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The CO2 molecule is of great interest for astrophysical studies since it can be found in a large variety of astrophysical media where it interacts with the dominant neutral species, such as He, H2, or H2O. The CO2–He collisional system was intensively studied over the last two decades. However, collisional data appear to be very sensitive to the potential energy surface (PES) quality. Thus, we provide, in this study, a new PES of the CO2–He van der Waals complex calculated with the coupled-cluster method and a complete basis set extrapolation in order to provide rotational rate coefficients that are as accurate as possible. The PES accuracy was tested through the calculations of bound state transition frequencies and pressure broadening coefficients that were compared to experimental data. An excellent agreement was globally found. Then, revised collisional data were provided for the 10–300 K temperature range. Rate coefficients were compared to previously computed ones and are found to be up to 50% greater than previously provided ones. These differences can induce non-negligible consequences for the modeling of CO2 abundance in astrophysical media. [ABSTRACT FROM AUTHOR]

In this study, a bespoke single-stage swirl burner was used to experimentally investigate the effects of residence time on emissions from premixed ammonia-methane-air flames. The residence time was altered in two ways: by modifying the combustion chamber's length or by modifying the swirl number. Exhaust emissions of O 2 , CO 2 , CO, NO, NO 2 , and N 2 O were measured at an absolute pressure of 2 bar for equivalence ratios between 0.50 and 0.95 and ammonia fractions in the fuel blend between 0 and 100%. Spatial distributions of NO and OH radicals were also imaged using PLIF inside the combustion chamber at different heights above the nozzle. Data shows that increasing residence time can further advance chemical reactions, as evidenced by a reduction in O 2 concentration in the exhaust. Increasing the swirl number reduces emissions of NO, NO 2 , and N 2 O more efficiently than tripling the chamber's length. However, a decrease in the combustion efficiency may be responsible for a fraction of this NOx reduction when the swirl number is increased for some equivalence ratios. NO emissions are not modified when the chamber's length is increased, which is consistent with the fact that the NO-LIF signal does not decay when the distance from the nozzle increases. Therefore, NO formation is somehow restricted to within the main reaction zone of the swirling flame, that is, the zone whose height does not exceed 60 mm for this burner. Conversely, tripling the chamber's length reduces the concentrations of NO 2 and N 2 O. This reduction is not reflected in a measurable increase in NO concentration because NO is present in much larger quantities than NO 2 and N 2 O in flames examined here. Consistent with the fact that OH promotes NO formation via fuel-NOx pathways, a positive correlation is found between NO- and OH-LIF intensities. [ABSTRACT FROM AUTHOR]

This work investigates the UV and visible chemiluminescence signatures of laminar ammonia-hydrogen-air flames. A counterflow burner was used to stabilize flat and steady premixed ammonia-hydrogen-air twin-flames for wide ranges of ammonia fuel fractions (0.55 ≤ X NH 3 ≤ 0.90), equivalence ratios (0.35 ≤ ϕ ≤ 1.70), and strain rates (50 ≤ a ≤ 300 / s). The chemiluminescence spectra in the UV and visible regions were measured. The important contributors to the chemiluminescence of ammonia-hydrogen-air flames were first identified and their sensitivities to equivalence ratio and ammonia fuel fraction were then quantified. Promising ratios of chemiluminescence intensities for the non-intrusive optical sensing of equivalence ratio and ammonia fuel fraction in premixed ammonia-hydrogen-air flames were also identified. Among the 36 ratios that could be formed with the 9 contributors to chemiluminescence that were defined, 3 are particularly promising, namely, OH*/NO*, OH*/ violet (violet refers to the 350 to 400 nm range), and red/blue (blue and red refer to the 450 to 500 nm and 650 to 750 nm ranges, respectively). Ratios OH*/NO* and OH*/ violet were found to provide suitable measures of equivalence ratio for lean and rich ammonia-hydrogen-air flames, respectively, because these ratios are very sensitive to equivalence ratio, are insensitive to ammonia fuel fraction, and are marginally sensitive to strain rate. Once equivalence ratio is known, the ammonia fuel fraction can then be measured with ratio red/blue because it is sensitive to the ammonia fuel fraction and it is globally insensitive to strain rate. [ABSTRACT FROM AUTHOR]

