N2 Diluent Research Articles

Atmospheric chemistry of (Z)‐CF2HCF=CHCl: Kinetics and products of reaction with Cl atoms and OH radicals

AbstractLong path length FTIR‐smog chamber techniques were used to study the title reactions in 650 Torr of N2, oxygen, or air diluent at 296 ± 3 K. Values of k(Cl + (Z)‐CF2HCF = CHCl)═(6.6 ± 0.7) × 10−11 and k(OH + (Z)‐CF2HCF═CHCl)═(4.1 ± 0.7) × 10−12 cm3 molecule−1 s−1 were measured. The IR spectrum of (Z)‐CF2HCF═CHCl is reported. The atmospheric lifetime of (Z)‐CF2HCF═CHCl is determined by the reaction with OH and is approximately 2.8 days. Reaction of (Z)‐CF2HCF═CHCl with Cl atoms gives HC(O)Cl and CF2HC(O)F as major primary products. Under environmental conditions, the OH radical initiated oxidation gives CF2HC(O)F and HC(O)Cl in yields of (98 ± 8)% and (100 ± 4)%, respectively. Accounting for non‐uniform horizontal and vertical mixing leads to a 100‐year time‐horizon global warming potential value for (Z)‐CF2HCF═CHCl of essentially zero.

Characteristics of OH formation during single coal particle ignition and volatile combustion in O2/N2 and O2/CO2 atmospheres

The behaviors of volatile combustion and ignition of lignite coal were assessed on a concentrating light heating platform using hydroxyl-Planar laser-induced fluorescence (OH-PLIF) over a range of 21–60% O2 in both N2 and CO2 diluent gases. The results indicated that when the O2 concentration was below 40%, substituting CO2 for N2 delayed the ignition delay time (tign). This was evident as no ignition occurred in the 21% O2/CO2 mixture, and a nearly 1.0 s difference in tign emerged when substituting CO2 for N2 in 30% and 40% air atmospheres. Additionally, the weaker flame luminosity and the shorter volatile flame duration time (tvol) were also observed in O2/CO2 compared with that in O2/N2. Correspondingly, a significantly lower OH signal intensity was observed in O2/CO2 compared to O2/N2, which was primarily due to physical and chemical effects of CO2. Firstly, the higher heat capacity and lower diffusion rate of O2 in O2/CO2 leads to a lower volatile release rate and decreasing flame temperature, as evidenced by the closer proximity of the flame front to the coal particle surface. The lower flame temperature and volatile release rate would reduce the number of hydrocarbon molecule (RH) and the reaction rate of RH→hydrocarbon radical (R) + H, leading to a decrease in the concentration of OH radical from the reaction: H + O2→OH + O. Secondly, CO2 participates directly in H + OH + three-body (M)→H2O + M reaction, competing with the primary OH formation pathway, H + O2→OH + O, for H radicals, thus suppressing the OH generation. However, when O2 concentration exceeded 40%, the tign was shorter in O2/CO2 by about 1.2–1.4 s than in O2/N2 with the same O2 concentration. Simultaneously, compared to the O2/N2, similar flame luminosity and tvol were observed in the O2/CO2. An obvious increase in OH intensity was also observed in O2/CO2. With higher O2 concentrations in the O2/CO2, the absorption and emission radiation characteristics of CO2, increased O2 diffusivity and the decreased specific heat capacity in the O2/CO2 gas mixture, synergistically facilitate temperature rise and volatile release, which promotes the generation of RH, and then increases the H concentration due to the reaction RH→R + H. This would lead to a substantial increase in concentration of OH produced by the reaction H + O2→OH + O, which was detected by OH-PLIF.

