Low-temperature Oxidation Reaction Research Articles

Ozone-assisted low temperature oxidation of methanol and ethanol

Ozone-assisted combustion is an advanced combustion technology that is considered a promising means for the active control of combustion. Ozone addition can enhance combustion processes and extend the experimental parameters to extreme conditions. In this work, ozone-assisted low temperature oxidation of methanol and ethanol in a jet-stirred reactor (JSR) was carried out at atmospheric pressure, with a fuel initial mole fraction of 0.005, an equivalence ratio of 0.28, and in the temperature range of 330–800 K. Significant conversions of methanol and ethanol were observed in the low temperature region when ozone was added. Numerous intermediate species were analyzed and quantified by synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography, which are crucially important for unraveling the low temperature oxidation reaction network. The kinetic model of NUIGMech1.1 is tentatively updated to better explain the measured results, although the improvements of the C1–C2 core mechanisms are difficult. Ozone addition enhances the action of the reaction channel of related radicals. Model analysis shows that the kinetics of Ö/ȮH/HȮ2 atoms/radicals are crucial for the overall reaction progress, as well as the reaction of HȮ2 radicals with ozone, which mainly contributes to the formation of ȮH radicals during the initial reaction stage. Inconsistency between measurements and model predictions highlights the considerable uncertainty in the C1-C2 alcohols subchemistry at lower temperatures. The experimental results obtained in this work and model development will motivate further study of the low temperature oxidation chemistry of methanol and ethanol.

Experimental and kinetic modeling studies on low-temperature oxidation of Polyoxymethylene Dimethyl Ether (DMM1-3) in a jet-stirred reactor

In this paper, based on the pyrolysis kinetics model of DMM1-3 previously constructed, the low-temperature oxidation kinetics model of DMM1-3 (500 K∼950 K) was established by using the jet-stirred reactor (JSR) to conduct low-temperature oxidation experiments of DMM1-3 with different equivalence ratios. The model was fully verified experimentally, and the simulation results can well reproduce the trend of fuel and important intermediate specie concentrations in the temperature range of 500 K ∼ 950 K. 9 species were identified and quantified by GC/MS in the low-temperature oxidation process of DMM1-3. Results show that DMM1 has an oxidative decomposition process after dehydrogenation, while both DMM2 and DMM3 have strong low-temperature oxidation reaction and weak NTC process, but there are certain differences in the specific oxidation process. CH3OCHO and COCOC*O are important intermediates in the low-temperature oxidation process of DMM1-3, and their peak concentrations in the high-temperature region are not affected by equivalence ratios. And the peak concentrations of CH3OCHO and COCOC*O in the low-temperature oxidation experiments of DMM2 and DMM3 increased with decreasing equivalence ratios. The current detailed model and corresponding experimental results can be helpful for the construction of reliable reduced DMMn mechanisms.

Precise control of Pt encapsulation in zeolite-based catalysts for a stable low-temperature CO oxidation reaction

Precise control of Pt encapsulation in zeolite-based catalysts for a stable low-temperature CO oxidation reaction

Athabasca Toe-to-Heel Air Injection Pilot: Evaluation of the Spontaneous Ignition Based on Apparent Atomic Hydrogen-Carbon Ratio Variation

