Mutual effects between a gliding arc discharge and a premixed flame

Mutual effects between a gliding arc(GA)discharge at atmospheric pressure and a premixed CH_(4)/air flame were experimentally investigated.Effects of the flame on the GA were studied using simultaneous measurements of the current,the voltage,and the instantaneous images of the plasma columns.The GA in the flame has a thicker and more diffusive plasma column,and it is more frequently ignited at a smaller breakdown voltage than that in the air.The GA extension velocity and the gliding velocity in the flame are larger than those in the air.The electrode voltage drop of the GA discharge in the flame is about 160 V,whereas that in the air is about 220 V.Compared with the GA in the air,the different features of the GA in the flame can be explained by high-temperature,weakly ionized,and species-abundant environment that are generated by the premixed CH_(4)/air flame.Effects of the gliding arc discharge on the premixed flames were demonstrated using planar laser-induced fluorescence of hydroxyl radicals(OH)and formaldehyde(CH_(2)O).OH and CH_(2)O can be formed in the CH_(4)/air mixture in the presence of the GA due to kinetic effects,and the increase of OH and CH_(2)O shows the great potential of the GA for combustion enhancement.

Improved combustion stability of biogas at different CO_(2) concentrations using inhomogeneous partially premixed stratified flames

Biogas is a renewable and clean energy source that plays an important role in the current environment of lowcarbon transition.If high-content CO_(2) in biogas can be separated,transformed,and utilized,it not only realizes high-value utilization of biogas but also promotes carbon reduction in the biogas field.To improve the combustion stability of biogas,an inhomogeneous,partially premixed stratified(IPPS)combustion model was adopted in this study.The thermal flame structure and stability were investigated for a wide range of mixture inhomogeneities,turbulence levels,CO_(2) concentrations,air-to-fuel velocity ratios,and combustion energies in a concentric flow slot burner(CFSB).A fine-wire thermocouple is used to resolve the thermal flame structure.The flame size was reduced by increasing the CO_(2) concentration and the flames became lighter blue.The flame temperature also decreased with increase in CO_(2) concentration.Flame stability was reduced by increasing the CO_(2) concentration.However,at a certain level of mixture inhomogeneity,the concentration of CO_(2) in the IPPS mode did not affect the stability.Accordingly,the IPPS mode of combustion should be suitable for the combustion and stabilization of biogas.This should support the design of highly stabilized biogas turbulent flames independent of CO_(2) concentration.The data show that the lower stability conditions are partially due to the change in fuel combustion energy,which is characterized by the Wobbe index(WI).In addition,at a certain level of mixture inhomogeneity,the effect of the WI on flame stability becomes dominant.

液相色谱-质谱对预混饲料水解液中一碘酪氨酸与二碘酪氨酸的检测

A new LC-MS method has been established for determination of momoiodotyrosine(MIT) and diiodotyrosine(DIT) in the hydrolysate of premix feeds.Samples was hydrolyzed with 4.0 mol·L-1 NaOH for 16 h at 110 ℃,then the hydrolysate was cleaned up with a SPE cartridge and injected directly for LC-MS analysis.Chromatographic separation was performed on a 2.1 mm×150 mm,5 μm particle,C18 column with a mixture of acetonitrile and 0.1%(by volume) acetic acid as mobile phase at a flow rate of 0.2 mL· min-1.ESI+ mass spectrometry detection was run on SIR mode with m/z 308,262 for MIT,and m/z 434,388 for DIT.Quantification was carried out with external standard method.Validation data indicated the method was linear in the concentration ranges investigated with regression coefficients(R2) of more than 0.99.The limits of detection(LOD) were 8 μg·L-1 and limits of quantification(LOQ) were 30 μg·L-1.The recoveries were range of 93%-110% with relative standard deviations of 6.5%-13.2%.The method was sensitive,accurate,and was applied in the determination of MIT and DIT in real sample with satisfactory results.