Atmospheric chemistry of 1,1-difluoroacetone, CHF2C(O)CH3: Kinetics, products and mechanisms of the Cl atom and OH radical initiated oxidation

Smog chamber techniques were used to study the Cl atom and OH radical initiated oxidation of 1,1-difluoroacetone (CF2HC(O)CH3) in 700 Torr of air or N2 diluent at 297 K. Using relative rate methods k(Cl + CF2HC(O)CH3) = (5.0 ± 0.8) × 10−14 cm3 molecule-1 s−1 and k(OH + CF2HC(O)CH3) = (2.6 ± 0.7) × 10−14 cm3molecule-1s−1 were determined. The atmospheric lifetime of CF2HC(O)CH3 with respect to reaction with OH radicals is estimated at 1.2 years. Atmospheric oxidation yields COF2, CO and CO2. The data suggests that Cl atoms primarily attack the –CF2H group, whereas OH radicals also attack the –CH3 group.

Effect of N2 Diluent on Soot Formation Characteristics in Ethylene Diffusion Flames

Effect of N2 Diluent on Soot Formation Characteristics in Ethylene Diffusion Flames

NO emission characteristics for the HTC and MILD combustion regimes with N2, N2/CO2 and CO2 diluents: effect of H2 addition to CH4

In this paper, the effect of H2 addition to CH4 on the NO emission of oxy-fuel, oxygen-enriched, and air-fuel MILD combustion is studied by numerical and chemical calculations. In the CFD section, the University of Lisbon MILD furnace is modeled. The results show that H2 added to CH4 is associated with a higher NO emission in the same oxidant composition. It is due to higher NO formation by NNH and thermal mechanisms. It can be found that by transformation from air-fuel to oxy-fuel MILD regimes, NO emission is reduced significantly. Moreover, the addition of H2 prevents flame extinction that often occurs under MILD conditions when CO2 replaces N2. Reaction pathway analysis displays that dominant routes of NO emission in the H2-lean are N2O-intermediate for the air-fuel and oxygen-enriched conditions and NNH for the oxy-fuel MILD regime. In the H2-rich condition, the NNH mechanism plays the most important role in the NO production.

Fully-resolved simulations of volatile combustion and NO[formula omitted] formation from single coal particles in recycled flue gas environments

The interaction of coal particles and recycled/recirculated flue gas (RFG) with elevated temperatures and low levels of oxygen occurs in various pulverised coal combustion scenarios. In this work, the effect of oxygen level and temperature on single coal particle combustion characteristics and NOx formation in N2 diluent is studied by means of fully-resolved particle simulations. Comprehensive gas-phase kinetics are utilised to consider the critical pathways of NOx formation including tar-N. Results show that higher RFG temperatures decrease the time to reach the peaks of temperature and species profiles and increase the corresponding peak values. When decreasing O2, irrespective of the RFG temperature, the fuel release period is prolonged, the volatile combustion time increases and the combustion process becomes overall less intense. The reduction of O2 in RFG results in a significant decrease of NO production, while the reduction of the RFG temperature has a smaller effect. The analysis of the key reactions that contribute to NO production in the region around stoichiometry shows that fuel-NOx is the major contributor. Both NH3 and HCN in fuel-N play a major role, while tar-N only contributes in the case with the lowest temperature and O2 concentration. The classical NOx formation pathways are negligible and the initiation reaction of the Zeldovich mechanism is even reversed, i.e. NO⟶+NN2 is dominant and contributes to NO destruction. The destruction of NO mainly occurs in a rich region close to the particle surface where abundant tar species and their derivatives play a major role for NO destruction via the re-burn mechanism. The prompt mechanism is also active in this region and eventually contributes to NO reduction via production of HCN which is the feed to the re-burn mechanism.