Summary An in-depth analysis was performed to determine the ignition delay via the enhanced spontaneous ignition (ESI) method on three well pairs (each pair constituted by one vertical injector and one horizontal producer) belonging to the Toe-To-Heel Air Injection (THAI) pilot in Athabasca. ESI consisted of preheating of the surroundings of injection wells by injecting a steam slug for 3 to 4 months just before starting air injection. At first, the ignition delay had been determined based on both the oil production and on the bottomhole temperatures (BHTs) recorded in the observation wells as well as at the toe of the horizontal producer. For the purposes of this paper, a more rigorous evaluation was carried out based on the variation in time of the apparent atomic hydrogen-carbon ratio (AAHCR) calculated from detailed gas analyses for a long period of time. AAHCR is a very strong synthetic parameter giving a direct indication of the peak temperature value before, during, and after the in-situ combustion (ISC) front is generated. Therefore, it provides complete information on the occurrence of high-temperature oxidation and low-temperature oxidation (LTO) reactions. Using the variation of the AAHCR, it was found that the ignition time was shorter than those determined by the previously mentioned methods. In the case of first well pair, ignition took 3 weeks as compared to the 1 month determined by the previous methods. The second well pair ignited in 1 month as compared to the previously calculated 2 months, and for the third well pair, ignition time was approximately 2 months in both cases. As an additional and complementary approach, estimation of the ignition time was also based on the variation of individual components of the produced gas. This allowed for the discovery of a new method for ignition time determination. This was possible in the THAI process, unlike conventional ISC processes, significant concentrations of hydrogen (H2) are produced, and the interpretation of its variation can give an indication of the ignition time. The new method is very simple to use, as the percentage of hydrogen in the produced gas starts to take off only after the full establishment of an ISC front, as hydrogen production is associated with high-temperature bond scission reactions in the ISC front. In general, the ignition delay is overestimated to some degree when using this method.

Accelerated low-temperature oxidation for sand consolidation and production control

Sand production that occurs in poorly consolidated oil and gas reservoirs causes many serious operational problems. Industry experts have used both chemical and mechanical sand control techniques to overcome this challenge; however, these techniques have various technical and economic limitations. For example, a technique that employed in-situ low-temperature oxidation (LTO) of an asphaltic solution saturating the near-wellbore area helped increase the formation's compressive strength while retaining its permeability; however, this technique was time-consuming at low reservoir temperatures. This study employed thermochemicals to preheat the sand and thereby accelerate the LTO reaction and shorten the consolidation process. First, small packs of loose sand saturated with an asphaltic solution were oxidized via external heating until consolidation. The optimal conditions involved continuous airflow for 6 h at 180 °C, which produced consolidated sand with a compressive strength exceeding 12.4 MPa. Second, a similar but insulated saturated sand pack was flooded with several pore volumes of thermochemicals, which raised its temperature from 75 °C to 188 °C; this was followed by 6 h of air injection. The consolidated sand had a compressive strength of 10.27 MPa and showed excellent stability against acid and crude oil floods as well as prolonged soaking in toluene.This study demonstrated the potential of using thermochemicals for the in situ heating of the wellbore area to elevated temperatures for sand consolidation. By shortening the treatment time, the thermochemicals improved the cost-effectiveness of sand consolidation via LTO without adversely affecting the consolidation quality.

Exploring low temperature oxidation of iso-octane under atmospheric pressure

Iso-octane is the dominant component of primary reference fuel (PRF), with high knock resistance during the combustion process. Understanding the low temperature oxidation chemistry of iso-octane aids in clarifying the auto-ignition properties of gasoline surrogates and developing their kinetic models. However, its low temperature oxidation performance has only been observed under high pressure conditions; no report in the literature includes detailed speciation, hindering a comprehensive examination of the iso-octane low temperature oxidation mechanism. In this work, low temperature oxidation behavior of iso-octane was clearly observed in jet-stirred reactors (JSRs) under an initial fuel mole fraction of 0.01, residence time of 2 s, equivalence ratio of 0.25, and pressure of 1 bar. The low temperature oxidation reaction networks of iso-octane were explored by measuring low temperature oxidation intermediates in three experimental approaches: synchrotron vacuum-ultraviolet photoionization mass spectrometry (SVUV-PIMS), gas chromatography (GC), and cw-cavity ring-down spectroscopy (cw-CRDS). More than 80 intermediates were qualitatively analyzed in combination with the photoionization efficiency (PIE) spectrum, quantum chemistry calculation of the ionization energies, and GC analysis. Hydroperoxides derived from iso-octane low temperature oxidation were reported experimentally for the first time, including keto-hydroperoxides (KHP) and/or hydroperoxyl cyclic ethers (HPCE). Approximately 40 products were quantified, including aldehydes, ketones, olefins, and carboxylic acids, etc. Kinetic models in the literature have been examined using the datasets obtained from this work and reaction pathways for the important intermediates discussed. Comparison indicated that the iso-octane models in the literature must be improved to accurately capture the performance of iso-octane low temperature oxidation.

