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Polyimide (PI) is widely used in the field of microelectronics because of its excellent thermal, mechanical, optical, and electrical properties. With the development of electronics and information industry, PI as a dielectric material needs to possess low dielectric loss. PI/carbon quantum dots (PI/CQDs) composite films with low dielectric loss were prepared by introducing CQDs into PI matrix. At 25°C and 1 kHz voltage, the dielectric loss of pure PI film is about 0.0057. The dielectric loss of PI/CQDs composite film is about 0.0018, which is about 68% lower than that of pure PI film. The dielectric loss of PI/CQD composite film is greatly reduced while the mechanical properties and thermal properties of PI/CQDs composite film roughly remain unchanged. Due to the cross-linking structure formed between CQDs and PI molecular chain, the relative movement of PI molecular chain is hindered.

Different plasticizers have obvious differences in plasticizing properties. As one of the important indicators for evaluating plasticization performance, the substitution factor (SF) has great significance for product cost accounting. In this research, a genetic algorithm with “variable mutation probability” was developed to screen the key molecular descriptors of plasticizers that are highly correlated with the SF, and a SF prediction model was established based on these filtered molecular descriptors. The results show that the improved genetic algorithm greatly improved the prediction accuracy in different regression models. The coefficient of determination (R2) for the test set and the cross-validation both reached 0.92, which is at least 0.15 higher than the R2 of the unimproved genetic algorithm. From the results of the selected descriptors, most of the descriptors focused on describing the branching of the molecule, which is consistent with the view that the branching chain plays an important role in the plasticization process. As the first study to establish the relationship between plasticizer SF and plasticizer molecular structure, this work provides a basis for subsequent plasticizer performance and evaluation system modeling.

FLT3 mutations are the most frequently identified genetic alterations in acute myeloid leukemia (AML) and are associated with poor prognosis. Multiple FLT3 inhibitors are in various stages of clinical evaluation. However, resistance to FLT3 inhibitors resulting from acquired point mutations in tyrosine kinase domain (TKD) have limited the sustained efficacy of treatments, and a “gatekeeper” mutation (F691L) is resistant to most available FLT3 inhibitors. Thus, new FLT3 inhibitors against both FLT3 internal tandem duplication (FLT3-ITD) and FLT3-TKD mutations (including F691L) are urgently sought. Herein, we identified KX2-391 as a dual FLT3 and tubulin inhibitor and investigated its efficacy and mechanisms in overcoming drug-resistant FLT3-ITD-TKD mutations in AML. KX2-391 exhibited potent growth inhibitory and apoptosis promoting effects on diverse AML cell lines harboring FLT3-ITD mutations and AC220-resistant mutations at the D835 and F691 residues in TKD and inhibited FLT3 phosphorylation and its downstream signaling targets. Orally administered KX2-391 significantly prolonged the survival of a murine leukemia model induced by FLT3-ITD-F691L. KX2-391 also significantly inhibited the growth of 4 primary AML cells expressing FLT3-ITD and 2 primary AML cells expressing FLT3-ITD-D835Y. Our preclinical data highlight KX2-391 as a promising FLT3 inhibitor for the treatment of AML patients harboring FLT3 mutations, especially refractory/relapsed patients with F691L and other FLT3-TKD mutations. Supplementary Information The online version contains supplementary material available at 10.1186/s13045-021-01098-y.

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...

To solve problems of the low burn-off rate and the flame instability in a conventional rapidly mixed tubular flame (RMTF) burner and problems of the flashback and the narrow extinction limits in a ...

