Methanol Air Research Articles

Laminar flame speed measurement and combustion mechanism optimization of methanol–air mixtures

AbstractLaminar flame speeds of methanol/air mixtures at 338–398 K are measured by the heat flux method, extending the range of equivalence ratio up to 2.1. And a new optimized methanol mechanism with 94 reactions is proposed by using the particle swarm algorithm, adjusting 20 Arrhenius pre‐exponential factors in their uncertainty domains. The optimized model is compared with eight methanol combustion mechanisms and experimental data published in recent years, covering a wide range of initial temperatures (298–1537 K), pressures (0.04–50 atm) and equivalence ratios (0.5–2.1). The results show that the optimized mechanism not only improves the accuracy of ignition delay time with rapid compression machine at low temperature but also moderately improve the description of laminar flame speed in lean and stoichiometric conditions. Meanwhile, the optimized model significantly enhances the prediction accuracy of CH3 and CH2O radical, and perfectly captures the evolution trend of HCO radical in laminar flat flame. Overall, the optimized mechanism provides the best overall description of the currently available measurements, leading to more accurate and comprehensive prediction of ignition delay time, laminar flame speed and species concentration.

Volatile organic compound sensing in breath using conducting polymer coated chemi-resistive filter paper sensors.

In this work, a disposable sensor array was designed based on the chemi-resistive behavior of the conducting polymers to detect three volatile organic compounds (VOCs), i.e., acetone, ethanol, and methanol in air and breath. Four disposable resistive sensors were designed by coating polypyrrole and polyaniline (in their doped and de-doped forms) on filter paper substrates and tested against VOCs in air. Change in conductivity of the polymer resulting from exposure to various VOC concentration was measured as percentage resistance change using a standard multimeter. The lowest concentration detected for acetone, ethanol, and methanol vapors was 400ppb, 150ppb, and 300ppb, respectively within 2min. These VOC-responsive sensors, housed in an indigenous inert chamber, showed good stability, repeatability, and reversibility while sensing, thus making it suitable for environmental pollutant detection at room temperature. Furthermore, the non-specific nature of these easy to fabricate sensors towards all VOCs is considered favorable and upon classifying with principal component analysis (PCA), the gases were qualitatively distinguished in separate clusters. These developed sensors were also tested and analyzed using VOC spiked real breath samples as proof of concept.

On the Mechanism of Promoting the Autoignition of Rich Methanol–Air Mixtures by Small Additions of Hydrogen Peroxide

On the Mechanism of Promoting the Autoignition of Rich Methanol–Air Mixtures by Small Additions of Hydrogen Peroxide

Catalyst‐Free Multicomponent Tandem Polymerizations of Aliphatic Amines, Activated Alkyne, and Formaldehyde toward Poly(tetrahydropyrimidine)s

AbstractPoly(tetrahydropyrimidine)s are promising heterocyclic polymers with unique biocompatibility, antibacterial ability, inherent fluorescence property, and so on, whose development is limited by their synthetic approaches. Multicomponent polymerizations (MCPs) are a group of powerful tools for the facile construction of heterocyclic polymers from simple monomers. Herein, a catalyst‐free multicomponent tandem polymerization of aliphatic diamines, activated alkyne, and formaldehyde was developed at 60 °C in methanol in air to construct poly(tetrahydropyrimidine)s with well‐defined structures, high molecular weights (Mw up to 57700 g mol−1), high yields (up to 84%), and satisfactory thermal stability. The MCP was featured with commercially available monomers, high efficiency, catalyst‐free economic and mild condition, which was applicable to aliphatic diamines with complicated chemical reactivity, providing a robust and efficient approach for the synthesis of diversified heterocyclic polymers such as poly(tetrahydropyrimidine)s.

