Time-history Profiles Research Articles

Shock-tube study of the oxidation of ammonia by N2O

The oxidation of ammonia by N2O was studied by following the time history of ammonia in a shock tube with a spectroscopic laser diagnostic. Dilute (99.5 % Ar) mixtures were studied around atmospheric pressure for several equivalence ratios: 0.25, 0.85, 1.0, and 2.0. The time at which the ammonia concentration reaches 50 % of its original value (τ50%) was also measured. Results were compared to several detailed kinetics models from the literature. Based on past work from the authors and a literature mechanism, a tentative model was also assembled to better represent the experiments at the conditions investigated herein. The quantitative NH3 diagnostic shed light on the limitations associated with the passivation method to counterbalance ammonia adsorption on the reactor's surface and showed that an ammonia diagnostic is necessary and critical to know the initial conditions for dilute mixtures. Experimental results show a relatively large effect of the equivalence ratio on the mixture's reactivity. The main outcome of this study is that while τ50% can be accurately predicted by all models considered, large variations are observed when comparing with the full NH3 time-history profile. Key features of the experimental profiles were not captured by the models, and large variations were observed between the models. Overall, the most recent models and the tentative models from this study performed the best, but more work remains necessary to fully capture the oxidation of ammonia by N2O. The effect of the third-body collision coefficient on N2O (+M) ⇆ N2 + O (+M) was investigated for several species, but no effect was found under the conditions investigated. However, it is likely that studying N2O (+NH3) ⇆ N2 + O (+NH3) is necessary for real-world applications.

Laminar Flame Speed, Ignition Delay Time, and CO Laser Absorption Measurements of a Gasoline-like Blend of Pentene Isomers.

The combustion properties of a gasoline-like blend of pentene isomers were determined using multiple types of experimental measurements. The representative mixture (Mix A) is composed of 5.7% 1-pentene (1-C5H10), 39.4% 2-pentene (2-C5H10), 12.5% 2-methyl-1-butene (2M1B), and 42.4% 2-methyl-2-butene (2M2B) (% mol). Laminar flame speeds were measured at equivalence ratios of 0.7-1.5 in a constant-volume combustion chamber, and ignition delay times (including both OH* and CH* diagnostics) as well as CO time-history profiles were performed in shock tubes, in highly diluted mixtures (0.995 He/Ar), at a stoichiometric condition for temperatures ranging from 1350 to 1750 K, and at near-atmospheric pressure. Two additional unbalanced mixtures removing either 2M2B (Mix B) or 2-C5H10 (Mix C) were studied in a shock tube to collect CO time histories, representing the most stringent validation constraints, as these two pentenes constitute the biggest proportions in Mix A and exhibit opposite behaviors in terms of reactivity due to their chemical structure differences. Numerical predictions using a recent validated chemical kinetics mechanism encompassing all pentene isomers from Grégoire et al. ( Fuel2022, 323, 124223) are presented. The use of a complex blend of four pentene isomers in the present paper provided a capstone test of the current mechanism's ability to model pentene-isomer combustion chemistry, with very good results that reflect positively on the current state of the art in pentene isomer kinetics modeling.

Development of a reduced chemical mechanism for ammonia/n-heptane blends

A reduced chemical mechanism for ammonia/n-heptane blends, which consists of 495 reactions and 74 species, is proposed in this study. This reduced mechanism is developed using the direct relation graph with error propagation (DRGEP) method based on the latest detailed kinetic mechanism of ammonia/n-heptane blends, which includes the important interactive reactions between n-heptane and ammonia (n-C7H16 + NH2 <=> C7H15 + NH3). The reduced mechanism was first validated against experimental ignition delay times (IDTs) and laminar burning velocities (LBVs) for different ammonia/n-heptane blends and can capture well these data. Moreover, both the detailed and reduced mechanisms were used to simulate the combustion and emission characteristics of a homogeneous charge compression ignition (HCCI) engine fueled by different ammonia/n-heptane blends. The simulation results show that the predicted auto-ignition timings and peak pressure values of the reduced mechanism match reasonably well with those of the detailed mechanism for different ammonia/n-heptane blends. Also, the predicted time-history profiles of the important pollutants, including NO, NO2, N2O and HCN, show reasonably good agreement between the detailed and reduced mechanisms, and the maximum discrepancy of the peak concentration is within a factor of two. The important reaction pathways of pollutant formations at HCCI engine conditions are discussed in detail. Furthermore, the current reduced mechanism is also used to simulate the combustion process of an ammonia/diesel dual-fuel engine. Overall, the engine combustion phasing, peak pressure, and heat release can be well simulated using the current mechanism, and the computational efficiency is acceptable.

