Oxygen Concentration In Gas Research Articles

Model development for intake gas composition controller design for commercial vehicle diesel engines with HP-EGR and exhaust throttling

Developers of modern diesel engines have to face rigorous restrictions in emission of nitrogen-oxides and particulate matter. Among several methods (DPF, SCR, improved injection etc) which are used to handle these exhaust gas components precise control of the cylinder charge composition seems to be a cost effective solution. The oxygen concentration of the intake gas has a significant impact on the combustion process hence on the pollutant formation. Moreover the precise adjustment of the cylinder charge oxygen concentration can be used to control low temperature combustion processes. The amount of the backflowing exhaust gases is limited by the pressure difference on the EGR duct. To solve this problem the authors suggest the use of novel exhaust brakes with extended functionality: backpressure adjustment for the precise control of the intake gas composition. This way arbitrary EGR rates can be achieved in any engine operation point. For the implementation of such a function the design of an intake manifold oxygen controller is needed, where the control inputs are the EGR valve and the exhaust throttle. This paper demonstrates the development of a control oriented model of the air path system as the first step of this task. The model considers three balance volumes in the air path and has five state variables. Its performance has been evaluated and validated with engine dyno measurements on a medium duty diesel engine.

Physical scaling of water mist fire extinguishment in industrial machinery enclosures

Froude-based scaling relationships had previously been theoretically extended to, and experimentally validated in the laboratory for, water mist suppression of fires in open environment and in enclosures, which were shown applicable to gas, liquid and solid combustible fires. Before applying these relationships to real-world settings, their applicability needs to be further evaluated for the intended protection. This paper presents such an evaluation on scaling water mist fire extinguishment in an industrial machinery enclosure. In this evaluation exercise, a full-scale water mist protection set-up tested for a 260-m3 machinery enclosure was selected as the benchmark. A ½-scale machinery enclosure test replica was then constructed, together with a ½-scale nozzle whose orifices were geometrically similar to those of the full-scale nozzle. Spray measurements indicated that the ½-scale spray closely met the scaling requirements, in terms of discharge K-factor, water mist flux, droplet velocity and droplet size distribution. Two spray fires and one pool fire, which were scaled with the respective full-scale fires, were used to challenge the water mist protection in the ½-scale enclosure. At least five replicated tests were conducted for each of the four tested fire scenarios. Overall, the instantaneous local gas temperature and oxygen concentration measured inside the ½-scale enclosure for each fire scenario agreed reasonably well with those measured at the corresponding locations inside the full-scale enclosure, meeting Froude modeling's requirement that scalar quantities be preserved in different scales. The fire extinguishment times obtained from the ½-scale tests for each fire scenario were also statistically consistent with that observed in the corresponding full-scale test. Based on the obtained results, it is concluded that, for machinery enclosures and other similar occupancies, the previously laboratory-validated scaling relationships for water mist fire suppression can be used to determine the fire extinguishing performance of a full-scale water mist protection in a ½-scale test facility.

In Situ Measurement of Alkali Metals in an MSW Incinerator Using a Spontaneous Emission Spectrum

This paper presents experimental investigations of the in situ diagnosis of the alkali metals in the municipal solid waste (MSW) flame of an industrial grade incinerator using flame emission spectroscopy. The spectral radiation intensities of the MSW flame were obtained using a spectrometer. A linear polynomial fitting method is proposed to uncouple the continuous spectrum and the characteristic line. Based on spectra processing and a non-gray emissivity model, the flame temperature, emissivity, and intensities of the emission of alkali metals were calculated by means of measuring the spectral radiation intensities of the MSW flame. Experimental results indicate that the MSW flame contains alkali metals, including Na, K, and even Rb, and it demonstrates non-gray characteristics in a wavelength range from 500 nm to 900 nm. Peak intensities of the emission of the alkali metals were found to increase when the primary air was high, and the measured temperature varied in the same way as the primary air. The temperature and peak intensities of the lines of emission of the alkali metals may be used to adjust the primary airflow and to manage the feeding of the MSW to control the alkali metals in the MSW flame. It was found that the peak intensity of the K emission line had a linear relationship with the peak intensity of the Na emission line; this correlation may be attributed to their similar physicochemical characteristics in the MSW. The variation trend of the emissivity of the MSW flame and the oxygen content in the flue gas were almost opposite because the increased oxygen content suppressed soot formation and decreased soot emissivity. These results prove that the flame emission spectroscopy technique is feasible for monitoring combustion in the MSW incinerator in situ.