CFD Simulation of a bubble column evaporator

The combined principles of computational fluid dynamics (CFD) and heat and mass transfer are applied to design process equipment capable of performing both batch and continuous solvent swap operations at low temperature in the pharmaceutical industry. A bubble column evaporator was chosen a low temperature evaporator as it is a primitive, scalable and robust unit operation employed in a broad range of industries. A CFD analysis using OpenFOAM was subsequently performed on batch and continuous bubble column evaporators (BCE) for the methanol air system to provide data which experimental analysis cannot collect (with the same degree of detail) such as temperature distributions, concentration gradients and velocities across the column, which can then be used to predict methods of enhancing efficiency and evaporation rate. The effects of the gas flowrate, gas temperature and liquid flowrate on mass transfer in a BCE were investigated and the resulting system was analysed. Detailed analysis revealed that the gas was saturated almost instantaneously upon entering the column. It was concluded that both the gas flowrate and gas temperature are important factors affecting the rate of evaporation. An increased outlet gas temperature enhanced the rate of mass transfer in the system by up to 100% by increasing the gas phase saturation concentration of the solvent. This method proved particularly successful for the methanol-air system as the liquid had a significantly higher specific heat capacity than the gas and therefore the increased inlet gas temperatures had negligible effects on the liquid temperature.

Air‐Processed Efficient Organic Solar Cells from Aromatic Hydrocarbon Solvent without Solvent Additive or Post‐Treatment: Insights into Solvent Effect on Morphology

Most of the recent organic solar cells (OSCs) with top‐of‐the‐line efficiencies are processed from organic solvents with a high vapor pressure such as CF in nitrogen‐filled glovebox, which is not feasible for large‐area manufacturing. Herein, we cast active layers with both aromatic hydrocarbon solvents and halogenated solvents without any solvent additive or post‐treatment, as well as interlayers with water and methanol in air (35% relative humidity) for efficient OSCs, except cathode electrode's evaporation is in vacuum. Compared to the PM6:Y6 system that is processed from CF, the PM6:BTP‐ClBr2 system demonstrates good efficiency of 16.28% processed from CB and the device based on PM6:BTP‐4Cl achieves 16.33% using TMB as its solvent for the active layer. These are among the highest efficiencies for CB‐ and TMB‐processed binary OSCs to date. The molecular packing and phase separation length scales of each combination depend strongly on the solvent, and the overall morphology is the result of the interplay between solvent evaporation (kinetics) and materials miscibility (thermodynamics). Different solvents are required to realize the optimal morphology due to the different miscibility between the donor and acceptor. Finally, 17.36% efficiency was achieved by incorporating PC71BM for TMB‐processed devices. Our result provides insights into the effect of processing solvent and shows the potential of realizing high‐performance OSCs in conditions relevant for industrial fabrication.

Effects of ambient methanol on pollutants formation in dual-fuel spray combustion at varying ambient temperatures: A large-eddy simulation

Large-eddy simulation with a finite-rate chemistry model is carried out to investigate the formation of soot and nitrogen oxides (NOx) in the dual-fuel spray combustion. Liquid n-heptane is injected into a constant volume chamber, filled with a premixed methanol–air mixture with an equivalence ratio (ϕm) of 0.3. Three dual-fuel cases are simulated under initial temperatures of 900, 950 and 1000 K. Three single-fuel cases, with the same configurations, but with pure air being used as ambient gas composition are also simulated and used as baselines for comparison purposes. The paper aims to identify the main mechanisms of soot and NOx reduction in dual-fuel spray combustion under conditions relevant to internal combustion engines. The numerical model is validated using the Engine Combustion Network n-heptane fuel experimental data. It is found that soot emission has a strong non-linear dependence on ambient temperature in dual-fuel combustion. At high temperatures, soot emission is enhanced whereas at lower temperatures, it is suppressed. For the presently studied cases, the results show that the enhanced mixing is the primary reason for soot reduction in the 900 and 950 K cases, whereas the onset auto-ignition in ambient methanol/air mixture, which leads to a shortened lift-off length of the n-heptane spray flame and reduced ambient oxygen concentration, is the mechanism behind the enhanced soot emission in the 1000 K case. The methanol dilution effects of oxygen concentration and heat capacity on ignition delay time and the maximum flame temperature are minor in the current dual-fuel configurations. Regarding NOx emission in dual-fuel combustion, it is found that the effect of methanol on NOx formation also depends on the ambient temperatures. The NOx formation rate in the dual-fuel case is lower than that of the single-fuel case at 900 K. However, an opposite trend of NOx formation rate is observed in the 1000 K cases. The main reason for the increased NOx emission is the larger high temperature region resulted from the interaction of the spray flame and the ambient mixture ignition.

