Nucleation Mode Research Articles

Pre‐Activation of Ice Nucleating Particles in Deposition Nucleation Mode: Evidence From Measurement Using a Static Vacuum Water Vapor Diffusion Chamber in Xinjiang, China

AbstractPre‐activation of ice nucleating particles (INPs) is a potential mechanism to enhance ice generation in mixed‐phase clouds, but evidence of INP pre‐activation is still limited. In this study, the pre‐activation of INPs in deposition mode is investigated using refreezing experiments in a static vacuum water vapor diffusion chamber with aerosols sampled in Xinjiang, China. The results indicate that the activation efficiency of INP was enhanced after pre‐activation. Statistically, the INP concentration increased by 266%, 112%, and 70% at −10°C, −14°C, and −17°C after pre‐activation, and more than half of the samples showed an increase in INP concentration. The increase in INP concentration has a positive correlation with the primary INP concentration before pre‐activation. The analyses provide new evidence that the pre‐activated INPs can act as better nuclei at temperature as warm as −10°C, and highlight the importance to find a way to consider this mechanism in models.

The optimization of bimetallic electrodes’ sensitivity using copper nucleation on metallic substrates to detect nitrates in seawater

• The investigation of the electrocrystallization of copper on gold, platinum and stainless steel 316L electrodes in aqueous media by cyclic voltammetry and chronoamperometry showed progressive nucleation. • The optimum theoretical cutoff charge to form sensitive bimetallic electrodes were verified experimentally by square wave voltammetry. • The modified electrodes were tested for their ability to detect low level of nitrates in seawater. The aim of this work is to highlight the beneficial impact of the nucleation mode study on controlling the electrodeposition of a metal on a substrate, in order to form high sensitivity bimetallic electrodes. Actually, optimizing the electrodeposition operating conditions allows generating the largest active surface, and so, increasing electrode sensitivity. For this purpose, the nucleation phenomena and the initial growth of copper nuclei on gold, platinum and stainless steel 316L electrodes were investigated using cyclic voltammetry (CV) and chronoamperometry in aqueous media. The experimental results were compared to theoretical models for the two possible nucleation modes: instantaneous and progressive. Chronoamperometric results showed that the electrodeposition process involves progressive nucleation for copper on the three substrates, which was confirmed by scanning electron microscopy (SEM). Optimal operating conditions were determined for the preparation of the highest active surface area. Subsequently, copper deposition runs were carried out on the three electrode substrates. The formed bimetallic electrodes were tested for their ability to detect low nitrate concentration in artificial seawater using square wave voltammetry (SWV).

Particle number size distributions and formation and growth rates of different new particle formation types of a megacity in China

To understand the contribution of new particle formation (NPF) events to ambient fine particle pollution, measurements of particle size distributions, trace gases and meteorological conditions, were conducted at a suburban site (NJU) from October to December 2016 and at an industrial site (NUIST) from September to November 2015 in Nanjing. According to the temporal evolution of the particle size distributions, three types NPF events were observed: typical NPF (Type A), moderate NPF events (Type B) and strong NPF (Type C) events. The favorable conditions for Type A events included low relative humidity, low concentration of pre-existing particles, and high solar radiation. The favorable conditions of Type B events were similar to Type A, except for a higher concentration of pre-existing particles. Type C events were more likely to happen with the higher relative humidity, lower solar radiation and continuous growth of pre-existing particle concentration. The formation rate of 3 nm (J3) was the lowest for Type A events and highest for Type C events. In contrast, the growth rates of 10 nm and 40 nm particles were the highest for Type A, and lowest for Type C. Results show that NPF events with only higher J3 would lead to the accumulation of nucleation mode particles. Sulfuric acid was important for the formation of particles but had little effect on the growth of particle size.

Nucleation-accumulation mode trade-off in non-volatile particle emissions from a small non-road small diesel engine.

