Increase In OH Concentration Research Articles

Numerical simulation of soot and NO formation in DME/gasoline laminar co-flow diffusion flames

Dimethyl ether (DME) is regarded as a promising alternative fuel to reduce greenhouse gases and soot emission. However, the application of DME in actual engines is difficult because of its low calorific value and viscosity. DME is commonly utilized as a supplementary component in traditional fuels to enhance their combustion efficiency and emission performance. This study investigated the effect of DME blending on the soot and NO formation in laminar diffusion gasoline flames. The results showed that the peak soot volume fraction (SVF) reduced by 12.3 %, while the peak temperature increased by 19.2 K and the peak concentration of NO increased by 18.2 % when the blending ratio of DME increased from 0 % to 15 %. The primary reason for the reduction in the soot inception rate was the decrease in benzo(ghi)fluoranthene (BGHIF) concentration. The formation of BGHIF was controlled by the C6H5CH3 → A1 → A1-→A1C2H → A2R5 → A2 → A2-→BGHIF pathways. The decrease of initial soot particles led to a reduction in Hydrogen Abstraction Carbon Addition (HACA) surface growth rate. The increase in A4 concentration was due to the increase in the concentration of C4H2 in the reaction A2R5 + C4H2 = A4. Therefore, more benzo[a]pyrene (BAPYR) was formed through A4 + C4H2 = BAPYR, promoted the process of soot condensation. The increase in OH concentration promoted the oxidation of OH, and the decrease in soot inhibited the oxidation of O2. The majority of NO was primarily produced through the NO thermal pathway in the DME/gasoline flame, and N + OH = NO + H was the main reaction to form NO. The increase of O, H and OH radicals caused the increase in NO concentration.

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.

Characterization of the chemical activity of a pulsed corona discharge above water

A pulsed corona discharge above liquid combined with ozonation has been investigated for the degradation of organic pollutants in water, as well as regarding the generation of several oxidizing species: ozone in gas phase, hydrogen peroxide and hydroxyl radicals in the liquid. A considerable improvement in the energy efficiency for organic compounds removal has been observed when reducing the width of the discharge pulses. This finding was correlated with the efficient formation of oxidizing species in case of short pulses. Recycling of the effluent gas from the plasma also enhances contaminants degradation. This was mainly attributed to an in situ peroxone process, i.e. the reaction between plasma-generated O3 and H2O2, forming highly reactive OH radicals, largely responsible for organic compounds degradation. This assumption is supported by the decline in O3 and H2O2 concentrations and simultaneous increase in OH concentration detected in plasma-ozonation experiments as compared to results obtained with plasma alone.

Untangling the Mechanisms of GdYVO4:Eu3+ nanoparticle Photocatalytic Activity

This work reports abnormal dynamics of hydroxyl radicals generation under UV irradiation of water solution containing small (d = 2 nm) GdYVO4:Eu3+ nanoparticles (NPs). An analysis of the increase in OH concentration in time allows two parts in the OH generation curve to be revealed. The first slower part is shown to be associated with a predominate radical scavenging mechanism and explained by the presence of ions with a changeable valence state (V4+/V5+) and oxygen vacancies in the structure of GdYVO4:Eu3+ NPs. The second faster part is associated with photo-induced holes interaction with water molecules adsorbed at the surface of NPs followed by the hydroxyl radical production. The mutual contributions of the two mechanisms are changed in time and the depletion of the scavenging mechanism is observed in about 90 min after UV irradiation start. Our finding is a next step to understand the mechanism of NPs redox-activity for taking greater advantage of such nanomaterials in biomedical applications.

Investigation of fuel dilution in ethanol spray MILD combustion

MILD combustion is a promising technique for low heating value fuels. In this paper, spray MILD combustion of diluted liquid fuel is numerically studied. The modelling framework is based on the RANS approach, the EDC combustion model with a skeletal chemical mechanism, and the Lagrangian tracking of droplets. The validated numerical model is used to simulate the combustion of ethanol diluted with water is studied for different oxidizer temperatures and O2 concentrations under MILD condition. Results indicate that a low-level fuel dilution up to 5 percent has tendency toward expansion of MILD region, but higher degrees fuel dilution within the range of 5–20 percent results in a reduction of MILD combustion regions due to domination of physical effect contribution of addition of water to ethanol fuel compared to its chemical effect. Fuel water addition also leads to an increase in OH concentration due to H2O dissociation through O + H2O → 2OH, which assist the oxidation of fuel driven species, CO in particular. Changing the oxidizer stream temperature can lead to considerable changes in the flame structure: the typical flame shape is converted to a bifurcation style by reducing hot co-flow stream temperature from 1400 K to 1200 K. Moreover, for liquid fuel dilution, preheating and inlet air dilution do not lead to monotonic strengthening the MILD zone in spite of gaseous fuels.

