Excess Air Research Articles

Экспериментальные исследования воспламенения и горения каменного угля с применением плазменной активации

This work presents experimental studies of a promising method of ignition and combustion of coal fuel using plasma activation. Experimental studies were carried out on a bench with a thermal power of up to 5 MW. As an experimental sample, hard coal of the GD grade was chosen selected after a ball drum mill with a sieve residue of R90 = 15%. The conditions were close to industrial ones used when lighting coal boilers. The operating range of pulverized coal flow velocities in the electric arc unit has been determined. It has been established that a stable process of ignition and further combustion of coal is possible at flow rates on the electric arc unit from 6 to 13 m/s. The experimental stand was kindled from a cold state to a temperature of 1000 °C at excess air coefficients a from 0.5 to 0.7, the kindling time did not exceed 200 seconds. Based on the experiments, CFD modeling determined whether the process conditions were met.

Simulation study on nitrogen transformation characteristics of NH3/Coal Co-firing under deeply air-staged condition

Carbon emissions have become a prominent global concern, with the utilization of fossil fuels serving as the primary contributor. Ammonia, being a hydrogen carrier without carbon, has the potential to be utilized through combustion, resulting in the production of water and nitrogen as ideal byproducts, which are environmentally benign. However, individual ammonia is difficult to combust due to its unfavorable combustion characteristics. Hence, ammonia needs to be blended with other fuels that possess superior combustion characteristics. Additionally, NH3 inherently contains a significant amount of nitrogen, a fuel element that can contribute to the increased release of NOx emissions. In this work, a simulation was conducted using CHEMKIN to investigate the nitrogen transformation characteristics during ammonia/coal co-firing under deeply air-staged combustion. Experimental studies primarily focus on macroscopic factors, such as temperature and pressure, while often neglecting the analysis of reaction mechanisms. The utilization of the chemical reaction kinetics simulation method can provide valuable insights into the reactions and substances that exert the most significant impact on the formation of NOx, as well as elucidate the pathway of fuel-nitrogen conversion during combustion. Simulation results demonstrate that as the NH3 co-firing ratio (CR-NH3) increases, the volume content of NOx initially rises, reaching its peak at approximately 10% CR-NH3, and subsequently declines. The conversion rate of NOx increases as the combustion temperature in the primary combustion area rises. The primary reactions have a greater influence on the formation of NO at low-temperature conditions. However, it is important to note that low temperature also decreases the combustion efficiency. The incorporation of overfire air (OFA) in advance has the potential to mitigate nitrogen reduction in the primary combustion area, while simultaneously improving NOx emissions. With the oxygen concentration of primary air increased, the conversion rate of NOx gradually decreases. It undergoes a sharp change before reaching 21% oxygen concentration, after which it levels off. In addition, high oxygen concentration increases the pathway of NO consumption. When the excess air coefficient of OFA falls within the range of 0.35–0.45, the NOx conversion rate can be minimized. The present study aims to offer technical assistance and guidance for effectively controlling NOx emissions in ammonia/coal co-firing boilers.

A study on nitrogen oxide emission prediction in Taichung thermal power plant using artificial intelligence (AI) model

In recent studies, artificial intelligence models have been developed for the prediction of nitrogen oxide emissions from thermal power plants. This research utilizes an artificial intelligence prediction model with more coal input features than boiler features, including volatility, ash content, sulfur content, fixed carbon, total moisture, calorific value, grinding rate, fuel ratio, coal feeding rate, boiler efficiency, total air volume, and excess air volume. The paper delves into the importance analysis of input features for artificial intelligence models. Moreover, feature importance analysis is not only a prerequisite for predicting nitrogen oxide emissions but also a study providing insights into model performance. An artificial neural networks (ANN) regression model is employed to predict nitrogen oxide emissions, and the results demonstrate that the number of feature importance significantly impacts model performance. The best model performance is achieved with eight specific input features. Finally, after the training and validation processes, the ANN model yields the optimal coefficient of determination (R2) value.

Analyzing Burner Performance and Combustion Phenomenon in an Olefin Plant's Industrial Furnace: A CFD Study.