Small (< 8kW) non-road engines are a significant source of pollutants such as particle number (PN) emissions. Many small non-road engines do not have diesel particulate filters (DPFs). They are so designed that air-fuel ratio (AFR) can be adjusted to control visible diesel smoke and particulate matter (PM) resulting from larger accumulation mode particles. However, the effect of AFR variation on smaller nucleation mode nanoparticle emissions is not well understood. Several studies on larger engines have reported a trade-off between smaller and larger particles. In this study, AFR was independently varied over the entire engine map of a naturally aspirated (NA) non-road small diesel engine using forced induction (FI) of externally compressed air. AFR's ranged from 57 to 239 compared to the design range of 23-92 for the engine, including unusually high AFR's at full-load operation, not previously reported for conventional combustion. As expected, larger accumulation mode particles were lowered (up to 15 times) for FI operation. However, the smaller nucleation mode nanoparticles increased up to 15 times. Accumulation mode particles stopped decreasing above an AFR threshold while nucleation particles continuously increased. In-cylinder combustion analysis showed a slightly smaller ignition delay and higher burn rate for FI cases relative to NA operation. Much higher peak cylinder pressures were accompanied by much lower combustion and exhaust gas temperatures (EGT), due to higher in-cylinder mass during FI operation. Peak nucleation mode emissions were shown to be negatively correlated to EGT for all the data, collapsing on a single curve. This is consistent with some other studies reporting increased nucleation mode emissions (and higher accumulation mode particles) with decreased load, lower speed, lower EGR, advanced combustion phasing, and higher injection pressure, all of which reduce EGT. The nucleation-accumulation trade-off has been explained by the 'adsorption hypothesis' by some investigators. In the current work, an alternative/supplemental argument has been made for the possibility that lower cylinder temperatures during the late-burning phase (correlated to lower EGT) phase hampers oxidation of nucleation mode particles and increases nucleation mode emissions.

Ultralow Sulfur Diesel and Rapeseed Methyl Ester Fuel Impact on Performance, Emitted Regulated, Unregulated, and Nanoparticle Pollutants.

The operation of engines using rapeseed methyl ester (RME) and ultralow sulfur diesel (ULSD) was tested for the combustion properties, emitted regulated, unregulated exhaust pollutants, and the size of nanoparticles. The combustion analysis showed higher apparent heat release rate and shorter ignition delay period during RME combustion than during ULSD combustion. The ULSD engine has a combustion chamber maximum pressure relatively higher than that of RME. This study showed that the heat release rate of ULSD is always higher than that of RME while more fuel consumption occurred from the combustion of biodiesel in comparison with diesel. When the engine is running on RME, HC and NOx formation increased at high loads up to 15% and 13%, respectively; meanwhile, CO concentrations reduced by 30.9% for the same conditions. Most of the particulate matter (PM) emitted from a diesel engine has a particle size from 5 to 100 nm, while the particle size from ULSD ranged from 5 to 40 nm. Overloading the engine caused a decrease in the sizes of emitted PM for both fuels. The smoke number for RME was less than that for ULSD by 33.9% at high loads. For high engine load, the cumulative concentration number for the nucleation mode decreased, while it increased for the accumulation mode. Furthermore, measurements of formaldehyde, ethane, methane, acetylene, ethylene, propylene, and isocyanic acid emissions showed the presence of these harmful substances at very low concentrations (8 ppm) for both fuels.

Long-term trends of ultrafine and fine particle number concentrations in New York State: Apportioning between emissions and dispersion

In the past several decades, a variety of efforts have been made in the United States to improve air quality, and ambient particulate matter (PM) concentrations have been used as a metric to evaluate the efficacy of environmental policies. However, ambient PM concentrations result from a combination of source emission rates and meteorological conditions, which also change over time. Dispersion normalization was recently developed to reduce the influence of atmospheric dispersion and proved an effective approach that enhanced diel/seasonal patterns and thus provides improved source apportionment results for speciated PM mass and particle number concentration (PNC) measurements. In this work, dispersion normalization was incorporated in long-term trend analysis of 11–500 nm PNCs derived from particle number size distributions (PNSDs) measured in Rochester, NY from 2005 to 2019. Before dispersion normalization, a consistent reduction was observed across the measured size range during 2005–2012, while after 2012, the decreasing trends slowed down for accumulation mode PNCs (100–500 nm) and reversed for ultrafine particles (UFPs, 11–100 nm). Through dispersion normalization, we showed that these changes were driven by both emission rates and dispersion. Thus, it is important for future studies to assess the effects of the changing meteorological conditions when evaluating policy effectiveness on controlling PM concentrations. Before and after dispersion normalization, an evident increase in nucleation mode particles was observed during 2015–2019. This increase was possibly enabled by a cleaner atmosphere and will pose new challenges for future source apportionment and accountability studies.

