Low Temperature Oxidation Regime Research Articles

Oxidation characteristics of heavy oil and its SARA fractions during combustion using TG-FTIR

The oxidation reactions between air and crude oils play a key role in in-situ combustion (ISC). This study is intended to explore the oxidation characteristics of one heavy oil and its SARA fractions by thermogravimetry associated with Fourier transform infrared spectroscopy (TG-FTIR). The results indicated the release behavior of typical evolved gases (hydrocarbons, CO2, CO, and H2O) during oxidation for the oil and its SARA fractions existed huge difference because of different structures and compositions. The heavy oil encountered appreciable weight loss at the low temperature oxidation (LTO) region where hydrocarbons, CO2, H2O, etc., were released. Quite a few coke could be formed from the LTO residue of heavy oil during fuel deposition (FD), thus resulting in a pronounced high temperature oxidation (HTO) stage characterized with apparent mass loss and one notably sharp peak of CO2. Saturates experienced a great amount of mass loss and release of hydrocarbons in the LTO regime. Aromatics showed obvious LTO and FD intervals in terms of mass loss and evolved gases, but its most of intermediate products during FD were evaporated with the temperature leading to the occurrence of weak HTO reactions. Resins was subjected to a small amount of mass loss and release of hydrocarbons and H2O in the LTO interval, and some of its intermediate products during FD formed coke through condensation reactions, which consequently led to a pronounced HTO stage. For asphaltenes, almost no hydrocarbons, CO2 and CO were released in the LTO region, and most of intermediate products at the initial FD stage condensed with each other to form coke. During HTO of asphaltenes, an extremely distinctive peak of CO2 and a small shoulder peak of CO and H2O were observed, verifying the occurrence of fierce combustion reactions.

Reaction Pathways, Thermodynamics, and Kinetics of Cyclopentanone Oxidation Intermediates: A Theoretical Approach.

Despite the promising role of cyclopentanone as a bioderived fuel, thermodynamic and kinetic data are lacking for low temperature oxidation regimes. In this study, ab initio calculations at the CBS-QB3 level explore the subsequent reactivity that results from O2-addition to 2- and 3-oxo cyclopentyl radicals, including expected reaction classes such as intra-H migration, HO2-elimination, cyclic ether formation, and β-scission along with their thermodynamic parameters. Some of the rates are similar to the analogous reactions of cyclopentane, but some other reactions of cyclopentanone are very different. The carbonyl group hinders H-migration from the α' position but promotes HO2-elimination. Enol peroxy formation from some hydroperoxy alkyl radicals of cyclopentanone is unexpectedly important, and so is HO2-elimination by β-scission. Our calculations also indicated that at engine relevant conditions the α-RO2 prefers to go back to the reactants 2-oxo cyclopentyl radical and O2. Therefore, the reactions resulting from HO2-addition to 2-oxo cyclopentyl are also provided. The lowest barrier channel identified on the singlet surface corresponds to an unexpected intra OH-migration path concerted with ring opening. This valuable information will advance the construction of improved kinetic models for the oxidation of cylopentanone.

Low-temperature chemistry triggered by probe cooling in a low-pressure premixed flame

Previous studies on sampling probe effects in the premixed flat flame showed that the temperature in the preheat zone can be lowered down to low-temperature oxidation regime (e.g., 400–800 K). In order to investigate the contribution of the low-temperature chemistry in flame-sampling experiments, a stoichiometric laminar premixed flat flame of ethylene/oxygen/argon was investigated at 30 Torr using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) in this work. Ethyl hydroperoxide (C2H5OOH) was identified and quantified in the present experiment, providing an experimental evidence for the existence of low-temperature chemistry in flame-sampling experiments. In addition to C2H5OOH, the formation of several other intermediates like ethanol and formaldehyde was also influenced by the low-temperature chemistry in the present flame-sampling experiment. A literature kinetic model (Hashemi et al., 2017) was used for predictions and analyses. The difference between the predicted maximum mole fractions of C2H5OOH with the perturbed and unperturbed temperature profiles can reach up to five orders of magnitude. The great improvement of the predictions with the perturbed temperature profiles indicates that the observed low-temperature chemistry in the present flame sampling experiment originates from the probe-induced perturbations, which lowers down the temperature window of the preheat zone and leads to a temperature drop of more than 400 K compared with the unperturbed temperature profile. Through modeling analysis, the low-temperature oxidation chemistry of ethylene involved in the present flame-sampling experiment was discussed. The influence of low-temperature chemistry in the present experiment has also been demonstrated by comparing the model predictions with/without key reactions at low temperatures. It is concluded that predicted maximum mole fractions of several low-temperature chemistry related intermediates, i.e. C2H5OOH, ethanol and formaldehyde, are strongly reduced without these reactions, while low-temperature chemistry only has negligible influence on the predictions of the fuel and the majority of flame intermediates. Furthermore, preliminary experiments were also conducted in ethane, propene and n-butane flames under similar conditions, where hydroperoxides can also be observed.

