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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 evaporation characteristics of multi-component fuel have significant effects on the fuel–air mixing process and subsequent processes, such as ignition, combustion, and harmful pollutants emission formation. When a multi-component fuel is directly injected into the combustion chamber, spatial and temporal equivalence ratio stratification may happen due to the preferential evaporation of components with different volatilities. However, there is a lack of effective optical diagnostics of the spatial stratification in a multi-component fuel spray. In this study, new optical technique based on ultraviolet absorption and visible light schlieren (UAVS) is for the first time proposed to measure the stratification of vapor distributions stratification in a binary-component fuel spray. UAVS technique was applied to investigate the effects of mixing ratios in a binary-component fuel spray (p-xylene and n-hexane) and ambient temperature on the stratification of components with different volatilities. The results denote the UAVS technique as the effective method for the observation of stratification of a multi-component fuel spray. In this study, the stratification phenomenon was the most evident at the ratio of 1:1. At the same time, when the ambient temperature is much higher than the dew point temperature of mixture, the stratification rarely occurs, because of the rapid evaporation thus providing time not enough for preferential evaporation. Graphic abstract

The cyclic variations of vapor distributions of a binary-component fuel spray were experimentally investigated. Ultraviolet–visible laser absorption/scattering technique was adopted for quantitative measurement of vapor mass distributions in a binary-component fuel spray. n-Hexane and p-xylene were chosen to form the binary-component test fuel. Intersection-over-union, an important concept in object detection, was firstly introduced to characterize more precisely the spray cyclic variations, in comparison with other traditional methods including presence probability image and coefficient of variation in spray penetration. As a result, a larger fluctuation was observed in vapor distributions of the higher boiling point component (p-xylene) in the binary-component fuel compared to that of the pure p-xylene spray, indicating that evaporation characteristic of multi-component fuel spray is one of the significant factors that affects the cyclic variations. Based on large amount of experimental observations, a concept of spray vapor distribution area with consideration of cyclic variation was proposed to give a more reasonable expression of spray structure, and a new empirical formula of spray vapor distribution area was given for prediction and numerical model validation.

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.

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.

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...

The effects of split injection with various dwells and mass ratios on the spray and mixture characteristics in an ambient environment similar to the late stage of compression stroke in direct injection spark ignition (DISI) engines were investigated by using the laser absorption scattering (LAS) technique. Through splitting the fuel injection process with appropriate dwells and mass ratios, some benefits for the stratified charge formation of DISI engines can be achieved. First, the phenomenon of high-density liquid phase fuel piling up at the leading edge of the spray can be circumvented and the subsequent reduction in the spray penetration length for both liquid and vapour phases is seen. Second, the radial width of the ‘combustible mixture’ (equivalence ratio of vapour φv in a range of 0.7 ≤ φv ≤ 1.3) is significantly extended. Finally, the quantity of ‘over lean’ (φv < 0.7) mixture in the spray is significantly reduced. These results are believed to contribute to the stratified lean operation and the reduction in smoke and unburned hydrocarbons (UBHC) emissions of DISI engines. Further, the mechanism behind these effects of the split injection was clarified by analysing the interactions between the two pulsed sprays and the spray-induced ambient air motion using the LIF-PIV technique.

The effect of split injection on the mixture characteristics of DISI (Direct Injection Spark Ignition) engines was investigated firstly by the Laser Absorption Scattering (LAS) technique. Through splitting the fuel injection process, two possible benefits were found: 1) High density liquid droplets piling up at the leading edge of the spray can be circumvented, subsequently the reduction of the spray tip penetration; 2) The quantity of over lean (Φ v < 0.7, Φ v : equivalence ratio of vapor) mixture in the spray can be significantly reduced. These are believed to contribute to the reduction of the engine-out smoke and HC emissions. In order to clarify the mechanism behind the effect of the split injection, the spray-induced ambient air motion was investigated by the LIF-PIV technique. The strong ambient air entrainment into the tail region of the spray and a counter-vortex structure were found in both the single and split injections. In the case of the single injection, the spray develops in extending its length, subsequently a larger volume results and thus it is diluted to over lean by the ambient air entrainment. In contrast, in the case of split injection, the second spray is injected into the tail region of the first spray and its evaporation is promoted by the ambient air motion induced by the first spray. Hence the replenishment of the liquid fuel into the leading edge of the first spray is reduced. As a consequence, the high density liquid droplets piling up at the leading edge is avoided. Furthermore, a more compact spray results so that the ambient air motion plays a positive role on evaporating the spray into more combustible (0.7 < Φ v < 1.3). This is especially true in the tail region of the spray and the region where the counter-vortex motion is occurring.

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.

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.

To evaluate the atomization and evaporation processes of liquid fuel, there are several laser diagnostics available in present. In this paper, the recent progress in laser diagnostics for atomization and evaporation will be introduced, as two categories: atomization and evaporation. The diagnostics for the former includes the primary breakup from liquid jet to ligaments or droplets and the secondary atomization from a bigger droplet to a smaller one, and the latter includes the droplet evaporation and the vapor distributions in a spray.

