Excess Air Factor Research Articles

Numerical Study of the Combustion Process in the Vertical Heating Flue of Air Staging Coke Oven

To investigate the combustion process and reduce Nitric Oxide (NO) emissions in the vertical heating flue of air-staged coke ovens, a three-dimensional computational fluid dynamics method was applied to simulate the combustion process. The model integrates the k-ε turbulence model with a multi-component transport combustion model. The impact of air staging on the flow field and NO emissions in the vertical fire chamber was assessed through comparative validation with experimental data. The impact of air staging on the flow field and NO emissions in the vertical fire chamber was assessed through comparative validation with experimental data. Based on this research, the effects of the excess air coefficient and air inlet distribution ratio on NO emission levels at the flue gas outlet were further investigated. Analysis of the flow field structure, temperature at the center cross-section, component concentration, and NO emission levels indicates that as the excess air coefficient increases, the NO emission levels at the flue gas outlet initially decrease and then increase, accompanied by corresponding changes in outlet temperature. At an air excess factor of 1.3 and an air inlet distribution ratio of 7:3, NO emission levels are at their lowest—53% lower than those in a conventional coke oven—and the temperature distribution in the riser channel is more uniform. These results provide a theoretical foundation for designing the air-staged coke oven standing fire channel structure.

Numerical Simulation Study of Combustion under Different Excess Air Factors in a Flow Pulverized Coal Burner

The basic national condition that is dominated by coal will not alter in the foreseeable future. Coal-fired boiler is the main equipment for coal utilization, and cyclone burner is a practical type of burner. There is a cyclone formation, a primary air duct inside the center air duct, and a secondary air duct. Introducing a small stream of pulverized coal gas or oil mist stream or gas directly into the reflux zone in the center duct ignites first a stable combustion and a small fluctuation of ignition pressure. In this paper, the variation of furnace temperature for cyclone pulverized coal burner corresponding to different excess air factors and the composition of gases such as O2, CO, CO2, and NOX produced by combustion were investigated using fluent software. A single cyclone pulverized coal burner from an actual coal-fired boiler is used, and a combustion zone applicable to the study of a single pulverized coal burner is established to study the actual operation of a single pulverized coal burner at different excess air coefficients. The findings indicate that the ignition position of pulverized coal combustion advances with decreasing α (Excess Air Factors); however, the length of the produced high-temperature flame gets shorter. As the value of α decreases, the burnout in the furnace decreases and the CO emission concentration increases, with a maximum CO mole fraction of 0.38% at α = 1.2 and a maximum CO mole fraction of 3.13% at the axial position when α decreases to 0.8. The furnace’s concentration of NOX, the NOX emission level decreases significantly with decreasing α. The NOX mole mass increases gradually with increasing α, and in the bottom portion of the primary combustion zone, more NOX is produced. The concentration of NOX in the chamber changes significantly after α exceeds 1.0, and the NOX at the outlet surges from 417.25 ppm to 801.07 ppm, which is attributed to the increase in the average temperature of the chamber, which promotes the generation of thermophilic NOX. The distribution pattern of O2 mole fraction along the furnace height cross-section at different excess air factors is basically the same, with a maximum at the burner inlet and a gradual decrease in the O2 content as it enters the combustion chamber to react with the pulverized coal in a combustion reaction. The value of α = 0.8 when the air supply is obviously insufficient, the fuel cannot be fully combusted, and only a small amount of CO2 is produced.

Retrofitting Natural Gas–Fired Boiler for Hydrogen Combustion: Operational Performance and NOx Emissions

Abstract The effects of hydrogen fraction (HF: volumetric fraction of H2 in the fuel mixture of CH4 + H2) from 0% to 100% by volume, on the thermal and environmental performance of a 207-MW industrial water tube boiler, are investigated numerically at a fixed excess air factor, λ = 1.15. This study aims to determine the hardware modifications required for boilers to be retrofitted for pure hydrogen operation and investigates how NOx emissions are affected by hydrogen enrichment. The results showed insignificant increases in maximum combustion temperature with increasing the HF, though the distributions of temperature profiles are distinct. In reference to the basic methane combustion, H2 flames resulted in a positive temperature rise in the vicinity of the burner. Increasing the HF from 0% to 2% resulted in higher average thermal NOx emissions at the boiler exit section from 37 up to 1284 ppm, then it decreased to 1136 ppm at HF = 30%, and later it leveled up to 1474 ppm at HF = 100%. The spots for higher differences in NO formation compared to the reference case are shifted downstream at higher HFs. The effect of hydrogen enrichment on CO2 and H2O as radiation sources, as well as the volumetric absorption radiation of the furnace wall and the heat flux at furnace surfaces, has all been presented in relation to the effect of hydrogen addition on boiler performance.

