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Growing demand for low-emission and high-efficiency propulsion systems spurs interest in understanding low-temperature and ultra-high-pressure combustion of alternative biofuels like diethyl ether (DEE). In this study, DEE oxidation experiments are performed at 10 and 100 atm, over a temperature range of 400-900 K, at fuel-lean, stoichiometric, and fuel-rich conditions by using a supercritical pressure jet-stirred reactor (SP-JSR). The experimental data show that DEE is very reactive and exhibits an uncommon low-temperature oxidation behavior with two negative temperature coefficient (NTC) zones. The first NTC zone is mainly governed by the competition reactions of QOOH + O

This work investigated the structure and oxidation reactivity of soot sampled from a laminar coflow diffusion flame of ethylene. A capillary-nozzle-hybrid sampling method was developed to extract soot from five sampling positions along flame axis, covering both early-stage and mature soot samples. The results reveal that residence time plays an important role in modifying surface functional groups. Oxygenated and aliphatic groups gradually disappear, soot structure becomes more organized. As a consequence, the rate of mass losses is impaired during thermo-chemical conversion. The derivative thermogravimetry (DTG) results show that oxidation of early-stage soot can be separated into low-temperature (low-T) conversion and carbonaceous substances oxidation processes. The former process including both volatile organic fraction (VOF) releasing and early oxidation reactions generates the first maximum mass loss rate at about 510 °C, while the latter forms the second maximum mass loss rate at about 600 °C. Recognizing that the two processes are partially merged, the distributed activation energy model (DAEM) was introduced to decouple the bimodal behavior of DTG curves. The DAEM results reveal that with increased degree of soot maturity, relative contribution from low-T conversion process decreases abruptly, and DTG curve eventually becomes unimodal and can be well simulated by considering only carbonaceous substances oxidation process.

In this work, pyrolysis experiments of ethyl valerate were performed in a flow reactor over 705–1051 K at low and atmospheric pressures and in a jet-stirred reactor over 633–1013 K at near-atmospheric pressure. Products were measured with synchrotron vacuum ultraviolet photoionization mass spectrometry in the flow reactor pyrolysis and gas chromatography in the jet-stirred reactor pyrolysis. Valeric acid and ethylene were observed as the most abundant pyrolysis products in both experiments. Laminar burning velocities of ethyl valerate/air mixtures were also measured in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 443 K and initial pressures of 1–10 atm. A kinetic model of ethyl valerate combustion incorporated with recent theoretical progress was developed to predict the new experimental data in this work, as well as the speciation data under flame conditions and laminar burning velocities at different initial temperatures and pressures in literature. Experimental observations and modeling analyses both confirm the significant role of the intramolecular elimination reaction of ethyl valerate producing valeric acid and ethylene. In particular, this reaction has exclusive significance in decomposition of ethyl valerate under pyrolysis conditions, indicating pyrolysis experiments can provide crucial constraints for its rate constant. Subsequent decomposition reactions of valeric acid at higher temperatures enrich the intermediate pool, especially radicals, and can continue producing ethylene to make its mole fraction keep growing under the investigated temperature ranges in the jet-stirred reactor pyrolysis. Under the flame propagation conditions, C0 C1 reactions have the highest sensitivity coefficients to the flame propagation, while ethylene- and vinyl-involved reactions also play important roles due to the abundant production of ethylene.