Under idle operations of a spark-ignition direct-injection engine, issues such as misfire, unstable combustion, and power imbalance between individual cylinders are often encountered, which worsen the fuel economy and tailpipe emissions. These undesired phenomena have close relations with cyclic variations of the fuel sprays in the cylinder. In this article, the spray cyclic variations under idle operations have been investigated at a constant volume chamber using ultraviolet/visible laser absorption/scattering imaging technique and Mie scattering optical diagnostics combined with different statistical methods such as probability presence image, intersection over union, and edge fluctuation length. The variations in spray morphology of liquid/vapor phases and vapor mass distributions have been characterized. It was found that the cyclic spray variation after the end of injection is too large to ignore, implying that this cyclic variation should be taken into consideration when matching the spray to a combustion chamber or numerical modeling. The effects of injection pressure and fuel temperature on spray cyclic variations have been quantitatively examined. The results show that the higher injection pressure or the higher fuel temperature is, the larger variation in spray morphology and vapor mass distributions was observed, indicating that adopting an appropriately lower injection pressure or lower fuel temperature is helpful to a stable ignition and combustion under idle conditions for a non-homogeneous spark-ignition direct-injection engine.

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.

A new combustion system, which consists of an evaporator and a tubular flame burner with multi-stage inlets, has been developed to meet the growing concerns over the fuel flexibility and flame stab...

IRF8 is a key regulator of innate immunity receptor signaling and plays diverse functions in the development of hematopoietic cells. The effects of IRF8 on hematopoietic stem cells (HSCs) are still unknown. Here, it is demonstrated that IRF8 deficiency results in a decreased number of long‐term HSCs (LT‐HSCs) in mice. However, the repopulation capacity of individual HSCs is significantly increased. Transcriptomic analysis shows that IFN‐γ and IFN‐α signaling is downregulated in IRF8‐deficient HSCs, while their response to proinflammatory cytokines is unchanged ex vivo. Further tests show that Irf8 −/− HSCs can not respond to CpG, an agonist of Toll‐like receptor 9 (TLR9) in mice, while long‐term CpG stimulation increases wild‐type HSC abundance and decreases their bone marrow colony‐forming capacity. Mechanistically, as the primary producer of proinflammatory cytokines in response to CpG stimulation, dendritic cells has a blocked TLR9 signaling due to developmental defect in Irf8 −/− mice. Macrophages remain functionally intact but severely reduce in Irf8 −/− mice. In NK cells, IRF8 directly regulates the expression of Tlr9 and its deficiency leads to no increased IFNγ production upon CpG stimulation. These results indicate that IRF8 regulates HSCs, at least in part, through controlling TLR9 signaling in diverse innate immune cells., This study reveals the effects of IRF8 function on hematopoietic stem cells (HSCs). Irf8 −/− mice exhibit a decrease number yet enhanced repopulation capacity of HSCs. Mechanistically, IRF8 affects the release of proinflammatory cytokines by controlling the development of monocytes/macrophages and dendritic cells and the expression of TLR9 in NK cells. Consequently, the cytokine‐mediated HSC proliferation and exhaustion are reduced.

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.

Flash boiling is an effective way to enhance both atomization and evaporation characteristics of liquid fuel spray by introducing explosion of vapor bubbles, compared with the conventional high pressure injection. However, the evaporation characteristics and mechanism of flash boiling spray, especially, that associated with the explosion of vapor bubbles at high superheat degree, is still unknown. In this study, the vapor and liquid mass distributions in flash boiling sprays were quantified by use of ultraviolet/visible laser absorption/scattering (UV-LAS) imaging technique over a broad range of superheat degree. Based on the results of macro-structure characteristics of liquid/vapor phase spray and total evaporated vapor mass, influence of bubble explosion on detailed evaporation characteristics of flash boiling spray are investigated. And, by associating with our previous work on breakup mechanism of superheated droplet and liquid jet, the effect of two evaporation regimes, namely surface evaporation and flashing evaporation, on evaporation of flash boiling spray has been successfully identified for the first time. These results provide insightful information for understanding the evaporation mechanism of a superheated liquid jet and modeling a flash boiling spray.