Numerical simulation of ammonia combustion with coal in a 135 MW tangentially fired boiler

This study conducted a simulation of coal and ammonia co-combustion in a 135 MW tangentially fired utility boiler using Fluent. The combustion process was modeled using a gas-phase non-premixed approach based on finite-rate/turbulent dissipation. Additionally, NO generation and conversion were simulated through multi-step chemical reactions. Upon verifying the accuracy of the proposed model, the effects of ammonia co-firing ratios and injection modes on boiler combustion characteristics and NO emissions were investigated. The results indicate that as the co-combustion ratio increases, the boiler temperature decreases. Concurrently, NO emissions from the furnace exhibit a trend of initial decrease followed by an increase, reaching a minimum of 136.21 ppm at a mixing ratio of 15 %. With a co-firing ratio of 30 %, a significant reduction in NO emissions can be achieved by decreasing the proportion of primary and secondary air. As the excess air factor of ammonia decreases from 0.3 to 0.1, NO emissions initially decrease, followed by a subsequent increase. Overall, optimizing the ammonia injection mode and air distribution ratio can reduce NO emissions to below 220 ppm when the ammonia co-combustion ratio is below 30 %. This study serves as a valuable reference for retrofitting utility boilers for coal-ammonia co-combustion.

Comparative Analysis of Exhaust Emission of Retrofitted SI Engine Runs by Different Fuels

The purpose of this study was to experimentally inspect the pollutant emission of a retrofitted SI engine using octane, compressed natural gas, and liquefied petroleum gas fuels operated at different speeds. The study was conducted using a retrofitted SI engine. The engine was coupled with an exhaust gas analyzer to measure the composition of the exhaust emission gas. The results showed that the carbon dioxide (CO2) and carbon monoxide (CO) content is lower when CNG is used compared to octane. The CO2 emission was even lower for LPG than CNG, as LPG has a lower carbon-energy ratio and higher octane quality than LPG and burns faster as a lean mixture. The O2 emission supports that octane and CNG burn as a lean mixture whereas LPG burns as rich. Again, the HC emissions are more prominent and CO emissions are higher for LPG than CNG. Because, it showed incomplete combustion with LPG as fuel due to inappropriate air-fuel mixture in the gas-air mixing chamber, which was specifically designed for CNG. Nitrogen oxide (NOx) emission was minimal when the engine was operated with LPG due to incomplete combustion, and it was found maximum for octane, where medium NOx content was found in the case of CNG. Moreover, the relative air fuel ratio or excess air factor, λ increased as the engine operating speed was raised. Because at high speed, there is some turbulence effect and increased combustion duration.

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.

Air Jet Assisted Combustion of Oil Diffusion Flames: Effects of Injection Location and Excess Air Factor

Air Jet Assisted Combustion of Oil Diffusion Flames: Effects of Injection Location and Excess Air Factor

Modelling the Mechanism of Sulphur Evolution in the Coal Combustion Process: The Effect of Sulphur–Nitrogen Interactions and Excess Air Coefficients

The efficient use of coal resources and the safe operation of coal-fired boilers are hindered by high-temperature corrosion caused by corrosive sulphur components. To predict the impact of sulphur–nitrogen interactions on sulphur’s evolution and its mechanism of action, a conventional sulphur component evolution model (uS–N) and an improved sulphur component evolution model (S–N) that considers sulphur–nitrogen interactions were proposed in the present study. The models were built using OpenFOAM–v8 software for the coal combustion process, and the generation of SO2, H2S, COS, and CS2 was simulated and analysed under different air excess coefficients. The simulations were conducted to analyse the patterns of SO2, H2S, COS, and CS2 generation at different air excess factors. The results show that, compared with the uS–N condition, the simulated values of coal combustion products (SO2, H2S, COS, and CS2) under the S–N condition were closer to the experimental values, and the errors of different sulphur components at the furnace exit were all less than 5%. As such, the S–N model can more accurately predict the evolution of sulphur components. In the simulation range, when the air excess factor increased from 0.7 to 0.9, the production rate of SO2 increased, while the production rates of corrosive sulphur components H2S, COS, and CS2 decreased significantly by 41.3%, 34.8%, and 53.8%, respectively. Further, the mechanism of the effect of sulphur–nitrogen interactions on the generation rates of different components was revealed at different air excess coefficients. Here, the effect of sulphur–nitrogen interactions on SO2 and COS was found to be more significant at smaller air excess coefficients, and the effect of sulphur–nitrogen interactions on H2S and CS2 was more significant at larger air excess coefficients. The present study can provide a theoretical basis for predicting the evolution of sulphur components during coal combustion and improving the high-temperature corrosion problems caused by such a process.