In order to study the combustion chemistry of carboxyl functionality, the laminar burning velocity of acetic acid/air and propanoic acid/air mixtures was investigated in a high-pressure constant-volume cylindrical combustion vessel at 423 K, 1 atm and equivalence ratios of 0.7–1.4. Experimental results reveal that the flame propagation of propanoic acid flame is much faster than that of acetic acid flame, especially under rich conditions, and the laminar burning velocity of propanoic acid/air mixtures peaks at richer conditions than that of acetic acid. The present theoretical calculations for the isomerization and decomposition of propanoic acid radicals indicate that the primary radical products are HOCO, H and C2H5, while those in acetic acid flame are CH3 and OH based on previous studies. A kinetic model of the two acids was developed mainly based on previous and the present theoretical calculation results. It could reasonably capture the measured laminar burning velocities of acetic acid/air and propanoic acid/air mixtures in this work, as well as the previous experimental data in literature. Based on the present model, CH3- and ketene-related pathways play an important role in acetic acid flames. Under rich conditions, ketene is mostly converted to CH3 via CH2CO+H CH3+CO, and the chain-termination reaction of CH3+H(+M)=CH4(+M) is enhanced, which strongly inhibits the propagation of rich acetic acid flames. In contrast, C2H5 and ethylene chemistry play an important role in propanoic acid flames. Rich conditions promote the decomposition of C2H5, yielding ethylene and H, which can facilitate the flame propagation. This can explain the shift of the peak laminar burning velocity of propanoic acid/air mixtures towards a slightly richer condition compared with that of acetic acid/air mixtures.

This work reports an experimental and kinetic modeling investigation on the laminar flame propagation of three butylbenzene isomers (n-butylbenzene, iso-butylbenzene and tert-butylbenzene)/air mixtures. The experiments were performed in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 423 K, initial pressures of 1–10 atm, and equivalence ratios (ϕ) of 0.7–1.5. The laminar burning velocities of butylbenzene/O2/He mixtures were also measured at 423 K, 10 atm and ϕ = 1.5 to provide additional experimental data under conditions that the butylbenzene/air experiments are susceptible of cellular instability. Comparison among the laminar burning velocities of butylbenzenes including both the three isomers investigated in this work and sec-butylbenzene investigated in our recent work [Combust. Flame 211 (2020) 18–31] shows remarkable fuel isomeric effects, that is, iso-butylbenzene has the slowest laminar burning velocities, followed by n-butylbenzene and tert-butylbenzene, while sec-butylbenzene has the fastest laminar burning velocities. A kinetic model for butylbenzene combustion was developed to simulate the laminar flame propagation of butylbenzenes. Sensitivity analysis was performed to reveal important reactions in laminar flame propagation of butylbenzenes, including both small species reactions and fuel-specific reactions. Kinetic effects are concluded to result in the different laminar burning velocities of four butylbenzene isomers. Small species reactions control the laminar flame propagation under lean conditions, which results in small differences of laminar burning velocities. Chain termination reactions, especially fuel-specific reactions, have important contributions to inhibit the laminar flame propagation under rich conditions. The structural features of butylbenzene isomers can significantly affect the formation of some crucial radicals such as methyl, cyclopentadienyl and benzyl radicals under rich conditions, which leads to remarkable fuel isomeric effects on their laminar burning velocities, especially at high pressures.

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.

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.

Ammonia is attracting more and more attentions due to its role as both a carbon-free fuel for gas turbines and an effective H2 carrier. Only a limit number of investigations on the laminar flame propagation and laminar burning velocity of ammonia have been performed on elevated pressures, which were focused on ammonia/air mixtures and suffered strong buoyancy effect. In this work, laminar flame propagation of ammonia/O2/N2 mixtures covering wide ranges of equivalence ratios, oxygen contents and initial pressures was investigated in a high-pressure constant-volume cylindrical combustion vessel. The oxygen enrichment speeds up the spherically expanding flames and consequently reduces buoyancy effect on the laminar flame propagation of ammonia. The laminar burning velocity was observed to increase with the increasing oxygen content, but decrease with the increasing initial pressure. A kinetic model of ammonia combustion consisting 38 species and 265 reactions was constructed from previous models with updated rate constants of important reactions. The present model can reasonably reproduce the laminar burning velocity data in this work and literature, as well as the ignition delay time and speciation data in literature. Based on the model analysis, effects of oxygen enrichment, equivalence ratio and initial pressure on laminar burning velocities of ammonia were analyzed in detail. It is revealed that the enhanced flame propagation with oxygen enrichment is mainly due to the increase of adiabatic flame temperature which in turn leads to higher concentrations of key radicals like H, OH and NH2. For NH3 and its major decomposition products like NH2 and NH, reactions with oxygenated species such as OH, O, O2 and NO are generally more important in the lean flames, while the role of reactions with H, NH and NH2 becomes crucial in the rich flames. The calculated pressure dependent coefficient indicates that NH3/O2/N2 flames exhibit clear pressure dependence, while this pressure dependence is weaker than those of the hydrocarbon and biofuel flames.

