Combustion Kinetics Research Articles

In‐Flight Synthesis of Core–Shell Mg/Si–SiOx Particles with Greatly Reduced Ignition Temperature

AbstractMagnesium is a promising candidate as a solid fuel for energetic applications, however, the diffusion‐controlled oxidation mechanism impedes its reaction with an oxidizer, often resulting in diminished performance. In this study, non‐thermal plasma processing is implemented to modify the surface of magnesium nanoparticles with silicon in‐flight, in the gas‐phase to enhance the rate of interfacial reactions and tune the ignition pathways. Allowing the silicon coating to partially oxidize provides direct contact between the fuel and oxidizer, resulting in a nanostructured thermite system at the single particle level. The proximal distance between oxidizer and fuel directly impacts the ignition temperature and, therefore, the combustion kinetics. An intermetallic reaction occurs within the magnesium/silicon system to supplement the heating of the magnesium fuel to initiate its reaction with the oxidizer, resulting in highly reduced ignition thresholds. The ignition temperature is lowered significantly from ≈740 °C for magnesium particles with a native oxide layer to ≈520 °C for particles coated via the in‐flight plasma process.

Experimental and modelling study of syngas combustion in CO2 bath gas

Syngas produced from coal and biomass gasification has been proposed as a potential fuel for direct-fired supercritical power cycles. For instance, the Allam-Fetvedt cycle can offer price-competitive electricity production with 100 % inherent carbon capture while utilizing CO2 dilution of about 96 %. In this work, ignition delay times (IDTs) of syngas have been measured in CO2 diluted conditions using a high-pressure shock tube at two pressures (20 and 40 bar) over a temperature range of 1100 – 1300 K. Syngas mixtures in this study were varied in equivalence ratio and H2:CO ratios. The datasets were compared against the predictions of AramcoMech 2.0 and the University of Sheffield supercritical CO2 2.0 (UoS sCO2 2.0) kinetic models. Quantitative comparative analysis showed that the UoS sCO2 2.0 was superior in its ability to predict the experimental IDTs of syngas combustion. We found that the reaction of CO2 and H to form CO and OH caused the separation of H2 and CO ignition in two events, which increased the complexity of determining the IDTs. We investigated this phenomenon and proposed a method to determine simulated IDTs for an effective comparison against the experimental IDTs. The chemical kinetics of syngas combustion in a CO2 and N2 bath gas are contrasted by sensitivity and rate-of-production analyses. By altering the ratio of H2 and CO as well as mixture equivalence ratio, this work provides vital IDT data in CO2 bath gas for further development and validation of relevant kinetics mechanisms.

Spontaneous Combustion Characteristic Stages of Active FeS and Its Inhibition Effect by Gas-Phase Passivation

ABSTRACT To explore the spontaneous combustion characteristic stages of active ferrous sulfide (FeS) and its inhibition effect by gas-phase passivation. Active FeS samples were prepared and then the spontaneous combustion characteristics of active FeS and commercial FeS samples were compared. The active FeS spontaneous combustion process was divided into several characteristic stages from the perspective of spontaneous combustion kinetics. Furthermore, the inhibition effect of gas-phase passivation on the characteristic stages and the kinetics and thermal effects of active FeS spontaneous combustion process were investigated to further reveal the inhibition mechanism. The results indicate that spontaneous combustion process of active FeS is divided into the room temperature (RT) spontaneous combustion, oxygen-adsorption-induced weight gain, high-temperature combustion and burnout stages, while the spontaneous combustion process of commercial FeS excludes the RT spontaneous combustion stage. Active FeS presents greatly advanced characteristic stages, stronger spontaneous combustion reactivity and more intense reaction in the RT spontaneous combustion and high-temperature combustion stages, which agrees more with the sulfur corrosion products under actual on-site working conditions. The spontaneous combustion tendency of passivated FeS weakens gradually with the increase of passivation time until it loses its RT spontaneous combustion reactivity after 6 h passivation. After the oxide film formed on the surface of passivated FeS is destroyed, its high-temperature combustion reaction becomes relatively intense. The activation energy of passivated FeS in the spontaneous combustion reaction is much higher than that of active FeS, and their activation energies both soar with the deepening of passivation, indicating that the gas-phase passivation technology can effectively inhibit the FeS spontaneous combustion process. The gas-phase passivation time must be maintained for over 6 h despite the weakening inhibitory effect of passivation treatment on the FeS spontaneous combustion process.

