Adiabatic Combustion Temperature Research Articles

Air humidity influence on combustion of R-1234yf (CF3CFCH2), R-1234ze(E) (trans-CF3CHCHF) and R-134a (CH2FCF3) refrigerants

The influence of air humidity on flame propagation in mixtures of hydrofluorocarbons (HFCs) with air was studied through numerical simulations and comparison with measurements from the literature. Water vapor added to the air in mixtures of fluorine rich hydrofluorocarbons (F/H ≥ 1) can be considered as a fuel additive that increases the production of radicals (H, O, OH) and increases the overall reaction rate. The hydrofluorocarbon flame is typically a two-stage reaction proceeding with a relatively fast reaction in the first stage transitioning to a very slow reaction in the second stage which leads to the combustion equilibrium products. The transition to the second stage is determined by the consumption of hydrogen-containing species and formation of HF. Despite a relatively small effect of water on the adiabatic combustion temperature, its influence is significant on the reaction rate and on the temperature increase in the first stage of the combustion leading to the increase in burning velocity. The main reaction for converting H2O to hydrogen-containing radicals and promoting combustion is H2O + F = HF + OH, as demonstrated by reaction path analyses for the fluorine rich hydrofluorocarbons R-1234yf, R-1234ze(E), and R-134a (F/H = 2). The calculated burning velocity dependence on the equivalence ratio ϕ agrees reasonably well with available experimental measurements for R1234yf and R-1234ze(E) with and without the addition of water vapor. In agreement with experimental data, with water vapor, the maximum of burning velocity over ϕ is shifted to the lean mixtures (near ϕ = 0.8).

Equilibrium Composition of Products in a Hafnium Dioxide–Calcium–Nitrogen–Carbon Mixture at Adiabatic Combustion Temperature

Equilibrium Composition of Products in a Hafnium Dioxide–Calcium–Nitrogen–Carbon Mixture at Adiabatic Combustion Temperature

Термодинамическое моделирование высокоэнергетических термитных систем на основе йодата кальция

The article presents the results of a thermodynamic study of the component content influence and their physical and chemical properties on the regulation of the main energy characteristics and combustion product characteristics of thermite systems based on calcium iodate containing Al, B and Ti. The adiabatic combustion temperature, enthalpy of combustion products, specific impulse, exhaust velocity of combustion products, mass fraction of condensed phases, content of gaseous and condensed combustion products are determined. The influence of the metal oxide/metal fuel content in the thermite system composition on the main energy characteristics was assessed. Based on a comparison of the calculation results of the thermite systems thermodynamic and thermophysical characteristics, it seems possible to divide the studied thermite systems into 3 functional groups according to their application. Taking into account the ratio of components, these can be: 1) thermite systems for welding processes and 2) thermite systems for perforating, cutting metal structures (CaI2O6/Al and CaI2O6/Ti); 3) thermite systems as a component of energy compositions capable to inactivate harmful aerosol spores and bacteria (CaI2O6/B), since due to the low combustion temperature of CaI2O6/B, a longer burning time of such systems leads to a gradual release of iodine.