In this work, laminar flame speeds of CH4/CO/air mixtures were measured at the unburnt temperature of 353 K and pressures from 1 to 10 atm in a high-pressure constant-volume cylindrical combustion vessel. Effects of pressure, equivalence ratio and CO content in CH4/CO mixtures on laminar flame speeds were investigated. A kinetic model for CH4/CO combustion was developed based on recent progress in elementary reactions and validated against previous and present experimental targets. It is found that both the thermal effect originating from different adiabatic flame temperatures and chemical effect originating from differences in the radical pool play important roles in the variation of laminar flame speed. The separate contribution of each effect varies at different pressures, equivalence ratios and CO contents. Besides, the transition from CH4-related chemistry to CO-related chemistry can be monitored by the increasing concentration of O atom in the radical pool under all the investigated conditions. Based on the modeling analysis, R18 (CH3 + CH3 (+M) = C2H6 (+M)), R19 (HCO (+M) = H + CO (+M)), R6 (CH4 (+M) = CH3 + H (+M)) and R7 (CH4 + H = CH3 + H2) have major contributions to the transition chemistry, especially under the rich conditions. Compared with the atmospheric pressure conditions, R20 (CO + O (+M) = CO2 (+M)) and R22 (H + O2 (+M) = HO2 (+M)) are enhanced at high pressures, which leads to the decrease of O atom in the radical pool at high pressures.

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.

The laminar flame propagation of 1-heptene/air mixtures covering equivalence ratios from 0.7 to 1.5 is investigated in a constant-volume cylindrical combustion vessel at 373 K and elevated pressures (1, 2, 5, and 10 atm). Laminar flame speed and Markstein length are derived from the recorded schlieren images. A kinetic model of 1-heptene combustion is developed based on our previous kinetic model of 1-hexene. The model is validated against the laminar flame speed data measured in this work and the ignition delay time data in literature. Modeling analyses, such as sensitivity analysis and rate of production analysis, are performed to help understand the high temperature chemistry of 1-heptene under various pressures and its influence on the laminar flame propagation. Furthermore, the laminar flame propagation of 1-heptene/air mixtures is compared with that of n-heptane/air mixtures reported in our previous work. The laminar flame speed values of 1-heptene/air mixtures are observed to be faster than those of n-heptane/air mixtures under most conditions due to the enhanced exothermicity and reactivity.

A joint schlieren imaging, pressure recording and tunable diode laser absorption spectroscopy (TDLAS) thermometry technique was developed to simultaneously determine the flame radius, pressure and line-of-sight averaged temperature of spherically expanding flames of n-butane/air mixtures at initial temperature of 298 K, initial pressure of 1 atm and equivalence ratios of 0.9–1.5. To probe the flame temperature, a mid-infrared interband cascade laser at 4.2 µm was used to measure the time-resolved direct absorption spectra of CO2 which are strongly related to flame temperature, CO2 mole fraction, flame radius and pressure. Quantitative line-of-sight averaged temperatures of burnt gas were obtained by fitting the normalized absorbance spectra. Three typical stages, including the spark affected initial stage, quasi-steady stage and the pressure induced growing stage are determined from the evolution of measured temperature as a function of time and flame radius. The relation between flame temperature, stretch rate and burning velocity of burnt gas are analyzed. Stretch rate is found to have minor effect on the measured temperature in the quasi-steady stage. The relative variation of temperature is much smaller than that of velocity. The flame with lower normalized temperature tends to propagate slower.