Determination of High Iodine Levels by ICP-OES after Separation from Excess Phosphate by Co-precipitation

For determination of iodine,dissolution or oxidation of an organic matrix by acid K-chlorate in dilute nitric acid to obtain non-volatile iodate immediately,is a method of choice.Optical emission spectroscopy is usually sensitive enough to control iodized table salt.Spectral interference by P upon the most sensitive I-emission line,e.g.in mineral feeds and marine algae,was overcome by co-precipitation of P with Al-or Fe hydroxide,leaving iodate(and also borate)in solution.After addition of Al or Fe nitrate or sulfate,ammonia was added to reach pH 8.8,and the resulting precipitate separated by cetrifugation and decantation.Al-hydroxide was more efficient,and its precipitation was facilitated by adding 10-30 mg of a natural clay to 5 mL sample.Correct results with materials from former ring tests were obtained down to 15 mg/kg by an ICP 20 years of age.Highlights:This method enables to use optical emission ICP for determination of high levels of iodine after a simple separation of phosphate from oxidizing acid digests,thus avoiding catalytic or spectrophotometric methods,or high blanks in an ICP-MS utilized for ambient iodine levels.

Numerical Simulation of Flameless Premixed Combustion with an Annular Nozzle in a Recuperative Furnace

This paper reports an investigation of Computational Fluid Dynamics(CFD)on the influence of injection momentum rate of premixed air and fuel on the flameless Moderate or Intense Low oxygen Dilution(MILD) combustion in a recuperative furnace.Details of the furnace flow velocity,temperature,O2,CO2 and NOx concentrations are provided.Results obtained suggest that the flue gas recirculation plays a vital role in establishing the premixed MILD combustion.It is also revealed that there is a critical momentum rate of the fuel-air mixture below which MILD combustion does not occur.Moreover,the momentum rate appears to have less significant influence on conventional global combustion than on MILD combustion.

A novel method for chemistry tabulation of strained premixed/stratified flames based on principal component analysis

The principal component analysis （PCA） is used to analyze the high dimen- sional chemistry data of laminar premixed/stratified flames under strain effects. The first few principal components （PCs） with larger contribution ratios axe chosen as the tabu- lated scalars to build the look-up chemistry table. Prior tests show that strained premixed flame structure can be well reconstructed. To highlight the physical meanings of the tabu- lated scalars in stratified flames, a modified PCA method is developed, where the mixture fraction is used to replace one of the PCs with the highest correlation coefficient. The other two tabulated scalars are then modified with the Schmidt orthogonalization. The modified tabulated scalars not only have clear physical meanings, but also contain passive scalars. The PCA method has good commonality, and can be extended for building the thermo-chemistry table including strain rate effects when different fuels are used.

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.

Quantitative measurements of one-dimensional OH absolute concentration profiles in a methane/air flat flame by bi-directional laser-induced fluorescence

The one-dimensional （1D） spatial distributions of OH absolute concentration in methane/air laminar premixed flat flame under different equivalence ratios at atmospheric pressure are investigated by using bi-directional laser-induced flu- orescence （LIF） detection scheme combined with the direct absorption spectroscopy. The effective peak absorption cross section and the average temperature at a height of 2 mm above the burner are obtained by exciting absorption on the Q1（8） rotational line in the A2∑＋ （Dt = 0） ←- X2∏ （v = 0） at 309.240 nm. The measured values are 1.86×10-15 cm2 and 1719 K, respectively. Spatial filtering and frequency filtering methods of reducing noise are used to deal with the experi- mental data, and the smoothing effects are also compared using the two methods. The spatial distribution regularities of OH concentration are obtained with the equivalence ratios ranging from 0.8 to 1.3. The spatial resolution of the measured result is 84μm. Finally, a comparison is made between the experimental result of this paper and other relevant study results.