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

Impact of nitric oxide (NO) on n-heptane autoignition in a rapid compression machine

This paper investigates the impact of nitric oxide (NO) on n-heptane ignition in a rapid compression machine (RCM). The ignition delays of stoichiometric mixtures of n-heptane and varying amounts of NO (0–400 ppm) are measured in an argon diluent at 9 bar and over 650–1000 K. In the low temperature oxidation regime (≤ 720 K), ignition of n-heptane was promoted by NO up to 100 ppm, whilst higher NO levels do not further promote ignition. Stronger promoting effects are observed in the negative temperature coefficient (NTC) regime and at higher temperatures where the ignition delays are monotonically reduced with up to 400 ppm NO addition. Such impacts significantly suppress the NTC behaviour of pure n-heptane's oxidation. Kinetic modelling is then conducted using the mechanisms of Anderlohr et al. (2009) and Contino et al. (2013) to simulate the measured ignition delays, as well as the species profiles in a jet stirred reactor (JSR) reported in the literature. This modelling indicates that the reactions between NO and hydrocarbon species larger than C2 are important for reproducing both the RCM and JSR data. However, the rate constants for some of the reactions in the mechanism of Anderlohr et al. appear to be overestimated when compared to the literature, and also cause overprediction of the retarding effect on n-heptane autoignition at low temperatures. Use of these previously published rate constants in a revised mechanism is then found to significantly improve the agreement with the low temperature RCM data whilst retaining the good agreement with the higher temperature RCM data and the JSR data.

OXIDATION PROCESS IN IRON ORE MATERIALS AT LOW TEMPERATURES

Using methods of physico-chemical analysis (differentially– thermal and mineralogical) helped to study the oxidation process of magnetite (titanium magnetite) on samples from Olhovsk magnetite and Kachkanar titanium magnetite concentrates at low temperatures (200 –400 °C). Kinetic curves for the studied materials were obtained at different temperatures; they are typical for topochemical processes. Meanings of specific speeds of oxidation of magnetite various size at different temperatures were calculated and sizes of apparent energy of activation of the process were defined. The influence of partial pressure on kinetics of oxidation in gas phase was studied to expose the limiting point of the process of oxidation of magnetite and titanium magnetite. The order of oxidation reaction on oxygen at definite temperatures and the oxidation degree was calculated using graphical methods. The influence of titanium inclusions in magnetite on kinetics of phase change of magnetite–hematite was examined at the temperature interval of 200 –400 °C, it happens in mixed operational parameters. Then the process comes to diffusive operational parameters. Kinetic principles and the character of oxidation of the studied materials in nonisothermical conditions were defined at different speeds of heating. These results are of some interest and can be used to optimize the low temperature oxidation regimes of iron ore materials on a conveyor roasting machine.

Consumption and hydrocarbon growth processes in a 2-methyl-2-butene flame

This paper is concerned with the investigation of the chemical structure of a low-pressure, fuel-rich (ɸ = 1.8) premixed laminar flame fueled with 2-methyl-2-butene employing flame-sampling molecular-beam mass spectrometry with vacuum-ultraviolet single-photon ionization. Partially isomer-resolved mole fraction profiles can be explained by a decomposition scheme based on hydrogen abstraction and addition reactions. The presence of 9 allylic CH bonds compared to only one vinylic CH bond is the key feature that governs the fuel consumption and subsequent hydrocarbon growth reactions. Compared to other alkenes, including e.g., 1-butene, 2-butene, and iso-butene (Schenk et al., 2013), 2-methyl-2-butene shows a remarkable tendency to form soot precursor molecules such as toluene. In particular, experimental evidence is provided here that toluene, o-xylene, and styrene can be a starting point for PAH formation, thus serving as first aromatic rings besides benzene. The formation of toluene, o-xylene, and styrene can be traced back to the reactions of the resonantly stabilized C4H5 [∙CH2CCCH3 and CH2CH∙CCH2] radicals and the C5H7 [CH2C(CH3)∙CCH2] radicals that are readily formed through fuel-specific decomposition channels. Our experimental data in form of mole fraction profiles as a function of height above the burner for a mass range from 2 to 210 u can serve as reliable validation targets for model development. A preliminary comparison to the model of Westbrook et al. [1] that was optimized to capture ignition delay times and the low-temperature oxidation regime, shows promising elements already for the initial fuel consumption.

An atmospheric pressure high-temperature laminar flow reactor for investigation of combustion and related gas phase reaction systems.