Data-Reconciliation Based Fault-Tolerant Model Predictive Control for a Biomass Boiler

This paper presents a novel, effective method to handle critical sensor faults affecting a control system devised to operate a biomass boiler. In particular, the proposed method consists of integrating a data reconciliation algorithm in a model predictive control loop, so as to annihilate the effects of faults occurring in the sensor of the flue gas oxygen concentration, by feeding the controller with the reconciled measurements. Indeed, the oxygen content in flue gas is a key variable in control of biomass boilers due its close connections with both combustion efficiency and polluting emissions. The main benefit of including the data reconciliation algorithm in the loop, as a fault tolerant component, with respect to applying standard fault tolerant methods, is that controller reconfiguration is not required anymore, since the original controller operates on the restored, reliable data. The integrated data reconciliation–model predictive control (MPC) strategy has been validated by running simulations on a specific type of biomass boiler—the KPA Unicon BioGrate boiler.

Co-firing coal and biomass blends and their influence on the post-combustion CO2capture installation

Co-firing of biomass with coal for energy production is a well-known technology and plays an important role in the electricity sector. The post-combustion capture integrated with biomass-fired power plants (Bio-CCS) seems to be a new alternative for reducing greenhouse gas emissions.This study refers to the best known and advanced technology for post-combustion CO 2 capture (PCC) based on a chemical absorption in monoethanolamine (MEA). The co-firing of hard coal with four types of biomass was investigated using a laboratory fixed bed reactor system. The comparison of gaseous products emitted from the combustion of coal and different biomass blends were determined using gas chromatography.Research proved that co-firing of biomass in fossil fuel power plants is beneficial for PCC process. It may also reduce the corrosion of CO 2 capture installation. The oxygen concentration in the flue gases from hard coal combustion was comparable with the respective value for a fuel blend of biomass content of 20% w/w. It was also noted that an increase in biomass content in a sample from 20 to 40 % w/w increased the concentration of oxygen in the flue gas streams. However, this concentration should not have a significant impact on the rate of amine oxidative degradation.

Numerical Simulation of In Situ Combustion of Oil Shale

This paper analyzes the process of in situ combustion of oil shale, taking into account the transport and chemical reaction of various components in porous reservoirs. The physical model is presented, including the mass and energy conservation equations and Darcy’s law. The oxidation reactions of oil shale combustion are expressed by adding source terms in the conservation equations. The reaction rate of oxidation satisfies the Arrhenius law. A numerical method is established for calculating in situ combustion, which is simulated numerically, and the results are compared with the available experiment. The profiles of temperature and volume fraction of a few components are presented. The temperature contours show the temperature variation in the combustion tube. It is found that as combustion reaction occurs in the tube, the concentration of oxygen decreases rapidly, while the concentration of carbon dioxide and carbon monoxide increases contrarily. Besides, the combustion front velocity is consistent with the experimental value. Effects of gas injection rate, permeability of the reservoir, initial oil content, and injected oxygen content on the ISC process were investigated in this study. Varying gas injection rate and oxygen content is important in the field test of ISC.

Au/SiO2 nanoparticles in TiO2:Sm3+ films for improved fluorescence sensing of oxygen

Increase–decrease in oxygen gas concentration results in increase–decrease in fluorescence of TiO2:Sm3+ films; this effect is especially pronounced around the Au/SiO2 nanoparticles with which the samples are decorated.