PROSPECTS OF USING ALTERNATIVE FUELS FOR HEATING OF REGENERATIVE AIR HEATERS FOR BLASТ FURNACES

Landfill gas as one of the promising artificial gaseous fuels is analyzed for use in heating system of regenerative air heaters for blast furnaces. Increasing the temperature of blast is one of the most effective ways for metallurgical coke saving and increase the productivity of blast furnaces. To increase this temperature, a mixture of blast-furnace and coke oven gases is used as fuel for regenerative heat exchangers. Considering the current shortage of coke oven gas, landfill gas, the main combustible element of which is methane, is proposed as a high-calorie additive to the main fuel. Calculations were made for the combustion of a mixture of gaseous fuels in three combinations: blast-furnace gas, blast-furnace and coke gases mixture, blast-furnace and landfill gases mixture. The possibility of increasing the temperature of the hot blast to 1250 °C for the air supply system of a blast furnace with a volume of 1033 m³ was considered. Calculations showed that in order to achieve such a temperature, the adiabatic combustion temperature should be 1423 °C, and the flue gas temperature in the crown should be 1300 °C. Such temperatures cannot be reached using only blast-furnace gas, so two possible options were considered. The first option is the use of a coke and blast furnace gases mixture with a coke gas content of 6.3 % and combustion air heating to 180 °C by exhaust gases from blast furnace air heaters. The second option is combustion of a mixture of blast-furnace and landfill gas with combustion air heating to 180 °C (the content of landfill gas is 7.6 %). The flow rate of the fuel mixture for the second option is 68,523 m³ /h, and the required amount of landfill gas is 5208 m³ /h. The volumes of gas output from landfills in large cities are reported to be 5–10 MCM a year, which is less than the amount of biogas required to heat an air heater. Therefore, to achieve the required temperature it makes sense to consider a tree gas mixture that is blast-furnace, coke and landfill gases an appropriate proportions. The use of landfill gas contributes to the solution of an important environmental problem of land and atmosphere pollution during the accumulation of municipal solid waste.

DFT-assisting discovery and characterization of a hexagonal MAB-phase V3PB4

A 314-type MAB phase V3PB4 with hexagonal crystal structure is synthesized by self-propagating high temperature combustion synthesis (SHS), with the help of the full first-principles predictions for the phase stability and adiabatic combustion temperature of SHS. Using XRD and TEM, V3PB4 crystallizes in the space group of P6¯m2, with the lattice parameters a = 3.030 Å and c = 9.148 Å, of much interest, well with the predicted one. Furthermore, the electronic structure, chemical bonding, and elastic properties of hex-V3PB4 are predicted by first-principles. No bandgap around Fermi energy indicates its electronic conductor. And the strong covalent bonding is present between the B and V atoms with, significantly, much weaker V-P bond. With the help of the theoretical model of bond stiffness, the significantly high ratio of bond stiffness of weakest bonds to the strongest ones (0.873) of hex-V3PB4 indicates its poor damage tolerance and fracture toughness. The high bond stiffness results in its high moduli in comparison with other MAB phases. As the number of inserted P atoms increases, the engineering elastic modulus decrease, without the price of an increase in density.

Process design and thermal-calculation of a novel entrained-flow gasifier using fine ash as feedstock

Fine ash from gasification is produced in huge quantities, and has the carbon content of around 20–––40%. The treatment of fine ash is urgently needed to be resolved. However, large-scale industrial utilization of fine ash has not yet been realized. The ash content of fine ash is 60––70%. The calorific value of fine ash is usually lower than that of coal. The adiabatic combustion temperature of fine ash gasifier is lower than that of pulverized coal gasifier, and the outlet temperature is also lower. This paper pointed out the reason why the outlet temperature of the entrained-flow gasifier was low when fine ash produced by Ende gasifier was used as the gasification feedstock. A novel process of using the entrained-flow gasifier to utilize the carbon in fine ash was proposed. Fine ash in raw syngas was captured by a bag dust collector, mixed with pulverized coal, and transported to the entrained-flow gasifier. The gasification parameters of the process were obtained. When fine ash was used alone as feedstock, it was difficult to reach the required temperature for the discharge of liquid slag. When fine ash and coal were co-gasified, the outlet temperatures were 1461 and 1529 ℃, which could meet the gasifier’s safe operational requirements for smooth discharge of liquid slag. The syngas concentrations were greatly affected by the carbon content of fine ash. The results of the current work provide a useful reference for industrial design and application of fine ash in atmospheric entrained-flow gasifier.

