Rate Of Production Analysis Research Articles

Study on oxidation and pyrolysis of carbonate esters using a micro flow reactor with a controlled temperature profile. Part I: Reactivities of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate

Carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are widely used as electrolyte solvents in a lithium-ion battery (LIB) and are considered as one of potential fire causes. This study investigates a difference in gas-phase reactivities of DMC, EMC and DEC. Species measurements for oxidation (equivalence ratio of 1.0) and pyrolysis of DMC and DEC at maximum wall temperatures of Tw,max = 700–1300 K and atmospheric pressure were performed using a gas chromatograph connected to a micro flow reactor with a controlled temperature profile (MFR). Measured mole fractions of C2H4 and CO2 in the DEC case started increasing at a low temperature (Tw,max = 750 K), while those of CH4 and CO2 in the DMC case started increasing at an intermediate temperature (Tw,max = 1050 K). Gas-phase reactivities of the three carbonate esters were found to be DMC < EMC ≈ DEC through observation of their weak flames. Computational species and heat release rate profiles of DEC showed a three-stage reaction: thermal decomposition, oxidation of decomposition products to CO and CO oxidation to CO2. This three-stage reaction of DEC is distinct from the one driven by low-temperature oxidation observed with n-heptane and DME in earlier studies. Rate of production analysis indicated that principal fuel consumption reactions of DMC were H-atom abstraction reactions and that of DEC was a thermal decomposition reaction producing C2H4. Based on reaction path analysis of DEC oxidation, initial-stage reactions produced few active radicals at the low temperature region. The reactivity difference between DMC and DEC is, therefore, mainly driven by the difference in the primary fuel consumption reactions that relies on fuel molecular structure. Considering the existence of ethyl ester group in EMC, a dominant EMC consumption reaction would be similar to DEC.

Experimental and kinetic study of hydrocarbon fuel pyrolysis in a shock tube

A pyrolysis study of hydrocarbon fuels (n-heptane and iso-octane) in a shock tube was conducted at temperatures range of 1200–2100 K and pressures range of 0.22–0.28 MPa. Several pyrolytic products were detected and quantified using gas chromatography. Different kinetic models were selected to simulate the fuel pyrolytic processes under the same experimental conditions. The results show that CH4, C2H2, C2H4, and C3H6 are the main products in the pyrolysis of n-heptane and iso-octane. The sensitivity and rate of production analysis indicate that olefins are the most important products in the pyrolysis, with the main decomposition pathways of n-heptane and iso-octane being hydrogen abstraction and C-C bonds scissions, respectively. In the pyrolysis of n-heptane, the main decomposition pathway is the hydrogen abstraction reaction by H/CH3 radicals, with ethylene as the main olefin product. In the pyrolysis of iso-octane, the main decomposition pathways are the direct cleavage reactions of the C-C bonds and isobutylene is the main olefin product. The difference in the pyrolysis characteristics between n-heptane and iso-octane is mainly caused by their different molecular structures.

Development of a Reduced Chemical Reaction Mechanism for n-Pentanol Based on Combined Reduction Methods and Genetic Algorithm.

To gradually reduce the demand for fossil energy and accelerate energy transformation, alcohol fuels are being vigorously developed and utilized in the world. n-Pentanol as a common alcohol fuel has attracted increasing attention in recent years owing to its many advantages. In this study, a reduced mechanism of n-pentanol containing 148 species and 575 reactions was established based on combined reduction methods including the direct relationship graph with error propagation, reaction pathway analysis, rate of production analysis, and temperature sensitivity analysis methods. Then, the reaction rate parameters were optimized using the nondominated sorting genetic algorithm II. A verification experiment for the oxidation of n-pentanol was conducted in a jet-stirred reactor (JSR) with gas chromatography-mass spectrometry. The main species mole fractions were quantitatively analyzed in the temperature range 700–1100 K, equivalence ratios of 0.5–2.0, and a pressure of 1 atm. Extensive validations were performed over wide experimental conditions by comparing the experimental data of the ignition delay time, species concentration profiles in the JSR, and laminar flame speed. It was found that the predicted values were in good agreement with the experimental values. Therefore, the reduced mechanism developed in this study can accurately predict the experimental results, which is capable of reasonably applying to the simulation of combustion behaviors of n-pentanol in internal combustion engines.