Simultaneous capture of liquid length of spray and flame lift-off length for second-generation biodiesel/diesel blended fuel in a constant volume combustion chamber

Simultaneous imaging of OH∗ chemiluminescence and Mie scattering of fuel spray have been performed under reacting conditions in a constant volume combustion chamber aimed for a second-generation biodiesel/diesel blended fuel. Mie scattering of 532nm laser light technique was used for the liquid fuel measurement. In order to remove the interference signal from soot radial, filtered Mie scattered light from the fuel droplet was recorded with a charge coupled device (CCD) camera. The spray liquid length and the flame lift-off length for this high cetane-number fuel were investigated under different ambient gas conditions (temperature, density, oxygen concentration) and injection pressure. Experiments showed that the spray liquid length under the reacting condition was shorter than that under non-reacting condition. The flame lift-off length was significantly influenced by the ambient gas temperature, density, oxygen concentration and injection pressure, while the spray liquid length was slightly affected by the injection pressure and oxygen concentration. The overlap between liquid fuel and combustion flame easily happened at high temperature, high oxygen concentration, and low injection pressure conditions.

Quantitative measurement and indication of pulverized coal ignition temperatures in O2/CO2 environments

The method on quantitative determination of the ignition condition of pulverized coal particles in a laminar drop tube furnace (DTF) was proposed with the continuous measurement of the evolved oxygen concentration in flue gas at variable furnace wall temperatures. Then the method was adopted to quantitatively determine the coal ignition temperatures in different O2/CO2 and air environments for five coal ranks with the measurement of the separate axial temperature profiles in the furnace centerline with and without coal particles feeding. The result shows that the coal ignition temperature in 21%O2/79%CO2 environment measured by DTF method is higher than that in air environment for each coal rank. Moreover, the coal ignition temperature significantly decreases with the increasing oxygen partial pressure in O2/CO2 environments, and the coal ignition temperature in O2/CO2 environment can match that in air environment when the oxygen partial pressure is increased to the value ranging from 25.8% to 44.1%, which is relative to different coal ranks.

Improvement of oxidation resistance of 9 mass% chromium steel for advanced-ultra supercritical power plant boilers by pre-oxidation treatment

Effect of pre-oxidation treatment on oxidation resistance in steam at 650°C has been investigated for 9 mass% chromium (Cr) steel for advanced ultra-supercritical power plants. The formation of thin scale of Cr2O3-rich oxides is achieved by pre-oxidation in argon gas containing 0.3ppm oxygen, which significantly improves the oxidation resistance of the steel in steam at 650°C for a long time exceeding 20,000h. Effects of pre-oxidation conditions, such as oxygen concentration in argon gas and pre-oxidation temperature and time, and of silicon concentration in the steel on the oxidation resistance in stream are systematically investigated.

Investigation on coal moderate or intense low-oxygen dilution combustion with high-velocity jet at pilot-scale furnace

An experiment of coal MILD combustion was carried out in a 0.3MWth down-fire furnace. By increasing the jet velocity to 112m/s, a sufficient internal recirculation was obtained inside the furnace. Therefore the coal MILD combustion could be achieved without highly temperature preheating. Under same condition, a numerical investigation was also carried out as a comparison, and the modeling data can fit the measured data well. Under MILD condition, the peak value of temperature decreased, and the temperature distribution became uniform. Due to high velocity jet, the reaction zone was largely extended and moved toward the exit, in which the reaction rates were decreased for all oxidation reactions. The flame appeared as an integration of dark spark and flame fragment. The NOx emission largely decreased due to the lower flame temperature and deoxidized atmosphere. The carbon burnout rate decreased due to the reduced particle residence time, in turn the CO and oxygen concentration in the exhaust gas also increased. However, the ignition delay increased, and the flame stability decrease without the highly temperature preheating.