High Sensitivity Bimetallic Electrode Generation through the Study of Copper Electrocrystallisation on Metallic Substrates (Md/Ms) in Acidic Media

The electrochemical nucleation of copper on metallic substrates in acidic media was investigated using cyclic voltammetry and chronoamperometry. The purpose is to optimize the operating conditions for preparing a high sensitivity bimetallic electrode. Indeed, optimizing the electrodeposition parameters whereby two different metals are present: deposited metal Md and substrate metal Ms, allows the generation of a large number of microelectrodes, correspondingly, yield the largest active surface, and so, increasing the electrode sensitivity.The aim of this study is to highlight the positive impact of controlling the electrodeposition process of a metal on a substrate and determining the operation conditions towards the augmentation of the active surface area of an electrode.This work is focused on studying the first instance of copper nuclei formation on the electrode surface and the growth of these nuclei over time. Factors influencing deposit quality and allow to yield the highest specific surface area were considered, principally the overvoltage and the deposit cutoff charge. The nucleation phenomena and the initial growth of the copper nuclei on three different metallic substrates was studied. The plot of the experimental results were compared to theoretical models for the two possible nucleation modes: instantaneous and progressive. The nucleation phenomena was overseen on cyclic voltammetry recorded and the electrodeposition overvoltage were determined for each couple (Md/Ms). Chronoamperometric measurements evidenced that copper electrodeposition process involves progressive nucleation on the substrates, which was confirmed by scanning electron microscopy (SEM). Afterward, the germination rates were determined.The optimum theoretical cutoff charges were calculated from chronoamperograms using Faraday’s law and were experimentally verified.Optimal operating conditions were determined for the preparation of bimetallic electrodes with the largest active surface area. Subsequently, copper deposition runs were carried out on the three electrode substrates. The formed bimetallic electrodes were tested using square wave voltammetry for their ability to detect species requiring high sensitivity identification tools such as nitrates in seawater. In open ocean, the concentration of nitrates can drop from few dozens of micromolars to as littles as few nanomolars.The copper nuclei fount out to be unstable on the substrate in maritime area due to corrosion and attack by dissolved oxygen. A cathodic polarization by applying a direct current was applied to protect the deposited copper.

INP concentration from the lab experiments of pre-activation of INP in deposition nucleation mode

INP concentration from the lab experiments of pre-activation of INP in deposition nucleation mode

Changes in the new particle formation and shrinkage events of the atmospheric ions during the COVID-19 lockdown

Impacts of environmental changes at Pune, India during the lockdown period imposed due to the Covid-19 pandemic, on the characteristics of the atmospheric ions and the new particle formation (i.e. the formation of molecular clusters and their subsequent growth to larger sizes) and shrinkage events have been investigated. The increase in the small and big cluster ion concentrations and the decrease in intermediate ion concentrations observed during the lockdown period have been associated with the decrease in the aerosols and precursor gases, respectively. During the NPF events, the nucleation mode particles of both polarities grow in size. However, during the unique shrinkage events observed here, particles increase in concentration but do not grow in size during the morning-to-noon period and shrink in the noon-to-evening period during the lockdown period. Simultaneously, the concentration of particles of >25 nm decrease i during the morning hours and increase during the afternoon hours .On the shrinkage event days, solar irradiance is higher and relative humidity is lower throughout the day than on the NPF/no-event days. Occurrence of shrinkage events has been proposed to be associated with the change in saturation vapour pressure of different chemical species with temperature/solar irradiance.

Nonthermal melting of charge density wave order via nucleation in VTe2

Ultrafast optical control of phase change materials is of great importance from fundamental and practical points of view. Transition-metal dichalcogenides are of significant interest in this research field because of the photoinduced phase transition originating from the nonthermal melting of their charge density wave (CDW) orders. In this work, we investigated the ultrafast optical response of ${\mathrm{VTe}}_{2}$ by using broadband coherent optical phonon spectroscopy with subpicosecond time resolution. With an increase of laser-excitation fluence, a characteristic oscillation around 4.4 THz appeared in the transient reflectivity change. This suggests photoinduction of the high-temperature phase, i.e., a CDW-melt state, of ${\mathrm{VTe}}_{2}$ within a picosecond. Such an ultrafast transition would be induced by a purely electronic effect, but as with thermodynamic melting, it is strongly suggested that the phase transition dynamics induced spatially by laser irradiation proceeds inhomogeneously via a nucleation mode.

Interstitial concentration effects on incipient plasticity and dislocation behaviors of face-centered cubic FeNiCr multicomponent alloys based on nanoindentation

• The interstitial concentration effects on dislocation behavior and incipient plasticity of a typical equiatomic FeNiCr multicomponent alloy are newly investigated via systematic nano-mechanical experimental study. • The dislocation nucleation of FeNiCr alloy processes in a manner of heterogenous nucleation mode with an activation volume exceeding one single principal atom, by the exchange between primary atoms and vacancies. • Interstitial-atom effects severely suppress the mobility of dislocations in the FeNiCr multicomponent alloys, which hinder the occurrence of pop-ins. • With increasing the concentration of interstitial atoms, both the critical shear stress and activation volume corresponding to the onset of incipient plasticity are enhanced. Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic (FCC) lattice, can significantly affect the dislocation behaviors on deformation. Recently, interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent, often termed high-entropy alloys (HEAs) or medium-entropy alloys (MEAs). However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear. Therefore, in the present work, an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading. The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field, regardless of the interstitial concentration. Moreover, the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration, which definitely suggests the participation of interstitial atoms in the nucleation process. Besides, it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration. Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations. Furthermore, the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion, which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens. The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys, which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.

