Halide perovskite colloidal nanocrystals (NCs) have enabled considerable progress in light conversion applications. However, the presence of unavoidable defect states and phase transition effects can accelerate undesirable rapid charge recombination of the photogenerated charge carriers. To address this issue, chromophores with an anchoring moiety are often used to modify the surface of the NCs, promoting prolonged charge separation through electron or energy transfer processes for optoelectronic applications. Here, steady-state and time-resolved spectroscopy methods are combined with density functional theory (DFT) calculations to explore and decipher the excited-state interaction in colloidal CsPbX3 (X = Br, I) NCs with a rhodamine 6G (Rh6G) hybrid assembly. The results show that Rh6G dimerizes even at low concentrations, as evidenced by DFT calculations. The binding of Rh6G on the NC surface is confirmed by FTIR and NMR spectroscopy techniques. In addition, transient absorption spectroscopy reveals directional sub-ps electron transfer from Rh6G to CsPbI3 NCs, whereas energy transfer occurs from CsPbBr3 to Rh6G, which ultimately recombines in the µs time regime. The findings highlight the simplest and most practical approaches for studying and tailoring the excited-state interaction in colloidal perovskite NCs and chromophore assembly.

Controlling the wetting and spreading of microdroplets is key to technologies such as microfluidics, ink-jet printing, and surface coating. Contact angle goniometry is commonly used to characterize surface wetting by droplets, but the technique is ill-suited for sub-millimetric droplets. Here, we attach a micrometric-sized droplet to an Atomic Force Microscope (AFM) cantilever to directly quantify contact-line friction on different surfaces (superhydrophobic and underwater superoleophobic) with sub-nanonewton force resolutions. We demonstrate the versatility of our approach by performing friction measurements using different liquids (water and oil droplets) and under different ambient environments (in air and under water). Finally, we show that underwater superoleophobic surfaces can be qualitatively different from superhydrophobic surfaces: contact-line friction is highly sensitive to contact-line speeds for the former but not for the latter surface.

Dielectric barrier discharges (DBDs) bring a long history of application and leave many interesting scientific questions. A positive streamer concept describes a temporal development of a microdischarge well, and memory charge effect explains spatially distributed microdischarges over the entire area of DBD. To properly model plasma chemistry occurring in a DBD, knowledge of microdischarges, distributed spatially and temporally, is essential. Here we present experimental result of multiple microdischarges, occurring successively and rooted at the same location. By employing a triangular waveform to a pointed electrode and a high conductivity layer at a surface of a dielectric barrier, a physical mechanism of the successive microdischarges was revealed: a slew rate of an external alternating current compensated a voltage drop caused by memory charges from a former microdischarge. A time interval between two neighboring microdischarges was inversely proportional to the slew rate, and the number of microdischarges depended primarily on an applied voltage. The number of microdischarges with an uncoated barrier was higher than that with an Ag-coated barrier; however, the charges delivered by each microdischarge were smaller in cases with an uncoated barrier. To investigate interactions between spatially separated microdischarges, this study will be extended to a configuration having multiple pointed electrodes. The effect of the successive microdischarges on plasma chemistry will also be a future study.

The prediction of the stabilization regime of partially premixed H2/air flames above an injector is a main subject of interest for the development of gas turbines powered by hydrogen. The way the flame is stabilized has an impact on NOx emissions, thermal stress on the injector, and combustion stability. A model based on the triple flame speed is revisited and improved to predict flame stabilization using information gathered at cold flow conditions. The model is called TFUP for Triple Flame Upstream Propagation. According to this model, the flame can anchor to the injector only if a zone with a flammable mixture and a sufficiently low local flow velocity exists continuously from the lifted flame to the injector lips. The TFUP model is applied to the case of a H2/air coaxial, dual swirl injector in which both the hydrogen and air streams are swirled. Fuel is injected through the central channel and oxidizer through the external channel. Particle image velocimetry and one dimensional Raman scattering measurements made at strategic locations are used to predict the edge flame speed for which a lifted flame should re-anchor to the injector. These predictions made in isothermal conditions are compared to observations of the flame stabilization regime. The central flow of hydrogen can be mixed with methane and helium and the external flow of air with nitrogen in order to prescribe different theoretical values for the triple flame speed. Predictions agree well with the observations made for all swirl levels conferred to the central fuel stream, fuel injection velocities, hydrogen contents in the fuel mixture injected in the central channel, and nitrogen contents in the oxidizer annular channel tested in the study. Validity limits are also discussed. The methodology presented in this study provides a simple framework to predict flame stabilization on coaxial injectors that can optionally be equipped with swirl vanes.