(Invited) Design of Highly Sensitive and Selective Diode-Type H2 Sensors

Numerous efforts have been directed to developing highly sensitive and selective H2 sensors, because H2, which is the most promising alternative to fossil fuels, is highly flammable and explosive in a wide concentration range (4–75% in air). However, general gas sensors (e.g., semiconductor-type and catalytic combustion-type sensors) cannot operate under O2-free atmosphere, because the effective reaction of H2 with negatively-charged oxygen adsorbates on the oxide surface is essential for the large H2 response. We have thus far demonstrated that diode-type gas sensors using noble-metal (N) sensing electrodes and an anodized titania film (N/TiO2 sensors) show quite large H2 response under oxygen-free atmosphere as well as relatively excellent H2 selectivity to other inflammable gases, in comparison with other gas sensors. Use of Pd as the sensing-electrode material especially resulted in quite large H2 response1 , 2 ), and alloying of Pd with Pt (Pd-Pt) effectively improved the H2 response and the long-term stability3). However, the H2 response of these sensors abruptly decreased with an increase in oxygen concentration in target gas. On the other hand, a Pt/TiO2 sensor showed lower H2 response than the Pd/TiO2 and Pd-Pt/TiO2 sensors, but the coating of the Pt-sensing electrode with a slight amount of Au drastically enhanced the magnitude of H2 response in air, probably due to a decrease in the amount of oxygen adsorbates on the Pt electrode4,5). Therefore, effects of the Au coating of the Pt-sensing electrode on the H2-sensing properties have been investigated in this study. A polished Ti plate (10 mm × 5 mm × 0.5 mm) was annealed at 600°C for 1 h in air, and the half part was anodized at 20°C for 30 min at a current density of 50 mA cm-2 in 0.5 M H2SO4 aqueous solution. A pair of Pt electrodes (3 mm × 3 mm) was fabricated on the surface of both the TiO2 thin film and the Ti plate by magnetron sputtering for 6 min at 300 W in Ar. Subsequently, Au was coated on the Pt electrodes by magnetron sputtering at 40 W in Ar (sputtering time (n): 10–120 s) and Au wires were attached on both the electrodes by using Au paste. The sensing properties of the obtained sensors (Au(n)/Pt/TiO2 sensors, after annealing at 600°C for 1 h in air) to 5–8000 ppm H2 balanced with air or N2 under dry or wet atmosphere were measured at 250°C, while applying a dc voltage of 100 mV to the sensors under forward bias condition (Au(n)/Pt(+)–TiO2–Ti(−)). The response of a Pt/TiO2 sensor to 8000 ppm H2 in dry air was three orders of magnitude smaller than that in dry N2, but Au coating on the Pt electrode drastically enhanced the forward current of the Pt/TiO2 sensor in air. The Au(20)/Pt/TiO2 sensor showed the largest H2 response in dry air among all Au(n)/Pt/TiO2 sensors, but the magnitude of H2 response in dry air was still smaller than that in dry N2. The addition of moisture to the atmosphere further enhanced the H2 response of the Au(20)/Pt/TiO2 sensor in air, while it decreased the H2 response in N2. Consequently, the response of the Au(20)/Pt/TiO2 sensor to 8000 ppm H2 in air was comparable to that in N2 under the most humidified atmosphere (AH: 12.8 g m-3). The Au(20)/Pt/TiO2 sensor showed linear relationship between the H2 response and the logarithmic H2 concentration, and the sensor could respond to 50 ppm H2 in dry and wet air, while the sensor easily responded to even 5 ppm H2 in dry and wet N2. In addition, the Au(20)/Pt/TiO2 sensor showed quite excellent H2 selectivity against propane and propene. These results indicate that the optimal Au coating on the Pt electrode was quite effective in improving both the H2 response and H2 selectivity in air as well as reducing oxygen-concentration dependence of the H2response, especially under wet atmosphere. 1) Y. Shimizu, N. Kuwano, T. Hyodo, M. Egashira, Sens. Actuators B 83(2002) 195. 2) Y. Shimizu, K. Sakamoto, M. Nakaoka, T. Hyodo, M. Egashira, Adv. Mater. Res. 47-50(2008) 1510. 3) T. Hyodo, M. Nakaoka, Y. Shimizu, M. Egashira, Sens. Lett. 9(2011) 641. 4) T. Hyodo, T. Yamashita, Y. Shimizu, ECS Transactions 50(12) (2012) 171. 5) T. Hyodo, T. Yamashita, Y. Shimizu, Sens. Actuators B 207 (2015) 105.