Theoretical studies of real-fluid oxidation of hydrogen under supercritical conditions by using the virial equation of state

The Virial equation of state (EoS) was employed to describe the real-fluid impact on H2 oxidation simulation. Different from conventional empirical EoS methods fitted by using critical pressures and temperatures, such as Redlich-Kwong (RK) EoS, the Virial method was constructed with including intermolecular interactions, potentials, and molecular polarizations coupled with real-fluid partition function theory in this work. The Virial method was for the first time incorporated into Cantera software to realize real-fluid simulations with deeper-level physical insights. A series adiabatic/isothermal flow reactor and ignition delay simulations in H2O, N2, and CO2 diluents were performed. The calculations of species compressibility factors and thermodynamic properties by using the Virial method showed a better agreement with experimental data in literature than using the RK method. The Virial method also possessed a better performance in predicting experimental H2 ignition delay times and H2 speciation profiles from literatures. The effects of real fluid through corrections of compressibility factors, thermodynamic properties, and chemical potentials on supercritical H2 oxidation simulations in H2O diluents have been rigorously analyzed, respectively. Moreover, the Virial method performed well at adiabatic conditions in the bath gas of polar molecules like H2O, due to its consideration of molecular polarizations and higher accuracy of thermodynamic property calculations. We believed the Virial method could not only provide accurate estimations of real-fluid behavior, but also provided physical insights in the intermolecular interactions under supercritical conditions.

Effect of H2 enrichment ratio and N2/CO2 dilution on swirl-stabilized partially premixed H2/CH4/C3H8 SNG combustion

This paper discusses the N2 and CO2 dilution effects and H2 enrichment ratio of H2/CH4/C3H8 synthetic natural gas (SNG). As H2 enrichment ratio increases, the dump plane temperature and the combustion zone temperature increase because of shortened length of H2 flame. Even with a shorter flame length and a narrower chemical reaction regime, NOx emissions increase at same heat load because energy density is inversely proportional to flame length. As the CO2 diluent has a higher specific heat than the N2 diluent, the flame temperature is more greatly reduced by the effect of diluent heat capacity. Even a small amount of CO2 dilution can effectively reduce NOx emissions. The H2 enrichment ratio increases the OH radicals in the flame due to the increase in flame temperature. In addition, the burning velocity increases because the reaction rate in the flame increases, resulting in a decrease in flame length. NOx emissions increase exponentially with respect to global OH∗ chemiluminescence intensity per heat load, and these fit well into a single line. The results show that N2 and CO2 diluents can be used in SNG turbine combustors to control NOx emissions and that the H2 enrichment ratio in SNG.

Natural Gas-Oxygen Combustion in a Super-Critical Carbon Dioxide Gas Turbine Combustor

The paper presents results for chemical kinetics of combustion process in the combustor of oxy-fuel cycle super-critical carbon dioxide gas turbine based on the Allam thermodynamic cycle. The work shows deviation of the normal flame propagation velocity for the case of transition from the traditional natural gas combustion in the N2 diluent environment to the combustion at super-high pressure up to 300 bar in CO2 diluent. The chemical kinetics parametric study involved the Chemkin code with the GRI-Mesh 3.0 kinetic mechanism. This mechanism provides good correspondence between calculation results and test data. The CO2 and N2 diluents temperature, pressure and contents influence the flame propagation velocity and the chemical kinetics parameters in the two gas turbine types. It is demonstrated that the CO2 diluent slows down chemical reactions stronger than the N2 one. The flame propagation velocity in carbon dioxide is four time smaller than in the N2 one. In the oxy-fuel cycle combustor a pressure increase reduces the flame propagation velocity. Increase of the CO2 content from 60 to 79% reduces the flame propagation velocity for 65% at atmospheric pressure and for 94% at super-critical pressure. An increase of the combustor inlet mixture temperature from 300 to 1100 K at super-critical pressure causes the flame propagation velocity increase for 94%. The flame propagation velocities compatible with the traditional gas turbines may be reached at the CO2 diluent content of the O2 + CO2 mixture in the active combustion zone must be below 50%.