To explore the fuel isomeric effect on ether combustion characteristics, pyrolysis, and laminar flame propagation of di-n-propyl ether (DPE) and diisopropyl ether (DIPE) were investigated. A new kinetic model of DIPE was developed based on our recent DPE model [Fuel 298 (2021) 120797]. The pyrolysis experiments were carried out in two jet-stirred reactors at near-atmospheric pressure with good agreement on the measurements using synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography/mass spectrometry. The decomposition profile of DIPE showed a faster trend than that of DPE, which can be attributed to the faster alcohol elimination reaction of DIPE. The dominant roles of alcohol elimination reaction and H-abstraction reactions in fuel consumption explain the production of fuel-specific oxygenated species, i.e. n-propanol and propanal in DPE and i-propanol, acetaldehyde and acetone in DIPE. The laminar burning velocities of DPE and DIPE were also measured in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 373 K and pressures of 1–10 atm. It was found that the linear DPE propagated faster than DIPE with the branched structure under all investigated conditions. Rate of production analysis and sensitivity analysis were also performed to elucidate the key radicals and reactions responsible for the remarkable reactivity of isomeric fuels. Fuel structures have a great influence on the distribution of radical pools, resulting in the easy formation of active radicals in DPE flames such as vinyl and ethyl and stable radicals in DIPE flames like methyl and allyl. The successive decomposition reactions of these dominant radicals promote the DPE flame and inhibit the DIPE flame propagation respectively, which explains the higher laminar burning velocities and reactivity of DPE than that of DIPE. Furthermore, the present model was also examined against the literature data, including pyrolysis and oxidation in the jet-stirred reactor and flow reactor.

The pyrolysis of methyl decanoate (MD), an ideal surrogate of biodiesels, was investigated in a flow reactor at the pressures of 30 and 760 Torr and the temperature ranging from 773 to 1198 K. A great variety of pyrolysis products including free radicals, n-alkanes, 1-alkenes, alkynes, unsaturated esters and aromatics were comprehensively observed and identified by employing synchrotron vacuum ultraviolet photoionization mass spectrometry. A new kinetic model for MD pyrolysis was constructed and applied to validate the experimental data. Modeling analyses involving rate of production analysis and sensitivity analysis were performed to help explore the pyrolysis kinetics of MD and the formation mechanisms of key species. The analysis results show that the decomposition of MD is determined by the H-abstraction and unimolecular dissociation reactions during the whole pyrolysis process, whereas the contributions of H-abstraction reactions are enhanced as the pressure elevates. C4-C9 unsaturated esters are principally yielded from the β-scission of ester radicals; while the β-scission reactions of MD radicals are responsible for the formation of C5-C9 1-alkenes. In addition, 1-alkenes can be further decomposed to form small radicals and molecules. Through the combination reactions such as the reaction routes of C3 + C3, C4 + C2 and C5 + C2, these radicals and molecules can be transformed into benzene and benzyl radical, which are demonstrated as the crucial precursors of polycyclic aromatic hydrocarbons. In conclusion, the pyrolysis of MD would not only significantly enhance the cognitions of various pollutant formation mechanisms but also have a guiding significance for the combustion in the fuel-cooled engine.