Hydrogen exhibits special burning characteristics such as fast laminar and, thereby, turbulent flame speed, and a wide flammability limit. Because of these features, the existing numerical models that have been developed for e.g., natural gas or fuels with unity Lewis number assumption could be limited or even unusable. This chapter discusses the models for turbulent flame speed and local displacement speed of pure lean hydrogen premixed flames, particularly for a wide range of turbulence levels. Moreover, the predictive capability of the probability density function (PDF) modeling adopting the widely used laminar flamelet concept for Reynolds averaged Navier–Stokes (RANS) or large-eddy simulation (LES) approaches is assessed a priori using a set of state-of-the-art direct numerical simulation (DNS) data. The general conclusion suggests that the main turbulent parameter dictating the turbulent flame speed is found to be the size of the most energy-containing eddies rather than non-dimensional numbers such as Reynolds (Re) or Karlovitz (Ka) numbers. The local displacement speed models also suggest that a model developed for moderate turbulence level (Ka ≈O(10)) predicts well flames with Ka >O(1,000). PDF modeling using the flamelet concept is evaluated up to Ka >O(100), for which the mass fractions of major species are reasonably well predicted.

This paper shows that nanosecond repetitively pulsed discharges were able to mitigate the response of lean methane-air swirl flames to acoustic excitations, at pressures up to 3 bar. Flame transfer functions with and without plasma discharges were investigated at pressures of 1.2, 2.0, and 3.0 bar, in a frequency range 48–380 Hz. Results show that the plasma discharges decreased by up to 50% the gain of the flame transfer functions, regardless of the pressure. Mechanisms responsible for this effect are discussed.

A typical step in the electroplating of metals to polymer substrates is the preparation of a substrate surface through sulfochromic acid etching, which is well known for modifying the chemistry and morphology of the treated surfaces. While this process has existed for decades, the relative contributions of chemical interactions and mechanical interlocking towards the final adhesion are not well understood. As sulfochromic acid is toxic and hazardous to the environment and human health, understanding how this acid etching promotes adhesion, and especially what are the real contributions of chemistry and mechanics respectively, becomes critical to be able to replace this treatment with greener techniques. However, such knowledge is still ambiguous, since decoupling the chemical and morphological contributions is challenging because both effects occurred simultaneously during etching. In this study, we proposed various sample preparation strategies to address these issues. First, we minimized the etching duration to achieve similar chemistry as that after the standard etching while avoiding strong modifications in surface morphology. Second, we passivated the etched samples to ensure that most of the adhesion properties of prepared samples are from morphological effects. Results indicated that chemical contribution was critical to ensure good wetting during the electroless plating, while mechanical interlocking was the major contributor (90%) for the ultimate adhesion of electroplated copper to acrylonitrile-butadiene-styrene interfaces.

Chemical kinetic experiments involving the oxidation or pyrolysis of fuels can be complex, especially when multiple species are formed and consumed simultaneously. Therefore, a diagnostic strategy that enables fast and selective detection of multiple species is highly desirable. In this work, we present a mid-infrared laser diagnostic that can simultaneously detect multiple species in high-temperature shock-tube experiments using a single laser. By tuning the wavelength of the laser over 3038 – 3039.6 cm−1 wavelength range and employing a denoising model based on deep neural networks (DNN), we were able to differentiate the absorbance spectra of ethane, ethylene, methane, propane, and propylene. The denoising model is able to clean noisy absorbance spectra, and the denoised spectra are then split these into contributions from evolving species using multidimensional linear regression (MLR). To the best of our knowledge, this work represents the first successful implementation of time-resolved multispecies detection using a single narrow wavelength-tuning laser. To validate our methodology, we conducted pyrolysis experiments of ethane and propane. The results of our experiments showed excellent agreement with previous experimental data and chemical kinetic model simulations. Overall, our diagnostic strategy represents a promising approach for detecting multiple species in high-temperature transient environments.

