Study of the kinetic behaviour of biomass and coal during oxyfuel co-combustion

In this study, the thermogravimetric analysis(TGA) method has been used to evaluate the kinetic behavior of biomass, coal and its blends during oxyfuel co-combustion. The thermogravimetric results have been evaluated by the Coats–Redfern method and validated by Criado's method. TG and DTG curves indicate that as the oxygen concentration increases the ignition and burn out temperatures approach a lower temperature region. The combustion characteristic index shows that biomass to coal blends of 28% and 40% respectively can achieve enhanced combustion up to 60% oxygen enrichment. In the devolatilization region, the activation energies for coal and blends reduce while in the char oxidation region, they increase with rise in oxygen concentration. Biomass, however, indicates slightly different combustion characteristic of being degraded in a single step and its activation energies increase with rise in oxygen concentration. It is demonstrated in this work that oxygen enrichment has more positive combustion effect on coal than biomass. At 20% oxygen enrichment, 28% and 40% blends indicate activation energy of 132.8 and 125.5 kJ·mol~(-1) respectively which are lower than coal at 148.1 kJ·mol~(-1) but higher than biomass at 81.5 kJ·mol~(-1) demonstrating synergistic effect of fuel blending. Also, at char combustion step, an increase in activation energy for 28% blend is found to be 0.36 kJ·mol~(-1) per rise in oxygen concentration which is higher than in 40% blend at 0.28 kJ·mol~(-1).     

Fuel properties and emissions of soybean oil esters as diesel fuel

The effects of using blends of methyl and isopropyl esters of soybean oil with No. 2 diesel fuel were studied at several steady-state operating conditions in a four-cylinder turbocharged diesel engine. Fuel blends that contained 20, 50, and 70% methyl soyate and 20 and 50% isopropyl soyate were tested. Fuel properties, such as cetane number, also were investigated. Both methyl and isopropyl esters provided significant reductions in particulate emissions compared with No. 2 diesel fuel. A blend of 50% methyl ester and 50% No. 2 diesel fuel provided a reduction of 37% in the carbon portion of the particulates and 25% in the total particulates. The 50% blend of isopropyl ester and 50% No. 2 diesel fuel gave a 55% reduction in carbon and a 28% reduction in total particulate emissions. Emissions of carbon monoxide and unburned hydrocarbons also were reduced significantly. Oxides of nitrogen increased by 12%.     

Cold start and fuel consumption of a vehicle fuelled with blends of diesel oil–soybean biodiesel–ethanol

Fuel consumption and cold start characteristics of a production vehicle fuelled with blends of N. 2 diesel oil (500 ppm sulfur content), soybean biodiesel (3%, 5%, 10%, and 20%) and hydrous ethanol (2% and 5%) were compared. A wagon-type vehicle equipped with a four-cylinder, 1.3-l, 63 kW diesel engine was tested in a cold chamber at the temperature of −5 °C for the cold start tests. Fuel consumption tests were performed following the 1975 US Federal Test Procedure (FTP-75). The results showed that the cold start time was satisfactory for all fuel blends tested, but it was longer for the blend containing 20% of soybean biodiesel (B20) in comparison with the blends with lower biodiesel concentration. The cold start time also increased with increasing with increasing ethanol content in the fuel blend. Specific fuel consumption was not affected by increasing biodiesel concentration in the blend or by the use of 2% of ethanol as an additive. However, the use of 5% of ethanol concentration in the B20 blend resulted in increased specific fuel consumption.     

Biodiesel combustion in an optical HSDI diesel engine under low load premixed combustion conditions

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the spray and combustion processes for biodiesel blends under different injection strategies. The experimental results indicated that the heat release rate was dominated by a premixed combustion pattern and the heat release rate peak became smaller with injection timing retardation. The ignition and heat release rate peak occurred later with increasing biodiesel content. Fuel impingement on the wall was observed for all test conditions. The liquid penetration became longer and the fuel impingement was stronger with the increase of biodiesel content. Early and late injection timings result in lower flame luminosity due to improved mixing with longer ignition delay. For all the injection timings, lower soot luminosity was seen for biodiesel blends than pure diesel fuel. Furthermore, NO_x emissions were dramatically reduced for premixed combustion mode with retarded post-TDC injection strategies.     