The low combustion intensity of ammonia (NH3) raises great research needs of combustion enhancement strategies for its practical applications. Considering the high proportion of hydrogen in cracked gas of NH3, partial fuel cracking is a feasible strategy to enhance NH3 combustion. This work reports an experimental and kinetic modeling study on the laminar flame propagation of partially cracked NH3/air mixtures (NH3/H2/N2/air mixtures) up to 10 atm. Laminar burning velocities (LBVs) of partially cracked NH3/air mixtures are measured at various cracking ratios and equivalence ratios using a high-pressure constant-volume cylindrical combustion vessel. Our recently reported NH3/syngas model is updated to simulate the experimental results, which shows satisfactory performance on predicting the partially cracked NH3/air LBVs in this work, as well as the LBV and speciation data of NH3 and NH3/H2 combustion in literature. modeling analysis is performed to provide insight into effects of equivalence ratio, cracking ratio and pressure on laminar flame propagation of partially cracked NH3/air mixtures. The modified fictitious diluent gas method reported in our recent work is adopted to separate thermal and other effects in enhancement of NH3 combustion. The analysis results indicate that thermal effect only plays a minor role in the enhancement of laminar flame propagation of NH3 in partial fuel cracking strategy, while chemical effect should be significant for the enhanced laminar flame propagation. Due to the presence of H2 in cracked gas, reaction H + O2 (+M) = HO2 (+M) shows enhanced importance and makes the laminar flame propagation of partially cracked NH3/air mixtures more pressure-dependent. Furthermore, NO formation characteristics with increasing cracking ratio is also numerically investigated, which shows that fuel NO is the major NOx formation source. The results reveal a dramatic non-monotonic behavior of NO formation as the cracking ratio increases, which originates from the transition of NH3 chemistry to cracked gas chemistry.

This work reports investigations on laminar premixed ethylene (C2H4) flames with special interests on measurements and kinetic modeling at elevated pressures. Chemical structures of laminar premixed C2H4/O2/Ar flames at 3 and 5 atm with the equivalence ratio of 1.4 were measured with molecular beam mass spectrometry. Both the stable and reactive species were identified and quantified in this work. Among them, the mole fractions of H and OH are evidently dependent on pressures. Laminar flame propagation of C2H4/air mixtures at 1 and 2 atm and that of C2H4/O2/He mixtures at 2 and 5 atm were also investigated in a high pressure constant-volume cylindrical combustion vessel at an unburnt temperature (Tu) of 298 K and equivalence ratios of 0.7–1.5. Besides, a kinetic model for C2H4 combustion was developed based on the evaluations of critical reactions with special concerns on recent theoretical calculation progress and validated against both the new data in this work and previous data of ethylene combustion in literature. The updated reactions of C2H4 + O from recent theoretical calculations in the present model can improve the predictions of both the flame speciation results and the laminar burning velocities (LBVs) under rich and elevated pressure conditions. Compared with previous models, C2H4 + O = 3CH2 + CH2O instead of C2H4 + O = CH3 + HCO becomes a major consumption pathway of C2H4 in the present model. This results in the lower production of CH3 which is responsible for the chain termination under rich and elevated pressure conditions. Therefore, the present model could lower down the predictions of the CH3-related speciation data and improve the LBV predictions under rich and elevated pressure conditions.

Devolatilization is a prerequisite for the analysis of chemical structure and oxidation reactivity of soot sampled from engine combustion or lab-scaled flames, while the effects of devolatilization temperature are not sufficiently understood. This work explores the effects of devolatilization temperature on soot chemical structure and oxidation reactivity. Virgin soot samples were collected from five positions along axis of a coflow diffusion ethylene flame using a recently developed capillary-nozzle-hybrid sampling method. Three temperatures (250, 450 and 650 °C) were selected to devolatilize virgin soot samples for further thermogravimetric (TG), Fourier transform infrared and Raman spectroscopic analyses. The results indicate that devolatilization can remove aliphatic and oxygenated groups away from soot surface, mainly below 450 °C. ID1/IG derived from deconvolution of Raman spectra presents positive correlation with nanocrystallite width, however, less sensitive to devolatilization temperature. These changes in chemical structure pose adverse impacts on soot oxidation reactivity, especially for early-stage soot. With increased degree of maturity, soot gradually shows almost overlapped TG curves under all investigated cases. The distributed activation energy model (DAEM) is used to analyze soot oxidation reactivity by decoupling two interrelated processes, i.e. low-temperature conversion and carbonaceous substances oxidation. After devolatilization, the resulted soot samples have narrow reaction temperature ranges in TG curves and higher activation energies. Among the three selected devolatilization temperatures, 650 °C can effectively remove VOF and retain reactivity features of soot sampled at different sampling positions or residence times.

