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The co-crystallization of square-planar tetracyanonickelate(II) [Ni(CN)4]2– with an excess of the strong halogen bond donor diiodoacetylene C2I2 in dichloromethane results in the formation of supra...

The simultaneous determination of multiple analytes has been an urgent demand in screening of antibiotic residues in food products of animal origin due to its higher analysis efficiency. Five aminoglycoside antibiotics (AGAs) have been monitored in milk, including gentamicin (GEN), kanamycin (KAN), neomycin (NEO), and streptomycin/dihydrostreptomycin (STR/diSTR). A chemiluminescence microarray immunoassay (CLMIA) based on nitrocellulose membrane had been developed for the detection of multiple AGAs, which the LODs for STR, KAN, NEO, and GEN were 4.74 ng/mL, 4.97 ng/mL, 2.99 ng/mL, and 4.42 ng/mL respectively. To improve the sensitivity of immunoassay, single-well carbon tubes (SWCNTs) were utilized as solid support for loading horseradish peroxidase-labelled goat anti-mouse antibody to obtain the multi-enzyme particles. After the optimization of usage of multi-enzyme particles and antibodies, the enhanced CLMIA was established and evaluated. The LODs were 1.25 ng/mL for STR, 0.64 ng/mL for KAN, 0.38 ng/mL for GEN, and 0.39 ng/mL for NEO, which was improved by threefold, sevenfold, 11-fold, and sevenfold compared with the conventional CLMIA developed. These methods presented higher specificity and repeatability. Finally, the enhanced CLMIA based on CNT-assisted multi-enzyme particles was utilized to analyze twenty-five milk samples from local market and dairy farm, which all the results were below the LOD. The enhanced CLMIA showed the great application potential for the detection of multiple targets simultaneously and provided efficient tool for the screening of pollutants in food.

The current study originally presents a detailed approach to implement the p-xylene based two-color PLIF for measuring gaseous mixture temperature and mole concentration field simultaneously. An 80...

It is of interest for engine combustion modeling to quantify the evaporation behaviors of fuel spray impinging on a wall as the fuel atomization, evaporation, and mixing with oxygen in the combustion chamber usually dominate the subsequent combustion processes. In this study, the vapor and liquid mass distributions in diesel-like fuel sprays were quantified using the ultraviolet-visible laser absorption scattering imaging technique. The sprays were injected from a single-hole nozzle with a common-rail injection system and impinged on a flat wall at an ambient pressure of 4 MPa and an ambient temperature of 833 K. The mass of the total fuel vapor, the spray volume covered by the vapor phase, and the air mass entrained into the spray were characterized. The results indicate that the time evolution of these parameters until shortly after the end of injection can be expressed by a power-law function, Yi = ki· ts1.5, where Yi represents the parameter like vapor mass and so on, ts is the time after start of injection, and ki is the coefficient corresponding to Yi. The physics behind this power-law function was analyzed and discussed based on the theory of atomization and evaporation, and verified using measurement data obtained under different conditions of injection quantity.

This paper develops and applies a model to characterize the vaporization of gasoline–methanol blends in applications such as homogeneous direct injection spark ignition (DISI) engines. In DISI engines, the fuel is injected during intake or early in the compression stroke. Thus, the fuel droplets must vaporize in a low-temperature environment. Because methanol’s relatively high latent heat, the gases cool significantly during vaporization. Opposed stagnation flow is a computationally efficient platform on which to base the study. The study predicts the effects of initial droplet size, temperature, fuel–air ratio, methanol fraction, and operating pressure. Results include liquid- and gas-phase profiles during the vaporization process. Parameter studies show the state of the droplets, the gas phase temperature, and composition near the end of the droplet’s lifetime. The results provide quantitative insight about optimizing ignition and combustion, including under engine cold-start conditions.