Experimental study of the effect of variable valve timing on hydrogen-enriched ammonia engine

To reduce carbon emissions and increase the efficiency of internal combustion engines (ICEs), it is necessary to use renewable alternative fuels and to use Miller cycle technology. Ammonia is an energy storage medium as well as a hydrogen storage medium. In this experiment, a Miller cycle ICE using ammonia-hydrogen fuel was investigated at 1500 rpm and 60% throttle opening. The excess air factor of 1 and the ammonia volume share of 70% were maintained during the experiment. The objective of the experiment was to vary the intake valve timing and investigate its effect on engine performance. The results show that when the intake valve timing is advanced and the valve overlap angle is kept larger, the combustion stability deteriorates, the flame development period (CA0-10) is prolonged, the cycle variation increases, COVpmax will exceed 25%, and the brake thermal efficiency (BTE) quickly dropped from 32.8% to 30%. When the intake valve timing is retarded by 25°CA, IMEP and BMEP can be increased by 8% and 16% compared with the minimum values. Generally speaking, the Miller cycle hydrogen-enriched ammonia engine is not suitable for the early opening strategy of the intake valve.

Waste tires pyrolysis oil and its blend with diesel fuel spectral flame analysis, temperature contours, and emissions

The purpose of this research paper is to investigate the energy valorization from the pyrolysis of waste tires using coaxial continuous flame burners. For such an investigation, both the Tire Pyrolysis Oil (TPO) along with its blend (B1) with light diesel oil (LDO) were prepared, physically and chemically characterized, and then combusted in coaxial burners. To distinguish the spectral emission peaks, for the vaporization and combustion zone and the hot recirculation zone of the produced flame, flame spectroscopy techniques were utilized. The mass-specific emission indices and the axial inflame temperatures were used as indicators of the flame radiation intensity in the flame zones. The coaxial flame was inspected for excess air factors of 1.33, 1.04, and 0.9. In the study, a higher radiation intensity of TPO/LDO blend flame was recognized in the B1 flame length which was taller than that of LDO by 48% at λ=1.33. Furthermore, a decrease in CO emissions levels was also noticed in the combustion of waste tire pyrolysis oil and B1 by an average of 4%–12% compared to that from HDO, and the NOx emissions were also reduced by 8.5%–26%. The highest axial inflame temperature of 1,205 °C was recorded for TPO at condition λ=0.9, where the presence of oxygen molecules in fuel helps flame improvements.

Reducing Emissions from Combustion of Grape Residues in Mixtures with Herbaceous Biomass.

The use of grape residues as a renewable energy source for combustion presents various problems. One of these is the excessive production of carbon monoxide and nitrogen oxides. Analyses and combustion tests were performed on white and red grape pomace as well as grape stems. To verify the possibility of a reduction in emissions, straw of Miscanthus sinensis was added to mixtures with red grape pomace. Emission concentrations of carbon monoxide and nitrogen oxides were determined on a grate combustion device with a nominal thermal output of 8 kW under steady-state conditions. In addition to these emission concentrations, the excess air factor and the flue gas temperature were monitored. The results show a high energy content in grape residues. In red grape pomace, the gross calorific value of dry matter reached 22.17 MJ kg−1. Unfavourable properties included high ash and nitrogen contents. During combustion tests on all types of grape residue, the emission concentrations of carbon monoxide were above the legal limit for the combustion of solid fuels. The addition of Miscanthus straw improved the behaviour during combustion. The maximum content of grape pomace in the mixture capable of meeting legislative emission requirements was 50% wt.