Methyl heptanoate (MHP) is a potential surrogate component for fatty acid methyl esters found in biodiesel. The carbon chain length of MHP is long enough to enable low temperature (low-T) reactivity and negative temperature coefficient oxidation behavior during the combustion experiments, similar to the real biodiesel fuels. This paper investigated the low-T oxidation of MHP at 780 Torr and equivalence ratios of 0.5, 1.0 and 1.5 in a jet-stirred reactor. Detailed speciation profiles of fuel, intermediates and products were obtained using synchrotron vacuum ultraviolet photoionization mass spectrometry. A comprehensive kinetic model with 779 species and 3594 reactions was developed and validated against the new experimental data. Model analysis indicated that the dominant reaction pathways for MHP consumption were H-abstraction reactions by radicals of OH, HO2 to produce MHP radicals under all experimental conditions. In this low-T oxidation region, O2 addition reactions were responsible for the consumption of MHP radicals. The formation pathways of unsaturated methyl esters were strongly related to the decomposition of cyclic ethers. Furthermore, the formations of CH3OOH and C2H5OOH were closely linked to the reactions of CH3O2 and C2H5O2 as well as the radicals of CH2O and HO2. This work provides detailed information relevant to low-T biodiesel oxidation chemistry and guidance for the application of biodiesel in internal combustion engines.

This paper presents large eddy simulation (LES) results of convective heat transfer and incompressible-fluid flow around a square cylinder (SC) at Reynolds numbers in the range from 103 to 3.5 × 105. The LES uses the swirling-strength based sub-grid scale (SbSGS) model. Several flow properties at turbulent regime are explored, including lift and drag coefficients, time-spanwise averaged sub-grid viscosity, and Kolmogorov micro-scale. Local and mean Nusselt numbers of convective heat transfer from the SC under isothermal wall temperature are predicted and compared with empirical results.

Casing deformation has been found to be a very significant issue in the development process of shale gas in China, while the coupling effect of transient temperature-pressure has a significant impact on casing stress, and worthy of study. This paper presented a new numerical investigation to understand the coupling effect of transient temperature-pressure on casing string during volume fracturing. A wellbore temperature model was established to obtain the required input parameters of dynamic temperature boundary. The numerical model considers the coupling effect of transient temperature-pressure and the various cement sheath shapes. The results showed that the temperature of casing changed drastically during fracturing. Under the influence of the coupling effect of transient temperature-pressure, (a) when the cement sheath shape was integrity, the casing stress increased greatly and showed dynamic changes: first increased and then decreased, (b) when there was deficiency in cement sheath, with the increase of the eccentric distance or deficiency angle, the casing stress increased aggravating risk of casing deformation. Rotating the casing string during the cementing process to avoid the deficiency in cement sheath or using warm fracturing fluids to minimize the influence of the coupling effect of transient temperature-pressure are possible innovative strategies to solve these difficult problems.

This paper presents large eddy simulation LES results of incompressible heat and fluid flows around a square cylinder SC at zero incident angle at high Reynolds numbers Re in the range from 1.25×105 to 3.5×105. LES results are obtained on the basis of swirling strength based sub-grid model, and a higher order upwind scheme developed with respect to the Taylor expansion. It was found that, for the zero incident SC wake flows at a Reynolds number in the range {Re5 = Re/105 ∈ [1.25, 3.5]}, the Strouhal number equals to 0.1079, completely independent of the Reynolds number; the coefficient of drag is around 1.835 with an uncertainty of about 1.9%, almost non-sensitive to the Re. When Re is beyond 3.0×105, the time-averaged peak value of sub-grid viscosity is over 340, implying that the role of sub-grid model is crucial in some regions where vortex motion is active and vortex interaction is intense. The time–spanwise t-z averaged sub-grid viscosity ratio profiles and the profiles of fluctuations of the sub-grid viscosity ratio and velocity components at four locations downstream of the SC are presented. The fields of the t-z averaged sub-grid viscosity ratio, and the instantaneous fields of streamwise and spanwise vorticities are also reported and discussed. The predicted mean Nusselt number is compared with empirical correlations, revealing that swirling strength based LES has its potential in predicting natural and industrial flows.