Laser-induced-fluorescence/Mie-scattering (LIF/MIE) was proven to be a useful diagnostic for Sauter Mean Diameter (SMD) measurements in non-evaporating sprays. However, the measurement is not reliable for cases of an evaporating spray due to the interference of the fluorescence signal from the vapor phase. In this work, simultaneous Laser-induced-exciplex-fluorescence/Mie-scattering (LIEF/MIE) imaging techniques were proposed to obtain the SMD distribution of evaporating sprays. A special experimental condition was used to generate the flash-evaporating spray, which includes a fuel temperature of 60 °C and an ambient pressure of 20 kPa. Different from the conventional LIF/MIE technique, the combination of LIEF and Mie techniques allows eliminating the effect of tracer fluorescence from vapor phase in an evaporating spray. In addition, carefully selected tracers and specially designed filters were used to decrease the effects of variation on tracer concentration and temperature dependency of fluorescence intensity during evaporation. The numerical analysis based on geometrical optics approximation (GOA) and experimental analysis was conducted to determine the calibration coefficient K . Finally, SMD distribution of an evaporating spray measured by both LIEF/MIE and conventional LIF/MIE techniques was compared to PDI measurement. The results show that the SMD of the flash boiling spray obtained from LIEF/MIE is very close to those measured by PDI, while the results measured by LIF/MIE and PDI show a large deviation of around 40%. It indicates that the evaporation effect cannot be ignored for evaporating sprays.

A computational model is developed and applied to study the vaporisation behaviour of three liquid fuels. This fundamental study is motivated by a need to understand how the performance of direct-injection-spark-ignition (DISI) engines may be affected by changes in fuel composition, especially alcohols. Currently, most DISI engines are designed for homogeneous-charge combustion, where the in-cylinder fuel injection, vaporisation and mixing is accomplished during the intake and early in the compression process. Thus the temperature and pressure are low, compared to post-compression conditions. The two-phase axisymmetric model is based upon an ideal opposed stagnation flow field. Liquid droplets are carried in one air stream that is met by an opposed air flow. Because of stagnation-flow similarity, the mathematical model can be represented as a one-dimensional boundary-value problem. Results show significant differences between methanol, ethanol and heptane fuels, which have potentially important impacts on...

The spray structural changes and vaporization processes for flash-boiling multi-hole sprays over a broad range of superheated conditions were investigated using Mie-scattering and Laser-induced-exciplex-fluorescence (LIEF) optical techniques. The fuel property effects were examined by characterizing n-hexane, methanol and ethanol fluids over a wide range of conditions consistent with that found in today’s spark-ignition-direct-injection (SIDI) engines. The macroscopic spray structure was quantified using spray penetration, spray-plume width and normalized distance between spray plumes. These structural parameters were correlated to the ratio of the ambient pressure to saturation pressure (Pa/Ps) that represents the superheated degree. Three continuous regions were identified by quantifying the spray transformation with increasing superheated degree; namely the non-flash-boiling, transitional flash-boiling and flare flash-boiling regions. Two critical values of Pa/Ps were identified, where the flash-boiling and spray collapsing transitions occurred at Pa/Ps values of 1.0 and 0.3, respectively. The evaporation process was examined using the LIEF optical technique for n-hexane, providing the relative vapor quantity throughout the spray transformation process. The correlations of the spray structural change and extent of vaporization with increasing superheated degree provided good insight into the mechanisms responsible for the observed behaviors during flash-boiling conditions.

This paper describes an investigation of the flame structure of wall-impinging diesel sprays injected by group-hole nozzles in a constant-volume combustion vessel at experimental conditions typical of a diesel engine. The particular emphasis was on the effect of the included angle between two orifices (0–15 deg. in current study) on the flame structure and combustion characteristics under various simulated engine load conditions. The laser absorption scattering (LAS) technique was applied to analyze the spray and mixture properties. Direct flame imaging and OH chemiluminescence imaging were utilized to quantify the ignition delay, flame geometrical parameters, and OH chemiluminescence intensity. The images show that the asymmetric flame structure emerges in wall-impinging group-hole nozzle sprays as larger included angle and higher engine load conditions are applied, which is consistent with the spray shape observed by LAS. Compared to the base nozzle, group-hole nozzles with large included angles yield higher overall OH chemiluminescence intensity, wider flame area, and greater proportion of high OH intensity, implying the better fuel/air mixing and improved combustion characteristics. The advantages of group-hole nozzle are more pronounced under high load conditions. Based on the results, the feasibility of group-hole nozzle for practical direct injection diesel engines is also discussed. It is concluded that the asymmetric flame structure of a group-hole nozzle spray is favorable to reduce soot formation over wide engine loads. However, the hole configuration of the group-hole nozzle should be carefully considered so as to achieve proper air utilization in the combustion chamber. Stoichiometric diesel combustion is another promising application of group-hole nozzle.