Probing pyrolysis chemistry of 1-heptene pyrolysis with insight into fuel molecular structure effects

The pyrolysis of 1-heptene was studied in a flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry at 0.04 and 1 atm and in a jet-stirred reactor using gas chromatography at 1 atm. Flow reactor pyrolysis products, including the allyl radical, cycloalkenes and aromatics, were identified and quantified. Alkenes are found to be the dominant product family, among which ethylene is the most abundant product. A detailed intermediate-to-high temperature model of 1-heptene was developed and validated against the new pyrolysis data in this work, as well as previous data of 1-heptene combustion in literature over a wide range of pressures, temperatures and equivalence ratios. Rate of production analysis and sensitivity analysis were performed to reveal the key pathways in fuel decomposition and product formation. The allylic CC bond dissociation reaction is concluded as the most important pathway in 1-heptene decomposition. Reactions of allyl, propargyl and cyclopentadienyl radicals play important roles in the formation of cycloalkenes and aromatics. Furthermore, comparative pyrolysis experiments of 1-hexene and n-heptane were also performed in the jet-stirred reactor at 1 atm using gas chromatography to explore fuel molecular structure effects on pyrolysis reactivity and product distributions among 1-alkene and n-alkane fuels. The comparison between 1-heptene and 1-hexene pyrolysis demonstrates that similar fuel molecular structure results in the similarities in primary fuel decomposition pathways and pyrolysis reactivity. Ethylene is the most abundant product in both 1-alkene pyrolysis, and the feature in 1-heptene molecular structure leads to enhanced formation of ethylene in its pyrolysis. The abundant formation of ethyl and methyl radicals leads to higher production of 1-pentene and 1-butene in 1-heptene and 1-hexene pyrolysis, respectively. The comparison between 1-heptene and n-heptane pyrolysis reveals that the existence of CC double bond enhances the pyrolysis reactivity of 1-heptene. Different from 1-heptene consumption, n-heptane consumption is dominantly controlled by H abstraction reactions instead of unimolecular decomposition reactions. Propene and 1-butene are prone to be produced in 1-heptene pyrolysis, while 1-hexene has higher mole fractions in n-heptane pyrolysis.

Experimental and kinetic modeling studies of 2-ethylfuran pyrolysis at low and atmospheric pressures

The pyrolysis of 2-ethylfuran (EF2) in a flow reactor was studied by using synchrotron vacuum ultraviolet photoionization mass spectrometry at 846 – 1319 K and at 30 and 760 Torr. Over 20 pyrolysis products were detected and measured. A detailed kinetic model was constructed by extending the reported comprehensive 2,5-dimethylfuran model to describe the pyrolysis of EF2 and validated against the current experimental results, including methyl, 2-furylmethyl, propargyl, acetylene , ethylene, propene , ketene, 2-vinylfuran, furan/vinylketene and benzene, etc. Rate of production analysis and sensitivity analysis indicate that the main reaction pathways of EF2 pyrolysis are H-abstraction reactions forming 1-(2-furyl)ethyl and 2-(2-furyl)ethyl, unimolecular decomposition reactions forming 2-furylmethyl, and H-addition reactions forming furan and vinylketene. The corresponding products, 2-vinylfuran, 2-furylmethyl and vinylketene, etc., are indicated to be the most key products in EF2 pyrolysis. Comparisons of the formation of aromatic hydrocarbons in the pyrolysis of EF2, 2-methylfuran and 2,5-dimethylfuran show that EF2 had a lower tendency to produce aromatic soot precursors.