In this study, the Muli gas hydrate reservoir in the Qilian Mountains was chosen as a test area for the geochemical exploration of gas hydrates in mid-latitude regions. Soil headspace gases, acid-extracted hydrocarbons and stable carbon isotopes of methane, and soil magnetic susceptibility as well as microbes were tested. The results show that the distribution of geochemical anomalies can be well correlated with the underlying gas hydrate reservoir. Acid-extracted hydrocarbons, soil headspace gases, and the stable carbon isotopes of methane can be considered as major indicators for geochemical exploration of gas hydrates, whereas magnetic susceptibility and microbes served as complementary indicators. The stable carbon isotopes of methane and the hydrocarbon composition of the surface geochemical anomalies indicated a thermogenic origin, which shows that the gas source of the potential gas hydrate reservoir in this area may be contributed by deep oil and coal-formed gases. An accumulation model for the gas hydrate reservoirs was also developed and an integrated exploration project for gas hydrate, oil and coal bed methane is also proposed for the Muli area.

A large number of oilfield water samples were analyzed in this work. Research on the relationship between the concentrations and distribution of dissolved hydrocarbons suggested that the contents and composition of dissolved hydrocarbons varied with the hydrocarbon-generating potential of reservoirs. The concentrations of dissolved hydrocarbons were low in dry layers, water layers and gas-water layers, but high in gas reservoirs and oil reservoirs, especially in gas reservoirs with condensed oil. Series of carbon-number alkanes were usually absent in oilfield water from dry layers, water layers and gas-water layers but abundant in oil-field water from oil-water reservoirs, gas reservoirs and oil reservoirs, whose carbon numbers varied most widely in oil reservoirs and least in gas reservoirs. A preliminary evaluation model for reservoir hydrocarbon-generating potential was established based on the characteristics of dissolved hydrocarbons in oilfield water to assist hydrocarbon exploration.

This is a report of the differences in abundances of pyrrolic nitrogen compounds and distribution of alkylated carbazoles among various oils from the Tarim Basin. At the same time, their geochemical significance is discussed.

The analyses of light hydrocarbons in oils from the Tarim Basin show that the Mango’s parameterK is about unity except those oils trapped in the eastern part of the Tazhong (Central Tarim) Fault Uplift. The regular variance ofK may indicates the accumulation and admixture of the oil populations in the eastern part of the Tazhong Fault Uplift.

Carbazole-type compounds were analyzed using GC and GC-MS-MS. A relatively high concentration of carbazole-type compounds was detected in crude oils of different types (marine and non-marine) and different maturities (low mature and mature) in Tarinl. Liaohe and Keilu basins. The results suggest the ratios of 1, 8-dimethyl-/2, 7-dimethylcarbazole and benu, [a] carbazole/benzo [e] carbazole might be taken as petroleum migration parameters.

A quantitative sterane biomarker study was conducted on a series of paralic freshwater lacustrine shale samples ranging in maturity from immature to near oil window maturity taken from Section 3 of the Shahejie Formation (Es3) in the Liaohe Basin, N.E. China. Concentrations of 5α(H),14α(H),17α(H)-20S and 5α(H),14β(H),17β(H)-steranes remain nearly constant throughout the sample suite. However, the decrease in the absolute concentrations of the 20R-5α(H),14α(H),17α(H)-C29 steranes with increasing maturity results in an increase in the conventionally defined maturity parameters, 20S/(20S + 20R)-ααα and αββ/(ααα + αββ) sterane ratios. In addition, the data suggest that relatively early generation of 5α(H),14α(H),17α(H)-20S and 5α(H),14β(H),17β(H)-steranes has occurred in lacustrine sediments with a vitrinate reflectance ∼0.3% (Ro). The data provide strong support for the major importance of relative thermal stability of epimers, but do not exclude the possibility of isomerization as a viable mechanism for production.