Combustion Chemistry of Rich Methanol–Air Mixtures

Chain branching and heat release processes and their influence on the burning velocity of premixed rich and near-stoichiometric methanol–air flames were studied by numerical simulation and sensitivity analysis. The phenomenon of superadiabatic temperatures in these flames due to the kinetic mechanism of methanol combustion was first detected. Comparison of the simulation results of the structure of methanol and formaldehyde flames shows that the formation of water in superequilibrium concentrations in flames does not necessarily lead to superadiabatic temperatures, as believed earlier. It was first found that decreasing the dilution of the CH3OH/O2/N2combustible mixture with nitrogen at a constant equivalence ratio enhances the superadiabatic temperature effect. According to simulation results, in a rich near-limit methanol flame, the role of the chain branching reactions H + O2 = O + OH and O + H2 = H + OH is negligible due to their low rate. At relatively low temperatures, branching occurs mainly in reactions involving HO2and H2O2peroxide compounds, whose concentration is orders of magnitude higher than the concentration of the main chain carriers H, O, and OH. From the sensitivity analysis, it follows that the burning velocity of methanol flames is positively influenced mainly by the reactions of formation of chain carriers and is negatively influenced by the reactions of consumption of chain carriers. reactions having a major contribution to heat release but are not involved in the formation and consumption of radicals have small sensitivity coefficients.

Numerical modeling of plasma-assisted combustion effects on firing and intermediates in the combustion process of methanol–air mixtures

The effects of plasma-assisted ignition and combustion on the ignition-delay time (Tid) and intermediates in methanol combustion were simulated numerically through a chemical-kinetics mechanism of methanol oxidation. Plasma-assisted ignition can considerably shorten the Tid. Plasma-assisted ignition is more conducive to a low temperature and the lean combustion of a methanol-air mixture. According to the shortest Tid, the active particle order is: O < CH3O < 220 Td < H < OH < CH2OH < CH3 < autoignition. The concentration of O atoms in active particles affects the Tid shortening. Plasma-assisted combustion can significantly shorten the time for the system temperature to reach a maximum. The concentrations of the reactants CH3OH and O2 decrease sharply for autoignition after the ignition-delay period, and the products CO, CO2 and H2O increase rapidly. In plasma-assisted combustion, the addition of active particles significantly increases the rate of chemical reaction of consumption of O2, promotes the rapid redox reaction of methanol–air mixtures, oxidizes methanol fuel to CO2 and H2O more rapidly, and accelerates combustion. The sensitivity coefficients of temperature and Tid for plasma-assisted combustion are lower than those for autoignition.

Experimental and kinetic investigation on the effects of hydrogen additive on laminar premixed methanol–air flames

The effects of hydrogen addition on laminar premixed methanol–air flames were studied both experimentally and numerically. To achieve this, a constant volume chamber (CVC) and the premix code in CHEMKIN were used. During the experiments, the equivalence ratios (ϕ) and hydrogen mole fractions (Xh) were set to 0.6 to 1.8 and 0%–100%, respectively. In addition, initial environmental conditions were set to 375 K and 1 atm. The results indicate that the laminar flame speed (LFS) and burning velocity (LBV) both increase when more hydrogen is added into the methanol–air mixtures. For premixed methanol–air flames, the Markstein length (Lb) decreases monotonically with an increase in the equivalence ratio; however, when the hydrogen fraction is greater than 40%, an increasing trend in the Markstein length is presented as the mixtures move toward the fuel-rich side. The variation in Markstein length is non-monotonic with the hydrogen fraction. A kinetics analysis indicates that methanol is mainly consumed by the dehydrogenation reaction caused from the impact of the active free radicals (OH and H). Reactions involving active free radicals and light intermediate species have the highest sensitivity and contribute the most to the propagation of a laminar flame. Therefore, the promotion effect of hydrogen additive is due to an enhancement in the radical pooling of H, OH, and O. The chain branching reaction R5 (O2 + H = O + OH) is essential for the geometric growth of free radicals. In addition, the amount of formaldehyde decreases owing to the hydrogen blending.

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.

Modeling and prediction of methanol air release from bleached chemi-thermo mechanical pulp board.