Determining Dynamic Mechanical Properties for Elastic Concrete Material Based on the Inversion of Spherical Wave.

The paper presents a new method to study the dynamic mechanical properties of concrete under low pressure and a high strain rate via the inversion of spherical wave propagation. The dynamic parameters of rate-dependent constitutive relation of elastic concrete are determined by measured velocity histories of spherical waves. Firstly, the particle velocity time history profiles in the low stress elastic region at the radii of 100.6 mm, 120.6 mm, 140.6 mm, 160 mm, and 180.6 mm are measured in the semi-infinite space of concrete by using the mini-explosive ball and electromagnetic velocity measurement technology. Then, based on the universal spherical wave conservation equation and the fact that the accommodation relationship in state equation satisfies linear elastic law, the inverse problem analysis of spherical waves in concrete (called "NV + T0/SW") is proposed, which can obtain the dynamic numerical constitutive behavior of concrete in three-dimensional stress by measuring the velocity histories. The numerical constitutive relation is expressed in the form of distortion, and it is found that the distortion law has an obvious rate effect. Finally, the rate-dependent dynamic parameters in concrete are determined by the standard linear solid model. The results show that the strain rate effect of concrete cannot be ignored with the strain rate range of 102 1/s. This study can provide a feasible method to determine the dynamic parameters of rate-dependent constitutive relation of concretes. This method has good applicability, especially in the study of the dynamic behavior of multicomponent composite materials with large-size particle filler.

Chemical kinetics investigation of toluene combustion in a shock tube using spectroscopic CO and H2O laser absorption

Toluene oxidation was investigated behind reflected shock waves using spectroscopic laser diagnostics to simultaneously measure carbon monoxide (CO) and water (H2O) time-history profiles. CO and H2O time histories are unique in the available database for toluene speciation as only a total of five H-atom profiles can be found in the literature and were carried out for pyrolysis instead. These new, high fidelity measurements can help in validating detailed chemical kinetics mechanisms over highly dilute conditions. The experiments cover three equivalence ratios (ɸ = 0.5, 1.0, and 2.0) with temperatures ranging from 1433 to 1921 K near atmospheric pressure. Comparisons with six models were conducted for a performance review: the Yuan et al. model shows the most accurate results and was selected to further understand toluene chemistry and identify the reaction pathways. Rate-of-production and sensitivity analyses support that toluene (A1CH3 in the model) decomposes via A1CH3 (+M) ⇄A1CH2 + H (+M) and mostly produces CO and H2O with the following sequences: A1CH3→ A1CH2→ A1CH2O → CH2O → HCO → CO and A1CH3→ A1CH2→ CH3→ H2O, respectively.

A shock-tube study of NH3 and NH3/H2 oxidation using laser absorption of NH3 and H2O