Numerical investigation of premixed hydrogen/air combustion at lean to ultra-lean conditions and catalytic approach to enhance stability

Premixed combustion of hydrogen/air over a platinum (Pt) catalyst is numerically investigated in a planar channel burner with the aim of stabilising the flame at lean to ultra-lean conditions. A steady laminar species transport model is examined in conjunction with elementary heterogeneous and homogeneous chemical reaction schemes and validated against experimental results. A stability map is obtained in a non-catalytic burner for the equivalence ratios (φ) of 0.15–0.20, which serves as the basis for the catalytic flame analysis. Over the Reynolds numbers (Re) investigated in the non-catalytic burner, no flame is observed for φ ≤ 0.16, and flame extinction occurs at Re < 571 and Re < 381 for φ = 0.18 and 0.20, respectively. Moreover, a significant amount of unburned H2 exits the burner in all cases. With the Pt catalyst coated on the walls, complete H2 combustion is attained for 0.10 ≤ φ ≤ 0.20 where the contribution of gas phase (homogeneous) reaction increases with Re. Furthermore, radiation on the wall and at the inlet affects the combustion kinetics and flame temperature. Finally, NOx emission is investigated under the same conditions and found to increase with equivalence ratio but has a negligible effect with the inflow Reynolds number.

Chemical mechanism of ammonia-methanol combustion and chemical reaction kinetics analysis for different methanol blends

As a carbon-free fuel, ammonia is considered as an attractive alternative fuel for internal combustion engines. However, ammonia has the problems of high ignition temperature and NOx emissions while using in engines. Methanol as liquid fuel is easy to store and transport. Ammonia-methanol blended fuel is probably-one of the most appropriate methods to solve the problem. However, there are few studies of chemical mechanism for the combustion of ammonia/methanol dual fuel. Moreover, it is important to study ammonia-methanol combustion by chemical reaction path analysis. In this paper, a chemical reaction mechanism of ammonia-methanol blends with 60 species and 399 reactions was developed. This mechanism can accurately predict the laminar burning velocity (LBV) and ignition delay time (IDT) in a wide range of equivalent ratios (Φ) and methanol blends. By using this chemical reaction mechanism, the effects of methanol addition on ammonia combustion and emissions at different equivalent ratios were numerically studied. Results showed that the addition of methanol significantly improves the chemical reactivity of ammonia, and blending a small amount of methanol can greatly reduce the IDT. However, the accumulation of radical HO2 caused by ammonia production enhances the fuel NOx path of NH2 → H2NO, which, together with high temperature and oxygen enrichment, leads to a NOx peak of 12500 ppm at equivalent ratio of 0.8. However, with the increase of equivalent ratio, NOx emission will decrease, which is only 2500 ppm at equivalent ratio of 1.4. Due to the existence of cross reaction of NH2 + CH3OH = NH3 + CH2OH and NH2 + CH3OH = NH3 + CH3O between ammonia and methanol, NH2 is difficult to participate in the thermal DeNOx process in the premixed combustion process, resulting in high NOx emissions. In addition, it is also found that after equivalent ratio of 1.1, H will replace OH as the most important chain propagation carrier.

