High-pressure Jet-stirred Reactor Research Articles

Insights into the oxidation kinetics of a cetane improver – 1,2-dimethoxyethane (1,2-DME) with experimental and modeling methods

A kinetic investigation was carried out in this work for an oxygenated fuel additive, 1,2-dimethoxyethane (1,2-DME) to reveal the oxidation chemistry responsible for its practical function as a cetane improver. Experiments were conducted for 1,2-DME/O2/N2 mixtures with different equivalence ratios (0.5, 1.0 and 2.0) in a high-pressure (10 atm) jet-stirred reactor (JSR) facility over the temperature range of 450–1100 K. Species concentration evolutions with the temperature were monitored with on-line Fourier transform infrared (FTIR) spectrometry and off-line gas chromatography (GC). The technique of photoionization molecular-beam mass spectrometry (PI-MBMS) was combined with another JSR setup operated at near-atmospheric pressure (700 Torr), for the purpose of probing reactive intermediates from 1,2-DME oxidation. A kinetic model was constructed based on the “reaction classes” strategy, which could satisfactorily predict speciation measurements in the current work. Pronounced low-temperature reactivity of 1,2-DME was observed under all investigated conditions, and crucial intermediates like ketohydroperoxides were detected with the PI-MBMS. Some specificities of 1,2-DME oxidation were elucidated through further model interpretations. The double ether groups imbedded in the fuel molecule make hydrogen abstractions easier and meanwhile hinder the chain-terminating concerted eliminations, so the low-temperature reactivity starts at relatively low temperatures (compared to n-hexane for example). Chain-branching reaction sequences following the second O2 additions proceed in the oxidizing mixtures, leading to the remarkable low-temperature reactivity of 1,2-DME which can be utilized as a cetane-improver.

Revisiting 1-hexene low-temperature oxidation

The low-temperature oxidation of 1-hexene has been studied in a jet-stirred reactor for temperatures from 500 to 1100 K, at atmospheric pressure, for equivalence ratios from 0.5 to 2 with a high dilution in helium. Product formation has been investigated using gas chromatography, as well as laser-single-photon-ionization time-of-flight mass spectrometry and cw-cavity-ring down spectroscopy. These two last techniques have allowed the quantification of ketene, C1–C3 alkylhydroperoxides, hexenyl hydroperoxides, C6 unsaturated ketohydroperoxides, and hydrogen peroxide.Starting from a previous model generated automatically, a new model has been developed for 1-hexene oxidation by updating some determinant reaction kinetics based on newly published theoretical calculations. This new model allows a good prediction of most of the newly obtained experimental results, as well as satisfactory simulation of literature data obtained for the high-temperature oxidation in a high-pressure jet-stirred reactor, in a rapid compression machine, and in two shock tubes.

ChemInform Abstract: Kinetic Modeling of Propane Oxidation and Pyrolysis

Propane oxidation in jet-stirred reactor was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1C4 hydrocarbons. The present detailed mechanism is able to reproduce experimental species concentration profiles obtained in our high-pressure jet-stirred reactor (900 ⩽ T/K ⩽ 1200; 1 ⩽ P/atm ⩽ 10; 0.15 ⩽ ϕ ⩽ 4) and in a turbulent flow reactor at 1 atm; ignition delay times measured in shock tube (1200 ⩽ T/K ⩽ 1700; 2 ⩽ P/atm ⩽ 15; 0.125 ⩽ ϕ ⩽ 2); H-atoms concentrations measured in shock tube during the pyrolysis of propane and burning velocities of freely propagating premixed propane-air laminar flames. The computed results are discussed in terms of pressure and equivalence ratio (ϕ) effects on propane oxidation. The same detailed kinetic reaction mechanism can also be used to model the oxidation of methane, ethylene, ethane, and propene in similar conditions. © John Wiley & Sons, Inc.