An experimental investigation of furfural oxidation and the development of a comprehensive combustion model

The oxidation of furfural has been studied experimentally in a jet-stirred reactor (JSR) under fuel-lean (Φ = 0.4) and fuel-rich conditions (Φ = 2.0) in the temperature range of 650–950 K; in addition, laminar burning velocity data have been measured at T = 473 K and p = 1 bar within a wide fuel-air range. From the JSR experiments, 13 species profiles have been identified and quantified by GC–MS and GC. A detailed kinetic reaction model involving 382 species and 2262 reactions was developed by exploiting the experimental data base provided within the present work as well as experimental data reported in literature. The rate coefficients of reactions of H abstraction, H addition as well as of decomposition of furfural were calculated by quantum chemical methods at CBS-QB3 level. A general agreement was achieved when simulating the experimental data. Rate of production analysis as well as sensitivity analysis were performed to get a deeper insight into the combustion of furfural, e.g. for the jet-stirred reactor data at around 50% fuel conversion, as well as sensitivity analysis of laminar flame speeds conducted for a fuel-air ratio Φ = 0.9, 1.2, and 1.6. According to the analysis, the main consumption pathways of furfural oxidation were identified as H abstraction reactions of the R-CHO (aldehyde) group by H, OH, O, and HO 2 to produce a furfural radical (furfural-6). At pyrolysis condition, the dominant pathways within the furfural decay were found to occur via ring opening by splitting the C O bond followed by isomerization to form α-pyrone (C 5 H 4 O 2 ). Even more, the measured laminar flame speed data are well reproduced by the reaction model developed within the present work. The experimental data base as well as the developed reaction model will assist and contribute to a more detailed understanding of the combustion behavior of furfural and of furan derivatives as well.

Construction of a Skeletal Oxidation Mechanism for 2,5-Dimethylfuran Using Decoupling Methodology and Reaction Class-Based Global Sensitivity Analysis

As a promising alternative biofuel, 2,5-dimethylfuran (DMF) has caused great concern recently. In this research, a new skeletal oxidation mechanism for DMF is built by merging the decoupling methodology with the reaction class-based global sensitivity analysis. First, the global sensitivity and path sensitivity analyses are used to identify the dominant reaction classes in the fuel-related submechanism of DMF. Then, the important isomers in the dominant reaction classes are chosen with the rate of production analysis. In addition, the vertical reaction lumping is performed to obtain global reactions for the reaction classes based on the steady-state assumption of the involved intermediate radicals. A skeletal C4–C6 submechanism is obtained. Based on the decoupling methodology, an original skeletal mechanism of DMF is constructed by adding the skeletal fuel-related sub-mechanism into a compact C0–C3 submechanism. Third, the reaction rate coefficients involving the fuel-related species are tuned within their uncertainty ranges through the genetic algorithm to ameliorate the predictions of the skeletal mechanism on autoignition times in shock tubes and key species evolution in jet-stirred reactors (JSRs). The final skeletal mechanism for DMF is obtained, consisting of 57 species and 212 reactions. The satisfactory agreement between the measurement and prediction shows that the final skeletal mechanism is able to well capture the ignition and combustion phenomenon of DMF under wide operating conditions.

Impact of small-amount diesel addition on methane ignition behind reflected shock waves: Experiments and modeling

