Incorporating unconventional fuel sources into the global energy mix is necessary to meet increasing energy demand. One attractive option is the gasification of residual fuels, such as heavy fuels, which produce clean combustible gases. Pyrolysis is the first step in the gasification process, so its understanding can help in the development of the gasification process. The information on the pyrolysis products can serve the development of chemical kinetics mechanisms for gasification of heavy fuels for their efficient utilization. In this study, pyrolysis of heavy fuel oil (HFO) and vacuum residue oil (VRO) is reported. Prior to the pyrolysis experiments, these fuels were characterized for proximate analysis, elemental and trace metal composition. The pyrolysis experiments were conducted in a wide temperature range of 400–1000 °C in a customized tubular furnace-based reactor. A two-stage condensation system was used to collect the condensable fraction evolved from the pyrolysis of HFO and VRO and non-condensable gases were collected in Tedlar® bags. Both liquid and gaseous products were characterized using a gas chromatography (GC)-mass spectrometry (MS)-flame ionization detector (FID) and Fourier transform–ion cyclotron resonance–mass spectrometer (FT-ICR-MS) to understand the presence of different types of compounds. The identified compounds were classified as benzene derivatives, naphthalene derivatives, polycyclic aromatic hydrocarbons, saturated and unsaturated hydrocarbons and sulfur-containing compounds. In order to better understand the liquid fraction, the heavy fraction (with high molecular weight) which could not be analyzed and identified in GC/MS-FID was analyzed in FT-ICR-MS. This shed significant insights on the deconstruction of HFO and VRO. Twenty lighter hydrocarbons ranging from C1-C5 were identified and quantified in the pyrolysis vapors of both fuels.

An on-chip photoacoustic transducer is proposed by monolithically integrating piezoelectric micromachined ultrasonic transducers (PMUTs) on metasurface lenses for applications such as single-cell metabolic photoacoustic microscopy (SCM-PAM)1 . As shown in Figure 1a, every PMUT cell has a ring-shaped top electrode, and the membrane center is transparent without piezoelectric and electrode materials. The laser beam, therefore, can travel through a PMUT cell after being focused by a metasurface lens bonded on the backside of the PMUT (see Figure.3). The on-chip photoacoustic transducer fully leverages current PMUT and metasurface technologies and does not rely on transparent piezoelectric and electrode materials like typical transparent ultrasonic transducers2 . Moreover, the on-chip photoacoustic transducer has a monolithic integrated achromatic metasurface lens (see Figure 3), which can easily and efficiently focus the visible light (wavelength range: 400-700 nm) at the same focus point. Design and process this and preliminarily test the performance of PMUT and metasurface.

Fast microjets can emerge out of liquid pools from the rebounding of drop-impact craters, or when a bubble bursts at its surface. The fastest jets are the narrowest and are a source of aerosols both from the ocean and from a glass of champagne, of importance to climate and the olfactory senses. The most singular jets, which we observe experimentally at a maximum velocity of 137±4 m s−1 and a diameter of 12 μm, under reduced ambient pressure, are produced when a small dimple forms at the crater bottom and rebounds without pinching off a small bubble. The radial collapse and rebounding of this dimple is purely inertial, but highly sensitive to initial conditions. High-resolution numerical simulations reveal a new focusing mechanism, which drives the fastest jet within a converging conical channel, where an entrained air sheet provides effective slip at the outer boundary of the conically converging flow into the jet. This configuration bypasses any viscous cutoff of the jetting speed and explains the extreme sensitivity to initial conditions observed in detailed experiments of the phenomenon.