The role of fuel chemistry in dictating nanostructure evolution of soot toward source identification

Abstract

Laser derivatization is proposed as a diagnostic technique toward identifying the sources contributing to combustion produced soot. Fuel chemistry and the resultant oxygen content in nascent soot have been shown to influence the evolution of soot nanostructure upon laser derivatization. This is illustrated using the spectroscopic and microscopic characterization of biodiesel soot, with a systematic variation in fuel chemistry used to generate the soot. Functionalized carbon black is used as the control to independently verify the influence of material chemistry on nanostructure upon laser heat treatment. Results track with those observed for biodiesel soot. Reciprocally, the similarity in soot nanostructure observed after laser heating is tied to the likeness in fuel chemistry of biomass-fueled sources. Understanding the origin of differences or similarities in soot nanostructure upon laser heat treatment can help differentiate sources based on their contribution, thereby aiding in effective air quality control.

Copyright © 2019 American Association for Aerosol Research     

Performance and emissions of bus engine using blends of diesel fuel with bio-diesel of sunflower or cottonseed oils derived from Greek feedstock

An experimental investigation is conducted to evaluate the use of sunflower and cottonseed oil methyl esters (bio-diesels) of Greek origin as supplements in the diesel fuel at blend ratios of 10/90 and 20/80, in a fully instrumented, six-cylinder, turbocharged and after-cooled, direct injection (DI), Mercedes-Benz, mini-bus diesel engine installed at the authors’ laboratory. The tests are conducted using each of the above fuel blends, with the engine working at two speeds and three loads. Fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides, carbon monoxide and total unburned hydrocarbons are measured. The differences in the measured performance and exhaust emissions from the baseline operation of the engine, i.e., when working with neat diesel fuel, and the two bio-diesels are determined and compared. Theoretical aspects of diesel engine combustion with the differing physical and chemical properties of these blends, aid the correct interpretation of the observed engine behavior.     

Chemical-looping combustion in a 300 W continuously operating reactor system using a manganese-based oxygen carrier

Chemical-looping combustion (CLC) is a method for the combustion of fuel gas with inherent separation of carbon dioxide. This technique involves the use of two interconnected reactors. A solid oxygen carrier reacts with the oxygen in air in the air reactor and is then transferred to the fuel reactor, where the fuel gas is oxidized to carbon dioxide and water by the oxygen carrier. Fuel gas and air are never mixed and pure CO₂ can easily be obtained from the flue gas exit. The oxygen carrier is recycled between both reactors in a regenerative process. This paper presents the results from a continuously operating laboratory CLC unit, consisting of two interconnected fluidized beds. The feasibility of the use of a manganese-based oxygen carrier supported on magnesium stabilized zirconia was tested in this work. Natural gas or syngas was used as fuel in the fuel reactor. Fuel flow and air flow was varied, the thermal power was between 100 and 300 W, and the air ratio was between 1.1 and 5.0. Tests were performed at four temperatures: 1073, 1123, 1173 and 1223 K. The prototype was successfully operated at all conditions with no signs of agglomeration or deactivation of the oxygen carrier. The same particles were used during 70 h of combustion and the mass loss was 0.038% per hour, although the main quantity was lost in the first hour of operation. In the combustion tests with natural gas, methane was detected in the exit flue gases, while CO and H₂ were maintained at low concentrations. Higher temperature or lower fuel flows increases the combustion efficiency, which ranged from 0.88 to 0.99. On the other hand, the combustion of syngas was complete for all experimental conditions, with no CO or H₂ present in the gas from the fuel reactor.     

Solubility of a diesel–biodiesel–ethanol blend,its fuel properties,and its emission characteristics from diesel engine

In this work, we studied the phase diagram of diesel–biodiesel–ethanol blends at different purities of ethanol and different temperatures. Fuel properties (such as density, heat of combustion, cetane number, flash point and pour point) of the selected blends and their emissions performance in a diesel engine were examined and compared to those of base diesel. It was found that the fuel properties were close to the standard limit for diesel fuel; however, the flash point of blends containing ethanol was quite different from that of conventional diesel. The high cetane value of biodiesel could compensate for the decrease of the cetane number of the blends caused by the presence of ethanol. The heating value of the blends containing lower than 10% ethanol was not significantly different from that of diesel. As for the emissions of the blends, it was found that CO and HC reduced significantly at high engine load, whereas NO_x increased, when compared to those of diesel. Taking these facts into account, a blend of 80% diesel, 15% biodiesel and 5% ethanol was the most suitable ratio for diesohol production because of the acceptable fuel properties (except flash point) and the reduction of emissions.     