This work presents a comprehensive study of the combustion performance of an industrial furnace in an olefin plant using computational fluid dynamics (CFD) simulations. The focus was on analyzing the heat release pattern of bottom burners to optimize the furnace efficiency in steam-cracking processes. The study developed an accurate computational fluid dynamics (CFD) model for predicting combustion behavior in a cracking furnace. The computational model was validated by comparing the simulation results with industrial data and was used to investigate the impact of burner clogging and the importance of small holes in the body of burners in the furnace. The results also provided insights into the influence of excess air, temperature distribution, fluid behavior, composition of combustion products, and thermal efficiency of the furnace. The presented results contributed to a better understanding of parameters controlling combustion performance in steam-cracking furnaces.

Study on Hydrogen Direct Injection in RNG Combustion under Various Ignition Timings for Power Generation in a Retrofitted Gas Engine

Renewable natural gas (RNG) is attractive for energy policy goals in the world. Therefore, a regional system is designed to explore RNG combustion for power generation in localities. This study investigates a direct injection (DI) engine fueled with hydrogen (H2) blended into the simulated renewable natural gas, which consists of 50% methane (CH4) and 50% carbon dioxide (CO2) in volume. In order to obtain higher efficiency, comparisons between DI and port fuel injection (PFI) of H2 addition were made. Then, the volume percentage of H2 was changed from 20% to 100% by keeping the volume ratio of CH4 and CO2 at 1:1. Finally, results of power output, brake mean effective pressure (BMEP), brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) were discussed. Results showed that in contrast to PFI, H2 DI injection could increase efficiency by 4%. Additionally, H2 DI could retard the MBT ignition timing at 5 °CA. Compared with CH4/CH4 + CO2 combustion, under stoichiometric combustion, BMEP increases with H2 addition but BTE decreases significantly. However, by enlarging the excess air ratio (λ) to 1.24, both BMEP and BTE increase obviously with H2 addition. Moreover, when λ < 1.3, the MBT ignition timing should be advanced from −10 to 15 °CA top dead center (TDC). But the MBT ignition timing is fixed at −25 °CA TDC when λ is larger than 1.3. Furthermore, if efficiency is the priority, 30% H2 addition with λ at 1.24 (−15 °CA TDC) should be selected. If higher BMEP is preferred, 20% H2 addition with λ at 0.99 (−10 °CA TDC) should be selected.

Combustion Characteristics of a Hydrogen-Fueled TJI Engine under Knocking Conditions

The use of a two-stage combustion system in a hydrogen-fueled engine is characteristic of modern internal combustion engines. The main problem with hydrogen combustion in such systems is knocking combustion. This paper contains the results of research under knock combustion conditions with a single-cylinder internal combustion engine equipped with a turbulent jet ignition system (TJI). A layout with a passive pre-chamber and a variable value of the excess air ratio range λ = 1.25–2.0 with a constant value of the center of combustion (CoC = 4 deg) after top dead center (TDC) was used. Two indicators of knock combustion were analyzed: maximum oscillation of pressure and the Mahle Knock Index. Analyses were also carried out taking into account the rate of heat release and the amount of heat released. As a result of the investigation, it was found that knock combustion occurs intensively at small values of the air excess ratio. Hydrogen knock combustion disappears for λ = 2.0 and greater. The pressure oscillation index was found to be more applicable, as its limiting value (>1 bar) allows easy diagnosis of knock combustion. The Mahle Knock Index is a quantity that allows interval analysis of the knock. The choice of classes and weighting coefficients requires an iterative operation, as they strictly depend on engine characteristics, load, and knock magnitude.