We employ the ECHAM5/MESSy2 atmospheric chemistry general circulation model (EMAC)that incorporates calculations of gas-phase and heterogeneous chemistry coupled with the ozone cycle and aerosol formation, transport, and microphysics to calculate the 1991 Pinatubo volcanic cloud. We considered simultaneous injections of SO2, volcanic ash, and water vapor. We conducted multiple ensemble simulations with different injection configurations to test the evolution of SO2, SO4, ash masses, stratospheric aerosol optical depth, surface area density (SAD), and 24the stratospheric temperature response against available observations. We found that the volcanic cloud evolution is sensitive to the altitude where volcanic debris is initially injected and the initial concentrations of the eruption products that affect radiative heating and lofting of the volcanic cloud. The numerical experiments with the injection of 12 Mt SO2, 75 Mt of volcanic ash, and 150 Mt of water vapor at 20 km show the best agreement with the observation of aerosol optical depth and stratospheric temperature response. Volcanic water injected by eruptive jets and/or intruding through the tropopause accelerates SO2 oxidation. But the mass of volcanic water retained in the stratosphere is controlled by the stratospheric temperature at the injection level. For example, volcanic materials are released in the cold point above the tropical tropopause, and most of the injected water freezes and sediments as ice crystals. The water vapor directly injected into the volcanic cloud increases the SO2− mass and stratospheric aerosol optical depth by about 5%. The coarse 4ash comprises 98% of the ash injected mass. It sediments within a few days, but aged submicron ash could stay in the stratosphere for a few months providing SAD for heterogeneous chemistry. The presence of ash accelerates SO2 oxidation by 10%–20% due to heterogeneous chemistry, radiative heating, lofting, and faster dispersion of volcanic debris. Ash aging affects its lifetime and optical properties, almost doubling the radiative ash heating. The 2.5-year simulations show that the stratospheric temperature anomalies forced by radiative heating of volcanic debris in our experiments with the 20 km injection height agree well with observations and reanalysis data. This indicates that the model captures the long-term evolution and climate effect of the Pinatubo volcanic cloud. The volcanic cloud’s initial lofting, facilitated by ash particles’ radiative heating, controls the oxidation rate of SO2. Ash accelerates the formation of the sulfate layer in the first 2 months after the eruption. We also found that the interactive calculations of OH and heterogeneous chemistry increase the volcanic cloud sensitivity to water vapor and ash injections. All those factors must be accounted for in modeling the impact of large-scale volcanic injections on climate and stratospheric chemistry.

Syngas produced from coal and biomass gasification has been proposed as a potential fuel for direct-fired supercritical power cycles. For instance, the Allam-Fetvedt cycle can offer price-competitive electricity production with 100 % inherent carbon capture while utilizing CO2 dilution of about 96 %. In this work, ignition delay times (IDTs) of syngas have been measured in CO2 diluted conditions using a high-pressure shock tube at two pressures (20 and 40 bar) over a temperature range of 1100 – 1300 K. Syngas mixtures in this study were varied in equivalence ratio and H2:CO ratios. The datasets were compared against the predictions of AramcoMech 2.0 and the University of Sheffield supercritical CO2 2.0 (UoS sCO2 2.0) kinetic models. Quantitative comparative analysis showed that the UoS sCO2 2.0 was superior in its ability to predict the experimental IDTs of syngas combustion. We found that the reaction of CO2 and H to form CO and OH caused the separation of H2 and CO ignition in two events, which increased the complexity of determining the IDTs. We investigated this phenomenon and proposed a method to determine simulated IDTs for an effective comparison against the experimental IDTs. The chemical kinetics of syngas combustion in a CO2 and N2 bath gas are contrasted by sensitivity and rate-of-production analyses. By altering the ratio of H2 and CO as well as mixture equivalence ratio, this work provides vital IDT data in CO2 bath gas for further development and validation of relevant kinetics mechanisms.

A flamelet/progress variable (FPV) model accounting for the differential diffusion (DD) effects is proposed and applied to large eddy simulation (LES) of turbulent oxy-fuel flames (Sevault et al. 2012). Based on tabulations with the detailed molecular diffusion and the equal diffusion (ED) assumption, a species-weighted flamelet (SWF) model is developed to represent the DD effects. The influences of combustion progress, mixture fraction, and turbulence on variable Lewis numbers are incorporated into the model. The model assessments are first conducted on a laminar coflow flame, showing that the effect of DD on temperature and species is accurately captured, in that the importance of DD is seen in the laminar flame. Subsequently the model is implemented in a fully coupled LES of oxy-fuel jet flames. The LES results show that DD plays an important role in the reaction zone and regions near the fuel nozzle, and its effect decreases farther downstream, consistent with the experimental observations. The LES with the SWF model yields good predictions on the mean temperature and major species at the fuel-rich side while slight deviation (less than 6%) at the fuel-lean side. In comparison, LES with the original unity Lewis numbers flamelet model (Pierce et al. 2004) predicts a full extinction because of neglecting the DD characteristics, while the variable Lewis number flamelet model provides the maximum deviation of 26% because of ignoring the ED characteristics produced by turbulent disturbance. The trend and location of localized extinction of oxy-fuel flame are also well predicted using the SWF model.