Ammonia (NH3) is an attractive carbon-free fuel, yet its low reactivity presents many challenges for direct use in combustion applications. These combustion challenges could be resolved by mixing NH3 with more reactive fuels such as hydrogen (H2). To further contribute to NH3 and NH3/H2 kinetics—which arguably still requires much improvement—new experiments were conducted over a wide range of temperatures (1474–2307 K), near-atmospheric pressure, several NH3/O2 mixtures (equivalence ratios varying from 0.56 to 2.07), and near-stoichiometric NH3/H2/O2 mixtures with NH3:H2 ratios of 80:20 and 50:50. During these experiments, laser absorption diagnostics near 10.4 µm and 7.4 µm were simultaneously employed to measure NH3 and H2O time histories, respectively. Characteristic parameters, such as NH3 half-life time and H2O induction delay time, were extracted from the time-history profiles, and these parameters present stringent speciation targets for mechanism validation. After an assessment of most modern kinetics models, three, most accurate, mechanisms were compared against the experimental results. Only one model was able to partially reproduce the pure NH3 experiments, yet none of the models were capable of predicting the NH3/H2 experiments. Reaction pathway analysis showed that NH3 oxidation proceeds via forming NH2 then followed three different routes to form N2. Importantly, the models considered showed different levels of importance for each route. Sensitivity analysis showed that the NH3/H2 experiment is mostly sensitive to NH3+OH⇄NH2+H2O. Interestingly, this reaction showed no sensitivity for the NH3/O2 experiments. Overall, the models exhibited significantly slower reactivity than the NH3/H2 experiments, and the kinetics analysis showed that the start of this reactivity is governed by the levels of H-atoms in the early stages of the experiments. At these early stages of the experiments, propagation and branching reactions in the H2/O2 system are the main contributors to generating H radicals, along with the reaction NH3+H⇄NH2+H2 which proceeds in its reverse direction.

Laser-absorption-spectroscopy-based temperature and NH3-concentration time-history measurements during the oxidation processes of the shock-heated reacting NH3/H2 mixtures

As a carbon-free fuel, NH3 has been considered as a potential and promising alternative energy carrier in the future transportation system. This study simultaneously measured the temperature and NH3-concentration time histories during the oxidation processes of the shock-heated NH3/H2 mixtures by combining laser absorption techniques. The v" = 0, P8 and v" = 1, R21 lines in the fundamental vibrational band of CO were selected for temperature time-history measurements. Nine transition lines in the v2 fundamental vibrational band of NH3 near 8.91 µm were selected for NH3-concentration time-history measurements. The temperature- and pressure-dependent NH3 absorption cross-section highly diluted in argon was measured at 1000–2200 K and 0.8–3.9 bar, respectively. The time-dependent temperature and NH3 concentration were then measured and compared with the predictions based on four mechanisms (Mathieu & Petersen, 2015; Glarborg et al., 2018; Wang et al., 2020; Shrestha et al., 2021). The four mechanisms were substantially slow in predicting the NH3-concentration time histories for the stoichiometric NH3/H2 mixtures. The Glarborg et al. mechanism and the Shrestha et al. mechanism showed very good agreements with the experiments for the fuel-rich NH3/H2 mixtures, especially in predicting the NH3-concentration time-history profiles in the burnout state. Comprehensive kinetics analyses illustrated that the NH3 addition evidently changed the mixture reactivity and formation and consumption processes of H and OH radicals. This study updated the rate coefficients of NH3 + OH = NH2 + H2O in the Glarborg et al. mechanism and the modified mechanism showed improved performances in predicting the NH3-concentration profiles.

Experimental and detailed kinetics modeling study of the fire suppressant properties of di(2,2,2trifluoroethyl) carbonate

To reduce the flammability of lithium-ion battery electrolytes, the fire suppressant effect of di(2,2,2trifluoroethyl) carbonate (DtFEC) was investigated experimentally and numerically using a new detailed kinetics model. DtFEC has a structure similar to diethyl carbonate (DEC), which is a very common component of battery electrolytes. This similar structure should allow for an integration of the fire suppressant without excessive degradation of the battery performance. To validate the model and assess the fire suppressant potential of DtFEC, several kinds of experiments were performed around atmospheric pressure. The high-temperature chemistry of DtFEC was investigated in shock tubes by measuring ignition delay times for a DtFEC/O2/Ar mixture and by measuring the CO formation during its pyrolysis using a laser absorption diagnostic. DtFEC's fire suppressant potential was assessed by measuring the effects of a small DtFEC addition on the ignition delay times and laminar flame speeds of well-known fuels, namely H2 and CH4. A model was assembled using a well-validated and modern base mechanism (NUIGMech1.1) coupled with existing chemistry for fluoroalkanes. Using ab-initio calculations, the DtFEC module and corresponding thermodynamics data were implemented. The resulting model performs well at predicting the global kinetics data (ignition delay time, laminar flame speed), but improvements on CO time-history profiles are still necessary.