Decoupled analysis of the effect of hydroxyl functional groups on delay of ignition with fictitious hydroxyl

The delay of ignition (DOI) affects engine performances and the fundamental reasons that affect DOI have not been fully explained. In this paper, taking biodiesel mixed with methanol as an example, the effect of the hydroxyl (-OH) functional group in the fuel on the DOI was studied. Through thermogravimetric analyzer and constant volume combustion chamber (CVCC), the activation energy and DOI of different blending ratios (0%, 10%, 20% and 30%) of biodiesel/methanol mixed fuel were determined. Using the fictitious hydroxyl (FOH-) method, the low-temperature oxidation of biodiesel/methanol/FOH- and the reaction path of ignition in the cylinder were analyzed. The results show that when the methanol blending ratio is less than 30%, as the blending concentration of FOH- groups increases, the low-temperature oxidation reaction activity of the mixed fuel increases, and the activation energy decreases. The physical and chemical effects of -OH can prolong and shorten DOI, respectively, and the influence of physical effects is more important than chemical effects. For every 10% increase in -OH functional group concentration, the DOI of biodiesel/methanol mixed fuel increases by 1.4%.

TEXTURAL AND CATALYTIC FEATURES OF SILICON SURFACE MODIFIED WITH ZnO IN THE REACTION OF HOMOGENOUS-HETEROGENEOUS ACTIVATION OF PROPANE-OXYGEN MIXTURES AT LOW PRESSURES

The textural and catalytic characteristics of the surface of silica gel modified with zinc oxide by the sol-gel method and by means of a chemical transport reaction (CTR) have been studied. It was found that catalytic activity of the obtained contacts depends on both the nature and the structural and textural characteristics of the supported ZnO. Using the example of the reaction of low-temperature oxidation of propane, it was found that lower limit of the release of radicals from the surface into the volume with the CTR modification method is lower by 15–20 degrees than in the case of the sol-gel method. It was shown that the catalyst obtained by applying the active phase on the surface of the support by the CTR method is more efficient due to the energy homogeneity of its active centers and the texture characteristics of the surface.

Influence of water on thermo-oxidative behavior and kinetic triplets of shale oil during combustion

The oxidation reactions between oxygen and shale oil directly affect the feasibility and performance of air injection. In this work, the influence of water on thermo-oxidative behavior of shale oil was studied using high-pressure differential scanning calorimetry (HP-DSC). Subsequently, the kinetic triplets for shale oil oxidation in the absence and presence of water were determined using Friedman and Ozawa-Flynn-Wall (OFW) models as well as one advanced integral master plots method. The HP-DSC results showed that at 5 MPa, the shale oil was vulnerable to obviously higher heat release at the low-temperature oxidation (LTO) region compared to the high-temperature oxidation (HTO) region, resulting in shortening the oxidative induction time and achieving in-situ upgrading of shale oil. Water delayed the initial heat release due to the fact that heat release yielded by LTO compensated the heat adsorption yielded by evaporation of water and light hydrocarbons. Additionally, the heat release was reduced with the elevated water saturation as a result of the reduction in exothermic rates and intensified evaporation of water and light hydrocarbons. The higher energy was needed to trigger off the LTO reactions while increasing water saturation from 10% to 20%. Therefore, it was believed that the presence of water extended the oxidative induction time, thereby hindering the smooth and rapid transition from the LTO to HTO stages. Water changed the reactivity of each oxidation stage for shale oil, resulting in higher energy required for the initial LTO reactions and lower energy required for the subsequent oxidation reactions. The water saturation range of 10% to 15% could accelerate the occurrence of high-temperature combustion most effectively, demonstrated by values of activation energy for the conversion greater than 0.6. The appropriate oxidation reaction models for shale oil alone and water saturations of 10%, 15%, and 20% were determined to be D2, F1, F3, and R3, respectively. The determination of kinetic triplets assisted in building the reaction schemes for modelling the air injection process of shale oil reservoirs.