This paper examines the changing nature of volatility spillovers among the U.S. and eight East Asian stock markets between two financial crises: the Asian currency crisis and the U.S. subprime credit crisis. Our empirical results suggest that volatility is not always spilled over from the directly affected markets to surrounding markets in crisis periods. The East Asian markets who directly suffered from the Asian currency crisis are the ones to which volatility is spilled over from other markets during the Asian currency crisis period, whereas uni-directional volatility spillovers from the U.S. market to other markets are observed during both crisis periods. This difference can be explained by a pre-determined hierarchy in which volatility spillovers tend to start from the U.S. market regardless of the geographical origin of the crisis. Furthermore, our results reveal that the markets in three major Asian financial hubs, i.e., Japan, Hong Kong and Singapore, are the markets to which volatility is spilled over uni-directionally from several other countries during the subprime credit crisis period, but not during the Asian currency crisis period. We attribute this difference to crisis-specific (currency or credit crisis), market-specific (credit derivatives market participation and foreign currency reserves), and time-specific (more integrated global market) factors.

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...

Flash-boiling atomization is an effective way to enhance fuel jet breakup by introducing explosion of vapor bubbles and thus improve the evaporation of fuel spray, compared with the conventional high pressure injection. However, the break-up mechanism of a superheated jet, especially, that associated with the explosion of vapor bubbles inside the droplets, is still unknown. In this study, a superheated droplet generator was developed for observing the droplet morphology variation and the breakup process resulting from the vapor bubbles inside a superheated droplet by microscopic imaging. It was found that the droplet morphology is mainly influenced by droplet temperature, but micro bubbles formation and the breakup of the superheated droplet are dominated by superheat degree, and the superheat degree of 25 °C is an important critical point at which the droplet breakup occurs resulted from the ever-increasing void fraction exceeding a value of approximately 50% and the breakup mode shifts from aerodynamic mode to thermodynamic mode. The surface tension of superheated droplet was also evaluated by the droplet morphology, and the results show that the maximum reduction in surface tension reaches 70% as superheat degree increases to approximately 25 °C, and this explains the sharp decrease in SMD for a flash boiling spray when the superheat degree approaches this level. These results provide insightful information for understanding the breakup mechanism of superheated droplets and liquid jet and its modeling.

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.

White organic light-emitting diodes (WOLEDs) with non-doped construction have compelling advantages, such as simplifying manufacturing process and reducing costs, thus attracting more attention. To improve the efficiency of non-doped WOLEDs, the selection of suitable interlayer is still a big problem to balance carriers. Here, for the first time, we employed a thermally activated delayed fluorescence (TADF) material with bipolar transport characteristics as the interlayer to modulate the exciton distribution, and fabricated efficient and ultrathin non-doped devices. The optimized monochromatic and white OLED exhibited maximum external quantum efficiencies of 18.1% and 15.6%, current efficiencies of 55.7 cd/A and 46.6 cd/A, as well as power efficiencies of 43.8 lm/W and 41.8 lm/W, respectively. More importantly, the devices adopted an ultrathin non-doped emissive layer architecture, and its thickness was only 3.6 nm, which was beneficial to reduce costs and simplify preparation process. Our results illustrated a new strategy that the bipolar TADF interlayer can suppress triplet-triplet annihilation (TTA) effect and improve the exciton utilization, which presents unprecedented opportunities for fabricating highly efficient, low cost and commercial WOLEDs.

Sorption thermal-energy storage plays a critical role in addressing the mismatch between thermal-energy consumption and supply. However, the previous evaluations of sorption thermal-energy storage materials and cycles were mainly based on the equilibrium results of energy storage density. In this study, we develop evaluation models to provide an optimal working pair selection reference for single-stage sorption/resorption cycles under short- and long-term storage modes, and compare the thermal-energy storage density in the discharging stage, the effective discharging time, the temperature gradient, the exergy output during the discharge phase (ΔEdis), and the exergetic coefficient of performance (ECOP). By considering ΔEdis as a criterion, the best halides are determined to be NH4Cl and CaCl2 for single-stage sorption cycles at heat-source temperatures of 60–80 °C and 90–180 °C, respectively; however multi-halide can be a better choice when the temperature varies over optimal temperature range of single-halide, i.e., from 80 °C to 160 °C. Resorption is also analysed in this study. The results show that multi-halide is not suitable for resorption cycles because a part of the components will fail to sorb during the discharging stage. The effective reaction-temperature ranges of the resorption cycles are wider than those of the corresponding sorption cycles, whereas the performance values decrease mainly because of the larger required sorbent mass.