Lean premixed combustion mode has become attractive for utilization in industrial gas turbines due to its ability to meet strict emissions regulations without compromising engine efficiency. In this combustion mode, the mixing process is the key player that affect the flame structure and stability, as well as the generated emissions. Many studies have investigated the aspects that influence premixed flames, including the effects of turbulence, combustor geometry, and level of partial premixing, while mostly using conventional natural gas fuel represented by methane. Recently, ammonia, a sustainable energy source, has been considered in gas turbines due to its carbon-free fuel producing no CO2. Utilizing 100% ammonia or a blend of methane and ammonia alters the combustion performance of a premixed flame due to the variation associated with the physical and chemical properties of ammonia. Thus, investigating the coupling between blend ratios and mixing length of methane-ammonia on flame stability and emissions is an essential step toward implementing ammonia in industrial gas turbines. In this study, the influence of various methane-ammonia blends, from 0 (pure methane) to XNH3 = 75%, and mixing lengths on the flame performance were studied. The mixing length was altered by delaying the injection (i.e., partially premixing) of the ammonia while using a fixed injection location for the reference methane-air mixture. This was done by using three fuel ports located at three different heights upstream of the combustion chamber. The results showed that the flame stability is negatively influenced by increasing (decreasing) ammonia fraction (mixing length ratio) and is more sensitive to the ammonia fraction than to the mixing length. At a constant equivalence ratio, the CO and NOx performances improved positively by increasing the ammonia volume fractions (especially at XNH3 = 75% compared to XNH3 = 25% and 50%) and the mixing length. [ABSTRACT FROM AUTHOR]

The results of a rigorous study of the two first pure rotational transitions of CO perturbed by Ar are presented. The experimental part is based on the use of three different spectrometers covering together the pressure range from 0.02 up to 1500 torr. The measurement results of collisional line shape parameters are supported by fully ab initio calculations, which are in remarkable agreement with retrieved data. A sub-percent uncertainty of line intensity measurements is achieved and the first firm evidence that the resonance spectrum of CO is observed on the continual pedestal is given. We analyze the results of our ab initio calculations on the basis of early analytical theories and demonstrate a good general applicability of the latter to the CO–Ar collisional system. [ABSTRACT FROM AUTHOR]

Ammonia is a very promising carbon-free fuel, but its combustion is prone to generate a large amount of harmful nitric oxide (NO). Designing NO reduction strategies for ammonia flames requires computational fluid dynamics and accurate kinetic mechanisms. However, there are currently no available experimental data that can be used to validate models describing chemistry-turbulence interactions in ammonia flames. This study introduces two non-premixed turbulent jet flames that emulate some features of the cracked ammonia combustion at 5 bar, relevant to micro gas turbines. These ammonia-hydrogen-nitrogen jet flames feature well-controlled boundary conditions and are particularly amenable to modeling. A one-dimensional NO laser-induced fluorescence (NO-LIF) method was implemented and combined with 1-D Raman spectroscopy to measure the NO mole fraction quantitatively. To avoid laser absorption by ammonia, excitation in the A 2 Σ + − X 2 Π (0–1) band near 236 nm was chosen instead of the more conventional (0–0) band near 226 nm. Due to the unsteady nature of turbulent jet flames, offline NO-LIF measurements are not useful, and undesirable interferences from Rayleigh scattering and oxygen LIF were instead quantified and removed using the temperature and major species mole fractions measured with Raman spectroscopy. NO quantification algorithms were optimized and validated first with a laminar NH 3 –H 2 –N 2 counterflow flame, and then applied to the turbulent jet flames. Results show that a large amount of NO (∼1500 ppm) is produced in the NH 3 –H 2 –N 2 jet flames. Increasing the ammonia cracking ratio from 14% to 28% reduces the NO concentration in laminar and turbulent NH 3 –H 2 –N 2 flames. Data also shows that turbulence smear effects of differential diffusion. To the best of our knowledge, this is the first available database featuring quantitative measurements of spatially-resolved NO mole fraction in turbulent NH 3 –H 2 –N 2 flames at a practically-relevant pressure. This unique database can be used in the future to validate turbulent combustion models for such flames. [ABSTRACT FROM AUTHOR]