A new high-temperature flow reactor experiment utilizing the powerful molecular beam mass spectrometry (MBMS) technique for detailed observation of gas phase kinetics in reacting flows is presented. The reactor design provides a consequent extension of the experimental portfolio of validation experiments for combustion reaction kinetics. Temperatures up to 1800 K are applicable by three individually controlled temperature zones with this atmospheric pressure flow reactor. Detailed speciation data are obtained using the sensitive MBMS technique, providing in situ access to almost all chemical species involved in the combustion process, including highly reactive species such as radicals. Strategies for quantifying the experimental data are presented alongside a careful analysis of the characterization of the experimental boundary conditions to enable precise numeric reproduction of the experimental results. The general capabilities of this new analytical tool for the investigation of reacting flows are demonstrated for a selected range of conditions, fuels, and applications. A detailed dataset for the well-known gaseous fuels, methane and ethylene, is provided and used to verify the experimental approach. Furthermore, application for liquid fuels and fuel components important for technical combustors like gas turbines and engines is demonstrated. Besides the detailed investigation of novel fuels and fuel components, the wide range of operation conditions gives access to extended combustion topics, such as super rich conditions at high temperature important for gasification processes, or the peroxy chemistry governing the low temperature oxidation regime. These demonstrations are accompanied by a first kinetic modeling approach, examining the opportunities for model validation purposes.

압축착화 엔진에서 분사압이 저온연소에 미치는 영향

Diesel low temperature combustion (LTC) is the concept where fuel is burned at a low temperature oxidation regime so that <TEX>$NO_x$</TEX> and particulate matters (PM) can simultaneously be reduced. There are two ways to realize low temperature combustion in compression ignition engines. One is to supply a large amount of EGR gas combined with advanced fuel injection timing. The other is to use a moderate level of EGR with fuel injection at near TDC which is generally called Modulated kinetics (MK) method. In this study, the effects of fuel injection pressure on performance and emissions of a single cylinder engine were evaluated using the latter approach. The engine test results show that MK operations were successfully achieved over a range of with 950 to 1050 bar in injection pressure with 16% <TEX>$O_2$</TEX> concentration, and <TEX>$NO_x$</TEX> and PM were significantly suppressed at the same time. In addition, with an increase in fuel injection pressure, the levels of smoke, THC and CO were decreased while <TEX>$NO_x$</TEX> emissions were increased. Moreover, as fuel injection timing retarded to TDC, more THC and CO emissions were generated, but smoke and <TEX>$NO_x$</TEX> were decreased.

Quantification of hydrogen peroxide during the low-temperature oxidation of alkanes.

The first reliable quantification of hydrogen peroxide (H(2)O(2)) formed during the low-temperature oxidation of an organic compound has been achieved thanks to a new system that couples a jet stirred reactor to a detection by continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared. The quantification of this key compound for hydrocarbon low-temperature oxidation regime has been obtained under conditions close to those actually observed before the autoignition. The studied hydrocarbon was n-butane, the smallest alkane which has an oxidation behavior close to that of the species present in gasoline and diesel fuels.

On the assumption of using n-heptane as a “surrogate fuel” for the description of the cool flame oxidation of diesel oil

Seven n-heptane oxidation chemical kinetic mechanisms of varied complexity are compared aiming to assess their performance in simulating the cool flame oxidative behaviour of diesel oil, as well as to investigate the validity of the utilization of n-heptane as a “surrogate fuel” for diesel oil. Computed temperature and species concentrations are compared to three different experimental data sets, corresponding to a range of perfectly stirred and plug flow reactor configurations, used for studying the low-temperature oxidation regime of n-heptane and diesel oil. In the cases of n-heptane oxidation, the quality of the kinetic mechanism predictions is found to decline with decreasing pressure levels. The detailed kinetic mechanisms outperform the predictions of the reduced mechanisms, exhibiting, however, discrepancies with the experimental data. In the case of diesel oil stabilized cool flame oxidation, detailed mechanisms fail to reproduce the observed thermo-chemical behaviour, whereas predictions of less detailed schemes show reasonable levels of agreement with the measurements, thus highlighting the limitations of the frequently utilized “surrogate fuel” assumption.

High Pressure Oxidation of Liquid Fuels From Low to High Temperature. 1. n-Heptane and iso-Octane.

Abstract Abstract–Normal heptane and iso-octane oxidations in a high-pressure jet-stirred reactor have been investigated experimentally in a wide range of conditions covering the low and high temperature oxidation regimes (550· 1150K, 10atm, 0.3 ≪Φ ≪ 1.5). Reactants, intermediates and final products have been measured providing a useful picture of n-heptane oxidation. The relatively high level of oxygenated compounds formed in the low temperature oxidation regime of n-heptane contrasts with the results obtained during iso-octane oxidation in the same conditions. The results are interpreted in terms of knocking and non-knocking tendencies related to fuel structure and low temperature oxidation mechanism.