Impacts of N2 and CO2 diluent gas composition on flame emission spectroscopy for fuel concentration measurements in flames

Flame emission spectroscopy (FES) is used to determine methane fuel concentration in a premixed flat-flame burner with varying diluent composition. Spectral profiles of the molecular emission bands of OH* (306.4 nm), CH* (431.5 nm), and C2* (520 nm) in the UV-to-visible range are recorded and analyzed for various equivalence ratios (0.72 < ∅ < 1.25), oxygen concentration (0.19 < XO2 < 0.35), and diluent gas species (N2, CO2). The importance of flame radiation, which is strong and reliable in the UV spectrum, is confirmed particularly for quantitative measurement purposes. In air-methane flames, the band intensity ratios of OH*/CH* and C2*/CH* are shown to be highly sensitive to fuel stoichiometry, and can thus serve as accurate indicators of ∅. In addition, the impact of diluent gas composition on flame radiation characteristics and FES utilizing band intensity ratios is investigated for potential applications such as clean combustion utilizing exhaust gas recirculation (EGR), and oxy-combustion in supercritical CO2 power plants. It is shown that the strength of the underlying broadband emission is strongly dependent on the diluent gas composition, and influences the sensitivity and accuracy of the FES-based ∅ measurement.

Atmospheric Chemistry of Pentafluorophenol: Kinetics and Mechanism of the Reactions of Cl Atoms and OH Radicals.

Fourier transform infrared smog chamber techniques were used to study the kinetics and mechanisms of the reactions of Cl atoms and OH radicals with pentafluorophenol (C6F5OH) in 700 Torr total pressure of air or N2 diluent at 296 ± 2 K. Rate constants k(OH + C6F5OH) = (6.88 ± 1.37) × 10-12 cm3 molecule-1 s-1 and k(Cl + C6F5OH) = (2.52 ± 0.31) × 10-11 cm3 s-1 molecule-1 in 700 Torr air diluent were determined. In 700 Torr N2, the rate constant for the reaction of C6F5OH with Cl atoms is linearly dependent on the Cl atom concentration. Product studies on this reaction in both 700 Torr air and 700 Torr N2 diluent show the formation of nonconjugated products. The photolysis constant of C6F5OH was determined by 254 nm UV irradiation of a C6F5OH and CH3CHO mixture in 700 Torr air or N2 at 296 ± 2 K and yielded a photolysis rate constant of J(C6F5OH) = (2.83 ± 0.25) × 10-3 s-1. Results are discussed with respect to the atmospheric chemistry of other halogenated aromatic species.

Exhaust CO emissions of a laminar premixed propane–air flame interacting with cold gas jets

This study investigates a laminar premixed flame interacting with cold gas jets, at different cooling jet mass flow fractions (m˙jet*) and diluent types, namely air and N2. A novel burner and wall configuration is used to experimentally induce flame-cooling-air interaction (FCAI). Flame chemiluminescence imaging, exhaust temperature (Texh) and exhaust CO emissions ([CO]exh) measurements are conducted to characterise the flame shape and [CO]exh response to the cooling jets. Flame imaging reveals that the cooling jets greatly affect the flame shape. Measurements of [CO]exh demonstrate a direct correlation with Texh, as decreasing Texh is observed to occur with decreasing [CO]exh. Additionally, the air diluent case shows consistently lower [CO]exh values, relative to the N2 diluent case.Using a novel modelling approach, the cooling jets are simulated using one-dimensional (1D) fully resolved simulations (FRS). The effect of jet dilution, jet cooling and exhaust gas cooling are independently and jointly investigated in these simulations. The FRS results support the experimentally observed behaviour, and show that exhaust gas cooling and exhaust gas oxygenation produce decreased CO concentrations. Using a chemical reactor network (CRN), the jet mixing process is modelled by a perfectly stirred reactor (PSR), while the exhaust gas cooling process is modelled by a plug flow reactor (PFR). The CRN modelling shows that the jet mass flow rates dictated by m˙jet*, the dilution time (tdil) assumed for cooling jet mixing, and the exhaust gas cooling residence time (tcool), play an important role in determining the [CO]exh. An equilibrium analysis illustrates that the relationship between [CO]exh, Texh and exhaust O2, is due to the thermodynamically favoured equilibrium states. Timescale analyses demonstrate that appropriate modelling of jet mixing, and accounting for the rate of exhaust gas cooling, are important for estimations of [CO]exh.