Numerical Modelling of Combustion in 1.5 MW Low-NOx Burner

Results from CFD simulations of swirling non-premixed gas flame using a low-NOx gas burner are presented and compared to experimental data measured during a testing campaign in a semi-industrial water-cooled combustion chamber. The burner is both fuel- and air-staged with maximum capacity of 1.5 MW. Numerical simulations are performed with Ansys Fluent software using Reynolds-averaged Navier-Stokes (RANS) turbulence model coupled with eddy-dissipation chemistry model (EDM) and discrete ordinates radiative heat transfer model. This modelling approach is preferable for large-scale combustion applications such as process fired heaters, where employing advanced models (e.g. Large Eddy Simulation) is still computationally demanding.It is shown, how results are sensitive to the mixing rate constant of EDM, which is employed in a simulation of swirling turbulent diffusion flame. Specifically, temperatures are overestimated with the constant being set to 4 (the default value in Ansys Fluent), which leads to false prediction of NOx formation. Temperature peaks are reduced by lowering the mixing rate constant. An acceptable agreement with measured outlet and peak flame temperatures is achieved, when the constant is set to 0.6. With this value, however, highly increased concentrations of unburned species are reported at the outlet. Predicted values deviate from the measurements about three orders of magnitude. Based on the concentrations of unburned species and oxygen in the flue gas at the outlet, the best results are obtained with the constant 1.2.

Effect of oxygenated and paraffinic alternative diesel fuels on soot reactivity and implications on DPF regeneration

A wide range of alternative fuels has recently emerged worldwide, as a means to reduce the dependence on fossil resources and to meet the stringent energy and emissions legislations. In the diesel market, oxygenated biofuels such as biodiesel and e-diesel (low content ethanol-diesel blends) and paraffinic fuels such as those derived from Fischer-Tropsch processes (GTL) or hydro-treatment of vegetable oils (HVO) stand out as the most promising ones. A current challenge that these fuels face is their effect on loading and regeneration performance in diesel particle filters –DPFs–, an aftertreatment technique commonly adopted to abate particulate emissions. This work analyses the oxidative behavior of soot under controlled temperature-atmosphere conditions. Five fuels (conventional diesel fuel, e-diesel, HVO, GTL and conventional biodiesel) were tested in a Euro 5 automotive engine. The effect of the oxidant gas composition (oxygen content and NO2 presence) and the engine injection strategy (small modifications around the original manufacturer setting) were analyzed. Results revealed a greater ability of soot from paraffinic and, especially, oxygenated biofuels to be oxidized under lower temperature conditions. In particular, e-diesel soot needed the lowest temperature and its oxidation pattern was the fastest and the least sensitive to the oxygen concentration in the exhaust gas, which makes feasible the use of exhaust gas recirculation during active regeneration. From the original injection strategy, small advances/delays and/or the presence of a fuel post-injection did not significantly alter the reactivity of soot. NO2 concentration in the exhaust gas showed no significant effect on the soot oxidation process at temperatures higher than 300°C.

Endpoint forecasting on composite regeneration by coupling cerium-based additive and microwave for diesel particulate filter

Numerical simulation has been carried out to investigate the major factors affecting the time of composite regeneration due to coupling cerium-based additive and microwave for diesel particulate f3ilter (DPF). Effect on the composite regeneration time from various factors such as mass flow rate of exhaust gas, temperature of exhaust gas, oxygen concentration of exhaust gas, microwave power and amount of cerium-based additive are investigated. And a mathematical model based on fuzzy least squares support vector machines has been developed to forecast the endpoint of the composite regeneration. The results show that the relative error of endpoint forecasting model of composite regeneration is less than 3.5%, and the oxygen concentration of exhaust gas has the biggest effect on the endpoint of composite regeneration, followed by the mass flow rate of exhaust gas, the microwave power, the temperature of exhaust gas and the amount of cerium-based additive.

Effect of oxygen concentration and reaction order on char inventory in fluidized bed combustion

Population balance modeling is applied to develop calculation methods for mass inventory of char in fluidized bed combustion (FBC). The focus is on the effect of gas oxygen concentration and the reaction order of char with respect to oxygen, which is important in understanding and simulating combustion in high oxygen concentration. The well-known shrinking particle model describing the single particle combustion is simplified by applying a dimensionless particle size and dimensionless time with a specifically chosen characteristic reference diameter and time constant. Methods and analytical solutions to calculate particle size distribution (PSD), particle combustion time and char mass in FBC are presented.