Investigation of NO x and CO formation in lean-premixed, methane/air, high-intensity, confined flames at elevated pressures

The coupling between NOx formation chemistry and the mixing/transport environment is of critical importance to the design of lean-premixed gas turbine combustors but is incompletely understood. In the present research, this problem was addressed via the study of NOx formation in a high-pressure jet-stirred reactor operating on lean-premixed methane/air. These experiments focused on the effects of residence time (0.5–4.0 ms), pressure (3.0, 4.7, and 6.5 atm), and inlet temperature (344–573K). The combustion temperature varied from 1815±5 K at the lowest residence times to 1910±30K at the largest residence times. The NOx was lowest at intermediate residence times, reaching higher values at the extremes. Increasing pressure and inlet temperature tend to reduce NOx concentrations. Concentration profiling in the reactor suggests two general environments: (1) a highly non-equilibrium reaction zone defined by high CO concentrations, and (2) a postflame environment. The NOx formation was concentrated in the region of strongly non-equilibrium combustion chemistry. The Damkohler number was 0.06≤Da≤1, and the ratio of turbulent intensity to laminar burning velocity was 28≤u′/SL≤356, indicating the combustion occurs in the high-intensity, chemical rate-limiting regime. The results were interpreted using a two-environment, detailed chemistry model in which the size and structure of the flame environment were established by matching the measured data, and which were independently verified using turbulent flame velocity/thickness correlations. The modeling suggests NOx formation is controlled by both the specific conditions in the non-equilibrium zone and by the size of the zone. Since both these features are influenced by the experimental parameters, a highly nonlinear scenario emerges with implications for minimizing NOx via combustor design. The modeling also suggests the unique case of well-stirred combustion for NOx at elevated pressure is obtained at low residence time conditions.

The Ignition and Oxidation of Tetrahydrofuran: Experiments and Kinetic Modeling

The ignition of tetrahydrofuran (THF) has been studied in a single-pulse shock tube under reflected shock wave conditions while the oxidation of THF was studied in a high-pressure jetstirred reactor (JSR). The present experiments cover a wide range of conditions: 2–10atm, 0.5≤ ≤2.0, 800–1800K. The ignition delays of THF, measured in a shock tube, have been used to propose an overall representation for the dependence of ignition delay time on the concentration of each component in the ignitable gas mixture: τall=10-14.4 exp (19590/T5)[c4h8O]0.272[O2 -0.984[AR]-0.189(units:s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of ThF were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 484 reactions (most of them reversible) of 71 species, describes the ignition of THF in reflected shock waves and its oxidation in a jet-stirred reactor. We observed a fairly good agreement between the experimental results and the computations. Detailed kinetic modeling enabled identification of the major reaction paths and sensitive kinetic parameters.

Characterization of NOx, N20, and CO for Lean-Premixed Combustion in a High-Pressure Jet-Stirred Reactor

A high-pressure jet-stirred reactor (HP-JSR) has been built and applied to the study of NOx and N2o formation and CO oxidation in lean-Premixed (LPM) combustion. The measurements obtained with the HP-JSR Provide information on how NOx forms in lean-premixed, high-intensity combustion, and provide comparison to NOx data published recently for practical LPM combustors. The HP-JSR results indicate that the NOx yield is significantly influenced by the rate of relaxation of super-equilibrium concentrations of the O-atom. Also indicated by the HP-JSR results are characteristic NOx formation rates. Two computational models are used to simulate the HP-JSR and to provide comparison to the measurements. The first is a chemical reactor model (CRM) consisting of two perfectly stirred reactors (PSRs) placed in series. The second is a stirred reactor model with finite rate macromixing (i.e., recirculation) and micromixing. The micromixing is treated by either coalescence-dispersion (CD) or interaction by exchange with the mean (IEM) theory. Additionally, a model based on one-dimensional gas dynamics with chemical reaction is used to assess chemical conversions within the gas sample probe.