Effects of non-equilibrium plasmas on low-pressure, premixed flames. Part 1: CH* chemiluminescence, temperature, and OH

In this paper, we investigate the effects of nanosecond, repetitively-pulsed, non-equilibrium plasma discharges on laminar, low-pressure, premixed, burner-stabilized hydrogen/O2/N2 and hydrocarbon/O2/N2 flames using CH* chemiluminescence and quantitative OH laser-induced fluorescence (LIF) diagnostics. Two different plasma sources, both of which generate uniform, low-temperature, volumetric, non-equilibrium plasma discharges, are used to study changes in chemiluminescence, temperature, and OH concentration when non-equilibrium plasmas are directly coupled to conventional hydrogen/hydrocarbon oxidation and combustion chemistry. Qualitative imaging of CH* chemiluminescence indicates that during plasma discharge, the luminous flame zone is shifted upstream towards the burner surface with little change in the CH* zone thickness. For the same plasma discharge and flame conditions, quantitative results using spatially-resolved OH LIF and multi-line, OH-LIF thermometry show significant increases in ground-state OH concentrations in the preheating zones of the flame. More specifically, for a particular axial position downstream of the burner surface, the OH concentration increases, which can be viewed as an effective “shift” of the OH profiles towards the burner surface. The increase in OH concentration is conceivably due to an enhancement of the lower-temperature kinetics including O atom, H atom and OH formation kinetics and temperature rise due to the presence of the low-temperature, non-equilibrium plasma.

The oxidation of 2-(2-methoxyethoxy)-ethanol and 2-(2-ethoxyethoxy)-ethanol by dihydroxydiperiodato nickelate(IV): A kinetic and mechanistic study

The kinetics of oxidation of 2-(2-methoxyethoxy)-ethanol and 2-(2-ethoxyethoxy)-ethanol by dihydroxydiperiodato nickelate(IV) (DPN) had been studied spectrophotometrically in alkaline medium in the temperature range of 293.2 to 313.2 K. The reaction rate showed first order dependence on DPN, 2-(2-methoxyethoxy)-ethanol and 2-(2-ethoxyethoxy)-ethanol. It was found that the pseudo-first-order rate constant k obs increased with an increase in concentration of OH - and a decrease in concentration of IO 4 - . There was a positive salt effect and no free radicals were detected. A plausible mechanism is proposed and the rate equations derived from the mechanism can explain all the experimental observations.

Kinetics and Mechanism of Oxidation of Triethylene Glycol and Tetraethylene Glycol by Ditelluratoargentate (III) in Alkaline Medium

The kinetics of oxidation of triethylene glycol and tetraethylene glycol by ditelluratoargentate (III) (DTA) in alkaline liquids has been studied spectrophotometrically in the temperature range of 293.2 K–313.2 K. The reaction rate showed first‐order dependence in DTA and fractional order with respect to triethylene glycol or tetraethylene glycol. It was found that the pseudo‐first‐order rate constant (kobs) increased with an increase in concentration of OH− and a decrease in concentration of H4TeO6 2−. There was a negative salt effect and no free radicals were detected. A plausible mechanism involving a two‐electron transfer was proposed, and the rate equations derived from the mechanism explained all the experimental results and observations. The activation parameters along with the rate constants of the rate‐determining step were calculated.

Kinetics and Mechanism of Oxidation of 3-phenoxy-1,2-propanediol by Ditelluratocuprate(III) in Alkaline Medium

The kinetics of oxidation of 3-phenoxy-1,2-propanediol by ditelluratocuprate(III) (DTC) in alkaline liquids has been studied spectrophotometrically in the temperature range of 293.2 K-313.2 K. The reaction rate showed first order dependence in DTC and fractional order with respect to 3-phenoxy-1,2-propanediol. It was found that the pseudo-first order rate constant k obs increased with an increase in concentration of OH - and a decrease in concentration of TeO 4 2- . The reaction rate changed with the position of hydroxyl group. There is a negative salt effect. A plausible mechanism involving a pre-equilibrium of a adduct formation between the complex and 3-phenoxy-1,2-propanediol was proposed. The rate equations derived from mechanism can explain all experimental observations. The activation parameters along with the rate constants of the rate-determining step were calculated.

