nC7:1.317%) by volume with methane as the major component are presented. The measurements were recorded using a high-pressure shock tube (HPST) for stoichiometric fuel in air mixtures at reflected shock pressures (p5) of 20–30 bar and at temperatures (T5) of 987–1420 K. The current results together with rapid compression machine (RCM) measurements in the literature show that higher concentrations of the higher n-alkanes (C4 – C7) ∼1.327% in the NG7 blend compared to the NG6 blend result in the ignition for NG7 being almost a factor of two faster than NG6 at compressed temperatures of (TC) ≤ 1000 K. This is due to the low temperature chain branching reactions that occur for higher alkane oxidation kinetics in this temperature range. On the contrary, at TC > 1000 K, NG6 exhibits ∼20% faster ignition than NG7 primarily because about 12% of the methane in the NG7 blend is primarily replaced by ethane (∼10%) in NG6, which is significantly more reactive than methane at these higher temperatures. The performance of NUIGMech1.2 in simulating these data is assessed and it can reproduce the experiments within 20% for all the conditions considered in the study. We also investigate the effect of hydrogen addition to the auto-ignition of these NG blends using NUIGMech1.2 which has been validated against the existing literature for natural gas/hydrogen blends. The results demonstrate that hydrogen addition has both an inhibiting and promoting effect in the low- and high-temperatures regime, respectively. Sensitivity analyses of the hydrogen/NG mixtures are performed to understand the underlying kinetics controlling these opposite ignition effects. At low temperatures, H-atom abstraction by ȮH radicals from C3 and larger fuels are the key chain-branching reactions consuming the fuel and providing the necessary fuel radicals which undergo low temperature chemistry (LTC) leading to ignition. However, with the addition of hydrogen to the fuel mixture, the competition for ȮH radicals by H2 via the reaction H2+ȮH↔Ḣ+H2O reduces the progress of the LTC of the higher hydrocarbon fuels thereby inhibiting ignition. At higher temperatures, since Ḣ+O2↔Ö+ȮH is the most sensitive reaction promoting reactivity, the higher concentrations of H2 in the fuel mixture leads to higher Ḣ atom concentrations leading to faster ignition due to an enhanced rate of the Ḣ+O2↔Ö+ȮH reaction.

This paper provides a description of the fuel flexibility tests performed in: • a gas turbine • a high pressure combustion rig • an atmospheric combustion rig with the combustion system used in Siemens recently developed gas turbine SGT-750. The gas turbine test campaign was run with natural gas blends with up to 50vol% nitrogen or 40vol% carbon dioxide. Ignition and engine starts with inert gas blends were also tested. The fuel flexibility tests were continued in a single burner high pressure combustion rig. Both inert and reactive gas blends were tested. High concentrations of inert gases were tested at simulated cold ambient conditions (down to −60°C) at high and low loads. Reactive gases, such as ethane, propane, butane and hydrogen, were tested at high load operation. Also syngas blends were tested. To simulate ignition at extreme arctic conditions an atmospheric rig test was performed with cold air supplied from evaporated liquid air. The different gas fuel blends were run with low NOx emissions, often below 10 ppm, without water injection. This paper includes description of the test setups and evaluation of the emissions and combustion stability for the tested gas blends.

The objective of this paper is to elucidate the recently observed strong correlation between derived cetane number (DCN) and lean blow out (LBO) characteristics for both petroleum-derived and alternative jet fuels, as well as their blends. In order to evaluate the variability of fuel physical and chemical properties for petroleum-derived jet fuels, the fuel property database appearing in the DSIC-PQIS 2013 report are rigorously analyzed and compared against fuel-specific data for 17 petroleum-derived and alternative jet fuels and their blends obtained previously in our works. The global combustion characteristics of each fuel for fuel/air mixture were characterized experimentally by determining their combustion property targets (CPTs) — the hydrogen to carbon molar ratio (H/C ratio), the derived cetane number (DCN), the average molecular weight (MW), and surrogate fuel mixtures and threshold sooting index (TSI). Surrogate mixtures of known hydrocarbon species were blended to match the CPTs of target real fuel. The known chemical functional group distributions of the surrogate mixtures for each fuel or fuel blend were then used to predict well-known fundamental combustion behaviors — reflected shock ignition delay times and laminar flame speeds — through quantitative structure-property relationship (QSPR) regression analyses developed from a validation base of single component, binary and ternary mixture database. The results show that the DCN is capable of representing ignition propensity and flame propagating characteristics for both petroleum-derived and alternative jet fuels as well as their mixtures with high fidelity. Finally, the chemical functional group distributions of the real fuels themselves were directly measured using 1H nuclear magnetic resonance (NMR) spectra results. QSPR predictions based upon the experimental NMR functional group measurements are shown to provide a rapid, small sample, characterization tool for predicting the above global combustion behaviors of petroleum derived and alternative jet fuel candidates as well as their blends. Through combustor as well as stirred reactor experiments, fuel DCN has been identified as having major influence on LBO in devices that are sensitive to fuel chemical properties.