Autoignition characteristics of methane/diesel mixtures with diesel fractions of 5%, 15%, and 30% were investigated in a heated shock tube over temperatures of 960–1500 K, pressures of 6–20 bar, and equivalence ratios of 0.5, 1.0 and 2.0. Generally, ignition delay times (IDTs) decrease with increasing reflected-shock pressure or diesel content. The total equivalence ratio exhibits a slight influence on IDTs, whereas a crossover for IDTs occurs at a higher temperature from fuel-lean to fuel-rich conditions. Besides, three mechanisms in conjunction with a well-validated diesel surrogate were used to predict the IDTs of dual-fuel mixtures. Mech-3 (CRECK-2003) demonstrates the best performance under all test conditions based on quantitative error analysis. Moreover, there is a nonlinear mixing effect for methane/diesel mixtures. The IDT-reducing effect of diesel to methane is more pronounced compared to n-heptane, especially at intermediate-temperatures. Furthermore, the impact of diesel-addition on methane ignition was explored with kinetic analyses including species evolution, brute-force sensitivity analysis and rate of production analysis. These active radicals produced at the initial stage, especially for H radicals rapidly generated through the decomposition of diesel, readily trigger H-abstraction reactions on CH4, resulting in the continuous production of H from HCO decomposition and eventually triggering the hot-ignition via the chain-branching reactions of H + O2 = O + OH and H2 + O = H + OH. Consequently, the main reason for the IDT-reduction by diesel-addition at the high temperature is the rapid decomposition of diesel to produce H during the initial ignition period.

Structure of premixed flames of propylene oxide: Molecular beam mass spectrometric study and numerical simulation

The knowledge of the combustion chemistry of oxygenated fuels is essential for the development of detailed kinetic mechanisms suitable for the combustion processes involving biofuels. Moreover, epoxidized olefins, are increasingly used as chemical intermediates or as bulk chemicals. Nevertheless, a dearth of data for their reactivity in the oxidative environment can be observed in the current literature. This study reports the experimental and the model characterization of the flame structure of propylene oxide at stoichiometric and fuel-rich conditions at atmospheric pressure. To this aim, the species mole fractions in three premixed flames stabilized on a flat-flame burner have been quantitatively measured by using the flame sampling molecular beam mass spectrometry. Three chemical kinetic mechanisms retrieved from the current literature involving propylene oxide chemistry have been validated against the novel experimental data. In general, the predictions appeared to be in satisfactory agreement with measurements except for acetaldehyde and ketene. The rate of production analysis in the flame has shown that the discrepancies observed for these species are related basically to the incorrect ratio between the rates of primary reaction pathways of propylene oxide destruction.

Influence of the functional group of fuels on the construction of skeletal chemical mechanisms: A case study of 1-hexane, 1-hexene, and 1-hexanol

To investigate the oxidation and combustion performance of practical fuels, surrogate fuels including various types of fuels are usually introduced. The unique functional groups of different fuels dominate the fuel oxidation behaviors of different fuels, thus it is crucial to take account of the impact of fuel function groups for the development of the skeletal chemical mechanisms of surrogate fuels. In this work, by integrating the reaction class-based global sensitivity analysis and the decoupling methodology, a skeletal chemical mechanism of fuels is built, and the influence of the functional group was specially considered in the construction of the chemical mechanisms. First, the reaction class-based global sensitivity and path sensitivity analyses were employed to recognize the important reaction classes in the fuel-related sub-mechanism, and the reaction classes relevant to the fuel function group were identified. Second, a representative reaction was selected from each important reaction class by the rate of production analysis, and the skeletal fuel-specific sub-mechanism was obtained. Third, the initial skeletal chemical mechanism of fuels was formed by assembling the skeletal fuel-specific sub-mechanism with a detailed C0–C1 sub-mechanism and a reduced C2–C3 sub-mechanism based on the decoupling methodology. Finally, the optimization aiming at the ignition delay times and the concentrations of fuel, H2O, CO, and CO2 was conducted based on the genetic algorithm by tuning the reaction rate coefficients in the fuel-specific sub-mechanism within their uncertainties to enhance the performance of the skeletal mechanism. Using the above method, a skeletal chemical mechanism for 1-hexane, 1-hexene, and 1-hexanol was established containing 72 species and 243 reactions. The validation results indicated that decent consistency between the simulated and experimental data in premixed and opposed flames, jet-stirred reactors, and shock tubes was achieved for the three fuels over wide operating conditions. Moreover, the unique oxidation behavior of 1-hexane, 1-hexene, and 1-hexanol was captured by the present skeletal mechanism due to the identification of the functional group reactions.