Preparation of Poly(p-phenylene sulfide)/Carbon Composites with Enhanced Thermal Conductivity and Electrical Insulativity via Hybrids of Boron Nitride and Carbon Fillers

The present work enhanced the thermal conductivity of poly（p-phenylene sulfide）/expanded graphites and poly（p-phenylene sulfide）/carbon nanotubes, by incorporating composites with hexagonal boron nitride, which simultaneously succeeded in raising the electrical conductivity of the systems. A two-step mechanical processing method which includes rotating solid-state premixing and inner mixing was adopted to improve dispersion of the hybrids, contributing to the formation of an interspered thermal conductive network. Similar synergic effect in thermal conductivity enhancement was discovered in the hybrid systems regardless of the dimension difference between the two carbon fillers. Such is postulated to be the one satisfying advantage generated by the afore-mentioned network; the other is the insulativity of the hybrid systems given by the effective blockage of hexagonal boron nitride as an insulating material in our network.

Large Eddy Simulation of Gasoline-Air Mixture Explosion in Long Duct with Branch Structure

Gas explosion is a process involving complex hydrodynamics and chemical reactions.In order to investigate the interaction between the flame behavior and the dynamic overpressure resulting from the explosion of a premixed gasoline-air mixture in a confined space,a large eddy simulation(LES)strategy coupled with sub-grid combustion model has been implemented.The considered confined space consists of a long duct and four branches symmetrically distributed on both sides of the long duct.Comparisons between the simulated and experimental results have been considered with regard to the flame structure,flame speed and overpressure characteristics.It is shown that the explosion process can qualitatively be reproduced by the numerical simulation.Due to the branch structure,vortices are generated near the joint of the branch and long duct.Vortices rotate in opposite directions in the different branches.When the flame propagates into the branch,the flame front is influenced by the flow field structure and becomes more and more distorted.The overpressure displays a similar behavior in the two branches which have a different distance from the ignition point.It is finally shown that the overpressure change law can directly be put in relation with the shape of flame front.

Flow characterization and dilution effects of N_2 and CO_2 on premixed CH_4/air flames in a swirl-stabilized combustor

Numerically-aided experimental studies are conducted on a swirl-stabilized combustor to investigate the dilution effects on flame stability, flame structure, and pollutant emissions of premixed CH4/air flames. Our goal is to provide a systematic assessment on combustion characteristics in diluted regimes for its application to environmentally-friendly approaches such as biogas combustion and exhanst-gas recirculation technology. Two main diluting species, N2 and CO2, are tested at various dilution rates. The results obtained by means of optical diagnostics show that five main flame regimes can be observed for Nz-diluted flames by changing excess air and dilution rate. CO2-diluted flames follow the same pattern evolution except that all the domains are shifted to lower excess air. Both N2 and CO2 dilution affect the lean blow- out （LBO） limits negatively. This behavior can be counter-balanced by reactant preheating which is able to broaden the flammability domain of the diluted flames. Flame reactivity is degraded by increasing dilution rate. Meanwhile, flames are thickened in the presence of both diluting species. NOx emissions are significantly reduced with dilution and proved to be relevant to flame stability diagrams： slight augmentation in NOx emission profiles is related to transitional flame states where instability occurs. Although dilution results in increase in CO emissions at certain levels, optimal dilution rates can still be proposed to achieve an ideal compromise.

Large eddy simulation of turbulent premixed and stratified combustion using flame surface density model coupled with tabulation method

Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds(FGM) method is employed to determine major scalars. This coupled sub-grid scale(SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the turbulence.The combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.

Effects of 5% Biological Compound Premix on Milk Perform ance and Quality in Dairy Cow

This study was to investigate the effect of biological compound premix on the performance and milk quality in dairy cows. Twenty Holstein cows, with the similar age, parity, lactating month, gestation period, milk quantity and body weight, were randomly divided into two groups. The cows in two groups were fed with either common compound premix as control or 5% biological compound premix as treatment group. Two treatments contained same basal diet but different composi- tions of premix. The feeding experiment lasting 74 days displayed that daily milk quantity in treatment group was significantly higher than control group （P 〈 0.05 ）. The milk fat percentage was increased significantly in treatment group with the extended lactation time than control group （P 〈 0.05 ）. The milk protein and solids percentage were raised, but no significant difference was found between the two treatments （P 〉0.05 ）. The results indicated that 5% biological compound premix supplied in basal diet could facilitate to increase the milk performance and to ameliorate the milk quality of dairy cows.