Diseño e implementación de un sistema de control para mejorar la calidad de los gases de combustión de una caldera pirotubular de 5 BHP

La presente investigación tiene como objetivo el diseño e implementación de un sistema para el control de la calidad de los gases de combustión de una caldera pirotubular de 5 BHP. En base al porcentaje de O2 presente en los gases de combustión, medido mediante una sonda Lambda, se determina el porcentaje de CO2 que se emite a la atmósfera. Un control proporcional PID se encarga de la regulación automática de la entrada de aire a la caldera mediante un actuador, según el valor de la concentración de oxígeno registrado en los gases de combustión. El sistema de control cuenta con una pantalla HMI y un PLC modular. Los resultados alcanzados aseguran la emisión de gases contaminantes dentro de los parámetros establecidos por las normas ambientales vigentes lográndose así, la calidad requerida de los gases de combustión y la reducción del consumo de combustible de la caldera.

Effect of gas temperature and oxygen concentration on single particle ignition behavior of biomass fuels

This work focuses on single particle ignition behavior of biomass fuels. Five biomass fuels were studied, namely, wheat straw, kiwi branches, vine branches, sycamore branches and pine bark. Coal was also tested for comparison purposes. Tests were carried out in an optical flat flame McKenna burner able to produce a confined laminar flow of combustion products, in which single particles were injected upward through a central hole. The equivalence ratio and the thermal input of the burner were adjusted to yield the following operating conditions in the ignition zone: five mean temperatures (1500, 1575, 1650, 1700 and 1800K) and three mean dry oxygen concentrations (3.5, 5.1 and 6.5vol. %). The ignition mode and the ignition delay time were evaluated through the analysis of images obtained by means of a CMOS high-speed camera. The effects of gas temperature and oxygen concentration on the ignition mode and ignition delay time were assessed. For the studied conditions, the ignition of the biomass particles generally occurred in the gas-phase, although surface ignition was also observed in some cases. The results suggest that the critical diameter for the ignition mode transition varies with the fuel type. All particles show a consistent trend of decreasing ignition delay time with increasing gas temperature, with the biomass particles presenting slightly higher values than the coal tested. The estimated drying times were subtracted from the total ignition delay time and the trends shifted, with the pine bark and wheat straw presenting a lower remaining time than the coal. Finally, for the studied oxygen concentration range, its variation did not have a significant impact on the ignition mode and delay time at high temperatures.

Effects of the sputtering gas conditions on the structural, optical and magnetic properties of Cu, Co codoped ZnO multilayer films

The Cu, Co codoped ZnO multilayer films were deposited by magnetron sputtering on silicon (100) in different sputtering gas and the substrates were held at 500 °C. The oxygen content in the films were correlated with the oxygen prevailed in the sputter chamber. The influences of the oxygen content in the sputtering gas on structural, optical and magnetic properties of Cu, Co codoped ZnO multilayer films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, UV absorption spectrophotometer and vibrating sample magnetometer. The results indicated that Cu2+ and Co2+ ions would uniformly substitute into the Zn2+ sites of ZnO lattice. The optical band gap of the films increased from 3.14 to 3.23 eV with increasing oxygen content of the sputtering gas. Oxygen concent have effected on the ferromagnetism of the samples.

Data-driven modelling and fuzzy multiple-model predictive control of oxygen content in coal-fired power plant

In the combustion system of a boiler, oxygen content in the flue gas is a significant economic parameter for combustion efficiency. As a combustion system is highly complex and there are many constraints in a real process, traditional control cannot achieve satisfying performance in the practical oxygen content tracking control problem. In this paper, we build a combustion process model with a data-driven method and present a multiple-model-based fuzzy predictive control algorithm for the oxygen content tracking control. The combustion process model is presented as a multiple-model form, which can represent the real process more accurately. A data-driven method with fuzzy c-means clustering and subspace identification is used to identify the model parameters. Then, model predictive control integrated with a fuzzy multiple-model is used to control the oxygen content tracking problem. As the coal manipulated variable is decided by the load demand in the real process, a real-time measured value is applied to the process. All data used to obtain the process model is historical real-time data generated from a 300-MW power plant in Gui Zhou Province, China. Real-time simulation results on the 300-MW power plant show the effectiveness of the modelling and control algorithms proposed in this paper.