A water droplet can bounce off superhydrophobic surfaces multiple times before coming to a stop. The energy loss for such droplet rebounds can be quantified by the ratio of the rebound speed UR and the initial impact speed UI; i.e., its restitution coefficient e = UR/UI. Despite much work in this area, a mechanistic explanation for the energy loss for rebounding droplets is still lacking. Here, we measured e for submillimeter- and millimeter-sized droplets impacting two different superhydrophobic surfaces over a wide range of UI (4–700 cm s–1). We proposed simple scaling laws to explain the observed nonmonotonic dependence of e on UI. In the limit of low UI, energy loss is dominated by contact-line pinning and e is sensitive to the surface wetting properties, in particular to contact angle hysteresis Δ cos θ of the surface. In contrast, e is dominated by inertial-capillary effects and does not depend on Δ cos θ in the limit of high UI.

Utilization of bottom-of-the-barrel petroleum products like heavy fuel oils (HFO) derived from vacuum residue oils (VRO) is essential for the sustainable use of crude oil. The high sulfur content and asphaltenes with metallic impurities of these products, such as vanadium and nickel, lead to the production of criteria pollutants and inorganic ash upon combustion, which has limited their widespread use in many industries and jurisdictions. Industrially mature thermo-chemical conversion technologies (e.g., cracking, pyrolysis, partial oxidation (POx), and gasification) have been utilized to upgrade and convert oil residues like HFO into cleaner fuels such as syngas and hydrogen. Among these processes, commercial POx and gasification typically proceed via catalyst free-operations. However, the novel variants of gasification processes that can improve the utilization of heavy oil residues can be benefited from using catalysts. That is because not only can catalysts facilitate the reactions within a smaller reactor, but also they can provide better control over the product composition. Nevertheless, the typical characteristics of high carbon, impurities, and sulfur content lead to the deactivation of the solid-state catalysts mainly due to the coking and poisoning. The use of molten salts, metal/metal oxide as catalysts or oxygen carriers, and hydrogen peroxide as a gasifying agent in the gasification of heavy hydrocarbons are identified to offer significant potential to overcome these challenges, albeit introducing alternative difficulties. This paper surveys and briefly discusses the state-of-the-art thermo- and catalytic chemical conversion technologies for petroleum residue derived fuels, focusing on the use of molten catalysts, oxygen carriers, and hydrogen peroxide as oxidizing agents. The paper also briefly reviews methane pyrolysis, dry reforming with molten metal catalysts, and liquid chemical looping gasification to find similarities and know-how that can be used for gasifying heavy oil residues with the molten metal/metal oxides being used as either catalyst or reaction medium.

Hypersonic flows are of great interest in a wide range of aerospace applications and are a critical component of many technological advances. Accurate simulations of these flows in thermodynamic (non)equilibrium (accounting for high temperature effects) rely on detailed thermochemical gas models. While accurately capturing the underlying aerothermochemistry, these models dramatically increase the cost of such calculations. In this paper, we present a model-agnostic machine-learning technique to extract a reduced thermochemical model of a gas mixture from a library. A first simulation gathers all relevant thermodynamic states and the corresponding gas properties via a given model. The states are embedded in a low-dimensional space and clustered to identify regions with different levels of thermochemical (non)equilibrium. Then, a surrogate surface from the reduced cluster space to the output space is generated using radial-basis-function networks. The method is validated and benchmarked on simulations of a hypersonic flat-plate boundary layer and shock-wave boundary layer interaction with finite-rate chemistry. The gas properties of the reactive air mixture are initially modeled using the open-source Mutation++ library. Substituting Mutation++ with the lightweight, machine-learned alternative improves the performance of the solver by up to 70% while maintaining overall accuracy in both cases.

Pre-chamber combustion (PCC) has the potential to extend the lean-burn limit in spark-ignition engines, which can promote engine efficiency and relieve the concern of emissions of nitrogen oxides. This work assessed the effects of pre-chamber (PC) and piston geometries on the combustion characteristics of an optical methane PCC engine with both experimental and computational approaches. Five active-type PCs with different volumes and nozzle diameters (12 nozzles distributed evenly in two layers) and two pistons (bowl and flat) were tested under lean-burn conditions. Multi-cycle pressure and heat release profiles, natural flame luminosity images, and OH* chemiluminescence images were measured and employed for CFD modeling validations. The PCs with the smaller nozzle diameter yielded more intensely-reacting jets from the upper layer of nozzles compared to the other PCs, attributed to the stronger gas choke there, which dramatically affected the flow fields. A larger PC volume allowed more air–fuel mixture to be trapped within the PC whose combustion then resulted in faster pressure buildup, which, however, led to higher heat transfer loss. Compared to the bowl piston, the flat piston generated a higher heat release rate during the late combustion period owing to the relatively longer jet propagation within the squish region.