CLIMATE AND ENVIRONMENTAL BACKGROUNDS OF FUEL UTILIZATION, INFLUENCING UPON ALTERATION THE EUROPEAN AND UKRAINIAN TRENDS OF GAS SUPPLY P.1 PRESENT REQUIREMENTS TO SELECTION THE GAS FUELS. THERMODYNAMIC EVALUATION THE PRINCIPAL CHARACTERISTICS OF GAS FUEL

The work examines the starting points on the formation of fuel markets in Europe within the framework of the concept of sustainable development of the countries’ economics, taking into account the main limitations, primarily the climatic and environmental consequences of fuels combustion. This approach has led in the past years to simultaneous increase in absolute volumes’ consumption of mineral (organic, carbon-rich) fuel’s flow rate and to reduction of their shares in the overall fuel balance. The relevant changes had occurred because of simultaneous production and consumption the alternative fuels, including renewable gas and energy sources. New schemes, methods and ways of fuel supply have been analyzed, including maritime transportation of liquefied fuels (liquefied natural gas LNG, liquid hydrocarbons LPG, ammonia NH3) along with creation of a modern tanker fleet with floating and land-based regasification and gas storage (FSRU) systems; systems of interconnecting the pipelines for fuel supply, including hydrogen-enriched natural gas (HENG). According to the cultivated opinion, the global warming is considered as a consequence of the carbonization of environment due to emission of C-rich combustion products (CO2) into the atmosphere. The specified contribution of CO2 to atmospheric pollution is caused by the insufficient efficiency of fuel use, for example, in heating furnaces (up to 40 % of the total amount of fuel consumed in the industry is burned in furnaces). If the emissions value of a conventional natural gas combustion systems in furnaces meets the level of emissions up to 0.45 kg СО2/kW.h, then in the case of equipping the furnace with an efficient waste gas heat recovery system, the emissions are reducing to 0.2–0.25 kg СО2/kW.h, (Wunning J.). The determinant role of the efficiency of fuel use ηf has been correlated with the scale of atmospheric pollution with greenhouse gases (CO2) emission by means of thermodynamic analysis of energy efficiency. The efficiency of fuel utilization: by enthalpy ηH and by exergy ηeff — has been computed for the cases of burning the widespread fuels and the comparative analysis has been performed. The calculations of thermal energy characteristics of the fuels have been carried out by using the original author’s methodology based upon assumption of equilibrium thermodynamics for the cases of using the widespread gas fuels within the temperature range T from the standard T0 to the theoretical combustion temperature TT. In accordance with original author’s method the most important heat engineering characteristics of the fuels have been studied by means of approaches of equilibrium thermodynamics. Higher and lower combustion heat, higher and lower Wobbe numbers, theoretical (adiabatic) combustion temperature of the widespread fuels have been determined. An influence of hydrogen content in CH4/H2 gas fuel mixtures on the mentioned properties has been determined. From the list of firing engineering characteristics, the formation of the methane number MN for different organic and alternative fuels have been considered. The accumulated numerical values of MN for the widespread types of fuels have been stated and compared. Bibl. 38, Fig. 4, Tab. 1.

OPERATION FEATURES OF ENVIRONMENTALLY EFFICIENT BOILER PLANTS OF MUNICIPAL THERMAL POWER ENGINEERING

The work is devoted to research on the improvement of thermal energy production technologies in gas-consuming heating boiler installations while improving their environmental performance and increasing the operation reliability. The work purpose is to study the heat and humidity modes of the air-supply ducts of boiler plants with exhaust gases recirculation systems into the blown air. The main objectives of the study are: to determine the thermal parameters of a heating boiler with a 2 MW heating capacity with a exhaust gases recirculation system mixed with blown air into its furnace space under conditions of using heat recovery technologies and without them; determination and analysis the heat and humidity parameters of this mixture in different operating modes of boiler plants. Known thermal calculation methods of boiler plants and data from our own experimental studies of heat transfer during deep cooling of boiler plant exhaust gases were used. The thermal calculation results of the heating boiler with a system for exhaust gas recirculation into its furnace space mixed with blown air are presented. The regularities of changes in the adiabatic combustion temperature and heat-humidity characteristics of the above mixture depending on the boiler heat load in different its operation modes during the heating period and the share of flue gas recirculation from 10 to 20 % were established. The research results show that the introduction of recirculation gases leads to a decrease by 150 – 250 °С of the adiabatic combustion temperature tad due to the need to consume fuel heat for heating the introduced ballast and the greater of the recirculation share s the lower the level of the indicated temperature. The research results also showed that gas recirculation causes insignificant (in the range of 0.5 – 4.7 °С) changes in the temperature of the boiler exhaust gases. Based on the data obtained, the change regularities in the heat-humidity characteristics (temperature and dew point) of the mixture of recirculated gases and air in different boiler operating modes during the heating period and under the studied recirculation shares were established. It is shown that recirculation causes condensate formation on the surfaces of air ducts in all operating modes of boiler and in some modes their icing is possible. To prevent these negative phenomena, it is necessary to apply measures to increase the temperature of the gas-air mixture by a value not less than Δtsum = 15 – 35 °С.