Atmospheric chemistry of a cyclic hydro-fluoro-carbon: kinetics and mechanisms of gas-phase reactions of 1-trifluoromethyl-1,2,2-trifluorocyclobutane with Cl atoms, OH radicals, and O3.

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N2 or air diluent at 296 ± 2 K. Values of k(Cl + 1-trifluoromethyl-1,2,2-trifluorocyclobutane (TFMTFCB)) = (1.16 ± 0.21) × 10-14 and k(OH + TFMTFCB) = (3.51 ± 0.88) × 10-14 cm3 molecule-1 s-1 were measured. No reactivity of TFMTFCB towards ozone was observed. The atmospheric lifetime of TFMTFCB is determined by the reaction with OH and is approximately 330 days. The chlorine initiated oxidation gives C(O)F2 and CF3C(O)F as the dominant products in yields of (92 ± 2)% and (89 ± 2)%, respectively. The OH radical initiated oxidation gives C(O)F2 and CF3C(O)F as the dominant products in yields of (91 ± 6)% and (84 ± 4)%, respectively. The GWP100 was calculated as 44. The atmospheric chemistry of the title compound, a cyclic halogenated alkane, is discussed in the context of other halogenated cyclo-alkanes.

Effects of N2 and CO2 dilution on the combustion characteristics of C3H8/O2 mixture in a swirl tubular flame burner

Premixed C3H8/O2 combustion has been investigated by adopting N2, CO2 and their mixture (50% N2-50% CO2 by volume) as the diluents, respectively. The oxygen content (mole fraction) in the oxidizer is varied from 0.13 to 0.35, which covers the operating conditions of EGR and OEC. The flame structures, temperatures, burning velocities and NOx emissions are examined under various oxygen contents. Detailed observations show that a steady, uniform tubular flame can be obtained over a wide range from lean to rich. By increasing oxygen content, the flame diameter increases slightly; the flame length decreases significantly, which is almost inversely proportional to laminar burning velocity. During decreasing the burning velocity to less than about 20 cm/s, a turning point appears and the flame length becomes extensively large. With the same oxygen content and equivalence ratio, by replacing half or all of the N2 diluent with CO2, the flame temperature and burning velocity decrease significantly. To obtain the same adiabatic flame temperature, the CO2 diluted mixture requires the highest oxygen content among the three diluents, however, its measured flame temperature is also highest. In the N2-CO2 diluted combustion, owing to thermal and chemical effects of CO2, the NOx emission reduces remarkably comparing with N2 dilution; under the same flame temperature, the NOx concentration reduces to almost 1/5 of that diluted by N2. The lean extinction limit raises by increasing CO2 content in the diluent, while the limit decreases with increasing oxygen content.

Atmospheric chemistry of hexanenitrile: Kinetics and products of the gas-phase reactions of CH3(CH2)4CN with Cl atoms and OH radicals

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure the kinetics of the reaction of CH3(CH2)4CN, 1-cyanopentane, with Cl atoms and OH radicals: k(CH3(CH2)4CN+Cl)=(1.34±0.22)×10−10 and k(CH3(CH2)4CN+OH)=(2.84±0.66)×10−12cm3molecules−1s−1 at a total pressure of 700Torr of air or N2 diluents at 296±2K. The atmospheric oxidation of alkyl nitriles proceeds through hydrogen abstraction leading to several carbonyl containing primary oxidation products. Based on the OH radical rate constants the atmospheric lifetime of CH3(CH2)4CN was estimated to be 4days.