Hyperspectral image reconstruction from colored natural flame luminosity imaging in a tri-fuel optical engine

The detection of chemiluminescence from various radicals and molecules in a hydrocarbon flame can provide valuable information on the rate of local heat release, combustion stability, and combustion completeness. In this study, chemiluminescence from the combustion process is detected using a high-speed color camera within the broadband spectrum of visible light. Whereon, a novel hyperspectral reconstruction approach based on the physically plausible spectral reconstruction (PPSR) is employed to reconstruct the spectral chemiluminescence signals from 400 to 700 nm with a resolution of 10 nm to provide 31 different spectral channels. The reconstructed key chemiluminescence signals (e.g., CH*, CH2O*, C2*, and CO2*) from the color images are further analyzed to characterize the chemical kinetics and combustion processes under engine conditions. The spectral chemiluminescence evolution with engine crank angle is identified to comprehend the effect of H2 fraction on flame characteristics and combustion kinetics. Additionally, in this study, a detailed kinetic mechanism is adopted to deepen the theoretical understanding and describe the spectral chemiluminescence from H2/CH4 and H2/CH4/n-dodecane flames at relevant conditions for various species including OH*, CH*, C2*, and CO2*. The results indicate that the PPSR is an adequately reliable approach to reconstructing spectral wavelengths based on chemiluminescence signals from the color images, which can potentially provide qualitative information about the evolution of various species during combustion. Here, the reconstructed chemiluminescence images show less than 1% errors compared to the raw images in red, green, and blue channels. Furthermore, the reconstructed chemiluminescence trends of CH*, CH2O*, C2*, and CO2* show a good agreement with the detailed kinetics 0D simulation.

The role of reservoir fluids and reservoir rock mineralogy on in-situ combustion kinetics

In-situ combustion (ISC) is a complex process with great potential. This study aims to simplify some of the complications associated with the reaction kinetics of ISC and investigate the impact of reservoir rock composition and crude oil fractions on the reaction kinetics of ISC.Sixty-six reaction kinetics experiments were conducted using Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC) on two heavy crude oil samples and two types of porous media (clays and carbonates). In these experiments, a 5 °C/min heating rate was used to simulate the low-temperature-oxidation (LTO) region, and a 20 °C/min heating rate was used for the high-temperature-oxidation (HTO) region. The role of crude oil composition on the reaction kinetics of combustion was also investigated through saturates, aromatics, resins, and asphaltenes (SARA) fractionation. The two crude oils were first separated into their SARA fractions, and then the reaction kinetics of individual fractions and their two and three component pseudo-blends were studied.‘To understand the contribution of aquathermolysis reactions, the crude oils and their SARA fractions were mixed with water, and the reaction kinetics tests were repeated in the presence of water. The chemical reactions occurring in the presence and absence of water in crude oil and their fractions were discussed using control experiments conducted on known simple hydrocarbons: n-decane (C10H22), n-decanal (C10H20O), n-decanol (C10H22O), and decanone (C10H20O). Additionally, the reactivity of the mineralogy of the porous media was examined, and both clay and carbonates were tested. All experiments were analytically modeled to obtain reaction kinetics parameters in terms of activation energy (Ea) and heat generation (ΔH).The results show that while emulsified water decreases the effectiveness of the combustion process, the presence of initial water increases it. This is due to the increase in heat generation and decrease in activation energy, which is mainly caused by the interaction between water and aromatics fractions (aquathermolysis reaction) at elevated temperatures. The amount of clay in the reservoir is critical for the success of the ISC process. If the reservoir has a higher clay content than a certain threshold, the combustion performance will be compromised. Resins fractions have a higher tendency to interact with carbonates during ISC in the HTO region.Overall, this study provides simplified analytical approaches based on experimental results to better understand the ISC chemical reaction kinetics for different types of crude oil and reservoir rocks.

Systematically derived one-step kinetics for hydrogen-air gas-turbine combustion

A previously derived one-step reduced chemical-kinetic mechanism, describing hydrogen flames under near-limit conditions involving peak temperature not far from the crossover temperature, is used in computations of hydrogen-air flamelets at elevated pressures typical of gas-turbine combustion. Besides freely propagating laminar deflagrations with compositions spanning the whole range of flammability conditions, the calculations address strained premixed and nonpremixed flames as well as partially premixed propagating fronts. The comparisons with results of detailed-chemistry computations reveal that, for most purposes, the one-step mechanism provides sufficiently accurate predictions of burning rates under all conditions of interest for gas-turbine combustion. The reduced-chemistry model, featuring an explicit analytic expression for the hydrogen oxidation rate in terms of the local temperature and the O2, H2, and H2O concentrations, can be easily implemented in numerical codes, thereby facilitating future numerical analyses based on direct-numerical and large-eddy simulations.