Effect of Mg-Al ratio on the combustion and infrared radiation properties of Al-Mg alloy/PTFE composition

The effects of Al-Mg alloys with different Mg/Al ratios on the burning rate, combustion products, radiation intensity and specific radiation energy of Al-Mg/PTFE infrared composition were investigated in this paper. The results show that the burning rate of Al-Mg/PTFE decrease with the increase of Al content in Al-Mg alloy. The results of theoretical calculations show that as the Al content increases, the adiabatic combustion temperature first decreases and then increases, taking the minimum value when the content of Al is approximately 58%. In addition, as the Al content of the alloy increases, the particle size of the reaction products gradually become larger, in which the unreacted Al and Al4C3 content increase, while the yield of C and MgF2 become less. The infrared radiation intensity also decreases with the decrease of burning rate. The specific radiant energy of Al-Mg/PTFE reaches the maximum value at 8-14 μm when the ratio of Mg/Al is 30/70 under the combined effect of burning rate and combustion temperature.

Tungsten and Copper (II) Oxide Mixtures as Gasless Time Delay Compositions for Mining Detonators.

The widespread use of pyrotechnic compositions in time delay detonators is the reason for research aimed at expanding knowledge of the combustion properties of new pyrotechnic mixtures, whose components react with each other in the solid or liquid state. Such a method of combustion would make the rate of combustion independent of the pressure inside the detonator. This paper presents the effect of the parameters of W/CuO mixtures on their properties of combustion. As this composition has not been the subject of previous research and is not described in the literature, the basic parameters, such as the burning rate and the heat of combustion, were determined. In order to determine the reaction mechanism, a thermal analysis was performed, and the combustion products were determined using the XRD technique. Depending on the quantitative composition and density of the mixture, the burning rates were between 4.1-6.0 mm/s and the heat of combustion in the range of 475-835 J/g was measured. The gas-free combustion mode of the chosen mixture was proved using DTA and XRD. Determination of the qualitative composition of the combustion products and the heat of combustion allowed estimation of the adiabatic combustion temperature.

A New Approach to Prepare LuFeMgO4

A new method for the production of LuFeMgO4 based on the combustion reaction of a gel-like precursor prepared from metal nitrates and fossil fuels has been proposed. The possibility to prepare this oxide from stoichiometric compositions of metal nitrates with polyvinyl alcohol (PVA) and glycine has been studied. The adiabatic combustion temperatures Tad have been estimated for the systems under consideration. The combustion products of PVA-nitrate and glycine-nitrate compositions before and after their heat treatment have been studied using X-ray diffraction analysis and IR spectroscopy. It has been established that the combustion reaction products of the PVA-nitrate composition are an X-ray amorphous powder, while those of the glycine-nitrate composition are a mixture of nanocrystalline oxides containing 52.5 wt % LuFeMgO4. According to X-ray diffraction and SEM data, 4-h annealing of this mixture at 1300°C leads to the formation of a single-phase LuFeMgO4 powder with a layered microstructure and a grain size of about 1–2 μm.