Laboratory investigation of the spontaneous combustion characteristics and mechanisms of typical vegetable oils

To effectively prevent and control the autoignition of vegetable oil, the spontaneous combustion characteristics and oxidation mechanisms of three typical vegetable oils were investigated. Microcal, TG-DSC, Raman spectroscopy and GC-MS were used to analyze the self-ignition characteristics of the samples at both macro- and micro-scales. The results showed that the initial exothermic temperatures were between 65 and 90 °C, after which vigorous oxidation began to release abundant heat. DSC data showed that the entire combustion process of the samples includes 4 typical stages: low-temperature oxidation stage, thermal decomposition stage, combustion stage, and after-combustion stage. The activation energy of the low-temperature oxidation stage reached as low as 33.13 kJ/mol, indicating that the vegetable oil is extremely prone to self-oxidation even when the temperature <200 °C. And the self-ignition tendency was in the order linseed oil > perilla seed oil > safflower seed oil. Based on analysis of the organic molecular structures, it was found that the unsaturated groups in vegetable oil are responsible for its autoignition behavior. Taking linseed oil as an example, 3 peroxide intermediates, namely 10,12-Octadecadienoicacid,9-hydroperoxy-, (10E,12Z)-;9,11-Octadecadienoicacid, 13-hydroperoxy-, (9Z,11E, 13S)-, and 9-Octadecenoic acid, 13-hydroperoxy-, (Z)-(8CI, 9CI) were marked as significant indicators to trace the low temperature oxidation reaction path of the oil samples.

Isothermal oxidation behavior of heavy crude oil and its low-temperature oxidized oils: Implications for in-situ upgrading of heavy oil

Oxidation of heavy oil is essential for the success of in-situ combustion (ISC) projects. However, the isothermal oxidation behavior of heavy oil has not been well understood. In this work, the static oxidation experiments at temperatures of 80, 120, 160, and 200 °C were conducted to obtain the low-temperature oxidized oils (LTOO). Subsequently, the heat release caused by oxidation reactions of heavy crude oil and its LTOO at temperatures of 100, 200, 300, 400, and 500 °C was thoroughly examined. The results indicated that heavy crude oil was subjected to heat release yielded by low-temperature oxidation (LTO) at 100 °C. At the initial oxidation stage, the peak heat flow at 400 °C for heavy crude oil was obviously greater than that at 500 °C, different from the cases of the other four oxidized oils. For all the heavy oils used, the combustion at 400 °C produced a more lasting thermal effect than that at 500 °C. All the heavy oils used showed similar exothermic behavior at 100 and 200 °C. But at 300 °C, the LTO of the oil oxidized at 160 °C released more heat in comparison with that of the oil oxidized at 200 °C, which was thought to be caused by the saturate and aromatic components present in these two oxidized oils. Compared to the other four heavy oils, the combustion at 400 °C for the oil oxidized at 200 °C released fairly higher heat. However, there were minor differences in the isothermal DSC curves at 500 °C for all the heavy oils, indicating that LTO reactions at temperatures no greater than 200 °C produced negligible influence on heavy oil combustion at 500 °C. For this reason, a reasonable increase in the ignition temperature was recommendable when achieving ISC of heavy oils with deep LTO degrees and ultra-heavy oils.

Low temperature oxidized coke of the ultra-heavy oil during in-situ combustion process: Structural characterization and evolution elucidation