Fuel sprays from outward-opening DISI engine injector were characterized under various fuel superheat degree (SD) conditions using laser sheet Mie-scattering and Phase Doppler Interferometer (PDI). N-hexane was used for a gasoline surrogate as it has a fixed boiling point and saturated vapor pressure. The macroscopic characteristics of the spray structure including the spray penetration and the spray angle, and the microscopic characteristics including Sauter Mean Diameter (SMD) and size distributions of droplets, were investigated. The ratio of ambient pressure to saturation pressure (Pa/Ps) is used as an indicator of the SD. The results show that the spray structure deforms from an “umbrella” shape to a “bell” shape when SD increases from non-flash-boiling to full-flash-boiling area. And as Pa/Ps decreases (SD increases), the spray penetration decreases at first and turns to increase at about Pa/Ps = 0.3. The spray angle keeps relatively steady until Pa/Ps decreases to about 0.3, but significantly decreases when Pa/Ps

Measurements of liquid phase temperature distributions in liquid–vapor co-existing conditions (such as in evaporating sprays) are important to understand the physics of droplet evaporation. The techniques based on laser-induced fluorescence are not suitable for evaporating case since both liquid and vapor phases emit fluorescence with the same wavelength. In this study, the fluorescence from liquid and vapor phases was separated by use of laser-induced exciplex fluorescence (LIEF) technique. Two fluorescence bands from the liquid phase fluorescence spectra were detected simultaneously, and their intensity ratio was correlated to the liquid phase temperature. For the LIEF imaging system, FB-DEMA-n-hexane was selected as it was a typical LIEF system for the vapor concentration diagnostic, and thus easily to be extended to a simultaneous diagnostic on the vapor concentration and the droplet temperature. The fluorescence spectra were obtained in the temperature range from 303 to 423 K. The effects of liquid temperature, liquid pressure, dopant concentration and laser energy on the temperature measurement were investigated. The results show a good linear relationship between the fluorescence ratio and the temperature function. Increasing the dopant concentration can raise the signal-to-noise ratio but deteriorate temperature sensitivity. The optimal range of the dopant concentration was found between 0.1 % and 0.5 %. After calibration, the technique was applied to a monosized droplet stream, and the measurement results demonstrated excellent measurement accuracy with error below 1 % in the range of 303–423 K.

Spark ignition direct injection (SIDI) gasoline engines employ high fuel injection pressure to promote the liquid fuel atomization and vaporization in the combustion chamber. However, high fuel injection pressures normally lead the fuel spray over penetrating in engine cylinder, resulting in wall and/or piston wetting which cause high level of engine unburned hydrocarbon (UHC) and soot emissions. Recently, it has been found the fuel temperature could play important roles in spray atomization and vaporization processes. Especially, when the temperature of the fuel exceeds its local boiling point, the fuel is superheated and flash boiling occurs. Experiments of flash boiling sprays from a multi-hole DI injector show that the spray would undergo significant structural transformation under the superheated conditions. Both the atomization and vaporization are improved when the phenomenon of flash boiling occurs. Meanwhile, since various types of SIDI engine combustion systems utilize different fuel injector configurations to achieve desirable mixture formation and combustion, it is necessary to extend the existing knowledge of flash boiling spray from multi-hole injector to other types of injector, and characterize their flash boiling spray behaviour under the similar superheated conditions. In this paper, flash boiling sprays from three types of SIDI injectors, namely, multi-hole, swirl and outward opening injectors are investigated at a high pressure constant volume chamber. The primary focus is the spray from a multi-hole injector as it is most widely used in modern SIDI engines. The temperature of the injector body can be regulated by placing the injector in a fixture which can be thermally controlled. Various laser diagnostics are applied to investigate the spray geometry, flow field, vaporization and droplet size distributions. The results show that the characteristics of flash boiling spray are mainly dominated by superheat degree, i.e., the difference between the fuel temperature and its boiling point, not as sensitive to the injection pressure as the non-flash boiling spray. The structures of flash boiling spray from all three types of injector differ from those of non-flash boiling spray significantly. However, the effects of injector configuration on the structure of flash boiling spray are insignificant, compared to the non-flash boiling sprays. This study reveals that using fuel temperature can be an effective parameter for controlling the spray structure, spray atomization and evaporation.

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.

The droplets and vapor distributions in a fuel spray were imaged by a dual-wavelength laser absorption-scattering technique. 1,3-dimethylnaphthalene, which has physical properties similar to those of Diesel fuel, strongly absorbs the ultraviolet light near the fourth harmonic (266 nm) of a Nd:YAG laser but is nearly transparent to the visible light near the second harmonic (532 nm) of a Nd:YAG laser. Therefore, droplets and vapor distributions in a Diesel spray can be visualized by an imaging system that uses a Nd:YAG laser as the incident light and 1,3-dimethylnaphthalene as the test fuel. For a quantitative application consideration, the absorption coefficients of dimethylnapthalene vapor at different temperatures and pressures were examined with an optical spectrometer. The findings of this study suggest that this imaging technique has great promise for simultaneously obtaining quantitative information of droplet density and vapor concentration in Diesel fuel spray.