Kinetics and Mechanism of Oxidation of 1-Methoxy-2-propanol and 1-Ethoxy-2-propanol by Ditelluratocuprate(III) in Alkaline Medium

The kinetics of oxidation of 1-methoxy-2-propanol and 1-ethoxy-2-propanol by ditelluratocuprate(III) (DTC) in alkaline liquids has been studied spectrophotometrically in the temperature range of 293.2–313.2 K. The reaction rate showed first order dependence in DTC and fractional order with respect to 1-methoxy-2-propanol or 1-ethoxy-2-propanol. It was found that the pseudo-first order rate constant kobs increased with an increase in concentration of OH− and a decrease in concentration of TeO42−. There is a negative salt effect. A plausible mechanism involving a pre-equilibrium of a adduct formation between the complex and 1-methoxy-2-propanol or 1-ethoxy-2-propanol was proposed. The rate equations derived from mechanism can explain all experimental observations. The activation parameters along with the rate constants of the rate-determining step were calculated.

Kinetics and mechanism of oxidation of sodium pyruvate by dihydroxydiperiodatonickelate(IV) in alkaline medium

The kinetics of oxidation of sodium pyruvate (SP) by dihydroxydiperiodatonickelate(IV) (DPN) was studied by spectrophotometry between 288.2 K and 303.2 K in alkaline medium. The reaction rate showed first order dependence in DPN and SP. It was found that the pseudo-first order ([SP]0 >> [ Ni(IV)]0) rate constant, k obs, increased with increase in concentration of OH− and SP, but decreased when the concentration of IO 4 − increased. There was a negative salt effect and no free radical was detected. In view of this, the dihydroxyperiodatonickelate(IV) species is assumed to be the oxidizing specie. A plausible mechanism involving a two-electron transfer is proposed and the rate equations derived from the mechanism can explain all the experimental results satisfactorily. The activation parameters, as well as the rate constants of the rate-determining step have been calculated.

Kinetics and mechanism of oxidation of 1,2-butanediol by argentate(III) complex in alkaline medium

The kinetics of oxidation of 1,2-butanediol by dihydroxyditellutoargentate(III) (DDA) is studied spectrophotometrically. The reaction rate shows first order dependence in DDA and 1 < nap < 2 order in 1,2-butanediol. It is found that the pseudo-first order rate constant k obs increases with the increase in concentration of OH− and decreases with the increase in concentration of TeO4 2−. There is a negative salt effect; no free radical is detected. In view of this, the dihydroxymonotelluratoargentate(III) species is assumed to be the active species. A plausible mechanism involving a two-electron transfer is proposed and the rate equations derived from mechanism explains all experimental results. The activation parameters along with the rate constants of the rate-determining step are calculated.

Electron paramagnetic resonance studies on labile intermediates in a free-burning methanol-air flame. Effects of water and hydrogen bromide additions

Labile intermediates in a premixed methanol-air flame burning freely at atmospheric pressure have been studied by probe sampling and EPR detection. H, O, and OH have been detected at a pressure of 0.45 torr in the EPR cavity. It was found that H and O atoms have their maximum concentrations in the inner flame region within 1 mm from the burner mouth, while the OH concentration slowly increases in the outer flame region to reach a maximum at about 8 mm from the burner mouth. The slow increase in OH concentration is attributed to the reaction H + O/sub 2/ ..-->.. OH + O effectuated by diffusion of O/sub 2/ from the surrounding air into the flame. Addition of H/sub 2/O reduced the O atom concentration and increased the OH radical concentration in the inner flame region. The reaction O + H/sub 2/O ..-->.. 2OH is suggested as an explanation. Addition of HBr gave additional signals from Br and was found to reduce the H, O, and OH concentrations in the flame. It also caused the flame to shrink probably as a result of H atom deficiency in the inner flame region leading to insufficient generation of O and OHmore » in the outer flame region. About 70% of the bromine was found to exist in the atomic form.« less

Changes in the concentration of mesospheric ozone during the total solar eclipse

Measurements of dayglow radiance of O 2( 1Δ g) and OH(7,2) bands are reported. Ground based photometers were used to monitor zenith radiance of 1270 and 694 nm emissions during the total solar eclipse of 16 February 1980. Altitude distribution of 1270 nm intensity was derived from ground based observations. A set of altitude distributions of O 2( 1Δ g) were thus obtained throughout the eclipse. These altitude distributions were converted into ozone distributions using the rate equations for formation and loss of ozone and O 2( 1Δ g) molecules. Results indicate an increase in the ozone concentration at mid-eclipse. OH(7,2) emission did not show enhancement during totality. This may mean that there was no increase in OH concentration during the eclipse.