Experimental and numerical investigation on nitrogen transformation in pressurized oxy-fuel combustion of pulverized coal

As a cutting-edge high-efficiency combustion technology, pressurized oxy-fuel combustion (POFC) has attracted worldwide attention. Although extensive investigations have been performed on POFC to clarify the effect of different operating parameters under high CO2 partial pressure conditions, the NOx emission behaviour is not entirely understood. Experimental analysis and numerical simulations were conducted in this research to understand the nitrogen transformation mechanisms for different operating parameters. When the system pressure was increased from 0.1 MPa to 1.6 MPa, the NO emissions decreased by 41%, which was caused due to both homogeneous and heterogeneous reductions. NO emissions increased by 1.56 times after a temperature increment from 700 °C to 1100 °C. It was also discovered that NO emissions increased by 5.32 times as the oxygen concentration went up from 10% to 60%. Numerical results were highly consistent with the experimental findings, which indicates that NO emissions were primarily impacted by six elementary reactions that involve multiple intermediate species, including NCO, HNO, and NH. The main reaction pathway from fuel-N to various N products was studied through a rate of production analysis. These results show the importance of understanding the impact of operating parameters on NOx emissions in pressurized oxy-fuel conditions, which will help to facilitate the application of POFC technology in large-scale boilers.

Exploration on laminar flame propagation of ammonia and syngas mixtures up to 10 atm

Reactivity enhancement is crucial for the potential applications of ammonia (NH3) as a gas turbine fuel. Doping more reactive fuels like H2, methane and syngas is a widely adopted strategy in this field, however fundamental combustion studies of NH3/reactive fuel mixtures under gas turbine-relevant high pressure conditions are still very limited. This work reports an effort to study laminar flame propagation of NH3/syngas mixtures up to 10 atm. Laminar burning velocities (LBVs) of NH3/syngas/air mixtures were measured at 298 K, various syngas contents in fuel mixtures (α) and H2 contents in syngas (β), and equivalence ratios of 0.7–1.5 in a high-pressure constant-volume cylindrical combustion vessel. A kinetic model was developed for NH3/syngas combustion based on our recent NH3 model and a recent syngas model in literature. It shows reasonable predictions on the present NH3/syngas LBVs at 1–10 atm, as well as previous data including NH3/syngas LBVs at 1 atm, NH3/syngas ignition delay times at various pressures and pure NH3 LBVs at various pressures. Modeling analysis including the sensitivity analysis and rate of production analysis provides kinetic interpretation for the effects of fuel composition (α and β), equivalence ratio and pressure on NH3/syngas LBVs. It is found that the addition of syngas shifts the chemistry from NH3 sub-mechanism to syngas sub-mechanism. A modified fictitious diluent gas method was proposed to separate the chemical and thermal effects of syngas addition, which shows that the chemical effect is more responsible for the enhanced laminar flame propagation. NH3/syngas/air flames have similar reaction networks but different preferred pathways under lean and rich conditions. Compared with pure NH3 flames, the addition of syngas also improves the importance of H + O2 (+ M) = HO2 (+ M) and consequently leads to strong pressure dependency of NH3/syngas/air flames.

Mechanism study of nitric oxide reduction by light gases from typical Chinese coals

Coal devolatilization plays an important role in NO formation and reduction. In this study, the coal pyrolysis experiment was performed in an entrained flow reactor to obtain the light gas release characteristics. Six typical Chinese coals with volatile content ranged from 8.8% to 38.3% were studied. The pyrolysis temperature was in the range from 600 to 1200 °C. A significant rank dependence of HCN, CO and C2H2/C2H4/C2H6 was observed and their release for high volatile coals was higher than that for low volatile coals. The HCN–N/NH3–N ratio ranged from 0.00 to 0.66 for anthracite coals and ranged from 1.63 to 3.90 for high volatile coals. Based on the experimental results, the effect of coal pyrolysis gas on NO reduction in a plug flow reactor at reducing atmosphere was kinetically calculated. The optimal excess air ratio(αopt) corresponding to the maximum NO removal efficiency decreased with an increase in reduction temperature. For the light gas from the HL coal pyrolyzed at 800 °C, the αopt decreased from 0.73 to 0.17 when the reduction temperature increased from 927 to 1327 °C. The rate of production analysis indicated that NO removal efficiency was determined by 3 competing reaction paths: NO reduction, NO formation and oxygen consumption by combustible species.