The effects of hydrogen fraction on laminar burning velocity, flame stability (Markstein number) and flame temperature of methane–hydrogen–air flame at global equivalence ratios of 0.7, 1.0 and 1.2 have been investigated numerically based on the full chemistry and the detailed molecular species transport. The effect of stretch rate on combustion characteristics is examined using an opposed-flow planar flame model, while the effect of flame curvature is identified by comparing a tubular flame to the opposed-flow planar flame. The difference in response on hydrogen fraction between the planar and curved flames has been observed. The results show when hydrogen fraction increases, the flame temperature and laminar burning velocity increases, and this effect is more significant at a large stretch rate; while Markstein length decreases. At a fixed stretch rate of 400 s−1, under which the flame approaches extinction limit, the flame temperature of the tubular flame is considerably higher than that of the planar opposed flow flame, which results most likely from the contribution of the positive flame curvature to the first Damkohler number.

This paper uses tubular flame similarity and computational models to investigate the characteristics of premixed methane-air flames with high swirl rates. As the swirl rate increases, thus increasing centrifugal forces within the flow field, pressure variations can be large. Results show that the radial pressure field significantly affects flame structure and overall burning characteristics. Molecular species transport is affected by pressure-diffusion and absolute pressure in the reaction zone, which can be significantly reduced. To assist isolating and interpreting swirl rate effects, results are compared with comparable flames in planar unstrained and opposed-flow twin flame settings. Results show that swirl rate can influence methane-air flames differently from comparable propane-air flames. These differences are explained in terms of the pressure fields and the first Damkohler number.

This paper provides the theoretical basis for modeling tangential injection into ideal tubular flames. For most practical tubular combustors, the present formulation provides significant advantages compared to the traditional model formulation. The mass, momentum, and energy associated with tangential injectors are represented as Gaussian-shaped source terms in the appropriate conservation equations. Incorporating the source terms alters the governing equations, but does not affect the similarity properties associated with ideal tubular flow. The system of equations form a nonlinear boundary-value problem, which can be solved computationally.

A laser imaging technique has been proposed in this article for measuring vapor distribution of lower and high volatile components in a multicomponent fuel spray, based on the LAS technique. For a two-component fuel spray which contains n-octane (boiling point: 399 K) and n-tridecane (boiling point: 508 K), vapor distribution of the low boiling point (LBP) component, n-octane, has been determined by using p-xylene (boiling point: 411 K) as its substitute, which has the similar physical properties and absorbs the ultraviolet light but not the visible light, according to the requirements of the LAS technique. Likewise, vapor behavior of the higher boiling point (HBP) component, n-tridecane, has been obtained by using α-methylnaphthalene (boiling point: 517 K). It has been found that difference in vaporization rate between the LBP and HBP components is great over the spray plume at 473 K, this difference, however, reduces significantly as the ambient temperature increases to 573 K; The LBP component...

This paper uses a computational model to characterize the effects of high rotation rates on the structure of swirl-type premixed tubular flames. The model incorporates an elementary propane–air reaction mechanism and multicomponent molecular transport. Because high rotation rates lead to large radial pressure variations, pressure diffusion is included in the molecular-transport model and the radial momentum equation is retained in the system of equations. A similarity formulation is used, leading to a two-point boundary-value problem. Both lean and rich mixtures are considered. Results show how rotation rate affects pressure variation, flame position, flame temperature, and flame velocity. Pressure diffusion is most significant when the flame is positioned close to the maximum circumferential velocity.