Experimental Investigation of Flame Structure and Combustion Limit During Premixed Methane/Air Jet Flame and Sidewall Interaction

The effects of inlet gas parameters and sloping sidewall angle on the flame structure and combustion limit with and without sidewall were experimentally investigated.Flame height and impact angle were obtained by chemiluminescence intensity analysis of CH*distribution.First,the combustion characteristics of flame with and without sidewall at different equivalence ratios were explored;then,the influence of Reynolds number and inlet gas temperature on flame structure and combustion limit of v-shaped flame with sidewall were analyzed,and the results with sidewall were compared with those without sidewall.Finally,the variation trend of flame parameters with different sloping sidewall angles was analyzed.The experimental results show that the existence of sidewall makes flame shape change from“M-shaped”to“inverted N-shaped”,and conical shape to trapezoidal shape.The inhibition effect of sidewall on flame stretching downstream is strengthened with the increase in Reynolds number;but as the temperature of the inlet gas increases,the inhibitory effect is obviously weakened.When sloping sidewall angle decreases from 90°to 55°at 5°intervals,flame height and impact angle of v-shaped flame reach the extreme value whenβ=80°.Compared with the case without sidewall,the range of v-shaped flame with sidewall has no obvious trend of broadening or shrinking when inlet gas temperature is increased;however,as sloping sidewall angle decreases,the range of the v-shaped flame shrinks obviously and flammability limit increases significantly.

Inerting characteristics of entrained atomized water on premixed methane-air flame

A combustion tube experiment platform was designed and used to study the inerting conditions and capacity of entrained atomized water on premixed methane–air flame. The structure of a laminar flame of premixed methane–air gas and the process of interaction between atomized water and flame was recorded, and the rules of combustion velocity, stability and strength rate of laminar flame were experimentally studied. The inerting process and mechanism was analyzed, and the characteristics of inerting premixed methane–air gas within explosion limits by atomized water were acquired. The research results show that: for the premixed methane–air gas with a concentration of 7%, the minimum inerting atomized water flux is 20.8 m L/(m2min); for the premixed methane–air gas with a concentration of 9%, the minimum inerting atomized water flux is 32.9 m L/(m2min); for the premixed methane–air gas with a concentration of 11%, the minimum inerting atomized water flux is 44.6 m L/(m2min). The research results are significant for extinguishing methane flame and inhibiting of methane explosion using atomized water.

Experimental Investigation of the Flame Propagation and Flashback Behavior of a Green Propellant Consisting of N2O and C2H4

Regarding the research on alternatives for monopropellant hydrazine, several so called green propellants are currently under investigation or qualification. Aside others, the DLR Institute of Space Propulsion investigates a N20/C2I-I4 premixed green propellant. During the research activities, flashback from the rocket combustion chamber into the feeding system has been identified as a major challenge when using the propellant mixture. This paper shows the results of ignition experiments conducted in a cylindrical, optical accessible ignition chamber. During the ignition and flame propagation process, pressure, temperature and high-speed video data were collected. The high speed video data were used to analyze the flame propagation speed. The obtained propagation speed was about 20 rn/s at ignition, while during further propagation of the flame speeds of up to 120 m/s were measured. Additionally, two different porous materials as flame arresting elements were tested： Porous stainless steel and porous bronze material. For both materials Peclet numbers for flashback were derived. The critical Peclet number for the sintered bronze material was around 20, while for the sintered stainless steel the critical Peclet number seems to be larger than 40. Due to the test results, sintered porous materials seem to be suitable as flashback arresters.