Effects of air/fuel combustion ratio on the polycyclic aromatic hydrocarbon content of carbonaceous soots from selected fuels

Patterns of polycyclic aromatic hydrocarbon (PAH) content were observed from GC/MS analysis of the extracts of soots at various air/fuel combustion ratios of three commonly used fuels: n-hexane, JP-8 (Jet fuel), and diesel. With increasing air/fuel ratio, from a simple diffusion flame up to an air/fuel ratio of 3.94, there is a significant loss of high molecular weight PAHs and an increasing abundance of oxidized lower molecular weight aromatics. The formation of high molecular weight PAHs is favored for JP-8 and diesel fuels at higher air/fuel combustion ratios than is the case with n-hexane, probably due to the aromatic content in JP-8 and diesel fuels acting as centers for large aromatic and soot nucleation. The efficiency and reproducibility of two techniques, Soxhlet and supercritical fluid extraction (SFE), used for extraction of PAHs from soot were compared. Electron paramagnetic resonance (EPR) measurements were performed on the soot both before and after supercritical fluid and Soxhlet extraction, and a substantial decrease in the spin density of soot following extraction indicates that extractable molecules are associated with 40–50% of the unpaired electrons in soot. This analysis generally supports trends observed in our earlier work for surface oxidation, surface area, unpaired electron spin density, hydration, and ozone oxidation.     

Gas and soot products formed in the pyrolysis of acetylene–ethanol blends under flow reactor conditions

The present paper reports a laboratory study on the pyrolysis of different blends containing acetylene, known as an important soot precursor, and ethanol, regarded as an appropriate additive to conventional fuels aiming to diminish the emission of pollutants coming from combustion processes. Pyrolysis experiments of acetylene–ethanol blends, for a total initial concentration of reactants of 50,000 ppm, with variable volume percentages of ethanol between 0 and 40% with respect to the total concentration of reactants, have been carried out in a quartz flow reactor working in a temperature range of 975–1475 K. The influence of both pyrolysis temperature and ethanol concentration in the blend on the gas and solid products has been evaluated. As the reaction temperature is increased, the soot production is higher and yield to carbonaceous gas products decreases. It is noticed that the presence of ethanol inhibits the production of soot and the diminution of soot formation does not present a linear dependency with the ethanol concentration; the influence is comparatively stronger when adding small amounts of ethanol. The analysis of the gas products reveals that increasing the ethanol percentage in the blend causes an increase of the concentration of some intermediates such as ethylene, ethane, methane or benzene, pointing to a variation of the reacting species which could prevent soot formation. A literature detailed gas phase kinetic mechanism including reaction subsets for acetylene and ethanol conversion has been used to simulate the experimental results. This theoretical study has been carried out with the purpose of analyzing the trends of the evolution of gas products and getting a better understanding of the gas phase processes involved in the pyrolysis of the different blends, although soot formation is not included.     

The use of iron oxide as oxygen carrier in a chemical-looping reactor

Chemical-looping combustion (CLC) is a method for the combustion of fuel gas with inherent separation of carbon dioxide. This technique involves the use of two interconnected reactors, an air reactor and a fuel reactor. The oxygen demanded in the fuel combustion is supplied by a solid oxygen carrier, which circulates between both reactors. Fuel gas and air are never mixed and pure CO₂ can be obtained from the flue gas exit. This paper presents the results from the use of an iron-based oxygen-carrier in a continuously operating laboratory CLC unit, consisting of two interconnected fluidized beds. Natural gas or syngas was used as fuel, and the thermal power was between 100 and 300 W. Tests were performed at four temperatures: 1073, 1123, 1173 and 1223 K. The prototype was successfully operated for all tests and stable conditions were maintained during the combustion. The same particles were used during 60 h of hot fluidization conditions, whereof 40 h with combustion. The combustion efficiency of syngas was high, about 99% for all experimental conditions. However, in the combustion tests with natural gas, there was unconverted methane in the exit flue gases. Higher temperature and lower fuel flows increase the combustion efficiency, which ranged between 70% and 94% at 1123 K. No signs of agglomeration or mass loss were detected, and the crushing strength of the oxygen carrier particles did not change significantly. Complementary experiments in a batch fluidized bed were made to compare the reactivity of the oxygen carrier particles before and after the 40 h of operation, but the reactivity of the particles was not affected significantly.     