Influence of initial electric arc root position on electric arc behavior with spark plugs in large lean burn spark ignited gas engines

Increasing efficiency while reducing emissions leads to high mean effective pressures, high compression ratios and increasingly lean operation for spark ignited large gas engines. Despite these boundary conditions, gas engines must be operated between knocking and misfiring at low cycle-to-cycle fluctuations. The excess air ratio and the ignition process of the lean mixture greatly influence the stability of the combustion process. To enable sufficiently low cycle-to-cycle fluctuation of the combustion process despite the ever increasing excess air ratio levels, it is necessary to understand and investigate the sub-areas of the engine process, for example, ignition, flow condition and mixture formation. This paper focuses on one sub-area of conventional spark ignition, the influence of the electric arc root position on the origin and stretching of the electric arc, because electric arc behavior is considered important in the subsequent combustion process. The results show that electric arc roots on the downstream end of the electrodes tend to enable a longer electric arc length at the first electric arc short circuit (i.e. the first abrupt shortening of the electric arc during its spark duration) than electric arcs with electric arc roots on the upstream ends of the electrodes.

Exergetic Analyses of Detonation Engine Cogeneration Plants

Efficiency improvements are very important in all research and technology. Detonation engines are high technology devices. In the last decades they attracted attention by many researchers. However, detonation engines for cogeneration are not researched efficiently. This article is about the detonation engines cogeneration cycles which analysed by using 1. and 2. law of thermodynamics and exergy analyses methods by the authors. The exergetic performance analyses, their advantage and disadvantages of the ZND-HRSG detonation engine cogeneration cycles were obtained. The exergetic performance analyses were done for various excess air rates to obtain the variations of the combustion exit pressures and temperatures, exergy efficiencies, electric heat rates, SFC and other parameters of their performance. Also, an optimization analysis was done for the ZND-HRSG by searching the optimum values for different excess air rates. The results showed that, the ZND-HRSG cycle have the optimum values of the performance at 1.6-1.8 of the excess air rates.

Prevention of dementia

With increasing life expectancy, the prevalence of dementia is increasing worldwide. Dementia is among the greatest challenges for healthcare and social systems of the future. Approximately 40% of newly diagnosed cases of dementia are associated with risk factors that can potentially be influenced by preventive measures. Based on the evidence from longitudinal studies, systematic reviews and meta-analyses, the Lancet commission on dementia prevention, intervention and care has defined 12risk factors that are associated with an increased risk for dementia: low level of education, hearing impairment, traumatic brain injury, arterial hypertension, diabetes mellitus, smoking, excessive alcohol consumption, depression, obesity, social isolation, and air pollution.

Impact of steam flow into a combustion chamber of a contact gas-steam installation on its energy characteristics

Relevance. Reduction of natural gas consumption and emissions of harmful substances into the environment based on introduction of water vapor into a combustion chamber of a contact gas-steam installation. Aim. To carry out numerical studies on the influence of relative steam flow into the combustion chamber of the contact gas-steam installation on its energy characteristics. Objects. Contact gas-steam installations based on gas turbines with steam injection into the combustion chamber. Methods. Numerical methods based on material and energy balances of systems and elements of gas-steam installations. Results. Based on the calculation of the thermal circuit of the contact gas-steam installation, the authors have studied the influence of the relative steam flow into the combustion chamber on its energy characteristics. It was determined that the absolute electrical efficiency of the contact gas-steam installation increases linearly with growth of relative steam flow into the combustion chamber. The range of changes in the relative steam flow into the combustion chamber strongly depends on the temperature of the gases behind the combustion chamber and the compression ratio in the air compressor; the smaller these parameters are, the greater the range of changes. The maximum efficiency of 56% for all options is achieved at the maximum relative steam flow into the combustion chamber. It was established that the excess air coefficient, depending on the relative steam flow rate, decreases linearly, and the higher the temperature of the gases behind the combustion chamber and the compression ratio in the air compressor, the greater the rate of decline and the smaller the range of changes in the relative steam flow rate. It was revealed that the efficiency coefficient strongly depends on the relative steam flow into the combustion chamber, the temperature of the gases behind it and the degree of compression in the air compressor; with increasing these parameters, it increases linearly. It was determined that the temperature of the gases at the outlet of the gas turbine also strongly depends on the relative flow of steam into the combustion chamber, the temperature of the gases at its outlet and the compression ratio in the compressor. With an increase in the relative flow of steam into the combustion chamber, this temperature increases linearly from 600 to 700°C, while the higher the temperature of the gases at the outlet of the combustion chamber and the compression ratio in the compressor, the higher the temperature of the gases at the outlet of the gas turbine. The authors revealed the dependence of useful work on a gas turbine shaft on the relative steam flow into the combustion chamber. With an increase in the relative steam flow, the useful work on the gas turbine shaft increases along the branch of the parabola. The higher the temperature of the gases behind the combustion chamber and the compression ratio in the compressor, the steeper the branch of the parabola, but the smaller the range of changes in the relative steam flow. It was established that with an increase in the relative steam flow, the gas flow to the gas turbine decreases according to a hyperbola. Moreover, the lower the temperature of the gases behind the combustion chamber and the compression ratio in the compressor, the more the gas flow to the gas turbine drops.