Activation energies and evolved gas analysis for Argonne premium coals

ABSTRACT A set of eight coals from the premium Argonne coal sample program were studied using thermogravimetric and evolved gas analysis. Gaseous combustion products were analyzed using an FTIR spectrometer and a chemiluminescence analyzer. Additionally, modulated thermogravimetric experiments were carried out to determine activation energies associated with the combustion of each sample. The exhaust from the thermogravimetric analyzer was directed to the gas analyzers for detecting and quantifying CO, CO2, and NO. Evolved gas analysis was conducted at a ramp rate of 5°C for CO, CO2 evolution, and 20°C per minute for nitric oxide evolution, with the furnace temperature varying between 20°C–750°C. Modulated thermogravimetric analysis experiments were carried out in the same temperature range. The temperature was increased at a rate of 2°C per minute for the modulated experiments. Each test had a superposed temperature modulation with amplitude ±5°C and a period of 200 seconds. The experiments provide valuable information on the combustion kinetics and emission characteristics of selected American coals.

Catalytic combustion kinetics of methyl butanoate over Pd/γ-Al2O3 catalysts: An experimental and theoretical study

Catalytic combustion technology is a promising prospect for the removal of pollutants and improvement of combustion efficiency. In this study, methyl butanoate (MB), a typical biodiesel surrogate was chosen to obtain insight into the catalytic reaction mechanism of biodiesels over Pd/γ-Al2O3 catalyst. By comparing the homogeneous and catalytic combustion experiment result, it is found that the reaction temperature of the same conversion in catalytic combustion is reduced by about 400 K. The formation of a large of methyl acrylate (MA) and the significant reduction of aldehyde products reflect the change of the catalytic combustion reaction path on the surface of Pd/γ-Al2O3. Density functional theory (DFT) calculation shows that two different initial reaction paths (Pd + MB and PdO + MB) have lower energy barriers for the generation of CH3CH2CHCOOCH3 (MB2J) radicals and the MB2J goes through subsequent decomposition to form MA, which is consistent with the experimental result.

Combustion simulations of AlH3 and ethanol nanofluid by ReaxFF

To alleviate the growing energy crisis, ethanol has been developed and applied gradually as an ideal biofuel to replace gasoline. The AlH3 nanoparticle is an excellent fuel additive with broad applications. In this work, the ReaxFF-lg reactive dynamics simulations were proceeded to explore the detailed mechanisms of AlH3 and ethanol nanofluid fuel. At varying temperatures, AlH3 exhibits different morphologies: branch-like expansion at the lower temperatures; micro-explosion and reaggregation into larger clusters at high temperatures. Overall, AlH3 accelerates the decomposition of ethanol and shortens the ignition delay. AlH3 also reduces the activation energy for ethanol decomposition from 79.09 to 69.05 kJ/mol. The conversion of coordination number for Al-O bonds indicates that Al2O3 is the final product of Al element. The simulation results reveal a new mechanism: AlH3 promotes the dissociation of H in the hydroxyl, making the initial decomposition of ethanol to C2H5O (CH3CH2O, CH3CHOH and CH2CH2OH) selective. The released H forms more OH and HO2 radicals to promote the conversion of intermediates to stable products. The Al2O3 oxide layer delays the ethanol combustion kinetics as well. This study provides an atomic perspective on the combustion mechanisms of AlH3 and ethanol nanofluid fuel and is expected to guide the development and application of AlH3-based fuels.