Gravity Effects on the Minimum Explosive Concentrations in 1-D Dust Explosion

ABSTRACT Theoretical predictions of dust-explosion characteristics, such as the minimum explosive concentration (MEC), can help improve the accuracy of quantitative risk assessment. This paper presents a continuum model to simulate one-dimensional dust-cloud combustion. It is found that the dilution of dust by thermal expansion reduces the propagation speed of a combustion wave through a dust cloud. At the same time, the delay in the increase of particle velocity due to relaxation time counteracts the dilution effect. Therefore, neglecting the relaxation time results in the underestimation of propagation speed. In the absence of heat loss, extinction occurs when the adiabatic combustion temperature decreases to the ignition temperature; MEC is independent of particle size in such cases. With the presence of heat loss, on the other hand, extinction occurs at a higher dust concentration; MEC increases with particle size. Accurate evaluation of ignition temperature is key to the quantitative prediction of MEC. A particular focus is given to gravity effects, reflecting recent experimental efforts to obtain fundamental insights into propagation mechanisms without being affected by gravity. In upward propagation, particles fall toward the reaction front, enhancing combustion and increasing the propagation speed. The situation in downward propagation is the opposite, and extinction occurs when the gravity level is beyond a critical value. In upward propagation, MEC can decrease with an increase in particle size, owing to the influence of gravity.

Development and characterization of a low-NOx partially premixed hydrogen burner using numerical simulation and flame diagnostics

The utilization of hydrogen as a fuel in free jet burners faces particular challenges due to its special combustion properties. The high laminar and turbulent flame velocities may lead to issues in flame stability and operational safety in premixed and partially premixed burners. Additionally, a high adiabatic combustion temperature favors the formation of thermal nitric oxides (NO). This study presents the development and optimization of a partially premixed hydrogen burner with low emissions of nitric oxides. The single-nozzle burner features a very short premixing duct and a simple geometric design. In a first development step, the design of the burner is optimized by numerical investigation (Star CCM+) of mixture formation, which is improved by geometric changes of the nozzle. The impact of geometric optimization and of humidification of the combustion air on NOx emissions is then investigated experimentally. The hydrogen flame is detected with an infrared camera to evaluate the flame stability for different burner configurations. The improved mixture formation by geometric optimization avoids temperature peaks and leads to a noticeable reduction in NOx emissions for equivalence ratios below 0.85. The experimental investigations also show that NOx emissions decrease with increasing relative humidity of combustion air. This single-nozzle forms the basis for multi-nozzle burners, where the desired output power can flexibly be adjusted by the number of single nozzles.

Combustion characteristics of lithium perchlorate-based electrically controlled solid propellants at elevated pressures

Electrically controlled solid propellants (ECSPs) exhibit specific combustion characteristics that offer multiple start/stop operations and variable combustion rates at different electrical power. The present study investigates ignition and pyroelectric combustion characteristics of ECSPs, based on lithium perchlorate (LP) oxidizer and poly vinyl alcohol (PVA) binder, in the elevated pressure range of 0.1 to 2.0 MPa, and to further understand the performance of tungsten (W) as a metal additive. Experiments are conducted for metallized ECSPs with 5% (M5), 10% (M10) and 15% (M15) W content, relative to the non-metallized case. Ignition delay time (Tign) for the baseline (M0) decreased substantially from 633 ms at 0.1 MPa to 178 ms at 2.0 MPa pressure. A similar decreasing trend for the minimum electrical energy required for ignition was also observed with increase in pressure. Addition of W decreased Tign and electrical ignition energy significantly by 33% and 66% respectively, for M15 relative to M0. Furthermore, thermochemical equilibrium analysis indicated that the adiabatic combustion temperature and specific impulse decreased with increase in W content due to increased fuel-rich stoichiometry. Overall, the metal addition significantly enhanced the combustion rates at all pressure range below 2.0 MPa. It is anticipated that the observed characteristics at elevated pressures provide insights into the design of electrically-controlled operations for future propulsion systems.