Comparative Study on the Formation and Oxidation of Polycyclic Aromatic Hydrocarbons in the Combustion of Four Butanol Isomers

The formation and oxidation of polycyclic aromatic hydrocarbons (PAHs) precursors during the combustion of n-, sec-, iso- and tert-butanol are computationally investigated at an equivalence ratio of 1.5, an initial pressure of 1.0 atm and a temperature range from 800 to 2000 K in a perfectly stirred reactor. The results indicate that branched chain structure led to an increase in the mole fraction of PAHs. Tert-butanol has the greatest ability in forming PAHs, it can be attributed to the advantage in the β-C–H bonds number. The rate of production analysis reveals that for the butanol isomers with the hydroxyl (OH) group attached to a terminal carbon (n- and iso-butanol), the role of OH radical in the oxidation process of PAHs is enhanced. Compared to the other three butanol isomers, a significant increase in the contribution ratios of C5 and C9 pathways to the formation of PAHs for tert-butanol is observed.

Detailed kinetic modeling of H2S formation during fuel-rich combustion of pulverized coal

The paper presents a detailed kinetic study on H2S formation during fuel-rich combustion of pulverized coal via tube furnace experiment and kinetic analysis with Chemkin. A new detailed kinetic model involving 34 species and 115 reactions was developed, with emphasis on CS2 as a source for H2S. The novel model was validated using experimental data with respect to the concentration distributions of H2, CO, H2O, CO2, SO2, H2S, COS and CS2. Sensitivity analysis shows that H2S concentration was very sensitive to reactions (2) H2S + H = SH + H2, (89) SO2 + CO = SO + CO2, (104) COS + H2O = H2S + CO2, (62) HOSO (+M) = H + SO2 (+M), (103) CS2 + H2O = H2S + COS, etc. Also, SH, S, and SO were the key free radicals for H2S production. Rate of production analysis (ROP) were also performed, which indicate that SH was the most important precursor of H2S. Based on the detailed kinetic model and ROP analysis, the simplified reaction path of H2S formation was constructed. Finally, the new model was compared with the Leeds University sulfur chemistry model. The two models have the same key free radicals and four major elementary reactions. The main difference is that CS2 was a notable source for H2S in our model targeted for coal combustion, and should be given special attention.

The role of chemistry in the oscillating combustion of hydrocarbons: An experimental and theoretical study

The stable operation of low-temperature combustion processes is an open challenge, due to the presence of undesired deviations from steady-state conditions: among them, oscillatory behaviors have been raising significant interest. In this work, the establishment of limit cycles during the combustion of hydrocarbons in a well-stirred reactor was analyzed to investigate the role of chemistry in such phenomena. An experimental investigation of methane oxidation in dilute conditions was carried out, thus creating quasi-isothermal conditions and decoupling kinetic effects from thermal ones. The transient evolution of the mole fractions of the major species was obtained for different dilution levels (0.0025⩽XCH4≤0.025), inlet temperatures (1080K⩽T≤1190K) and equivalence ratios (0.75⩽Φ≤1). Rate of production analysis and sensitivity analysis on a fundamental kinetic model allowed to identify the role of the dominating recombination reactions, first driving ignition, then causing extinction.A bifurcation analysis provided further insight in the major role of these reactions for the reactor stability. One-parameter continuation allowed to identify a temperature range where a single, unstable solution exists, and where oscillations were actually observed. Multiple unstable states were identified below the upper branch, where the stable (cold) solution is preferred. The role of recombination reactions in determining the width of the unstable region could be captured, and bifurcation analysis showed that, by decreasing their strength, the unstable range was progressively reduced, up to the full disappearance of oscillations. This affected also the oxidation of heavier hydrocarbons, like ethylene. Finally, less dilute conditions were analyzed using propane as fuel: the coupling with heat exchange resulted in multiple Hopf Bifurcations, with the consequent formation of intermediate, stable regions within the instability range in agreement with the experimental observations.