This paper reports on the modeling, prediction and evaluation approaches of methanol release from bleached chemi-thermo mechanical pulp (BCTMP) board during storage. A pseudo-first order desorption kinetics model of methanol release was established for describing the desorption behavior of methanol from BCTMP, i.e., , in which the desorption constant (K) and rate constant (kdes) were well described by van't Hoff and Arrhenius equations. Based on the simulation experiments at various temperatures, the desorption activation energy of methanol and its adsorption enthalpy is calculated and is 53.7 and −86.2 kJ mol−1 K−1, respectively. With the developed model, the risk of methanol release for the storage of BCTMP board can be examined by either the time-dependent kinetics model or a two-step thermodynamic approach using the equilibrium concentration of methanol in indoor air. This paper provides a valuable tool to assess the risk of methanol release for the paper industry and related warehouse departments.

Computational Study of the Laminar Reaction Front Properties of Diluted Methanol–Air Flames Enriched by the Fuel Reforming Product

The current work investigates the flame structure and the propagation of premixed laminar flame fronts for mixtures of diluted methanol–air enriched by fuel reforming products under spark ignition engine conditions. Two engine concepts were investigated: one with external fuel reforming (EFR) and one with reformed exhaust gas recirculation (R-EGR). Here, the fuel reformate (or syngas) is a mixture of H2, CO, and CO2 with a CO selectivity of 6.5%, which is used to represent the products of methanol steam reforming over a Cu–Mn/Al foam catalyst. The simulations were exercised over a wide range of dilution level and unburned gas temperature at 40 bar with a skeletal chemical kinetic mechanism using zero/one-dimensional codes. Two types of dilution—air and EGR—were compared at the same fuel-to-charge equivalence ratio (ϕ′). The results showed that the knock limit for spark-ignited operation is extended with rising dilution levels, especially when diluted by an R-EGR mixture. Syngas addition also leads to a re...

Development of methanol–air fuel cells with membrane materials based on new sulfonated polyheteroarylenes

New proton-conducting membranes were synthesized from sulfonated polynaphthoyleneimide (SPNI) and polytriazole (SPTA), which are of interest for use in portable methanol fuel cells. The membrane electrode assembly (MEA) based on SPNI and SPTA showed power and voltage-current characteristics comparable to those of MEA based on Nafion®-117. The direct and reverse polarization curves coincided almost completely in shape, indicating that the obtained characteristics are stable. At a voltage of 0.3 V and a temperature of 40°С, the current density and power density reached 68 mA cm–2 and 20.5 mW cm–2, respectively.

Measurement of laminar burning velocities of methanol–air mixtures at elevated temperatures

In this paper, the measurement of laminar burning velocities for liquid fuel (methanol)–air mixtures is reported at higher mixture temperatures using externally heated meso-scale diverging channel technique. Laminar burning velocity is determined using mass balance between the channel inlet and flame stabilization location for the planar flames appearing at certain conditions of mixture flow rate and equivalence ratio. A linear temperature gradient in the direction of fluid flow was employed to establish planar, stretch free and nearly adiabatic flames in an externally heated diverging quartz channel. Detailed experiments were carried out for an equivalence ratio range of 0.7–1.3 and a mixture temperature range of 350–650K at 1atm pressure with an uncertainty of ±5% of the actual value. Experimental results are compared with the available results. A good match was observed for Su,0 values at 300K with the literature data and mechanism values. The temperature dependence of laminar burning velocity was also assessed using the correlation Su=Su,0(Tu/Tu,0)α, where α is the temperature exponent. A minimum α value was observed for rich mixtures even at high temperature conditions.

Validation of a kinetic scheme for numerical investigation of hydrogen–methanol–air flames

Normal burning velocities in methanol–air mixtures and in the same mixtures with added 4.5 and 7.2% hydrogen as a second fuel were measured over a wide range of equivalence ratio and for initial conditions of 0.16 MPa and 354 K. It has been shown that the mechanism previously proposed for the combustion of mixtures of CO, CH2O and CH3OH with air is applicable to multicomponent mixtures containing hydrogen and methanol.