Experimental and modeling study of full- condition combustion characteristics of exhaust gas burners for solid oxide fuel cells

SOFC exhaust gas burner is an essential component of the SOFC thermal management system. The burner in the whole operating conditions of safe and stable combustion and smooth transition in the switching operating conditions is of great significance to the long-term and efficient operation of the SOFC power generation system. This paper builds an experimental test platform for the SOFC exhaust gas burner, tests the combustion performance of the burner in full operating conditions and operating conditions switching process, and establishes a prediction model for the combustion performance of SOFC exhaust gas burner by machine learning algorithm. The results show that the SOFC exhaust gas burner can meet the requirements of safe and stable combustion in all operating conditions and smooth transition between operating conditions; reliable combustion is achieved at the stable power generation condition with excess air factor of 7 ∼ 26, and the average cathode and anode pressure drop in the stable power generation condition is 142 Pa and 185 Pa, respectively; BP neural networks, support vector machines and random forests are used to establish a prediction model for the performance of the SOFC exhaust gas burner, and the random forests achieve the best prediction effect.

Experimental Investigation on Knock Characteristics from Pre-Chamber Gas Engine Fueled by Hydrogen

Hydrogen-fueled engines require large values of the excess air ratio in order to achieve high thermal efficiency. A low value of this coefficient promotes knocking combustion. This paper analyzes the conditions for the occurrence of knocking combustion in an engine with a turbulent jet ignition (TJI) system with a passive pre-chamber. A single-cylinder engine equipped with a TJI system was running with an air-to-fuel equivalence ratio λ in the range of 1.25–2.00, and the center of combustion (CoC) was regulated in the range of 2–14 deg aTDC (top dead center). Such process conditions made it possible to fully analyze the ascension of knock combustion until its disappearance with the increase in lambda and CoC. Measures of knock in the form of maximum amplitude pressure oscillation (MAPO) and integral modulus of pressure oscillation (IMPO) were used. The absolute values of these indices were pointed out, which can provide the basis for the definition of knock combustion. Based on our own work, the MAPO index > 1 bar was defined, determining the occurrence of knocking (without indicating its quality). In addition, taking into account MAPO, it was concluded that IMPO > 0.13 bar·deg is the quantity responsible for knocking combustion.

Effects of Excess Air and Energy Fraction on Heat Transfer for Co-firing of Eucalyptus Bark and Peanut Shell Blended Fuel in a Twin-Cyclonic Swirling Fluidized-Bed Combustor

Effects of Excess Air and Energy Fraction on Heat Transfer for Co-firing of Eucalyptus Bark and Peanut Shell Blended Fuel in a Twin-Cyclonic Swirling Fluidized-Bed Combustor

Technical feasibility of a 1000 MWe pulverized coal power plant under ammonia co-combustion conditions

Ammonia has attracted the attention as a practical way to reach carbon free power generation. Ammonia co-combustion characteristics in 1000MWe pulverized coal power plant was simulated by using Aspen Plus and evaluated under an excess air ratio of 1.0–1.2, air of 2642–3457 ton/hr, coal of 208.2–355.5 ton/hr, ammonia of 0–186.14 ton/hr and various coals. The influence of co-combustion ratios of different coals on emission characteristics and net efficiency was compared. For carbon dioxide emission reduction, the respective CO2 intensity reduction for KPU and BG was 36.44 and 37.76% in calorific value basis, 32.51 and 31.90% in weight basis. The net efficiencies of the power cycle showed a lower decrease as the fuel was supplied on the weight basis compared to the calorific value basis. Based on the obtained results, the KPU on the weight basis showed the lowest net efficiency decrement of 3.1%, but in terms of CO2 intensity reduction, BG on calorific value basis showed most drastic reduction of 37.76%. Consequently, these results showed an effective carbon reduction with ammonia co-combustion and provides a promising solution for the pulverized coal power plants to compass a meaningful reduction of carbon emissions and conservation of combustion efficiency.