Fundamental knowledge on the evolution of low temperature oxidized coke was a prerequisite towards a deep understanding of coke deposition and subsequent combustion of ultra-heavy oils during in-situ combustion (ISC) process. This study investigated the structural characterization (oxidation behavior, elemental composition, functional groups, and morphology) and elucidated evolution mechanism of cokes generated from the low temperature oxidation/pyrolysis of the ultra-heavy oil during ISC process. The results shown that, compared with pyrolytic coke, the intermediate groups of C-O/C-OH (1260–1060 cm−1) were further oxidized into C = O (1850–1650 cm−1) groups and finally converted into C = C groups (“coke peak”, 1590 cm−1) in highly conjugated aromatic structures for oxidized cokes. Besides, the oxidized coking condition would result in a higher degree of substitution (γCHAr1, γCHAr4) of aromatic rings (900–700 cm−1) and promote the evolution of N- and S- functional groups. Although >78 % of C 1 s belonged to the graphitic carbon for four cokes, morphologies of oxidized cokes were relatively coarse with much looser distribution. In addition, the corresponding enthalpies were in the order cokeLTO3 (25.51 kJ·g−1) > cokeLTP (24.22 kJ·g−1) > cokeLTO2 (23.23 kJ·g−1) > cokeLTO1 (17.45 kJ·g−1), indicating a considerable contribution of low temperature oxidation reactions on derived coke morphology, oxidizability and exothermicity, which contained complicated and crucial dehydrogenation, crosslinking and polymerization reactions to accelerate coke evolution.

A novel composite inorganic retarding gel for preventing coal spontaneous combustion

In order to better control the fire problem due to coal oxidations, a novel composite inorganic retarding gel material processed from sodium-based bentonite junction and kaolin, silica, hydrogen peroxide and silicon oxide is developed. For studying the gel's properties the scanning electron microscopy (SEM) and the thermogravimetry (TG-DTG) are used to characterize microscopical structures and mass losses with the temperature change process, respectively. For quantifying the inhibitory effect of the novel gel on the spontaneous combustion process of coal oxidation, laboratory tests such as temperature-programmed oxidation and infrared spectroscopy are carried out. Changes of the gases generated from the treated coal sample by the novel gel under the temperature increasing are analyzed. The inhibitory effects of mud and MgCl2 solutions on coal spontaneous combustion are compared. The results show that the surface of the gel is flat and smooth in microscopic scale. Under the a high-temperature, the gel is stable and is not easy to decompose. In detail, the quality loss is within 10%. The novel gel with a concentration of 20% has a good inhibitory effect on CO release and spontaneous combustion in coal combustion. In addition, the novel gel can significantly reduce the consumption of –OH, –CH and other functional groups in the low-temperature oxidation reaction. Hence, the novel gel is a kind of Inhibitor material with a better comprehension performance. This study provides a novel gel for better preventing and controlling the coal spontaneous combustion hazard.

Low-Temperature Heterogeneous Oxidation Catalysis and Molecular Oxygen Activation

ABSTRACT Many natural oxidations are relevant to the origin and running of life but usually proceeded under mild conditions using molecular oxygen (O2) in the air as the sole oxidant and enzymes as the catalysts. In modern society, catalysis plays an essential role in many industries, such as chemical and pharmaceutical industries. However, most heterogeneous catalytic reactions need high operational reaction temperature and pressure. Research interest is redirected to green catalysis in recent years, e.g., running catalytic reactions under mild conditions, employing green solvents and green oxidants such O2, particularly air. One question always exists: can these industrial catalytic processes be ultimately run similar to the natural oxidation processes in efficiency and operation conditions? For many catalytic oxidation reactions, the greatest challenge lies in activating molecular oxygen under mild conditions. Therefore, a molecular-level understanding of the interactions of O2 molecules with catalysts or substrates is necessary and crucial. In this review, we discuss the activation of O2 to different active species (e.g., O2 2− or O2 2−) and their participation in low-temperature (≤300 oC) catalytic oxidation reactions. The challenges, recent progress, and trends in some low-temperature oxidation reactions are discussed and highlighted. The early studies on the activation of oxygen on various catalysts mainly paid attention to the interaction between the molecular oxygen and the oxygen vacancies of metal oxides. In contrast, recent studies try to fully understand the generation, measurement, and catalytic roles of the various active oxygen species. Therefore, the design of catalysts that can facilely activate O2 at low temperatures is of importance. With such catalysts, it is possible to reduce the high energy consumption, improve the selectivity of catalytic oxidations, and ultimately realize the industrial oxidation reactions at conditions as mild as possible to that of many natural oxidation processes. Finally, from the current body of knowledge, we propose future directions that can effectively utilize O2 for solving practical problems at low temperatures and help understand the oxidation catalysis at the molecular level.