Abstract Fuel flexibility in gas turbine development has become increasingly important and modern engines need to cope with a broad variety of fuels. The target to operate power plants with hydrogen-based fuels and low emissions will be of paramount importance in a future focusing on electric power decarbonization. Ansaldo Energia AE94.3A engine acquired broad experience with operation of various natural gas and hydrogen fuel blends, starting in 2006 in the Brindisi (Italy) power plant. Based on the exhaustive experience acquired in the field, this paper describes the latest advancements characterizing the operation of the AE94.3A burner with high pressure combustion tests adding hydrogen blends ranging from 0 to 40% in volume. The interpretation of the test results is supported by reactive and non-reactive simulations describing the effects of varying fuel reactivity on the flame structure as well as the impact of fuel / air momentum flux ratio on the fuel / air interaction and fuel distribution in the combustion chamber. As expected, increasing amounts of hydrogen in the fuel are also associated with higher amounts of NOx production, however this effect could be countered by optimization of the fuel staging strategy, based on the mentioned CFD considerations and feedback from high pressure tests.

Abstract Hydrogen (H2) fuel for gas turbines is a promising approach for long duration storage and dispatchable utilization of intermittent renewable power. A major global discussion point, however, is the potential air quality impact of hydrogen combustion associated with nitrogen oxide (NOx) emissions. Indeed, several studies in the combustion literature have reported elevated NOx concentrations in terms of dry ppmv NOx at 15% oxygen (O2) as a fuel’s H2 fraction is increased. Yet, as emphasized in this work, this practice of directly comparing emissions on the basis of dry ppmv at a reference O2 concentration (ppmvdr) is inappropriate across hydrogen and hydrocarbon fuel blends due to differing concentration changes induced by drying and referencing the corresponding exhaust gasses. This paper addresses three distinct approaches for comparing emissions consistently across fuel blends. Furthermore, it presents examples that quantify the differences in the apparent pollutant emissions between each approach and the usual ppmvdr reporting practice across the full range of hydrogen-methane mixture ratios. In the first approach, ppmvdr emissions values are related to their actual volume concentration. Here, our calculations demonstrate that hydrogen and methane flames producing the same true pollutant concentration exhibit a 40% relative difference in ppmvdr values, resulting in a significant potential exaggeration of NOx emissions for high %H2 fuels. However, this concentration-based approach does not account for changes in the volumetric flow rate of exhaust gasses or the slightly different amounts of heat release required to achieve the same flame temperature across fuels. These effects are captured naturally in the second approach, where the emissions are quantified in terms of the emitted mass per unit of heat release. With this cycle-independent approach, our comparative calculations at equal mass-per-heat emission rates reveal 36% higher ppmvdr values for hydrogen flames than methane flames. Finally, the third approach accounts not only for the thermodynamic properties of the mixture, but also for the system’s overall cycle efficiency, which is shown to depend weakly upon the fuel composition. This method quantifies emissions in terms of the emitted mass per unit of useful shaft work output, a metric also used by environmental regulators. Illustrative results within a simulated F-class gas turbine cycle are presented, indicating 39% higher ppmvdr values for hydrogen flames at equal mass-per-work emission rates. Hence, in all of the considered approaches, ppmvdr emissions values are inflated for H2 fuel blends relative to hydrocarbon fuels, making them unsuitable for direct comparisons of emissions among conventional and alternative fuels.