Chemical kinetic analysis to study the potential of fuel staging in reducing the emissions from NH3/CH4-air combustion at different pressures

The combustion characteristics of ammonia/methane blends to enhance the reactivity of ammonia are investigated successfully for carbon–neutral energy applications. However, commercializing ammonia blends demands techniques to retrench the superfluous NOX emissions under fuel-lean conditions. The present study is a chemical kinetic analysis investigating a new ammonia-methane combustion strategy of injecting ammonia into hot methane combustion gases (ammonia fuel staging) to reduce the NOX propensity without ammonia slip. The combustion kinetics of NH3/CH4 mixtures are studied in chemical reactor networks (CRNs), depicting typical burner flow conditions with and without fuel staging. A comparison of the emission chemistry in the fuel-staged CRN model with the single-stage CRN model is carried out for the ammonia mole fraction (XNH3) in the fuel mixture ranging from 20 to 60 % and the equivalence ratio ranges (ϕ) of 0.6–0.9 at both low and high-pressures of 1 and 10 atm, respectively. It is observed that in the single-stage reactor, the entire reactor is an active reaction zone due to the reduced chemical kinetics of methane in the presence of ammonia. Recognizing the need of raising the radical concentration and temperature in the flame zone to enhance ammonia chemistry, a fuel-staged reactor model is proposed. In the fuel-staged model, staged combustion is achieved by injecting NH3 into the lean methane combustion products for the constant combustor power output of 25 kW. Results show that fuel staging enhances the ammonia chemistry at low and high-pressure conditions of 1 and 10 atm. In the fuel-staged reactor, the flame zone of the second stage is observed to be the active reaction zone with maximum NH3 consumption. At low-pressure conditions, fuel staging leads to a reduction in both CO and NOX emissions without ammonia slip. The NOX reduction is due to the stable availability of NO-consuming NHi radicals for the entire duration of combustion in the flame zone via the reactions: 2NH2→NH3+NH and NH3+OH→NH2+H2O. The CO-consuming reactions: NH2+CO→HNCO+H and OH+CO→H+CO2 further reduces the CO emissions from the second stage. However, the augment in ammonia chemistry adversely affected NOX reduction at high-pressure operating conditions due to the lack of NHi radicals for NO consumption. The study contributed to the NOX reduction from ammonia combustion by providing an active high-temperature combustion zone with a self-sustaining NHi environment.

Effects of non-equilibrium plasma and equilibrium discharge on low-temperature combustion in lean propane/air mixtures

A zero-dimensional (0D) non-equilibrium plasma assisted ignition/combustion (PAI/PAC) model is established by coupling plasma kinetics and combustion kinetics to investigate the effect of non-equilibrium nanosecond repetitively pulsed discharge (NRPD) plasma and equilibrium discharge on low-temperature combustion (LTC) stage of lean propane/air mixtures. The results show that the NRPD case has the fastest ignition, in comparison to equilibrium discharge (ED) with the same discharge energy. With NRPD before LTC, electrons, O(1D), as well as O and OH, are formed during discharge, promoting propane consumption dramatically. Electron collision with propane can promote propyls (NC3H7/IC3H7) and alkenes, but there is a competitive relationship in terms of discharge energy between them. The formed propyls are mainly consumed to produce propyl peroxyl (NC3H7O2/IC3H7O2) and accelerate low-temperature product formation, such as ketones and OH. The relaxations of vibrationally excited states are the dominant pathways of heat release, leading to the continuous temperature rising after NRPD. Finally, the negative temperature coefficient (NTC) performances under auto-ignition, NRPD, and ED are investigated. ED only shifts the NTC to the low-temperature zone, while NRPD eliminates the NTC phenomenon. The provided path fluxes of intermediates show that the promoted NC3H7/IC3H7 and NC3H7O2/IC3H7O2 induced by NRPD weaken the negative correlation between the oxidation rate of NC3H7/IC3H7 and temperature. The higher concentrations of NC3H7/IC3H7 and HO2 radicals during discharge can result in an advanced intermediate/high temperature reaction process.