Gradient boosted decision trees for combustion chemistry integration

This study introduces the gradient boosted decision tree (GBDT) as a machine learning approach to circumvent the need for a direct integration of the typically stiff system of ordinary differential equations that govern the temporal evolution of chemically reacting species. Stiffness primarily relates to the chemistry integration and here, hydrogen/air systems are taken to train and test the ensemble learning approach. We use the LightGBM (Light Gradient Boosting Machine) algorithm to train GBDTs on the time series of various self-igniting mixtures from the time of ignition to equilibrium composition. The GBDT model provides reasonable predictions of the species compositions and thermodynamic states at the next time step in an a priori study. A much more challenging a posteriori study shows that the model can reproduce a full time–history profile of the igniting H2/air mixtures, as the results agree very well with those obtained from a direct integration of the ODEs. The GBDT model can be deployed as standalone C++ codes and a speed-up by one order of magnitude has been demonstrated. The GBDT approach can thus be considered as an efficient method to represent the chemical kinetics in the simulation of reactive flows. It provides an alternative to deep artificial neural networks (ANNs) that is comparable in accuracy but easier to couple with existing CFD codes.

A Shock-Tube and Chemical Kinetics Model Investigation Encompassing all Five Pentene Isomers

Kinetic treatment of the full group of C5 olefins is presented with new measurements on 1-pentene (1-C5H10), 2-pentene (2-C5H10), and 3-Methyl-1-Butene (3M1B) combined with recently published data obtained at similar conditions from our group on 2-Methyl-2-Butene (2M2B) and 2-Methyl-1-Butene (2M1B). This extensive experimental database contains carbon monoxide and water time-history profiles, along with their measured CO and H2O induction delay times. The oxidation of the five pentene isomers was carried out at three equivalence ratios (0.5, 1.0, and 2.0) in mixtures highly diluted in 99.5% Helium-Argon. The experiments were performed for temperatures ranging from 1400 to 1900 K at near-atmospheric pressure. A unique comparison of the complete set of pentene isomers permits the understanding of the C=C double bond position and branching impacts on combustion properties, using the chemical kinetics mechanism of both linear and branched structures. The impact of the C = C double bond location – either the 1–2 or 2–3 bond site – is described using the linear molecules 1-C5H10 and 2-C5H10. Species induction delay times were measured for the five isomers for each equivalence ratio investigated. Results showed noticeable differences between isomers, with the induction delay time results for 3M1B being the shortest, closely followed by 2-C5H10, 1-C5H10, and then after a large leap in decreasing reactivity, by 2M2B and 2M1B. Numerical predictions using up to 9 models available in the literature were performed. An error score function was used to evaluate the properties of the pentene isomer models in the current literature.

An Engineered Multifunctional Composite for Passive Sensing, Power Harvesting, and In Situ Damage Identification with Enhanced Mechanical Performance

AbstractA multifunctional fiber‐reinforced composite with passive self‐sensing, energy‐harvesting, and damage detection capabilities is presented. Here, barium titanate piezoelectric microparticles are deposited on basalt fibers by a scalable, low‐cost, environmentally friendly continuous feed‐through process. The resulting composite derives a superior interlaminar shear strength from the microparticle‐modified fiber–matrix interfaces. The composite also demonstrates passive self‐sensing capabilities that produce electrical signals proportional to various dynamic loading events. Vibration and strain‐controlled experiments are performed on composite beams to quantify the sensitivity and power output as a function of input acceleration and strain. Furthermore, these composite‐generated electrical signals are used to identify in situ damage initiation for structural health monitoring to inform composite damage prior to structural failure. In brief, this truly multifunctional composite simultaneously displays a sensitivity of 0.5–2.6 mV g−1 at a resolution of 0.045–0.20g (g = gravitational acceleration), energy harvesting in the range of nW cc−1, and prediction of early damage by exhibiting 0.017–1.17 mV peaks in voltage–time history profiles while assuring ≈20% improved interlaminar shear strength.