The ultraviolet-visible laser absorption-scattering (LAS) technique was extended to simultaneous imaging of two-dimensional vapor/liquid mass distributions in a nonaxisymmetric evaporating diesel spray such as that injected into a two-dimensional model combustion chamber of direct-injection diesel engines. The main error for vapor measurement is incurred by the temperature dependence of molar absorption coefficients (TDMAC) of the test fuel. Thus, selecting a test fuel of negligible TDMAC can greatly increase the measurement accuracy. By means of this extended LAS technique, the overall mass, as well as the mass distribution of vapor and liquid phase per projection area perpendicular to the laser beam, was obtained, and then the behavior of split-injection diesel spray in a two-dimensional model combustion chamber in a high-temperature high-pressure constant-volume vessel was observed. Finally, the effects of injection mass ratios on the distributions of vapor and droplets and characteristics of fuel/air ...

The mixture formation characteristics in a temporally split injection diesel spray were studied through a series of measurements based on the laser absorption-scattering technique (LAS), which was developed by the authors and adopted the second harmonic (532 nm) and the fourth harmonic (266 nm) of a pulsed Nd:YAG laser as the incident light, and dimethylnaphthalene (DMN) as the test fuel. By applying this technique, imaging was made of DMN sprays injected into a high- temperature (833 K) and high-pressure (4.0 MPa) constant-volume vessel by a single-hole nozzle and a common rail injection system for a direct injection (DI) diesel engine. Quantitative information of the vapour evaporation and fuel distribution was obtained, and furthermore the fuel-air mixture was characterized. The effect of injection temporal splitting on the mixture characteristics was analysed and correlated with the characteristics of NO x formation in a DI diesel engine.

Recent experimental studies have shown that with split injection strategy, the soot and NOx emissions from a diesel engine can be reduced significantly in comparison with a conventional non-split injection. To understand the mechanism of emissions reduction, it is essential to clarify the process of mixture formation in the diesel spray. For characterizing the droplets and vapor concentration distributions inside a fuel spray, a dual-wavelength laser absorption-scattering technique (LAS) was developed by using the 2nd harmonic (532nm) and the 4th harmonic (266nm) of an Nd: YAG laser and using dimethylnaphthalene as a test fuel. By applying the ultraviolet-visible LAS imaging technique, the distributions of droplets and vapor concentrations in the spray, which was injected into a high-temperature and high-pressure nitrogen ambient in a constant volume vessel by a common-rail diesel injection system, were measured and quantitatively analyzed. The effect of injection mass ratio of double-pulse injections on distributions of equivalence ratios of vapor and droplets in the sprays was examined.

Fuel volatility has a great effect on its evaporation processes and the mixture formation and thus combustion and emissions formation processes in internal combustion engines. To date, however, instead of the actual gasoline or diesel fuel, many researchers have been using single-component fuel in their studies, because the composition of the former is too complicated to understand the real physics behind the evaporation and combustion characteristics. Several research groups have reported their results on droplets evaporation in a spray of multi-component fuel, carried out both numerically and experimentally. However, there are plenty of difficulties in quantitative determination of vapor concentration and droplet distributions of each component in a multicomponent fuel spray. In this study, to determine the vapor phase concentration and droplet distributions in an evaporating binary component fuel spray, a laser diagnostics based on laser extinction by droplet scattering and vapor absorption was developed. In practice, measurements of the vapor concentration distributions of the lower (n-tridencane) and higher (n-octane) volatility components in the binary component fuel sprays have been carried out at ambient temperatures of 473K and 573K, by substituting p -xylene for noctane or α-methylnaphthalene for n-tridecane. p -Xylene and α-methylnaphthalene were selected as the substitutes is because they have strong absorption band near 266nm and transparent near 532nm and, their thermo-physical properties are similar to those of the original component. As a demonstration experiment, vapor/liquid distribution of the lower boiling point (LBP) and higher boiling point (HBP) components in the binary component fuel spray have been obtained.