Optimizing a spark-ignition engine fuelled with methane using a two-zone combustion model

Methane which can be produced from biogas has a great potential to be used as an alternative renewable fuel for spark-ignition engines. However, engines need to be optimized for methane use. The aim of this study was to numerically optimize a spark-ignition engine fueled with methane and operated at a constant speed of 1,500 rpm via using a validated two-zone combustion model. The model was able to predict engine performance parameters, NO emission, and engine knock at different engine operating conditions including inlet pressure, compression ratio, and excess air factor. Engine knock was prevented by increasing the excess air factor up to 1.2 when the engine operated with higher inlet pressure and compression ratio. It was found that a maximum inlet pressure of only 120 kPa could be used with an engine compression ratio of 14 and excess air factor of 1.2 for knock free operation. The peak engine power was produced when the engine operated with an inlet pressure of 200 kPa and compression ratio of 8 or 9. It was also found that the optimum operating condition which resulted in high engine power accompanied with low fuel consumption and high efficiency was obtained when the engine operated with an inlet pressure of 180 kPa and a compression ratio of 11. This condition required the engine to operate with an excess air factor of 1.19 to prevent engine knock. However, operating the engine at this optimum condition would be accompanied with high NO emission.

Exploration of the ion current method universality and online combustion monitoring

To verify the universality of the ion current method, a new structure of ion current probe was employed and improved with the cavity structure of the constant volume combustion bomb to diagnose CH4/air premixed laminar combustion. The experiments were conducted in a constant volume combustion bomb at 0.1 MPa with excess air factors ranging from 0.9 to 1.45, and six sets of probes were used to obtain ion current signals simultaneously. Results show that the signals collected by the ion current probes installed at different locations exhibited high consistency. And the ion current signal can be used to monitor the combustion process online. Moreover, it provides a more timely and significant characterization of parameters, such as ignition moment and flame propagation phase, than pressure signal. It can be a new idea for real-time acquisition of flame propagation velocity.

Disposal of Wastewater from Mazout-Fired Boiler Plants by Burning Water–Mazout Emulsions

Liquid fuel can be an alternative to solid fuel in non-gasified locations. The mazout for municipal-energy boiler plants is much cheaper than fuel oil. However, this relates to the problem of wastewater disposal from such a boiler plant. A proprietary system for the disposal of bottom water and other sewage-containing mazout has been developed. The solution depends on the proper preparation and burning of a water–mazout emulsion (WME). The emulsion is prepared in a specially designed and developed dosing ejector. By burning the emulsion using the developed system, an efficiency increase of 2–3% was achieved for boilers operating on the mazout fuel. Such a result was achieved due to a reduction in the excess air factor. Moreover, emissions of nitrogen oxides and carbon monoxide were reduced by 30–35% and 70–80%, respectively. In addition due to cleaning the heat-exchange surfaces obtained when working on the WME, the amount of time for productive and more efficient use of the equipment has increased.

Novel method for flue gas flow of gas turbines in offshore oil production facilities

The flue gas flow in gas turbines is an important parameter for determining the accurate capacity of waste heat boilers for recovering the waste heat released by the flue gas of gas turbines in offshore oil production facilities. The theory of flue gas composition ratio pertaining to boiler combustion is applied to calculate the flue gas flow in gas turbines. The given gas fuel composition, fuel characteristic coefficient and tested dry combustion products of gas fuel are used to calculate the excess air factor α using the theory of flue gas composition ratio; thus, the flue gas flow of gas turbines can be obtained. The results show that the value of α of a gas turbine ranges from 7 to 3 with different loads and is significantly greater than the α value of boilers, which is obtained during the burning of gas fuel; moreover, the calculation mode of O d 2 while considering β coincides more with the actual operation data of gas turbines. This mode is useful for the engineering application of recovering the waste heat released by the flue gas of gas turbines and provides an important guidance to improve the waste heat recovery process in gas turbines.

A comparative study of calculated and experimental indicated diagrams of a S.I. Engine

The functioning of the engine in a closed loop with lambda sensor and catalyzer makes the excess air factor to be maintained as close as possible to the value 1=1. Based on an own model, the authors realized an analytical calculation of the indicated diagram. The indicated diagram was also raised on an experimental stand in p-V coordinates, and the real indicated diagram in p-a coordinates. The equations for the thermal processes that take place in the engine have been determined and, after that, these were introduced in a computer. Using these equations, the state parameters in the characteristic points of the engine cycle were calculated.