Shock-tube laser absorption measurements of N2O time histories during ammonia oxidation

The oxidation of ammonia was studied experimentally by monitoring the time history of the intermediate N2O species using laser absorption spectroscopy. Experiments were conducted in a shock tube for mixtures of NH3/O2 diluted in ∼96.7% Ar for equivalence ratios of 0.54, 1.03, and 1.84. The equivalence ratios were determined accurately using spectroscopic measurements of NH3 with another laser before each experiment. Experiments were performed at an average pressure of 1.2 atm and covered a temperature range of 1829 to 2198 K. For the same temperature, experiments revealed that increasing the equivalence ratio leads to less N2O formation. The time-history profiles showed that N2O is formed at the beginning of the experiments, mainly from the formed NO, until reaching a peak. The N2O is then fully consumed, mainly via its reaction with H-atom. Characteristic parameters, such as the N2O peak time and mole fraction, were extracted from the N2O profiles and compared with 15 recent NH3 kinetics models. The comparison revealed that none of the existing kinetics models were able to correctly predict both the peak N2O time and mole fraction together. Two of the models were selected to perform a chemical analysis, and an improvement of the predictive capability of one model is proposed. The N2O profiles reported herein are excellent validation targets that offer stringent constraints for the improvement of future NH3 kinetics models.

Statistical Analysis on Rate Parameters of the H2-O2 Reaction System.

Quantitative rate determination of elementary reactions is a major task in the study of chemical kinetics. To ensure the fidelity of their determination, progressively tightened constraints need to be placed on their measurement, especially with the development of various notable experimental techniques. However, the evaluation of reaction rates and their uncertainties is frequently conducted with substantial subjectivity due to data source, thermodynamic conditions, sampling range, and sparsity. To reduce the extent of biased rate evaluation, we propose herein an approach of uncertainty-weighted statistical analysis, utilizing weighted average, and weighted least-square regression in statistical inference. Based on the backbone H2/O2 chemistry, rate data for each elementary reaction are collected from the time-history profile in shock tube experiments and high-level theoretical calculations, with their assigned weight inversely depending on uncertainty, which would overall avoid subjective assessments and provide more accurate rate evaluation. Aided by sensitivity analysis, the rates of a few key reactions are further constrained in the less investigated low- to intermediate-temperature conditions using high-fidelity flow reactor data. Good performance of the constructed mechanism is confirmed with validation against the target of the high-fidelity flow reactor data. This study demonstrates a systematic approach for reaction rate evaluation and uncertainty quantification.

An experimental and modeling study of ammonia pyrolysis

Ammonia (NH3) is a promising carbon-free fuel and a hydrogen carrier. In recent years, there has been a large number of experimental and numerical studies to understand the chemical kinetics of NH3 in moderate to extremely complex systems. This study focused on understanding the chemical kinetics of NH3 in a simple system (pyrolysis). Shock-tube experiments were performed to monitor the NH3 time history profiles during pyrolysis, with and without the presence of H2, using a new laser absorption diagnostic near 10.4 µm. The pyrolysis experiments were conducted for mixtures of ∼ 0.5% NH3/Ar and ∼ 0.42% NH3/2% H2/Ar behind reflected shock waves, near atmospheric pressure, and over a temperature range of 2100–3000 K. Using the data from the present study as a guide, along with NH3 pyrolysis data from the literature, a detailed chemical kinetics mechanism for NH3 pyrolysis is proposed herein. This mechanism was assembled using available reaction rate constants from the literature. The mechanism showed excellent agreement with the experimental results, as well as with the literature data. Additionally, an assessment of 15 detailed NH3 chemical kinetics mechanisms on their capabilities of predicting the new pyrolysis experiments was performed. The assessment showed that these literature mechanisms yield significantly different predictions, with only one model producing acceptable results for the majority of the NH3 pyrolysis experiments. The effect of pyrolysis reactions on the prediction of oxidation data was investigated by updating the pyrolysis sub-mechanism of selected literature models with the reactions of the present pyrolysis model. The prediction of the updated literature models significantly improved for ignition delay time and flame speed literature data, indicating the importance of pyrolysis reactions for high-temperature oxidation chemistry.