Research on the flammability and explosion characteristics of typical low GWP refrigerants

Under the development requirements of green environmental protection, refrigerants are constantly updated. 2,3,3,3-tetrafluoropropene (R1234yf), difluoromethane (R32) and isobutane (R600a) are promising environmentally friendly refrigerants that are widely used in domestic air conditioners, automotive air conditioners and refrigerators respectively. Although the new refrigerants meet green requirements, they also pose safety risks, with refrigerant leakage leading to explosion accidents. This paper numerically calculated the adiabatic combustion temperature, explosion pressure, laminar burning velocity and combustion products of refrigerants under different environmental factors. The numerical analysis was verified with experimental data on burning velocity in the literature, which confirmed the reliability of the numerical simulation. The results showed that the adiabatic combustion temperature of R600a was the largest, R32 was the second largest and R1234yf was the smallest under the same conditions, while the explosion pressure of R32 was the largest, R1234yf was the second largest and R600a was the smallest under the same conditions. The burning velocity of R600a gradually decreased with the increase of the ambient humidity, while the burning velocity of R32 first increased and then decreased with the increase of the ambient humidity, and reached a maximum value (6.8 cm/s) when the ambient humidity was about 60%. The combustion products of R600a were mainly CO2 and H2O, the combustion products of R32 and R1234yf were mainly HF and CO2, due to R1234yf′s F/H > 1, the concentration of CF2:O and CF4 in the combustion products of R1234yf was not negligible.

Understanding the pyroelectric combustion behaviour of metallized electrically controlled solid propellants

Solid rocket propellants that demonstrate variable burning rates are highly desirable in various propulsion applications. Electrically controlled solid propellants (ECSPs) are one such kind that ignite and combust only when external electric power is applied, which enables to adjust/control their combustion rates. However, the knowledge on their combustion mechanisms is scant in the limited literature. In this study, pyroelectric combustion behaviour of metallized ECSPs, based on lithium perchlorate (LP) and poly vinyl alcohol (PVA), containing 5%, 10%, and 15% tungsten (W) are investigated, in comparison to the non-metallized baseline propellant. Theoretical performance parameters, heat release and mass loss from decomposition process, and combustion rates are obtained. Pyroelectric combustion of ECSPs involves electrolytic decomposition of LP producing oxidizer species, which react with fuel species from PVA and/or W in thermochemical reactions, to generate heat and products including LiCl, HCl, LiOH, WO3, etc. Results indicate that addition of W reduces the theoretical adiabatic combustion temperature and overall heat release from exothermic decomposition by 19% and 36% respectively, in ECSP-M15 containing 15% W, compared to the baseline case. However, relatively low voltage response time for metallized ECSPs implies that their ionic conductivity is higher than the baseline ECSP. More importantly, combustion rates of all ECSPs increase exponentially with increase in applied initial voltage in the 100–500 V range. Inclusion of W enhances the combustion rates significantly by 4.9 times at 100 V and by 1.7 times at 500 V for ECSP-M15 relative to the baseline propellant. This signifies that electrochemical mechanisms become the rate controlling step at high electric power, in governing the pyroelectric combustion behaviour of ECSPs. Further, these propellants were successfully tested for multiple burn/no-burn conditions under the application/removal of the external electric power, which is highly desirable for various propulsion systems.

Analysis of combustion synthesis method for Cu/CeO2 synthesis by integrating thermodynamics and design of experiments approach

Solution combustion synthesis (SCS) is a commonly used method for synthesizing nanomaterials due to its energy and time efficiency. Herein, we present an analysis of synthesis parameters to optimize a targeted property by integrating results from thermodynamic calculations with Design of Experiments (DOE) approach. The analysis is conducted on Cu/CeO2, a catalyst planned to be used for CO2 conversion reaction. The SCS reaction using Cu(NO3)2 and Ce(NO3)3 precursors as oxidizers and glycine (C2H5NO2) as a fuel were thermodynamically studied in detail to provide input parameters for DOE. Estimations of the adiabatic combustion temperature and product composition at the equilibrium conditions were accomplished on the basis of Gibbs free energy minimization principle. Two of the operative parameters in SCS; the fuel to oxidizer ratio (φ), and metal loading (Cu on CeO2); were optimized using the Central Composite Design approach (CCD) and the statistical software application Minitab. The analysis of combustion system was performed for two cases; without the excess external oxygen supply, and with excess oxygen presence. The results showed that the φ variable is the most significant factor effecting the adiabatic combustion temperature and total gaseous products. On the basis of 1 mol of solid product, the optimum predicted values to have the maximum adiabatic combustion temperature and maximum gas products for both the cases of without and with the use of excess oxygen being ∼1650 K, 15 mol and ∼2550 K and 30 mol, respectively.