A suite of samples from the Funan Mine, N.E. China, has allowed a comparison to be made between hydrocarbon-rich coals and coaly shales. These are immature coals and the known geological history suggests that they have experienced only a mild geothermal history. Analyses of the di- and sesquiterpenoid components show that compounds based on the kaurane skeleton are absent unlike Australian brown coals; and the diterpenes isopimarane, pimarane and 16α (H)-phyllocladane relate to a different community of higher plants such as Pinaceae and Taxodiaceae from those recognized in Australian brown coals. A consideration of geochimical parameters and biomarker composition leads to the conclusion that the geolipid concentrations in the sample suite are environmentally determined. It is concluded, therefore, that 22R-17β (H),21β (H)-bishomohopanoic acid and the 22R-17α (H),21β (H)-homohopane, both predominant components in their respective classes, are derived from different sources. Labdanic acids have been identified in these coals. They are likely to be derived from resin constituents of the coal and not from microbial biomass. They could potentially be developed as a maturation parameter. Cis and trans isomers of a triaromatic hydrocarbon based on the oleanane skeleton which has been previously identified in Victorian brown coal are present in the Funan coals. The more oxidizing the environment the less advanced is the isomerization of cis to trans and again the environment of deposition is the controlling factor. This study emphasizes the importance of understanding pathways of early diagenesis for the interpretation of data derived from more mature samples.

Oilfield waters from Cenozoic and Mesozoic terrestrial and Paleozoic marine environments in the Tarim Basin show no obvious difference in water chemistry except Br and isotopic compositions. The Paleozoic marine strata have higher Br concentrations than the terrestrial sediments, and the lack of obvious relationship between Br and I suggests that Br is not, for the most part, derived from the degradation of organic matter. The oilfield waters are characterized by high TDS (total dissolved solids), ranging from 120000 mg/L to 320000 mg/L, relatively low Mg, high Ca, Sr, and CF relative to Br of evaporating seawater, suggestive of enhanced water-rock interaction. OAA (organic acid anions) concentrations are generally lower than 1500 mg/L with high values occurring over the temperature range from 95°C to 140 °C, in the Cambrian to Jurassic systems, and nearby unconformities. Organic acids are considered to be generated mainly from thermal maturation of kerogens during progressive burial of the Jurassic-Triassic and Cambrian-Ordovician systems, biodegradation of crude oils nearby unconformities, and thermochemical sulfate reduction in part of the Cambrian and Ordovician strata. High Al concentrations up to 3 mg/L to 5.5 mg/L tend to occur in the waters of high OAA or petroleum- bearing intervals, suggesting the presence of organic complexing agents. Calculation by SOLMINEQ. 88 with updated database shows that AlAc2+ may account for more than 30% of the total Al. Isotopic measurements (δD, δ18O) provide evidence for the following types of waters: diagenetically-modified connate meteoric water from the Jurassic and Triassic strata; diagenetically-modified connate marine water from the Cambrian and Ordovician strata; subaerially-evaporated water from the Cenozoic and Cretaceous strata; and mixed meteoric-evaporated or/and diagenetically modified connate water from the Carboniferous strata and reservoirs adjacent to the J/C and T/C unconformities. Those waters with very negative δD values from −51.30‰ to −53.80‰ (SMOW) and positive δ18O values from 2.99‰ to 4.99‰ (SMOW) in the continuous burial of the Cambrian-Ordovician system are explained to have resulted from hydrocarbon-water and water-rock interactions.