Speciation measurements in shock tubes for validation of complex chemical kinetics mechanisms: Application to 2-Methyl-2-Butene oxidation

Abstract Shock-tube species time histories can be used to generate multiple validation targets to develop and validate detailed chemical kinetics mechanisms. In this study, new shock-tube species time-history data are provided to further validate the detailed mechanisms for 2-methyl-2-butene (2M2B). Experiments were conducted in mixtures of 2M2B/O2 diluted in 99.5% inert gas at three equivalence ratios of ϕ = 0.5, 1.0, and 2.0 over a temperature range of 1396 to 1752 K near atmospheric pressure. Time histories of CO and H2O were measured using laser absorption diagnostics near 4.6 and 1.4 µm, respectively. Chemiluminescence from OH* was also collected near 307 nm to allow ignition delay time determination. Detailed procedures and considerations for the data processing of the laser absorption experiments are provided. The results from the OH* profiles showed two distinct peaks: one near time-zero and the other later in the experiment corresponding to the main ignition. The predictions from three 2M2B kinetics mechanisms were compared with the experimental results. A quantitative comparison is also presented using the multiple characteristic times extracted from the species time history profiles to quantify the performance of the mechanisms. A reaction pathway analysis was performed on the decomposition of 2M2B, revealing clear discrepancies in the major reaction pathways of these mechanisms. A sensitivity analysis was also performed, leading to similar conclusions regarding the differences among the mechanisms. The sensitivity analysis also showed that the OH* peak near time-zero is mainly due to the rapid 2M2B fuel decomposition reactions, indicating that these reactions can be independently validated using the OH* peak near time-zero as a target. This paper provides not only the first detailed species time-history measurements for 2M2B in a shock tube, but it also documents the proper collection and interpretation of such data, which is useful for future studies.

Simultaneous needle lift and injection rate measurement for GDI fuel injectors by laser Doppler vibrometry and Zeuch method

Achieving an adequate knowledge of the fuel injector dynamic operation is an important step in the global effort of improving direct injection gasoline engine efficiency while limiting pollutant emissions. In this frame, needle displacement measurement is an important add-on to evaluate the injector actual performances and can be very useful for developing predictive numerical models to support both the component and engine development. In this study the dynamic behavior of a GDI injector was investigated by the simultaneous measurement of injector needle lift and of the resulting injection rate. With this methodology, the needle displacement is measured by laser Doppler vibrometry, while the injector is tested by an injection analyzer based on the Zeuch method. The vibrometer laser beam points on the needle back surface, passing through a quartz window allowing the fuel pressurization and the normal injector operation. The analysis of the simultaneously acquired needle displacement, injection rate, fuel inlet pressure and current time-history profiles allows a complete insight in the injector dynamic operation. The pressure effect on the needle dynamics was assessed with a detailed analysis of the opening and closing transients; further, multiple actuation strategies were analyzed focusing on the influence of dwell time on the injector dynamics evidencing how the resulting injection rate profile is affected by the needle inertia and by the pressure wave propagation along the fuel line.

Characterization of adhesive joints under high-speed normal impact: Part II – Numerical studies

This two-part article presents an experimental method with numerical verification of the characterization of adhesive bonds under normal impact loading. Part I presented the experimentally measured performance of static and impact behavior of two adhesives (a methacrylate and an epoxy). Part II presents the numerical modeling of the static and dynamic tests performed in Part I. The finite element simulations are used to determine approximate dynamic material modeling parameters. The simulations are also useful in estimating certain critical performance aspects of the adhesive for the proposed impact test such as the estimation of contact force time histories, the dynamic stress time history profiles within the adhesive, and to the various energy components in the adhesives and adherends.