Features of methane-hydrogen mixtures combustion in oxy-fuel power cycle combustion chamber

The paper is focused on the study of features of methane-hydrogen mixtures combustion in an oxy-fuel power cycle combustion chamber. The goal of the study is to find optimal combinations of thermodynamic parameters, allowing to bring the fundamental combustion characteristics, such as the normal flame propagation rate, the adiabatic combustion temperature, and the ignition delay time, closer to the parameters that are characteristic of traditional gas turbine plants. The research method includes digital experiments in the Chemkin-Pro software package using detailed kinetic patterns. The key features of the fuel combustion process in oxy-fuel power cycle combustion chambers are changing the diluent medium from atmospheric nitrogen to carbon dioxide, which is the working medium in the cycle, and applying a supercritical pressure (about 300 atm). Both changes negatively affect the combustion process intensity. To achieve the normal flame propagation rate and the maximum adiabatic temperature that are acceptable for the possible flame stabilization in the combustion zone, to exclude uneven heat release and large values of chemical underburning, the amount of CO2 diluent in the combustion zone shall be within the range of 10 to 20 % of the total amount of CO2 supplied to the combustion chamber.

Effects of hydrogen addition on combustion characteristics of a methane fueled MILD model combustor

Combined with need of the carbon emissions, the feasibility of Moderate or Intense Low-oxygen Dilution (MILD) combustion fueled with hydrogen/methane blends needs to be investigated. This paper discusses the pollutant emissions, the stable operating range and the flame morphology for a jet-induced MILD model combustor. The hydrogen/methane volume ratios range 0:10 to 5:5. The NOx emissions are less than 5 ppm@15%O2 when the hydrogen content is less than 50% by volume in the atmospheric conditions. The calculation using chemical reactor network (CRN) model demonstrates that the effect of heat loss on NOx emissions increases as the adiabatic combustion temperature increases, which is consistent with the experimental results. The maximum OH∗ signal intensity increased at higher hydrogen content, especially when the hydrogen content exceeds 30% by volume. Due to the increase in turbulent burning velocity and the enhancement in the reaction intensity, the reaction zones shrink with increasing hydrogen content. In addition, with increasing hydrogen content, the stable operation range of the combustor becomes narrower, and the stable combustion is not maintained when the hydrogen content exceeds 50% by volume. The findings of the paper help to further understand the effect of hydrogen content on the formation of MILD combustion in the jet-induced combustor.

Large Activation Energy Analysis of Nonadiabatic Strained Premixed Laminar Flames with Nonunity Lewis Numbers

ABSTRACT We present an asymptotic analysis of a strained premixed flame in the mixing layer between two counterflowing streams: one with fresh reactants at a temperature and other with the burned gases at temperature , which may be different from the adiabatic combustion temperature of the fresh gases. A one-step irreversible Arrhenius reaction model, of high activation energy, is used for the asymptotic analysis, together with the thermal-diffusive approximation of constant density and transport properties – easily generalized to variable density and transport properties with the use of a heat-conduction-weighted coordinate. The analysis for near unity Lewis numbers of the fuel by Libby, Liñán and Williams (1983) is extended here to arbitrary nonunity Lewis numbers, of relevance to a wide variety of applications, ranging from hydrogen-fueled combustors to heavy fuel systems. In analogy with Liñán’s analysis of counterflow diffusion flames, three asymptotic distinguished regimes are identified for premixed flames for large activation energies and the appropriate Damköhler numbers – the ratio of the characteristic diffusion and reaction times. These regimes are the premixed flame regime, the partial burning regime and the nearly frozen ignition regime. The analytical expressions obtained for these regimes, of the dimensionless reaction rate as a function of the Damköhler number, are seen to describe with good accuracy the results obtained from the numerical integration of the full problem.