CO2 aided H2 recovery from water splitting processes

Solar energy can be utilized to produce H2 via photocatalytic water splitting. One major drawback of the one-step approach is the co-production of H2 and O2 in the same reactor environment creating a potentially hazardous scenario. This obstacle can be avoided by utilizing CO2 as a flammability suppressant which is proven to be more effective than N2. In this case study, several membrane cascade designs were implemented to recover the H2 while maintaining compositions outside the flammability range. The optimizations are based on the use of commercially available composite polymer membranes from Membrane Technology and Research, Inc. (MTR) in the spiral wound architecture. Both the H2-selective membrane (Proteus™) and CO2-selective membrane (Polaris™) were explored in three layouts. The process optimization is solved by nonlinear programming. The aim of the study was to minimize the present value of all outgoing cash flow (no income) for the separation process and achieving 99% product (H2) purity. Optimization results showed that utilizing three membrane units of Proteus™ material with one recycle stream is the optimum layout over a wide range of recovery values. Incorporating the CO2-selective membrane (Polaris™) leads to more expensive process due to higher recycle flow rates to compensate for the low selectivity of this material. Overall, the best economic results for this process were obtained at 85% recovery rate with 99% product purity at a cost of 6.40 $/kg. Comparing to our previous study using a N2 diluent, higher purity product with lower specific cost can be achieved with CO2 diluent system but with slight decrease in recovery rate. As a final element to this study, comparative simulations were executed to demonstrate the potentially added value of using hollow fiber membranes versus spiral wound for this separation process.

Systematic optimization of H2 recovery from water splitting process using membranes and N2 diluent

Hydrogen can be produced by solar energy via photocatalytic water splitting. In the process, both hydrogen and oxygen are produced in the same environment. An inert gas (e.g. nitrogen) can be used in the reactor in order to eliminate the explosion hazards. In this case study, membrane cascade design was implemented to recover the hydrogen outside the flammability range using a commercial polyimide membrane from UBE® Industries (Japan). Two different ternary (H2, O2, N2) mixtures were investigated to recover and purify hydrogen outside the flammability range. Mixture (1) contains 4 mol-% hydrogen while Mixture (2) contains 6 mol-%. The process optimization is defined as a nonlinear programming (NLP). The aim of the objective function is to minimize the present value (PV) of all outgoing cash flows (no income) for the separation process with both flammability and recovery constraints to be satisfied. For a 100 kmol/h hydrogen feed basis, the results showed high investment and operating costs for Mixture (1) with a specific cost of 8.20 $/kg. The maximum recovery and purity that can be achieved, without further increase in cost, are 92% and 92.5%, respectively. Switching to Mixture (2) will result in a specific cost reduction of around 25% due to lower feed flow rates and higher molar concentrations of hydrogen. The maximum recovery is 90% with 95% purity. Beyond these values, the specific cost increase dramatically. This is the first fundamental process optimization considering safety issues as well as product recovery yield simultaneously from a tertiary gas mixture.

Atmospheric Chemistry of (CF3)2CF-C≡N: A Replacement Compound for the Most Potent Industrial Greenhouse Gas, SF6.

FTIR/smog chamber experiments and ab initio quantum calculations were performed to investigate the atmospheric chemistry of (CF3)2CFCN, a proposed replacement compound for the industrially important sulfur hexafluoride, SF6. The present study determined k(Cl + (CF3)2CFCN) = (2.33 ± 0.87) × 10-17, k(OH + (CF3)2CFCN) = (1.45 ± 0.25) × 10-15, and k(O3 + (CF3)2CFCN) ≤ 6 × 10-24 cm3 molecule-1 s-1, respectively, in 700 Torr of N2 or air diluent at 296 ± 2 K. The main atmospheric sink for (CF3)2CFCN was determined to be reaction with OH radicals. Quantum chemistry calculations, supported by experimental evidence, shows that the (CF3)2CFCN + OH reaction proceeds via OH addition to -C(≡N), followed by O2 addition to -C(OH)═N·, internal H-shift, and OH regeneration. The sole atmospheric degradation products of (CF3)2CFCN appear to be NO, COF2, and CF3C(O)F. The atmospheric lifetime of (CF3)2CFCN is approximately 22 years. The integrated cross section (650-1500 cm-1) for (CF3)2CFCN is (2.22 ± 0.11) × 10-16 cm2 molecule-1 cm-1 which results in a radiative efficiency of 0.217 W m-2 ppb-1. The 100-year Global Warming Potential (GWP) for (CF3)2CFCN was calculated as 1490, a factor of 15 less than that of SF6.