Visualization of combustion characteristic of diesel in premixed methanol–air mixture atmosphere of different ambient temperature in a constant volume chamber

Methanol has drawn increasing attention in recent years as an alternative fuel due to its potential to reduce NOX and soot emissions. In this work, the combustion characteristic of diesel in air atmosphere (AA) and premixed methanol–air mixture atmosphere (MAA) were studied in an optical constant volume chamber under different in-cylinder temperature, ranging from 840 to 960K. Time resolved images and natural flame luminosity were captured by a high speed camera, and flame lift-off lengths (FLoL) were acquired. It is found that MAA has longer ignition delay and lift-off length compared with AA at lower temperature until 920K, and is more sensitive to temperature variation. With the increase of ambient temperature, the ignition delay and FLoL of diesel for both atmospheres become shorter, and the difference between the two atmospheres due to methanol’s inhibitory effect gets smaller, and becomes almost negligible at 960K. Comparison of natural flame luminosity gives the same trend. The ambient temperature is shown to be critical to the combustion characteristics of diesel in MAA, which has an important effect on the chemical kinetics between methanol and diesel due to temperature sensitiveness of the conversion reaction of OH and H2O2.

A modeling study of the effect of surface reactions on methanol–air oxidation at low temperatures

A detailed modeling study was performed to investigate the inhibitory effect of the interior surface of a reactor in the process of low-temperature oxidation of methanol–air mixture. By using the reduction technique, which is for the gas-phase kinetic mechanism, a modified nine-step skeletal mechanism for the low-temperature methanol oxidation was developed. Important quenching species as well as surface reactions which have great influences on gas-phase branching reactions were identified. The adsorption of the species such as hydroxyl, hydroperoxyl, hydrogen peroxide and formaldehyde and the desorption of stable molecules generated by the recombination of the above adsorbents have constituted the surface kinetic model for methanol–air mixture. Computations based on the established heterogeneous radical quenching mechanism show excellent agreement with the experimental results from literatures, demonstrating that the radical quenching not only has significant inhibitory impact on slow oxidation, but also enables the retardation of ignition delay time. For the purpose of evaluating the inhibitory influence of the surface reactions on auto-ignition, a more in-depth five-step reduced mechanism combining the gas-phase reactions and the surface reactions was developed. Based on this mechanism, an explicit expression for the auto-ignition prediction was derived with the activation-energy asymptotic treatment. The formula can predict the ignition delay time with sufficient accuracy for both inert and high-reactive surfaces.

Catalytic combustion of methanol on Pt–Fecralloy foams prepared by electrodeposition

The catalytic combustion of methanol in air under lean dry conditions has been studied using Pt–Fecralloy catalysts. These catalysts were prepared by cathodic electrodeposition of Pt onto commercial 50ppi Fecralloy foams, controlling the noble metal loading through the Pt deposition charge. The catalysts were characterized by SEM and XRD at three different stages (as-prepared, after 2h pretreatment at 600°C in air and after use in methanol combustion) and their Pt surface area was estimated by cyclic voltammetry. In combustion tests, methanol oxidation started at temperatures as low as 80°C, and reached 100% conversion to CO2 at temperatures that decreased progressively for Pt loadings increasing from 0.8 to 13mgcm−3. The apparent activation energy of methanol combustion was estimated to be 68–70kJmol−1, independent of the Pt loading of the samples. Repeated combustion cycles converged with SEM, XRD characterization of used catalysts to prove the stability of Pt–Fecralloy, under the conditions employed in the tests.

Effect of intake pre-heating and injection timing on combustion and emission characteristics of a methanol fumigated diesel engine at part load

Diesel–methanol dual fuel (DMDF) engines at light loads suffer from low thermal efficiency and high unburned percentages of fuel. Pilot fuel injection timing and intake temperature are two important parameters which affect the combustion process in DMDF engines. In present experimental work, the combined effects of intake temperature and injection timing on the performance of a DMDF engine have been studied. The experiments were conducted on a methanol-fumigated diesel engine at 25% of full load and the results concerning performance, combustion characteristics and emissions were analyzed. Results show that the low efficiency at light loads can be improved significantly by raising the intake temperature and advancing the injection timing of direct-injected diesel. Increasing the intake temperature also significantly decreases the heat release rate of premixed combustion and increases the combustion rate of methanol burned by flame propagation. Flame propagation of the methanol–air mixture disappears gradually and DMDF combustion transforms into single stage combustion as the injection timing is retarded. When injection timing is retarded after 4.6° crank angle, misfire occurs at higher methanol substitute percent (MSP) and lower intake temperature, while the auto-ignition of methanol occurs at lower MSP and higher intake temperature. Under DMDF operation, soot and nitrogen oxides trade-off dilemma is completely broken at lower intake temperature and higher MSP.