Ignition delay time and species measurement in a rapid compression machine: A case study on high-pressure oxidation of propane

To understand and develop a robust kinetic model for describing the oxidation of a fuel, knowledge of different physicochemical parameters is essential. It can be global parameters like ignition delay times (IDTs) and laminar burning velocities or intrinsic local parameter like species mole fraction profiles. Different facilities have been utilized to provide such measured values from a wide range of conditions that aid in the validation of a detailed chemical kinetic mechanism. In this study, IDT and stable intermediate species mole fractions were obtained for a non-diluted stoichiometric mixture of propane/oxygen/inert gas at compressed pressures of 30 and 50 bar in a rapid compression machine. The species mole fractions during the ignition delay period were obtained at 747 K for 50 bar and 765 K for the 30 bar condition. The species measurement for non-diluted mixtures at such high pressures is vital as there is a change in the sensitivities of the important reactions at these conditions. The non-diluted mixture under this range of pressures represent the application relevant conditions, and the speciation measurement is, for the first time investigated at such conditions in an RCM. This aspect directly highlights the novelty of this study. The work elaborates, in detail, the methodology used for the measurement and simulation of the species mole fraction at the measured conditions with emphasis on the relevant uncertainties. The discussion also includes the significance of sampling from the reaction core and the outcome of the results when sampling from the boundary layer. The IDT measurements are utilized to find a suitable mechanism from the literature that well represents the reactivity both qualitatively and quantitatively in the measured regime. The selected mechanism is used for the simulation and comparison with the measured species mole fractions profiles. The sensitivity and rate of production analysis are performed using the selected mechanism to comprehend the important pathways leading to the formation of the key stable species observed in this experimental work.

Experimental and kinetic modeling investigation on sec-butylbenzene combustion: Flow reactor pyrolysis and laminar flame propagation at various pressures

This work reports the investigation on pyrolysis and laminar flame propagation of sec-butylbenzene. The pyrolysis experiments were performed in a flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry from 780 to 1166 K at 0.04 and 1 atm. The pyrolysis products were identified and their mole fraction profiles versus the heating temperature were evaluated. The laminar burning velocities of sec-butylbenzene/air mixtures were measured at the initial temperature of 423 K and initial pressures of 1–10 atm in a high-pressure constant-volume cylindrical combustion vessel with the equivalence ratio from 0.7 to 1.5. Furthermore, a kinetic model was developed to predict the pyrolysis and laminar flame propagation of sec‑butylbenzene. Validation of the present model was performed against the new experimental data in this work. Rate of production analysis and sensitivity analysis were performed to provide insight into the chemistry in fuel decomposition and polycyclic aromatic hydrocarbons (PAHs) formation. In the flow reactor pyrolysis, the consumption of sec‑butylbenzene is mainly controlled by the unimolecular decomposition reactions and H-atom abstraction reactions at both low and atmospheric pressures. Fuel specific pathways through propenylbenzene and α-methylstyrene become the dominant formation pathways of indene and naphthalene. In the laminar flame propagation, the laminar burning velocity of sec‑butylbenzene is sensitive to the reactions of both small species and fuel-relevant intermediates under all investigated conditions. In particular, the pyrolysis reactions in the fuel sub-mechanism play inhibition effects on the laminar flame propagation of sec‑butylbenzene under rich conditions. The laminar burning velocity of sec‑butylbenzene is also compared with benzene, toluene and ethylbenzene under same initial conditions. Both the thermodynamic and kinetic effects are responsible for the difference in laminar burning velocities of these aromatic fuels.