Spray tip penetration is one of the important characteristics for optimizing an engine combustion system. The conventional penetration models proposed so far have not considered cyclic variations of spray. The spray cyclic variation, however, is an inherent feature of a spray injected into turbulent ambient gas at a high speed. In this work, in order to study the effects of cyclic variations in spray structure on spray tip penetration, the liquid phase distributions of diesel sprays were measured 36 times (cycles) for each condition of injection pressure and ambient density at a constant volume chamber with wide optical windows. The experimental results were analyzed through such statistical methods as Probability Presence Image (PPI) and Intersection over Union (IoU). It was found that the spray cyclic variation gradually increased with time after start of injection and became obviously large at the late stage. This cyclic variation in spray structure might cause variation up to ± 9% in spray tip penetration. A spray tip penetration model was developed by introducing a factor to consider the effect of spray cyclic variation. The factor of cyclic variation (f) and the presence probability (PP) could be correlated through experiments and expressed by a cubic polynomial function.

A three-color imaging technique was proposed for simultaneous measurements on distributions of fuel/air mixture temperature and fuel vapor/liquid concentrations in evaporating sprays. The idea is based on that the vapor concentration is proportional to the absorption of vapor to UV light, the liquid-phase concentration is related to the light extinction due to scattering of droplet to visible light, and the mixture temperature can be correlated to the absorbance ratio at two absorbing wavelengths or narrow bands. For verifying the imaging system, the molar absorption coefficients of p-xylene at the three narrow bands, which were centered respectively at 265, 289, and 532 nm with FWHM of 10 nm, were measured in a specially designed calibration chamber at different temperatures (423–606 K) and pressure of 3.6 bar. It was found that the ratio of the molar absorption coefficients of p-xylene at the two narrow bands centered at the two UV wavelengths is sensitive to the mixture temperature. On the other hand, the distributions of fuel vapor/liquid concentrations can be obtained by use of absorbance due to ultraviolet absorption of vapor and visible light scattering of droplets. Combining these two methods, a simultaneous measurement on distributions of mixture temperature and fuel vapor/liquid concentrations can be realized. In addition, the temperature field obtained from the ratio of the two absorbing narrow bands can be further used to improve the measurement accuracy of vapor/liquid concentrations, because the absorption coefficients depend on temperature. This diagnostic was applied to an evaporating spray inside a high-temperature and high-pressure constant volume chamber.

This investigation is to evaluate and quantify the influence of bubble formation inside the nozzle on breakup characteristics of a superheated liquid jet outside the nozzle. The effect of fuel properties was examined using methanol, ethanol and butanol. A unique optically-transparent slit nozzle with a high-speed micro-imaging system were utilized for quantifying the bubble formation inside and the liquid jet breakup outside the nozzle. Correlation between bubble number density and breakup of superheated liquid jet was obtained for all the fuel. The bubble is demonstrated as the main driving forces enhancing the breakup of superheated liquid jet. By introducing a parameter K , it is easier to correlate the superheated liquid jet breakup to the bubble number density as Δ f = K ⋅ n . K is related with the superheat degree, Reynolds number, Weber number, and the ratio of liquid to ambient gas viscosities, which has different form at the transition stage (0.2 P a / P s ⩽ 0.3) and the flare flashing stage ( P a / P s ⩽ 0.2), implying different breakup regimes.