N yO x formation in lean premixed combustion of methane in a high-pressure jet-stirred reactor

A novel high-pressure jet-stirred reactor (JSR) has been used to study the formation of NOx, N2O, and CO in lean premixed combustion of methane-air mixtures at pressures up to 20 bars. Experiments were carried out at residence times of 1.0, 1.5, and 2.0 ms, at an equivalence ratio of 0.55 and at temperatures of 1510 and 1550 °C. The measured NOx concentrations show a distinct negative trend with increasing pressure and clearly decrease with decreasing residence times at pressures <5 bars. At higher pressures, the influence of residence time is diminished. The NOx and N2O concentrations are slightly lower than the predictions of a perfectly stirred reactor (PSR) using four well-known reaction mechanisms of the C−H−O−N system. However, the measured CO levels are considerably lower than the PSR predictions. This is mainly attributed to spatial inhomogeneities of the JSR, confirmed by measured temperature and concentration profiles at atmospheric conditions. To take these effects into account, the JSR was modeled as a series of two PSRs and one PFR (plug flow reactor). This model predicts the measured NOx, N2O, and CO concentrations well with all but one reaction mechanism: for NOx concentrations, significant deviations occur between measurements and predictions using the Miller-Bowman mechanism. The influence of finite-rate micromixing was studied by computations of a partially stirred reactor (PaSR), which show a minor influence on NOx and CO levels: for the CO concentrations, these effects are negligible compared to the macromixing effects.

Oxidation of oxygenated octane improvers: MTBE, ETBE, DIPE, and TAME

In this work, the oxidation of MTBE, ETBE, DIPE, and TAME was investigated experimentally in a high-pressure jet-stirred reactor (JSR) in the high-temperature oxidation regime (800–1150 K, 10 atm,=0.5–2, 0.1% of ether, and 0.5 s). New experimental data on mole fractions of reactants, intermediates, and final products were measured using probe sampling followed by gas chromatograph (GC) analyses. These data were used to extend an already available oxidation reaction model for primary reference fuels. This extension to the ether components only required the insertion of a small subset of new primary reactions where kinetic parameters are evaluated on the basis of similarity and analogy rules inside reaction classes and generalized prediction methods for H-abstraction reactions. The fair agreement observed between experimental data and model predictions in different operating conditions confirms the validity of the proposed approach and allows the modeling of oxidation and combustion of commercial gasoline.

The Ignition and Oxidation of Tetrahydropyran: Experiments and Kinetic Modeling

The ignition and the oxidation of tetrahydropyran have been studied in a single-pulse shock tube under reflected shock wave conditions, and also in a high-pressure jet-stirred reactor(JSR) These experiments cover a wide range of conditions: 2-10 atm, 0.5 ≤ 𝛗 ≤ 2.0,800- 1700 K. The ignition delays of tetrahydropyran measured in a shock tube have been used to propose an overall representation for the dependence of ignition delay time on the concentrations of each component in the ignitable gas mixture: τ all= 10−13.6 exp (15360/T5) [C5H10O] 0.0026[O2] −0.868 [Ar] 0.0274 (units: s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of tetrahydropyran were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 507 reactions (most of them reversible) of 72 species describes the ignition of tetrahydropyran in reflected shock waves and its oxidation in a jetstirred reactor. A fairly good agreement between the experimental results and the model was observed. Detailed kinetic modeling identified the major reaction paths.

The Oxidation of N-Heptane in the Presence of Oxygenated Octane Improvers: MTBE and ETBE

The oxidation of n-heptane and mixtures n-heptane-MTBE (50:50) and n-heptane-ETBE (50:50) has been studied experimentally in a high-pressure jet-stirred reactor in a wide range of conditions covering the low and high temperature oxidation regimes (570-1150 K, 10 atm, 0=1, 0.1% of fuel). The mole fractions of reactants, intermediates and final products have been measured. The influence of the additives on the formation of several pollutants has been addressed. The present results clearly show an influencing effect of MTBE and ETBE on the kinetics of n-heptane oxidation by a reduction of the mixture reactivity in the low temperature regime (570-800K). The results are interpreted in terms of knocking and non-knocking tendencies related to fuel structure and low temperature oxidation mechanism.