Influence of urban environment factors on morphometric parameters and accumulation of secondary metabolites in Cercis canadensis L. and Cercis siliquastrum ‘Alba’

Consideration of the role of green spaces in urban landscaping is extremely important, as they not only decorate the urban landscape, but also effectively reduce air pollution, regulate the microclimate and play an important role in improving the ecology and quality of life of residents. The purpose of the study was to determine the influence of urban environmental factors on the development and secondary metabolism of plants of the genus Cercis L. Plants growing in Kyiv (Ukraine) under conditions with different air humidity, anthropogenic load, and excess or lack of insolation were selected for the study. Plant growth processes were studied by morphometric parameters of annual shoots of Cercis siliquastrum ‘Alba’ and Cercis canadensis L. growing under different conditions. Morphometric methods, fluorescence microscopy, high-performance thin-layer chromatography and regression analysis were used in the study. The research data show that insufficient sunlight has a negative impact on shoot growth. The specificity of the phenolic profiles that can be used to distinguish between the species Cercis canadensis L. and Cercis siliquastrum ‘Alba’ was established. The principal component analysis confirmed that phenolic profiles depend on habitat conditions and affect plant growth and development. The Gaussian model was used to analyse the growth dynamics of annual shoots during the growing season, which allowed us to describe the specifics of internode formation during the growing season quite accurately. This model allowed us to detect the phenomenon of the last internodes falling off at the end of the growing season, which caused the deviation of the morphometric parameters of metameres from the normal distribution along the time axis. Anatomical studies confirmed that the separation of one or more of the last internodes was due to active corking of the internal tissues of the stem, blocking of the xylem and formation of a separating layer, which led to the fall of the shoot tip. This phenomenon shows signs of plant adaptation to low temperatures in winter. The tops of the shoots often do not have time to lignify and accumulate the required amount of cryoprotectants. With the formation of a separating layer, the available energy resources are redistributed to the lateral buds, which receive the necessary resources to prepare for the winter period and provide new growth in the next growing season. The adaptive potential of the two species of the genus Cercis L. confirms the prospects of their use in urban ecosystems, which can positively affect the conservation of biodiversity in general

Experimental and numerical study on a SI engine fueled with gasohol and dissociated methanol gas blends at lean conditions

Hydrogen-rich dissociated methanol gas (DMG) and ethanol are both promising alternative fuels for engines. The study investigates the performance of a spark ignition engine using various gasohol-DMG blends under lean conditions, aiming to evaluate the influence of fuel composition, excess air ratio, and operational parameters including engine load and speed. The results demonstrate that the introduction of DMG substantially enhances the engine's fuel economy, combustion efficiency, combustion stability, and the HC and CO emissions. The addition of ethanol has a distinct impact on engine performance, including increased peak cylinder pressure at lower DMG ratios and a subsequent decrease at higher DMG ratios. It also leads to substantial reductions in HC and NOx emissions but shows a non-linear effect on CO emissions with an increasing ethanol blending ratio. An increase in excess air ratio results in simultaneous reductions in peak cylinder pressure, HC, CO, and NOx emissions. Moreover, variations in engine load and speed respectively impact the cylinder's thermal environment and gas flow, consequently influencing combustion and emission characteristics.