Flash-boiling atomization is an effective way to enhance fuel jet breakup and evaporation and to improve the quality of fuel spray in an SIDI engine especially at the cold start condition, compared to the conventional high pressure injection. However, what happened inside the nozzle and how it affects the breakup and atomization characteristics of a superheated liquid jet (spray) is still unknown. In this study, a two-dimensional transparent nozzle was developed for quantitatively observing the bubble formation inside the nozzle and liquid jet breakup near the nozzle exit by high-speed microscopic imaging. It was found that the liquid jet breakup characteristics is strongly affected by the number density and size distribution of bubbles inside nozzle. The superheat degree has predominant effect on both characteristics of the jet breakup and the bubble formation. Superheat degree of 30 °C is a critical point at which the bubble formation rate and the atomization characteristics of the superheated jet changes significantly. These results provide insightful information for understanding the breakup mechanism of a superheated liquid jet and modeling a flash boiling spray.

This paper explores the characteristics of absorption and fluorescence spectra of p-xylene within the temperature range that is frequently encountered during the mixture formation in internal combustion engines. At 266 nm wavelength, the p-xylene absorption cross section shows a mean value of (3.4 ± 0.2) × 10−19 cm2/molecule within the temperature range from 423 to 623 K in N2. As expected, fluorescence peak intensity decreases by a factor of 3 when the temperature increases by 100 K, due to a increasing non-radiative decay rate of excited state at increasing temperatures. In addition, the suitability of p-xylene for temperature measurements in the gas phase via the single-wavelength excitation (at 266 nm) two-color detection laser-induced fluorescence imaging is explored. Combinations of spectral detection bands were compared and the combination of 320/289 nm provides the best temperature performance with a relative error of 2.6% within the investigated temperature range. It is also shown that the temperature field measurement has not been strongly affected by the laser attenuation.

Based on dynamic thermal rating technologies and taking into account of voltage drop and steady-statestability limitation, the model and algorithm of online valuing loadability of transmission line under operation are established. Considering the generator units voltage regulation characteristics, the variable parameter dual-port Norton equivalent model based on expanded power ∞ow is derived, and the online tracking of the equivalent parameters of the system is implemented. Based on the historical samples, time series method is used to analyze the variation law of the equivalent parameters to make the maximum loadability of transmission line under operation closer to the actual situation. Studies have shown that the dual-port Norton equivalence can very well re∞ect the efiect of parallel ∞ow on the transmission line loadability in interconnected systems, and the changes in the equivalent parameters re∞ect the nonlinearity and time-varying properties of power systems, and by the equivalent parameters variation, the time-varying nature of the electromagnetic power is re∞ected. The feasibility and efiectiveness of the equivalent model and the algorithm are conflrmed by the analysis of the loadability of Weihai 220 kV transmission line under operation.

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 macroscopic spray characteristics were quantified using dimensionless analysis by examining the role of the dominating forces associated with liquid-jet breakup. The Weber number, Reynolds number, and air-to-liquid density ratio dimensionless numbers were used to capture the primary forces including the inertia, viscous, surface tension, and aerodynamic drag forces. Planar Mie-scattering technique was applied to generate spray images over a broad range of conditions found in today’s spark-ignition-direct-injection (SIDI) engines, providing a relatively large range of dimensionless numbers. The effect of fuel properties were examined using gasoline, methanol and ethanol fluids. Six regions described on a Weber number versus Reynolds number domain were selected to identify the relative importance of the inertia force, surface tension force, and viscous force on macroscopic spray structure. The effect of aerodynamic drag was individually determined by characterizing the spray over a range of ambient air-to-liquid density ratios. As a result, for the non-flash-boiling multi-hole sprays in this study, the Weber number and air-to-liquid density ratio have much more profound effect on the spray penetration and spray–plume angle compared to the Reynolds number contribution. The inertia force and air drag force are more important factors compared to the viscous force and surface tension force. This analysis yielded dimensionless correlations for spray penetration and spray–plume angle that provided important insight into the spray breakup and atomization processes.

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.