Kinetics of self-heating and spontaneous combustion of coal dumps

Kinetics of self-heating and spontaneous combustion of coal dumps

Automating the generation of detailed kinetic models for halocarbon combustion with the Reaction Mechanism Generator

Originally developed to predict the chemical kinetics of hydrocarbon combustion via automated generation of detailed reaction mechanisms, Reaction Mechanism Generator (RMG) contains extensive thermokinetic data for C,H,O chemisty, and has more recently been expanded to nitrogen and sulfur. In this work, we present the addition of halogen (fluorine, chlorine, and bromine) chemisty to RMG to enable automated generation of detailed kinetic models for halocarbon combustion. RMG’s existing reaction templates are updated to include halogens, and 11 new reactions families are created specific to halogen chemistry. Notably, kinetics for more than 1000 elementary reactions are calculated via ab inito methods and transition state theory, and these kinetic data are combined with kinetics from literature sources to train rate rule decision tree estimators. Additionally, halogen groups are added to RMG’s statistical mechanics database, enabling model generation with RMG’s pressure dependence module and automated computation of microcanonical rate constants for unimolecular networks. Halogen groups are also incorporated in RMG’s transport database to provide estimated parameters for the Lennard-Jones potential, important for transport-dependent simulations including laminar flame speeds. To demonstrate RMG’s capability for predicting halocarbon combustion, RMG is used to build a flame suppression model for 2-BTP (CH2=CBrCF3) in methane flames. The laminar flame speeds of RMG’s 2-BTP model show good agreement with a published model under a variety of reaction conditions. Automating the generation of detailed kinetic models for halocarbon combustion will facilitate the exploration of previously unexplored reaction pathways, thereby accelerating the development of greener refrigerants and suppressants, as well as advancing the field of automated mechanism generation.

Математическая модель процесса сжигания сероводородных и аммиачных газов в реакционной печи Клауса с использованием вычислительной гидродинамики

Based on the method of computational fluid dynamics using the ANSYS Fluent software package, the combustion process in the Claus furnace of sour gas containing ammonia was simulated. The vortex dissipation model was used to describe the chemical kinetics of combustion (Eddy-dissipation model). The object of study was the sulfur recovery unit of the Heavy Residue Processing Complex. Options for increasing the efficiency of the process of burning ammonia-containing sour gases, depending on the scheme for supplying acid to the furnace, its moisture content, as well as the temperature of air and sour gases at the furnace inlet were considered.

Combustion and Performance Evaluation of Methanol (M15)-Fueled BS-VI Compliant Light-Duty Spark-Ignition Engine

Abstract This study investigated the effect of the methanol–gasoline blend (M15) on the combustion and performance characteristics of a commercial light-duty Bharat Stage-VI (BS-VI) 2020 spark-ignition (SI) engine. The M15 and baseline gasoline (G100) engine tests were performed at a wide range of engine loads and speeds. For the M15 operation, it was ensured that the lambda values matched with the baseline gasoline operation at each engine operating point by changing fuel quantity manually. The combustion characteristics of M15 were quite similar to gasoline at all operating points. Alcohol addition improves octane number and flame speed, which changes the combustion characteristics of the engine, but in this study, the combustion characteristics of M15 fuel were almost identical. It may be due to blending a small fraction of methanol and the engine's high compression ratio, which improved the combustion kinetics. The coefficient of variance of indicated mean effective pressure was slightly lower for M15 than gasoline, except at 1000 rpm, where the charge mixing might not be adequate at low engine speed for M15 due to lower methanol volatility. Engine's brake thermal efficiency improved with M15 fueling by ∼1%, compared to baseline gasoline, though brake-specific fuel consumption deteriorated by ∼6% due to the lower calorific value of M15. Higher combustion stability and possibly lower heat transfer losses, as observed from slightly higher exhaust gas temperature (EGT), might have improved the engine's performance for M15. This study demonstrated that M15 fueling exhibited identical combustion characteristics and higher thermal efficiency than baseline gasoline fueling at similar lambda values in a commercial light-duty BS-VI SI engine.