CFD Investigation of Methane Combustion with Excess Air in Can-Type Gas Turbine Combustor

This paper presents an investigation on the effect of excess air to combustion characteristics in a full-scale, gas turbine combustor, commonly used in power plant. The investigation was carried out using Computational Fluid Dynamics (CFD), and prior validation was made with the actual operation data of a power station, as well as the adiabatic flame temperature of methane. The mass fraction of CO<sub>2</sub>, O<sub>2</sub> and NO<sub>x</sub> emissions for blended methane with different percentages of excess air explosions was also investigated. The stoichiometric excess air varies from 0% to 30% with air-fuel mixture of 2.7 kg/s. The geometric model of the combustor is extracted from actual gas turbine combustor using 3D scanner and converted into CAD model for simulation. The Navier-Stokes equations were solved using commercial CFD code, ANSYS Fluent, with RNG k-ε chosen to close the turbulence. For reacting species, the species transport model is assumed. Results showed that the addition of excess air during combustor has little effect on the velocity and temperature distribution, both at the combustor interior, as well as at the exit. For the emission of CO<sub>2</sub> and O<sub>2</sub>, though there was no clear trend on the relations between the emission of these species and the excess air, the impact was quite significant. The production of NO<sub>x</sub> was also found to be independent on the excess air ratio, but instead, was a strong function of combustion and exhaust gas temperature.

Experimental study of spatial distribution of knock events in a turbocharged spark-ignition engine

An experimental investigation on the spatial distribution of knock events in a turbocharged spark-ignition engine for hybrid vehicle applications was conducted by using a multichannel fiber optic method. The knock positions were detected under different conditions to investigate the influence of crucial engine design and operating parameters on the knock characteristics including the spatial distribution in the combustion chamber and its relationship to knock intensity. The measured data reveal that the spatial distribution in the engine with a port fuel injection (PFI) system is mainly located on the exhaust side with insignificant influence of engine speed and load, which is attributed to the elevated thermal load around the exhaust valves. However, the knock events under gasoline direct-injection (DI) conditions were found to occur in more scattered locations with more occurring on the engine front-end and rear-end sides. These results indicate that the in-cylinder fuel-air mixing process may have a significant impact on the knock occurrence spots under DI conditions. The knock positions of the engine with different excessive air ratios, injection timings, and intake-valve timings were also detected, indicating that engine operating parameters have complex influences on the knock-region distribution in a DI engine. In addition, experiments were also carried out in two different cylinders to verify the cylinder-to-cylinder variations in knock regions which may be caused by the engine cooling design. Furthermore, no apparent correlations were observed between the knock position and the knock intensity by analysis of the experimental data.

Integrated Gasification of Biomass Residues (IBGCC)

A comprehensive outline of a new approach in integrated gasification of biomass residues including the material flow management in urban areas being targeted on the generation of electricity and district heating is presented. The feedstock is derived from civilian material by fully automated collection, sorting and separation. Thereby an outward transfer of inerts is executed, such as minerals, metals, glass and electronic scrap as well as sorted plastics being object to recycling. Finally a ligno cellulosic and a non-lignocellulosic fraction are gained. The for mer one is suitable for thermochemical conversion, the latter one for biological conversion into fuel gases which subsequently are oxidised completely at low air excess in a horizontally arranged cyclone combustion chamber. The heat recovered from the flue gases in the utility boiler is used to generate steam scooping in the supply of electricity and district heating. The basic design is scaled to an overall thermal capacity of 2-5 MW. This type is most capable of utilising renewable energy by converting the organic fractions of civilian material flows. The power plant is based on a reliable technology representing an on-site integrated biomass gasification combined cycle system including peripheral units specified for the treatment of complementary materials.

Study on Combustion Characteristics of Low Concentration Coalbed Methane Induced by Hydrogen Jet based on Excess Air Ratio

Low concentration coal bed gas used for power generation is a better treatment scheme at present, which solves the problem of environmental pollution caused by the direct emptying of coal bed gas. Coal bed methane is a methyl alkyl fuel, and slow combustion rate will cause abnormal combustion phenomena such as large combustion cycle changes. The initial ambient gas concentration has a great influence on the development and propagation of the flame. In this paper, a constant volume bomb model is established to change the excess air coefficient of methane air premix in the initial constant volume bomb, and the change law of combustion heat release is analyzed. The results show that when hydrogen participates in the combustion stage, the combustion rate increases with the increase of excess air coefficient. When hydrogen is burned out, the combustion rate decreases with the increase of excess air coefficient.