Effect of FFA of Crude Rice Bran Oil on the Properties of Diesel Blends

Crude rice bran oil (CRBO) with high free fatty acid (FFA) content is not suitable for eating purposes, however, it can be used as a fuel to partially replace or fully replace No.2 diesel. The main objective of the present work was to analyse the effect of FFA content of CRBO on the combustion properties such as viscosity, calorific value, volatility and aniline point. CRBO with different FFAs were collected and mixed with No.2 diesel to prepare CRBO-diesel blends. It was observed that the viscosity of the blends increased with increase in FFA while the calorific value decreased. Significant variations were observed in the distillation curve for the CRBO blends with different FFA. Aniline point of the blends was 10–15% lower than that of diesel and it is indirectly proportional to the FFA of CRBO in the blend. Experimental results showed that the combustion properties of CRBO are the function of the FFA in the oil. As a dilute blend with diesel, CRBO with high FFA content showed comparable combustion properties to that of diesel. The properties differed in magnitude by 10–15% when compared with diesel. From the present investigation it is concluded that in blended form, CRBO with high FFA can be a potential resource to utilize it as an alternative fuel for CI (compression ignition) engines.     

Optimization of the combustion of blends of domestic fuel oil and cottonseed oil in a non-modified domestic boiler

This study characterizes combustion of blends of DFO (domestic fuel-oil) and refined cottonseed oil produced in Burkina Faso at different percentages in a non-modified DFO burner by determining its overall performance (consumption and thermal capacity) and gas emissions (CO, CO₂, O₂, NO, NO_x, SO₂). The physical and chemical characteristics of the different blends confer on each blend the status of a special fuel requiring specific adjustment of the burner. The influence of combustion parameters such as equivalence ratio and fuel pressure is studied. Results show that emissions of CO, NO_x and CO₂ are similar for all fuel blends at the operating point corresponding to 0.86 equivalence ratio and 20 bars fuel pressure. Whatever the fuel pressure is, SO₂ emission is increasing with DFO percentage in blends.Experimental emission results obtained with suitable adjustments for a blend containing 30% cottonseed oil and 70% DFO are compared to the calculated results obtained using a combustion equation based on a global chemical mechanism. The results show that there is a satisfactory match between the calculation and experimental results.     

Combustion performance of bio-ethanol at various blend ratios in a gasoline direct injection engine

Bio-ethanol has the potential to be used as an alternative to petroleum gasoline for the purpose of reducing the total CO₂ emissions from internal combustion engines and this paper is devoted to the investigation of using different blending-ratios of bio-ethanol/gasoline with respect to spark timing and injection strategies. The experimental work has been carried out on a direct injection spark ignition engine at a part load and speed condition. It is shown that the benefits of adding ethanol into gasoline are reduced engine-out emissions and increased efficiency, and the impact changes with the blend ratio following a certain pattern. These benefits are attributed to the fact that the addition of ethanol modifies the evaporation properties of the fuel blend which increases the vapour pressure for low blends and reduces the heavy fractions for high blends. This is furthermore coupled with the presence of oxygen within the ethanol fuel molecule and the contribution of its faster flame speed, leading to enhanced combustion initiation and stability and improved engine efficiency.     

无卤抗冲阻燃材料研究

用自制的包覆红磷作主要阻燃剂,将包覆红磷、包覆红磷和其它助阻燃剂（水合金属氧化物、聚磷酸铵、三聚氰胺等）的复配物与高抗冲聚苯乙烯共混,进行燃烧测试分析,考察各种共混体系的燃烧行为,采用锥形量热仪研究红磷及其母粒在高抗冲聚苯乙烯实际燃烧模拟过程中的动态热效应、烟密度等,用氧指数等燃烧参数分析红磷及其它助阻燃剂在高抗冲聚苯乙烯共混物中的阻燃作用,得到了较好的阻燃体系,提出了红磷在共混物燃烧过程中“炭化     

A comparative reactivity and kinetic study on the combustion of coal-biomass char blends

The combustion behavior and kinetics of various biomass chars, a lignite and a hard coal char and their blends were investigated. Pure fuel chars were compared to blended chars with respect to their performance during combustion. Non-isothermal thermogravimetry experiments were performed in air atmosphere, over a temperature range of 25-850 °C and at a heating rate of 10 °C/min. Kinetic evaluation was performed using a power law model. Reaction kinetic parameters were obtained by modeling the combustion of biomass and coal chars as a single reaction, with the exception of lignite and olive kernel chars, the combustion of which was modeled by two partial reactions. A single reaction model was used in the case of coal-wood char blends, while for the lignite-biomass char blends two partial reactions were used. Reactivity was assessed using the specific reaction rate, as a function of conversion. Biomass chars were generally more reactive than those of hard coal and lignite. The combustion behavior of the blends was greatly influenced by the rank of each coal (hard coal or lignite) and the proportion of each component in the blend. Combustion performance of the blends showed some deviation from the expected weighted average of the constituent chars. An attempt was made to estimate the kinetics of the blends using, as a basis, the parameters estimated for the individual components. In this case, because of the interactions between the components of the blends, the kinetic parameters needed to be slightly modified. Alteration in reactivity was more pronounced in the case of lignite-biomass chars than coal-wood chars.     