The staged combustion of hydrogen-gasoline fuels in Divided Chamber Combustor.(Dept.M)

An experimental program to research, develop and demonstrate an axially two staged combustor with premixed gasoline/all and hydrogen/air mixtures is described. Radial and axially profiles for species concentrations and gaseous temperatures are obtained for a wide range air-fuel ratios and degree of charge stratification. Two design parameters were varies namely, the connecting orifice diameter and the burner diameter. Three different orifice diameters are used, those are 20, 25 and 30 mm, and two different burner diameters are used, 5 and 6 mm. The results obtained showed that at higher values of excess air factor in the main chamber, Co does not consumed completely before the exit from the combustor. At higher values of excess air factors in the pre- and pain chambers, the combustion efficiency was ensured within the combustor length. Decreasing the connecting orifice diameter improves the turbulent and decreasing the flame length. A stratified charge combustion has been studies for leaner combustion to improve emissions and fuel economy. The carbon monoxide is decreased while the combustion efficiency is increased with increasing the degree of charge stratification. The same benefits are obtained when increasing the amount of hydrogen fuel in the mixtures.

Modeling Combustion of Straw-Bitumen-Pellets in a Fluidized Bed.(Dept.M)

Recently straw-bitumen-pellets have been proposed as an alternative fuel. This work presents a mathematical model for steady state combustion of straw-bitumen-pellets in a bubbling fluidized bed. The combustor is divided into three zones; dense bed, splashing zone and freeboard. Important processes including volatile segregation, char comminution and elutriation, bed particles ejection; and post-combustion in splashing zone and freeboard have been considered and simplified. Submodels for hydrodynamic, volatile release and combustion, and char consumption have been implemented. Energy balance for splashing zone and freeboard has been set to predict axial temperature profile. Model results demonstrate that about 53% of volatiles combustion and about 62% of the total heat release take place within the bed. The fraction of heat released in the splashing zone is about 33% whereas the remainder portion (7%) releases in freeboard beyond the splashing zone. The ejected sand particles; however, recover back to the bed about 83% of heat released in the two latter zones. The model yields the axial profiles of different species concentrations in the two bed phases (bubble and emulsion), in the splashing zone and in the freeboard. Moreover, the model predicts the axial temperature profile in the splashing and the freeboard zones that characterizes by two maxima. A small peak is built in the splashing zone with a small overheating as the ejected sand particles recover the great part of released heat. Another maximum arises in the freeboard where the flux of the ejected particles turns out to be very few and its impact on gas temperature becomes insignificant. The second maximum has relatively much higher overheating temperature. The influences of operating variables on the combustion performance have been evaluated as well. In particular, the maximum overheating in freeboard gets higher with decreasing excess air factor, with lowering bed temperature and with increasing fluidization velocity. Bed temperature among the others has the highest impact on combustion performance. An acceptable agreement are found between the predicted and the measured concentrations and temperature profiles.

Investigation upon the operational factors influencing the smoke emissions from diesel engine

The results of laboratory examinations of the ecological characteristics of diesel internal-combustion engine are represented in this article. The powerful, economical and ecological parameters of a diesel engine investigated in this article are presented by the speed characteristics of effective torque, injected fuel per cycle, and fuel and air consumption per hour, temperature, and smoke emissions of exhaust gases. On the basis of the experimental dependences a mathematical model is designed. Parameters influencing significantly the smoke emissions of exhaust gases are investigated. The factors, injected fuel per cycle and excess-air factor, are examined at different operation regimes of the engine.

Analysis of Gas Recirculation Influencing Factors of a Double Reheat 1000 MW Unit with the Reheat Steam Temperature under Control

In this paper, the simulation software EBSILON is used to simulate the reheat units, and the reheat temperature control mode is deeply explored. In the benchmark system, the influence of different load intermediate point temperature on the flue gas recirculation (FGR) is analyzed. Then, the effects of load, coal quality, excess air factor, and feed water temperature on FGR are studied under the premise of intermediate point temperature as design value, and the cause for FGR change is analyzed by comparing the cutoff bypass flue (CBF) system. The results show that under any load, the FGR decreases with the increase of the intermediate point temperature, while under low load, the change of the intermediate point temperature has a greater impact on the FGR rate. When the intermediate point temperature remains constant, the FGR plunge has an increase of load at low load and is almost unchanged at high load; the FGR rate of coal with low calorific value and high moisture content is low and the coal with low volatile and high ash content has great influence on reheat steam temperature; and the excess air factor and feed water temperature are inversely proportional to the flue gas recirculation rate. In the CBF system, the change trend is similar to the reference system, but under the same working condition, the FGR rate is higher than the latter.