Experimental study of the oxidation of n-heptane in a jet stirred reactor from low to high temperature and pressures up to 40 atm

Normal heptane oxidation in a high-pressure jet-stirred reactor has been investigated experimentally in a wide range of conditions covering the low- and high-temperature oxidation regimes (550–1150 K, 1–40 atm, φ = 1). Reactants, intermediates, and final products have been measured in three different oxidation regimes, namely cool flame, negative temperature coefficient, and normal combustion. Concentration profiles of the major cyclic ethers formed at low temperature have been measured. The evolution of the transition from low to high temperature oxidation regime as a function of pressure was observed showing the quasi-disappearance of the negative temperature coefficient at 40 atm. The results are interpreted in terms of reaction mechanism.

SHORT COMMUNICATION High Pressure Oxidation of Liquid Fuels from Low to High Temperature. 3.n-Decane

Abstract The oxidation of n-decane in a high-pressure jet-stirred reactor (JSR) has been investigated experimentally in a wide range of conditions covering the low and high temperature oxidation regimes (550-1150K, lOatm, Ø = 0.1 to 1.5), Reactants, intermediates and final products have been measured providing a detailed picture of n-decane oxidation. Cyclic ethers resulting from the so-called Iwo-temperature oxidation chemistry of n-decane were identified. The results are interpreted in terms of reaction mechanism. A detailed chemical kinetic modeling of the high-temperature oxidation of n-decane is used to assess the influence of low temperature chemistry in the intermediate temperature range.

High Pressure Oxidation of Liquid Fuels from Low to High Temperature. 2. Mixtures of n-Heptane and iso-Octane

Abstract The oxidation of mixtures of n-heptane and iso-octane in a high-pressure jet-stirred reactor has been investigated experimentally in a wide range of conditions covering the low and high temperature oxidation regimes (550-1150K, 10 atm, o=1). The cool flame and negative temperature coefficient regimes were observed below 750K, Above 750 K, the normal high temperature oxidation of both fuels was observed. Reactants, intermediates and final products have been measured providing a useful picture of n-heptane-iso-octane mixtures oxidation. Cyclic ethers resulting from the low-temperature oxidation chemistry of n-heptane and iso-octane were identified. The evolution of their concentration as a function of RON have been measured. These results are interpreted in terms of reaction mechanism. Tentative correlations between RON and CO, CO2 and C2H4 in the cool flame region and for the high temperature oxidation (normal combustion) are presented.

Acetylene Oxidation in a JSR From 1 to 10 Atm and Comprehensive Kinetic Modeling

Abstract Acetylene oxidation in a jet-stirred reactor has been investigated at high temperature (800-1100 K) in the pressure range 1 to l0atm. Molecular species concentration profiles of H2, CO, CO2, CH4, C2H2, C2H4, C2H6 were obtained by probe sampling and GC analysis. Acetylene oxidation was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1,—C6 hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high-pressure jet-stirred reactor, ignition delay times measured in shock tube, atmospheric pressure C2H2/Air flame speeds, and C2H2/O2/Ar premixed flame structures obtained at low pressure on flat flame burners. The mechanism has also been used successfully to represent the kinetics of the oxidation of CH4, C2H4, C2H6, C3H6, C3H3, mixtures of CH4 with C2H6 and/or C3,H8 in the same conditions

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.

Kinetics of ethane oxidation in a high pressure jet-stirred reactor : experimental results

In this paper are reported the recent kinetic results obtained on ethane oxidation In our high pressure jet stirred reactor. The experiments were carried out in the pressure range 1 to 10 atm, at temperatures between 800 and 1200 K, for equivalence ratios of 0.1 to 1.5 at initial hydrocarbon mole fraction of 0.00125 to 0.0015. By means of computer modeling, the main reaction channels involved in ethane oxidation have been delineated. Such results are used for interpreting the present data.