This work reports on the chemiluminescence signature of premixed ammonia-methane-air swirling flames. Wide ranges of equivalence ratios (0.6 ≤ Φ ≤ 1.3), ammonia fractions in the fuel blend (0 ≤ X NH3 ≤ 0.70), and Reynolds numbers (10,000 ≤ Re ≤ 40,000) were investigated to understand effects of these parameters on the light emitted by these flames. Excited radicals contributing to chemiluminescence in the UV and visible ranges were confirmed, namely NO*, OH*, NH*, CN*, CO 2 *, CH*, and NH 2 *. With non-intrusive flame monitoring in mind, various ratios of chemiluminescence intensities were carefully studied because these allow removing effects of time-varying flame surface area that is inherent in turbulent flames. Consistent with previous findings in laminar flames, ratios CN*/OH*, CN*/NO*, and NH*/CH* were found to be promising candidates. Ratios CN*/OH* and CN*/NO* were identified as potential surrogates for equivalence ratio if X NH3 ≥ 0.20 and 0.05 ≤ X NH3 ≤ 0.50, respectively. Ratio NH*/CH* was identified as a potential surrogate for the ammonia fraction in the fuel blend provided that equivalence ratio is roughly known. Ratio Blue /NH 2 *, obtained exclusively from measurements in the visible range, is another interesting surrogate for the ammonia fraction but its sensitivity to Reynolds number may limits its range of applications. Trends of measured exhaust NO concentration with equivalence ratio and ammonia fraction were found to qualitatively match that of NO*, NH*, and CN*, implying that emissions from these excited radicals could be used to monitor the NO performance of practical ammonia-methane-air flames. [ABSTRACT FROM AUTHOR]

In this study, two series of pressurized turbulent jet sooting flames at 1, 3, and 5 bar with either fixed jet velocity or fixed Reynolds number are simulated to study the pressure effects on soot formation and evolution. Through a radiation flamelet progress variable approach with a conditional soot subfilter probability density function (PDF) model to consider the turbulence–chemistry–soot interactions, quantitatively good agreements are achieved for soot volume fraction (SVF) predictions compared with the experimental data, regardless different turbulent intensities and residence times. SVF source terms are then discussed to show the pressure effects on nucleation, condensation, surface growth, and oxidation at different axial positions in these flames. It is found that surface growth and oxidation increase by about three orders of magnitude from 1 to 5 bar, while nucleation and condensation only increase within one order of magnitude. The stronger SVF scaling on pressure than measured data is found to be attributed to the inaccurate surface growth and oxidation scaling on pressure. Further analysis indicates that (i) the uncertainty of C2H2 prediction at elevated pressures is likely a major reason for the too strong surface growth scaling; and (ii) taking account of pressure effects in the conditional subfilter PDF modeling for turbulence–soot–chemistry interactions is likely a key to improve oxidation prediction. The results in this study open up the possibilities for improving future turbulent sooting flame modeling by improving C2H2 chemistry and turbulence–chemistry–soot modeling at elevated pressures. [ABSTRACT FROM AUTHOR]

This work presents an experimental study on the influence of the pilot flame characteristics on the flame morphology and exhaust emissions of a turbulent swirling flame. A reduced-scale burner, inspired by that fitted in the AE-T100 micro gas turbine, was employed as the experimental platform to evaluate methane (CH4) and an ammonia-methane fuel blend with an ammonia (NH3) volume fraction of 0.7. The power ratio (PR) between the pilot flame and the main flame and the fuel composition of the pilot flame was investigated. The pilot power ratio was varied from 0 to 20% for both fuel compositions tested. The NH3 volume fraction in the pilot flame ranged from pure CH4 to pure NH3 through various NH3–CH4 blends. Flame images and exhaust emissions, namely CO2, CO, NO, and N2O were recorded. It was found that increasing the pilot power ratio produces more stable flames and influences most of the exhaust emissions measured. The CO2 concentration in the exhaust gases was roughly constant for CH4-air or NH3–CH4–air flames. In addition, a CO2 concentration reduction of about 45% was achieved for XNH3 = 0.70 compared with pure CH4, while still producing stable flames as long as PR ≥ 5%. The pilot power ratio was found to have a higher relative impact on NO emissions for CH4 than for NH3–CH4, with measured exhaust NO percentage increments of about 276% and 11%, respectively. The N2O concentration was constant for all pilot power ratios for CH4 but it decreased when the pilot power ratio increased for NH3–CH4. The pilot fuel composition highly affected the NO and N2O emissions. Pure CH4 pilot flames and higher power ratios produced higher NO emissions. Conversely, the NO concentration was roughly constant for pure NH3 pilot flames, regardless of the pilot power ratio. Qualitative OH-PLIF images were recorded to further investigate these trends. Results showed that the pilot power ratio and the pilot fuel composition modified the flame morphology and the OH concentration, which both influence NO emissions. [ABSTRACT FROM AUTHOR]