Combustion Behavior and Kinetics Analysis of Isothermal Oxidized Oils from Fengcheng Extra-Heavy Oil

The low-temperature oxidation (LTO) of heavy oil is of great significance for the combustion front stability, which directly influences the efficiency and safety of in-situ combustion (ISC). To provide feasible heating by artificial ignition before the implementation of ISC in the Xinjiang Fengcheng (FC) oilfields, this paper investigates the oxidation behavior of FC extra-heavy oil and its isothermal oxidized oils. Firstly, FC extra-heavy oil was subjected to isothermal oxidation experiments conducted utilizing an oxidation reactor, and the physical properties of the gaseous products and oxidized oils were analyzed. The combustion behavior of the FC extra-heavy oil and oxidized oils was then studied by non-isothermal thermogravimetry and differential scanning calorimetry. Subsequently, the Friedman and Ozawa–Flynn–Wall methods were adopted to perform kinetic analysis. Oxygen consumption was always greater than the production of CO and CO2, so oxygen addition reactions were the main pathway in heavy oil LTO. H/C decreased to 8.31% from 20.94% when the oxidation temperature rose from 50 °C to 150 °C, which deepened the oxidation degree. The density and viscosity of 200 °C to 350 °C oxidized oils increased at a slower rate, which may be related to the LTO heat effect. The change law of temperature interval, peak temperature, and mass loss of the oxidized oils had a good correlation with the static oxidation temperature. Compared with other oxidized oils, the peak heat flow and enthalpy of 350 °C oxidized oil increased significantly with high-temperature combustion, and were 42.4 mW/mg and 17.77 kJ/mol, respectively. The activation energy of 350 °C oxidized oil began to decrease obviously around a conversion rate of 0.4, which indicates that it was beneficial to coke deposition with stronger activity. Finally, we came up with LTO reaction mechanisms and put forward a reasonable preheating temperature for the application of ISC in FC oilfields.

Experimental and kinetic study on the pyrolysis and oxidation of isopentane in a jet-stirred reactor

An experimental and kinetic study on the pyrolysis and oxidation of isopentane (2-methylbutane) were conducted in this work. The experiments were performed in a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of oxygen, hydrogen, CO, CO2, C1C6 hydrocarbons and methanol were measured using a gas chromatograph (GC), at the initial fuel mole fraction of 0.5% and residence time at 2 s. Three literature kinetic models, named as the Bugler model, the NUIGMech1.1 model, and the LLNL model, were employed to predict the speciation profiles measured in this work, and the ignition delay times in the literature. Based on the model performances and kinetic analysis, some modifications were made to the LLNL model, by supplementing the beta-scission reaction aC5H11 = C4H8–1 +CH3, and updating the rate constants for the reactions iC5H12 + OH = cC5H11 + H2O, iC5H12 + OH = bC5H11 + H2O, C3H4-a = C3H4-p, C3H4-a + H = C3H4-p + H, and C2H6 + CH3 = C2H5 +CH4. After the modifications, the model predictions on mole fractions of 1-butene, ethane, allene and propyne in JSR pyrolysis and oxidation were improved, and the overestimations on the ignition delay times at low temperatures are significantly reduced. Reaction pathway and sensitivity analyses were carried out using the modified model. The results indicated that fuel consumption in pyrolysis is sensitive to the unimolecular decomposition reaction iC5H12 = iC3H7 + C2H5 across the temperature range of 900–1100 K. In addition, fuel low-temperature oxidation reactivity is sensitive to the mutual conversion between HO2 and H2O2, while the competition between OH and HO2 formation has a more pronounced effect at increased temperatures.

Oxidative Coupling of Methanol with Molecularly Adsorbed Oxygen on Au Surface to Methyl Formate.

Supported Au catalysts efficiently catalyze the oxidative coupling of methanol with O2 to methyl formate, in which the atomic O species (O(a)) formed via O2 dissociation on the Au surface has been considered as the active oxygen species. Herein we report for the first time that the oxidative coupling of methanol can occur facilely with molecularly adsorbed O2 species (O2(a)) on a Au(997) surface at temperatures as low as around 125 K, while that with O(a) occurs at around 175 K. Both experimental and theoretical calculation results demonstrate a novel reaction mechanism of oxidative coupling of CH3OH with O2(a) via a dioxymethylene (H2COO) intermediate, resulting in the production of both HCOOCH3 and HCOOCH3. These results reveal the unique reactivity of molecularly adsorbed O2 species on Au surfaces for low-temperature oxidation reactions.