The spray evaporation of gasoline and ethanol fuel was investigated qualitatively through the use of the planar laser induced exciplex fluorescence (PLIEF) technique in a constant volume chamber. The effect of fuel temperature and ambient pressure on spray evaporation was identified over a range of conditions. Both a swirl injector and a multi-hole injector were examined for each of the two fuels. A coevaporative mixture of benzene and triethylamine (TEA) was used as a fluorescent seeding material to study the evaporation processes of ethanol fuel. A mixture of fluorobenzene (FB) and diethylmethylamine (DEMA) in n-hexane, which has been proved to be a suitable seeding material for LIEF measurement, allowed for the investigation of the evaporation processes of gasoline fuel mixture. Remarkable spray evaporation processes were observed for both gasoline and ethanol fuel by increasing fuel temperature or by reducing ambient pressure to a vacuum. Especially after achieving flash-boiling, the vapor distribution of multi-plume spray increases dramatically, and the vapor phase of spray from swirl injector gathers to the centerline of injector by increasing the superheated degree. The collapsing of both liquid and vapor phases of n-hexane is stronger than that of ethanol spray for both swirl and multi-hole injectors.Copyright © 2010 by ASME

In order to investigate the effect of split injections on mixture formation processes in Direct Injection (DI) gasoline engine sprays, an experimental study was conducted applying the laser absorption and scattering (LAS) technique to the sprays using double pulse injections with various dwells and mass ratios. The effects of various dwells and mass ratios between the pulsed injections on the spatial concentration distributions in the spray, the penetration of vapor and liquid phases, and the mean equivalence ratios of the vapor phase and overall spray, were clarified. It was found that the phenomenon of high concentration liquid spray piling up at the leading edge of the spray is avoided by the double injections with enough dwell or appropriate mass ratio. The maximum penetration length of the spray significantly decreases, especially for the liquid phase with high concentration. Moreover, the mean equivalence ratios including vapor phase and overall spray are significantly affected by the double pulse injections with various dwells and mass ratios.

Mixture formation processes play a vital role on the performance of a D.I. Gasoline engine. Quantitative measurement of liquid and vapor phase concentration distribution in a D.I. gasoline spray is very important in understanding the mixture formation processes. In this paper, an unique laser absorption scattering (LAS) technique was employed to investigate the mixture formation processes of a fuel spray injected by a D.I. gasoline injector into a high pressure and temperature constant volume vessel. P-xylene, which is quite suitable for the application of the LAS technique, was selected as the test fuel. The temporal variations of the concentration distribution of both the liquid and vapor phases in the spray were quantitatively clarified. Then the effects of injection pressure and quantity on the concentration distributions of both the liquid and vapor phases in the spray were analyzed.

Some experimental investigations have shown that the trade-off curve of NOx vs. particulate of a D.I. diesel engine with split-injection strategies can be shifted closer to the origin than those with a single-pulse injection, thus reducing both particulate and NOx emissions significantly. It is clear that the injection mass ratios and the dwell(s) between injection pulses have significant effects on the combustion and emissions formation processes in the D.I. diesel engine. However, how and why these parameters significantly affect the engine performances remains unexplained. The effects of both injection mass ratios and dwell between injections on vapor/liquid distributions in the split-injection diesel sprays impinging on a flat wall have been examined in our previous work. In this paper, the behaviors of the split-injection diesel sprays in a 2-dimensional model combustion chamber, which was installed in a high-temperature and high-pressure constant volume vessel filled with nitrogen, was observed by use of the ultraviolet-visible laser absorption-scattering (LAS) imaging technique. The effect of the injection mass ratios and the effect of the dwell(s) between injections on the distributions of fuel vapor and droplets were clarified through qualitative imaging of the optical thickness of vapor and the optical thickness of droplets, respectively. The findings give an implication to the potential relation between the vapor/liquid behaviors in the split-injection sprays and the reduction mechanism of NOx and particulate emissions of the D.I. diesel engine.