A Novel Reagentless Biosensor Constructed by Layer-by-Layer Assembly of HRP and Nile Blue Premixed with Polyanion

A novel reagentless biosensor constructed by the organic dye nile blue (NB) and horseradish peroxidase (HRP) has been fabricated via layer-by-layer (LBL) self-assembly technique. NB premixed with polyanion poly (sodium-p-styrenesulfonate) (PSS) acts as the mediator between the immobilized HRP and the electrode surface. The response of the biosensor to hydrogen peroxide has been investigated. The linear range of the biosensor to hydrogen peroxide was from 0.20 mmol/L to 7.03 mmol /L with a sensitivity of 8.45 μA/(mmol/L).

The Effect of Swirl Intensity on the Flow Behavior and Combustion Characteristics of a Lean Propane-Air Flame

The effect of swirl number(Sn)on the flow behavior and combustion characteristics of a lean premixed propane FlameФ=0.5 in a swirl burner configuration was numerically verified in this study.Two-dimensional numerical simulations were performed using ANSYS-Fluent software.For turbulence closure,a standard K-εturbulence model was applied.The turbulence-chemistry interaction scheme was modeled using the Finite Rate-Eddy Dissipation hybrid model(FR/EDM)with a reduced three-step reaction mechanism.The P1 radiation model was used for the flame radiation inside the combustion chamber.Four different swirl numbers were selected(0,0.72,1.05,and 1.4)corresponding to different angles(0°,39°,50°,and 57.8°).The results show that the predicted model agrees very well with the experimental data,especially with respect to the axial and radial velocity and temperature profiles.An outer recirculation zone(ORZ)is present in the combustor corner at Sn=0 and an inner recirculation zone(IRZ)appears at the combustor centerline inlet at a critical Sn=0.72.When the Sn reaches an excessive value,the IRZ moves toward the premixing tube,leading to a flame flashback.The flame structure and its length are strongly affected by changes in the Sn as well as the formation of NOx and CO at the combustor exit.

Effect of equalising ignition delay on combustion and soot emission characteristics of model fuel blends

This paper examines the effect of equalizing ignition delay in a compression ignition engine.Two sets of tests were conducted,i.e.a set of constant injection timing tests with start of fuel injection at 10°crank angle degree(CAD)before top dead center(BTDC)and a set of constant ignition timing tests while also keeping the 10℃AD BTDC injection and adding ignition improver(2-ethylhexylnitrate-,2-EHN)to the fuel mixtures.Soot particles were characterized using DMS-500 instrument in terms of mass,size,and number.The experimental results showed that adding 2-EHN to the model fuel blends reduced the soot surface area,soot mass concentration and soot mean size.Replacing 20 vol%of a C 7-heptane with 20 vol%methyl-decanoate(an oxygenated C 11 molecule)did not affect the ignition delay or rate of fuel air premixing,the peak in-cylinder pressure or heat release rates.Toluene addition(0−22.5 vol%)to heptane increased the mean size of the soot particles generated by only 3%while also resulted in a slight increase in the peak cylinder pressure and peak heat release rates.Blending toluene and methyl-decanoate into heptane without adding 2-EHN increased the premix phase fraction by at least 13%.However,by adding 2-EHN(4×10^(−4)−1.5×10^(−3)),the premixed phase fraction decreased by at least 11%.

Numerical investigation of optimal geometry parameters for ejectors of premixed burner

An ejector of low NO~ burner was designed for a gas instantaneous water heater in this work. The flowing and mixing process of the ejector was investigated by computational fluid dynamics （CFD） approach. A comprehensive study was conducted to understand the effects of the geometrical parameters on the static pressure of air and methane, and mole fraction uniformity of methane at the outlet of ejector. The distribution chamber was applied to balance the pressure and improve the mixing process of methane and air in front of the fire hole. A distribution orifice plate with seven distribution orifices was introduced at the outlet of the ejector to improve the flow organization. It is found that the nozzle exit position of 5 mm and nozzle diameter d 〉1.3 mm should be used to improve the flow organization and realize the well premixed combustion for this designed ejector.