Numerical modelling of a three-zone combustion for heavy fuel oil in inert porous media reactor

Numerical model for heavy fuel oil and air mixtures combustion is presented to simulate the behavior of the fuel in an inert porous medium reactor for hydrogen production. Three-zone combustion of oil and petroleum cokes separated by temperature ranges starting from ambient temperature to 560 K, from 560 K to 673 K, and above 673 K, is presented. Hydrogen production is achieved using water gas shift equilibrium reaction on the combustion products at different temperatures. Results show a high enthalpy contribution due to coke combustion formed in the low temperature oxidation reaction, being the most important reaction in relation to its zone size. Simulations increasing filtration velocity (from 0.05 to 0.9 m/s) has a favorable effect on the maximum temperature and the combustion front velocity. The effect of the simplified combustion model lowers computational time, with acceptable results for temperature as well as hydrogen production in contrast to laboratory tests and other software simulation such as COMSOL Multiphysics.

Study of thermal characteristics and functional group changes of Yanghuopan Coal during spontaneous combustion

The generation and accumulation of heat is the major direct cause of the spontaneous combustion of coal. In the initial stage of coal spontaneous combustion, the heat is mainly released by low temperature oxidation reaction of coal. To investigate the thermal characteristics and the change of key functional groups in the process of coal oxidation, Yanghuopan coal sample was used for research. First, the heat flow curves of the Yanghuopan coal sample were measured by a microcalorimeter at different heating rates of 0.2, 0.4, and 0.6 °C min−1. Then, the infrared spectrogram of coal oxidation process was measured by Fourier transform infrared spectroscopy. The results indicated that the oxidation process of coal occurred in stages that had distinct characteristics. When the temperature increased, the heat flow curve of coal first decreased, then increased. And the heat flow curve was divided into three stages: endothermic, slow exothermic, and fast exothermic. By the study of the key functional groups and structural parameters of the characteristic temperature point, the endothermic and exothermic processes of coal oxidation at low temperature are mainly caused by the reactions of methyl, methylene, hydroxyl and carboxyl groups. The methyl and methylene first increased and then decreased. A increase was observed in the Carboxyl group with the increase in the temperature. And the hydroxyl group decreased greatly with the increase of temperature. This information can guide firefighting operations in the field and help develop firefighting materials.

Impact of a split injection strategy on mixing, ignition and combustion behavior in Premixed charge compression ignition combustion

Mixing, ignition and combustion behavior in a rapid compression and expansion machine operated under Premixed Charge Compression Ignition (PCCI) relevant conditions are investigated by combined passive optical and laser-optical high-speed diagnostics. The PCCI concept is realized using a split injection schedule consisting of a long base load injection and two closely separated short injections near top dead center. Previous studies of close-coupled double injections under constant ambient conditions showed an increased penetration rate of the subsequent fuel spray. However, the aerodynamic gain from the preceding injection is counteracted by the density rise during the compression stroke under transient engine conditions. The study confirms that the rate of mixing of the subsequent fuel spray is significantly increased. Regarding combustion behavior, the thermodynamic analysis exhibits contributions of low temperature oxidation reactions of more than 20% to the total heat release, with a notable amount of unburnt fuel mass varying from 25 to 61%. The analysis of the optical data reveals the multi-dimensional impact of changes in operating parameters on the local mixture field and ignition dynamics. The onset of low temperature reactivity of the first short injection is found to be dominated by the operating strategy, while the location is strongly related to the local mixing state. Low temperature ignition of the consecutive fuel spray is significantly promoted, when upstream low temperature reactivity of the preceding injection is sustained. Likewise, it is shown that high temperature ignition is accelerated by the entrainment of persistent upstream low temperature reactivity.