Effect of Metal Oxides on Combustion Characteristics of Excess Sludge

In this paper, it was studied that the effects of heating rate and four metal oxide on the combustion characteristics of excess sludge, such as CaO, Fe2O3, MgO and Al2O3, and the combustion kinetic parameters of sludge were obtained based on Coats-Redfern model. This result indicated that the ignition of sludge can be restricted with the increase of heating rate, but it was conducive to burnout, and the increasing about the flammability, stability and comprehensive combustion characteristic index of sludge. The addition of Fe2O3 and Al2O3 could improve the ignition performance of sludge to a certain extent, which was most obvious at the heating rate of 10 and 20 °C/min, respectively. Furthermore, the existence of Fe2O3, MgO and Al2O3 can improve the burnout performance of sludge, represented by MgO. Under the condition of low heating rate, the presence of Fe2O3 and MgO was beneficial to improve the comprehensive combustion characteristics of sludge. According to the distribution of combustion kinetics parameters, it was showed an increasing trend about the activation energy of sludge with the increase of heating rate at the range of 374.88-575.61 °C, which was also unfavorable to the combustion of fixed carbon. At the same heating rate, the activation energy decreased by adding Fe2O3 and Al2O3 at the range of 148.40-374.88 °C, which was beneficial to the release of volatiles and the combustion reaction, while the activation energy at the range of 374.88-575.61 °C decreased after adding CaO, which promoted the combustion of fixed carbon.

H2 impact on combustion kinetics, soot formation, and NOx emission of hydrocarbon fuel flames

Soot and carbon dioxide released from internal combustion engines became the key issues when using fossil fuels. The use of zero-carbon fuel, hydrogen, with hydrocarbon fuels can play an important role in reducing the exhaust effect on the environment and mitigating the reliance on nonrenewable energy resources. A numerical approach was executed to elucidate the H2 impact on combustion kinetics, soot formation, and NOx emission of hydrocarbon fuel under premixed and diffusion flame conditions. The results showed that hydrogen deteriorated the formations of particle number density, the volume fraction of soot, carbon monoxide, carbon dioxide and polycyclic aromatic hydrocarbons thru the reduction of small chain hydrocarbons at both premixed and diffusion flame conditions. The soot volume fraction and soot particle number density formation were prevailing in the air region of the combustion chamber at diffusion flame conditions. NO3 produced from fuel-related species such as CHO and air-related species such as NO. H2 reduced the peak molar fraction of small chain HC including CHO related species, resulting in a reduction in NO3 emissions. C3H3 species dominantly participated to reduce the CO2 and NO3 emissions, while C2H2 and C5H4CH2 were the main species to control the soot precursors formation in both HC fuel flames. Besides, NH3 emission was limited by C2H2 in DS flames.

Thermogravimetric Evaluation for the Pyrolysis Process of Pellets Produced from Quinoa and Amaranth Harvest Residues

In this study, the combustion properties of pellets produced from quinoa (C3 plant) and amaranth (C4 plant) harvest residues were evaluated by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG) methods. Pelletizing was carried out at 25% moisture content and at a material temperature of 70 °C. 7.5% molasses was used as the adhesive. The pellets were heated from 25 °C to 1000 °C in a thermal analyzer at a tracking rate of 10 °C min-1 and in N2 gas environment. The mass loss and mass loss rate occurring in this temperature range were recorded simultaneously and expressed in thermograms. Combustion stages are observed as a peak in the DTG curve and these peaks represent the mass losses in the combustion stages. According to the analysis results, the highest mass loss rate in the evaporation zone of water in the quinoa plant was 2.12% at 96.65 °C, and in the amaranth plant at 2.34% at 101.7 °C. However, in the next step, the mass loss rate decreased in both pellets. At this stage of the analysis, the water in the pellets completely evaporated and the mass loss was 12.43% in quinoa and 13.38% in amaranth, according to the initial mass. With the increase of volatile matter output, the mass loss rate increased again, and the highest mass loss rates were realized as 6.42% and 4.96%, respectively, at 320 °C for quinoa and 315 °C for amaranth. The rate-determining stage in the combustion kinetics of coal and biomass is the semi-coke combustion stage. At this stage, the lowest mass loss (0.89%) occurred in both pellet samples. TGA and DTG results showed that there were no significant differences between the combustion stages of quinoa and amaranth pellets, and their combustion behaviors were generally close to each other.