Experimental and kinetic modeling study of n-propanol and i-propanol combustion: Flow reactor pyrolysis and laminar flame propagation

Flow reactor pyrolysis and laminar flame propagation are investigated for n-propanol and i-propanol, which are the smallest alcohol fuels with isomeric structures. Pyrolysis products of propanol isomers at 0.04–1 atm are detected using the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Experimental observations demonstrate ethylene and propene are respective dominant hydrocarbon products in the n-propanol and i-propanol pyrolysis, while the most abundant oxygenated products are formaldehyde, acetaldehyde and ethenol in the n-propanol pyrolysis and acetone and acetaldehyde in the i-propanol pyrolysis. Higher concentrations of aromatic and oxygenated pollutants are observed in the i-propanol pyrolysis. The laminar burning velocities of propanol isomers are measured in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 423 K, pressures of 1–10 atm and equivalence ratios of 0.6–1.5. A general trend that n-propanol has much faster LBVs than i-propanol is noticed under all investigated conditions. A kinetic model of propanol isomers is developed and validated against the present experimental data, as well as other experimental data in literature covering wide ranges of temperatures, pressures and equivalence ratios. Rate of production analysis and sensitivity analysis are performed together to provide insight into the fuel isomeric effects on key reaction pathways and fuel reactivities. In the flow reactor pyrolysis, different dominant primary decomposition pathways of n-propanol and i-propanol lead to the differences in both molecular structures and concentration levels of pyrolysis products. In laminar flame propagation, different radical pool distributions of propanol isomers are illustrated and found to be largely influenced by fuel isomeric structures. The linear structure of n-propanol promotes the formation of more active radicals like formyl, vinyl and ethyl, while the branched structure of i-propanol facilitates the production of more stable radicals including methyl and allyl. Thus, the promoted chain-branching in n-propanol flames and enhanced chain-termination in i-propanol flames can explain the higher laminar burning velocities and reactivities of n-propanol than that of i-propanol.

Low to intermediate temperature oxidation studies of dimethoxymethane/n-heptane blends in a jet-stirred reactor

Kinetic research concerning fuel blends of ethers or dithers and larger alkanes at low temperatures is extremely scarce. In this work, a study of the oxidation of dimethoxymethane (DMM)/n-heptane fuel blends (neat n-heptane, 25/75, 50/50, neat DMM) was performed using an atmospheric pressure jet-stirred reactor over the temperature range of 500–1100 K, at a residence time of 2.0 s, at three equivalence ratios (0.5, 1.0, and 2.0), and at a constant fuel inlet mole fraction of 0.005 (with high dilution in argon). The reliability of the newly built JSR setup was validated against literature data. A chemical kinetic model capable of describing the low temperature chemistry of the fuel blends was constructed. The effect of using AramcoMech 1.3 and AramcoMech 2.0, respectively, as the base-mechanism has been tested and some important reactions such as Ḣ +O2 (+M) <=> HȮ2 (+M), have been found to be responsible for their different performances. Not unexpectedly, the reactivity of DMM is remarkably enhanced in the fuel blends and correspondingly, that of n-heptane is inhibited. To quantify the degree to which the reactivity of n-heptane is inhibited, an inhibiting coefficient was introduced. It is interesting that the correlation between the inhibiting intensity and equivalence ratio is non-monotonic. Rate of production analysis was conducted to investigate the chemical interaction effect on their respective decomposition pathways at lower temperatures. Kinetic analysis combined with the experimental observations indicate that the rate coefficients for H-abstraction reactions by ȮH from DMM were overestimated. Possible modifications to the reaction rate of this reaction type were suggested, leading to a better prediction. Three intermediate representatives were discussed in detail to elucidate the chemical interactions between the two fuel components.