Uncertainty analysis of heat release rate measurement from oxygen consumption calorimetry

Oxygen consumption calorimetry remains the most widespread method for the measurement of the heat release rate from experimental fire tests. In a first step, this paper examines by theoretical analysis the uncertainty associated with this measurement, especially when CO and soot corrections are applied. Application of theoretical equations is presented for chlorobenzene which leads to high values of CO and soot yields. It appears that the uncertainty of CO and soot corrections are high when the fuel composition is unknown. In a second step, a theoretical analysis is provided when the simplest measurement procedure is used for oxygen consumption calorimetry. The overall uncertainty can be dominated either by the uncertainty associated with the oxygen concentration, the assumed heat of combustion, the fumes mass flow rate or the assumed combustion expansion factor depending on the oxygen depletion. Copyright © 2005 John Wiley & Sons, Ltd.     

Physical and chemical properties of ethanol-diesel fuel blends

This paper discusses the physical-chemical properties of ethanol-diesel fuel blends. The attention is focused on the properties which influence the injection and engine characteristics significantly. Main properties have been investigated experimentally. The analysis of experimentally obtained fuel properties of tested fuels and their influence on engine characteristics are presented. Physical and chemical properties of diesel fuel and ethanol-diesel fuel blends were measured according to requirements and test methods for diesel fuel (EN590, 2003). The tested fuels were neat mineral diesel fuel (D100), 5% (v/v) ethanol/diesel fuel blend (E05D95), 10% (v/v) ethanol-diesel fuel blend (E10D90) and 15% (v/v) ethanol-diesel fuel blend (E15D85). It has been proved that, for ethanol-diesel fuel blends, some additives are necessary to keep stability under low temperature conditions. Also, cold weather properties test, such as cloud point and pour point tests are negatively affected by phase separation. The rest of the properties, excepting flash point, were within diesel fuel standard specifications. Based on this study, it can be concluded that using additives to avoid phase separation and to raise flash point, blends of diesel fuel with ethanol up to 15% can be used to fuel diesel engines if engine performance tests corroborate it.     

Effect of Alcohol Addition to Gasoline on Soot Distribution Characteristics in Laminar Diffusion Flames

Alcohols are widely used as alternative fuel for spark ignition engines to reduce soot emission. 2D soot distributions of alcohols‐gasoline blends were studied in laminar diffusion flames by two‐color laser‐induced incandescence technique. The soot volume fraction decreases significantly with the alcohol blending ratio. At the same blending ratio, the soot‐reducing ability declined with the carbon length of the alcohol, but the reducing effect for short‐chain alcohols, i.e., methanol and ethanol, deteriorated at high blending ratio while it remained constant for the long‐chain alcohol n‐butanol. At fixed oxygen content, the soot‐reducing ability of a short‐chain alcohol is still higher than that of a long‐chain alcohol, i.e., not only the oxygen content but also the molecular structure dominates the soot‐reducing ability.     

Long-term integrity testing of spray-dried particles in a 10-kW chemical-looping combustor using natural gas as fuel

Chemical-looping combustion, CLC, is a combustion concept with inherent separation of CO₂. The fuel and combustion air are kept apart by using an oxygen carrier consisting of metal oxide. The oxygen carriers used in this study were prepared from commercially available raw materials by spray-drying. The aim of the study was to subject the particles to long-term operation (>1000 h) with fuel and study changes in particles, with respect to reactivity and physical characteristics. The experiments were carried out in a 10-kW chemical-looping combustor operating with natural gas as fuel. 1016 h of fuel operation were achieved. The first 405 h were accomplished using a single batch of NiO/NiAl₂O₄-particles. The last 611 h were achieved using a 50/50_mass-mixture of (i) particles used for 405 h, and (ii) a second batch of particles similar in composition to the first batch, but with an MgO additive. Thus, at the conclusion of the test series, approximately half of the particles in the reactor system had been subjected to >1000 h of chemical-looping combustion. The reason for mixing the two batches was to improve the fuel conversion. Fuel conversion was better with the mixture of the two oxygen carriers than it was using only the batch of NiO/NiAl₂O₄-particles. The CO fraction was slightly above the equilibrium fraction at all temperatures. Using the oxygen carrier mixture, the methane fraction was typically 0.4-1% and the combustion efficiency was around 98%. The loss of fines decreased slowly throughout the test period, although the largest decrease was seen during the first 100 h. An estimated particle lifetime of 33 000 h was calculated from the loss of fines. No decrease in reactivity was seen during the test period.