Experimental and modeling study of the pyrolysis and combustion of 2-methyl-tetrahydrofuran

Saturated cyclic ethers are being proposed as next-generation bio-derived fuels. However, their pyrolysis and combustion chemistry has not been well established. In this work, the pyrolysis and combustion chemistry of 2-methyl-tetrahydrofuran (MTHF) was investigated through experiments and detailed kinetic modeling. Pyrolysis experiments were performed in a dedicated plug flow reactor at 170kPa, temperatures between 900 and 1100K and a N2 (diluent) to MTHF molar ratio of 10. The combustion chemistry of MTHF was investigated by measuring mole fraction profiles of stable species in premixed flat flames at 6.7kPa and equivalence ratios 0.7, 1.0 and 1.3 and by determining laminar burning velocities of MTHF/air flat flames with unburned gas temperatures of 298, 358 and 398K and equivalence ratios between 0.6 and 1.6. Furthermore, a kinetic model for pyrolysis and combustion of MTHF was developed, which contains a detailed description of the reactions of MTHF and its derived radicals with the aid of new high-level theoretical calculations. Model calculated mole fraction profiles and laminar burning velocities are in relatively good agreement with the obtained experimental data. At the applied pyrolysis conditions, unimolecular decomposition of MTHF by scission of the methyl group and concerted ring opening to 4-penten-1-ol dominates over scission of the ring bonds; the latter reactions were significant in tetrahydrofuran pyrolysis. MTHF is mainly consumed by hydrogen abstraction reactions. Subsequent decomposition of the resulting radicals by β-scission results in the observed product spectrum including small alkenes, formaldehyde, acetaldehyde and ketene. In the studied flames, unimolecular ring opening of MTHF is insignificant and consumption of MTHF through radical chemistry dominates. Recombination of 2-oxo-ethyl and 2-oxo-propyl, primary radicals in MTHF decomposition, with hydrogen atoms and carbon-centered radicals results in a wide range of oxygenated molecules.

Effects of N2, CO2 and H2O dilutions on temperature and concentration fields of OH in methane Bunsen flames by using PLIF thermometry and bi-directional PLIF

The effects of N2, CO2 and H2O dilutions on the two-dimensional (2D) temperature and concentration fields of OH in methane Bunsen flames were investigated by employing two-line planar laser-induced fluorescence (PLIF) thermometry and bi-directional PLIF technique, respectively. The spatial resolution of the measured temperature and concentration fields of OH radical was 41.7μm. It was found that the measured temperature fields in methane Bunsen flames with different diluents exhibited a non-uniform and a symmetrical structure. In terms of decreasing the flame temperature, the CO2 diluent achieved a good result compared with N2 and H2O diluents. The total uncertainties in PLIF thermometry measurements were estimated to be ±8.44%, ±8.17% and ±8.27% for each diluent, respectively. The OH peak absorption cross sections at different heights were obtained in methane Bunsen flames with different diluents. Finally, the 2D absolute OH concentration filed in methane Bunsen flames diluted with three different diluents were obtained by using bi-directional PLIF technique. The peak absolute OH number densities in the flames with H2O, N2 and CO2 diluents were 9.84×1017cm−3, 8.57×1017cm−3 and 7.84×1017cm−3, with the overall uncertainties of ±20.56%, ±19.04% and ±23.43%, respectively. The numerical simulations of chemical kinetics were performed by using a physical model of one-dimensional laminar premixed flame and a detail methane reaction mechanism of GRI-Mech 3.0 so as to investigate the difference between the simulation results and experimental values. The comparison results for the temperature and OH concentration indicated that the reaction mechanism of GRI-Mech 3.0 might underestimate the chemical effects of CO2 and H2O diluents on the production of OH radical in premixed methane flames.