Experimental study of ethanol oxidation behind reflected shock waves: Ignition delay time and H2O laser-absorption measurements

The oxidation of ethanol was investigated in shock tubes by measuring ignition delay times and water time history profiles. A laser absorption technique was used in the latter case. Ignition delay times were investigated for three equivalence ratios, 0.5, 1.0, and 2.0, and for pressures ranging from 1.3 to 53 atm. The fuel concentration and the type of diluent used were also varied. The ignition delay times were in very good agreement with results from the literature for the very few overlapping conditions, and most of the experimental conditions have never been studied before. A high level of accuracy was observed for the predictions of the ignition delay times from detailed kinetics mechanisms. Inhomogeneous ignition events were observed in some specific conditions, validating the notions of thermal diffusivity and flame thickness developed in the literature for the reasons behind such inhomogeneous ignition. The water time-history profiles showed the formation of water in two stages. These profiles were also modeled using well-known detailed kinetic mechanisms from the literature. Severe discrepancies were often observed for laser-absorption measurements, and this was the case with most of the models. A numerical analysis (sensitivity and rate-of-production) was conducted using the two best-performing literature mechanisms (namely, AramcoMech3.0 and CRECK).

Ignition delay time and H2O measurements during methanol oxidation behind reflected shock waves

To improve detailed chemical kinetics models, the oxidation of methanol was investigated behind reflected shock waves in shock tubes. Ignition delay times of methanol–air mixtures, with Ar as diluent, were studied between 940 and 1540 K in a heated shock tube, for pressures up to 14.9 atm and for equivalence ratios of 0.5, 1.0, and 2.0. Water profiles were measured by utilizing a laser absorption technique in the 1350-to-1600-K temperature range, at an average pressure of 1.3 atm and for similar equivalence ratios. The present study shows the ignition delay times of methanol to be in very good agreement with results from the literature (Fieweger et al., 1997), whereas the other conditions have never been investigated before. The ignition delay time data are also in good agreement with modern detailed kinetics mechanisms such as the AramcoMech 3.0 model. The water time-history profiles were modeled using well-known literature mechanisms. Discrepancies were observed between these kinetics mechanisms, and poor predictions were observed for the lower temperatures investigated. Sensitivity and rate-of-production analyses were performed using 3 literature mechanisms (namely, AramcoMech 3.0, Princeton, and JetSurfII). Discrepancies were found among the models when predicting important reactions dominating the oxidation of methanol as well as the rate-of-production of H2O.

Three-Dimensional Wave-Field Characteristics of Earth-Rock Dams with Different Hidden Hazards

The three-dimensional wave-field characteristics of dangerous earth-rock dams are the premise and foundation to identify the hidden hazards of the earth-rock dams via wave test method. Based on the equivalent elastic wave theory in isotropic mediums, the three-dimensional wave field of earth-rock dams with different defects was calculated using the finite element numerical simulation method. The characteristic and regularity of the three-dimensional wave field was explored. The result of the analysis shows that the size and position of the defects are closely related with the wave-field information received on the dam surface. The elasticity modulus and density of the defects have great effect on the wave field, and alternately, Poisson’s ratio of the defects has little effect on the wave field. The greater the difference between the wave velocity of the hazardous materials and the dam body is, the stronger the energy of the scattered wave will be, which in turn will produce clearer lineups of the scattered wave on the time-history profile. For a single wave movement signal, the dominant frequency amplitude is exponentially correlated with the longitudinal wave velocity of the hazardous materials. Therefore, in the process of wave detection for earth-rock dam hazards, the effect of the elasticity modulus, density, and wave velocity on the test signal should be taken into account. The dominant frequency amplitude can serve as one of the control parameters for interpretation of dam hazards by the analysis of the wave test signal.