In this work, a new design approach was developed to automatically and consecutively predict optimal preform geometry and optimal operating conditions for the stretch blow molding process. The numerical approach combines a constrained gradient-based optimization algorithm that iterates automatically over predictive finite element software. The strategy allows for targeting a specified container thickness distribution by manipulating consecutively the preform geometry (thickness and shape) and the operating parameters subject to process and design constraints. For the preform shape optimization, the preform geometry is mathematically parameterized for simplified treatment and the corresponding sensitivities are evaluated using a finite difference technique. A finite difference technique is also employed for the operating condition optimization. The constrained optimization algorithms are solved via the use of the sequential quadratic programming method that updates the design variables accordingly. Predicted optimization results obtained on an industrial case are presented and discussed to assess the validity when compared to experimental results and the robustness of the proposed approach. POLYM. ENG. SCI., 47:289-301, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION Stretch blow molding (SBM) is the process of choice for the production of PET containers, in particular for the food and beverage industry as well as the pharmaceutical sector. [...]

When polyethylene terephthalate (PET) is stretched, it exhibits strain-hardening properties, which are temperature and strain-rate dependent. In this paper, two grades of PET are experimentally characterized using biaxial tests. A visco-hyperelastic model is used to describe the stretching behavior for the polymer. A biaxial characterization method is employed to determine the model parameters using a robust nonlinear curve-fitting program. This model can represent adequately well the stretching behavior of PET. Based on this model, the membrane finite element formulation is developed to simulate the stretch blow molding process. Two bottles of different designs, produced based on the single-stage injection blow molding process, are used to validate the model. Good agreement with the bottle thickness profile is observed. Polym. Eng. Sci. 44: 1460-1472, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Because of its excellent properties, polyethylene terephthalate (PET) is used extensively in the food packaging industry, particularly for the production of soft drink bottles using the injection stretch blow [...]

In this work, a gradient-based numerical optimization scheme is proposed to determine the optimal process operating conditions to produce a blow molded part by with a given performance. Finite element simulations are used to relate the part performance to the processing conditions. A performance optimization is first performed to find the minimum part thickness distribution that minimizes the part weight while satisfying mechanical performance constraints such as maximum part deflection or maximum stress for an applied load. Then a process optimization finds the optimal operating conditions, e.g. the die gap opening profile, that minimize the part weight while respecting the minimum thickness distribution dictated by the performance optimization. The results show that the optimization scheme minimizes the pan weight with minimal constraint violation. The addition of a constraint associated with process stability is proposed., INTRODUCTION Product designers in today's global environment are under increasing pressure to reduce part development time to a minimum, while ensuring the maximum part quality and minimum manufacturing costs (better, [...]

Accurate measurements of collision-induced absorption by [O.sub.2] and [O.sub.2]-[N.sub.2] mixtures in the fundamental band near 6.4 [[micro]meter] have been made. A Fourier-transform spectrometer was used with a resolution of 0.5 [cm.sup.-1]. Absorption has been investigated in the 0-20-atm and 193-293 K pressure and temperature ranges, respectively. The current measurements confirm that the broad [O.sub.2] continuum carries small features whose attribution is not yet clear. Available experimental data in the 190-360 K temperature range have been used to build a simple, low cost computer, empirical model that is well adapted for computation of atmospheric [O.sub.2] absorption. Tests show that it is accurate, contrary to predictions of widely used atmospheric transmission codes. Key words: Oxygen, collision-induced absorption, infrared.

Measurements of pure C[O.sub.2] absorption in the 2.3-[[micro]meter] region are presented. The 3800-4700-[cm.sup.-1] range has been investigated at room temperature for pressures in the 10-50-atm range by using long optical paths. Phenomena that contribute to absorption are listed and analyzed, including the contribution of far line wings as well as those of the central region of both allowed and collision-induced absorption bands. The presence of simultaneous transitions is also discussed. Simple and practical approaches are proposed for the modeling of absorption, which include a line-shape correction factor [Chi] that extends to approximately 600 [cm.sup.-1] from line centers. Key words: C[O.sub.2] infrared spectra, induced band, far wings.