The study examined the effects of second injection timings and fuel injection pressures (FIPs) in a double-injection based partially premixed combustion (PPC) using a single-cylinder heavy-duty optical diesel engine equipped with two different configurations, namely all-metal and optical. The thermodynamic analysis of energy balance, exhaust emissions, and particulates characterization was conducted in an all-metal engine configuration. For the same base engine architecture, high-speed natural combustion luminosity, cool-flame, and electronically excited hydroxyl (OH*) chemiluminescence, and planar laser-induced fluorescence (PLIF) imaging of formaldehyde (HCHO-PLIF) were applied in the optical configuration. Additionally, 1D modeling using GT-Power was utilized to examine the distribution of heat transfer losses through the individual cylinder boundaries. The experiments were conducted at low-load conditions at a fixed fuel mean effective pressure (MEPfuel) using a primary reference fuel with a volumetric mixture of 50% n-heptane and 50% iso-octane (PRF50). The results demonstrated that for a fixed first injection, the second injection timing of −6°CA aTDC is the most favorable condition due to increased gross indicated efficiency, reduced exhaust losses, decreased uHC/CO/soot emissions with a slight compromise on heat losses and NOx emissions. Among the tested FIPs of 1200, 1500, and 1800 bar, 1500 bar showed higher efficiency, and overall lower energy losses and exhaust emissions. At higher FIPs, the overall flame development process revealed reduced luminous intensity with dispersed signals formed downstream of the nozzle due to increased premixed combustion. For 1800 bar FIP, both cool-flame and HCHO signals showed an increased rate of reaction zones close to the bowl-wall region from where the OH radicals developed. Not only the initial low- to high-temperature reaction transition was faster for 1800 bar FIP but the signal decay of HCHO signals by OH radicals was also rapid in the late cycle. These findings explained the root cause of increased heat transfer losses and higher uHC/CO emissions at 1800 bar FIP.

Mid-infrared laser polarization spectroscopy (IRPS) has been applied to measure the mole fraction of acetylene in rich premixed laminar C2H4/Air flat flames at equivalence ratios (Φ) of 1.7, 2.1, and 2.3, and under atmospheric pressure. The detection was conducted by probing the ro-vibrational P(19) transition at ~ 3.1 μm. The total collisional broadening coefficient of C2H2 was approximately 0.074 cm−1 atm−1 and varied within a range of 0.5% under different flame conditions, which made the effect of linewidth not obvious in the CH4/air flame. The calculated mole fraction of C2H2, using the Chemkin model, at Φ = 1.3 and 1.5 was used to calibrate the recorded IRPS signal intensities at different Height Above Burner (HAB). A single scaling factor was then used to quantify the measured C2H2 at highly sooting conditions, Φ = 1.7, 2.1, and 2.3, with a Limit of Detection (LoD) of 35 ± 5 ppm. The first observed C2H2 mole fraction appeared at HAB of 3 mm and measured as 2003 ppm, 2217 ppm, and 2495 ppm, for Φ = 1.7, 2.1, and 2.3, respectively. The mole fraction increased as the HAB increased to reach the maximum value of 2296 ppm, 2807 ppm, and 3478 ppm, for Φ = 1.7, 2.1, and 2.3, respectively, up to HAB of 5 mm. It was observed that the C2H2 mole fraction reaches a plateau region at HAB of ~ 8 mm. The production of C2H2 has been observed to be subject to a critical gas temperature of 1400 ± 30 K. The critical soot inception temperature, where the first incepted soot particles are observed, is the same as the gas temperature where χmaxC2H2 was detected, namely at 1500 ± 30 K. These measurements and calibration procedure demonstrate a plausible technique to probe other flames and to better understand soot inception and its correlation with C2H2.