Stabilities of the precipitates in CLAM steel during 30,000 h thermal aging

China Low Activation Martensitic steel (CLAM steel) was thermally aged for up to 30,000 h at 550 and 600 °C. Scanning electron microscopy and transmission electron microscopy were employed to characterize the evolutions of the Laves phase, the M23C6 phase and the MX phase. The relationships between the particle sizes of the three precipitation phases with time, and the Johnson-Mehl-Avrami (J-M-A) equation for the growth kinetics of the Laves phase during thermal aging at 600 °C were obtained. The results show that the relationship between the particle size of the Laves phase with time is different from those of the M23C6 phase and the MX phase; the Laves phase has the largest coarsening rate and the worst stability; the time exponent of the J-M-A equation of the Laves phase is large (n=2.8). In 9–12%Cr tempered ferritic/martensitic steels, the precipitation of the Laves phase tends to lag behind the M23C6 phase. The Laves phase has two nucleation modes: independent nucleation and dependent nucleation adhering to the M23C6 phase. There is no unified understanding of how the growths of the two phases in the assemblage affect each other after dependent nucleation. In this study, an enwrapping growth mechanism of the Laves phase was observed, which provides a new clue to this question. The dependent nucleation and enwrapping growth mechanism of the Laves phase is the reason for the linear growth of its particle size and the large time exponent.

New particle formation in coastal New Zealand with a focus on open-ocean air masses

Abstract. Even though oceans cover the majority of the Earth, most aerosol measurements are from continental sites. We measured aerosol particle number size distribution at Baring Head, in coastal New Zealand, over a total period of 10 months to study aerosol properties and new particle formation, with a special focus on aerosol formation in open-ocean air masses. Particle concentrations were higher in land-influenced air compared to clean marine air in all size classes, from sub-10 nm to cloud condensation nuclei sizes. When classifying the particle number size distributions with traditional methods designed for continental sites, new particle formation was observed at the station throughout the year with an average event frequency of 23 %. While most of these traditional event days had some land influence, we also observed particle growth starting from nucleation mode in 16 % of the data in clean marine air, and at least part of this growth was connected to nucleation in the marine boundary layer. Sub-10 nm particles accounted for 29 % of the total aerosol number concentration of particles larger than 1 nm in marine air during the spring. This shows that nucleation in marine air is frequent enough to influence the total particle concentration. Particle formation in land-influenced air was more intense and had on average higher growth rates than what was found for marine air. Particle formation and primary emissions increased particle number concentrations as a function of time spent over land during the first 1–2 d. After this, nucleation seems to start getting suppressed by the pre-existing particle population, but accumulation mode particle concentration keeps increasing, likely due to primary particle emissions. Further work showed that traditional NPF events were favoured by sunny conditions with low relative humidity and wind speeds. In marine air, formation of sub-10 nm particles was favoured by low temperatures, relative humidity, and wind speeds and could happen even during the night. Our future work will study the mechanisms responsible for particle formation at Baring Head with a focus on different chemical precursor species. This study sheds light on both new particle formation in open-ocean air masses coming from the Southern Ocean and local aerosol properties in New Zealand.

Micro-spectroscopic and freezing characterization of ice-nucleating particles collected in the marine boundary layer in the eastern North Atlantic

Abstract. Formation of atmospheric ice plays a crucial role in the microphysical evolution of mixed-phase and cirrus clouds and thus climate. How aerosol particles impact ice crystal formation by acting as ice-nucleating particles (INPs) is a subject of intense research activities. To improve understanding of atmospheric INPs, we examined daytime and nighttime particles collected during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign conducted in summer 2017. Collected particles, representative of a remote marine environment, were investigated for their propensity to serve as INPs in the immersion freezing (IMF) and deposition ice nucleation (DIN) modes. The particle population was characterized by chemical imaging techniques such as computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX) and scanning transmission X-ray microscopy with near-edge X-ray absorption fine-structure spectroscopy (STXM/NEXAFS). Four major particle-type classes were identified where internally mixed inorganic–organic particles make up the majority of the analyzed particles. Following ice nucleation experiments, individual INPs were identified and characterized by SEM/EDX. The identified INP types belong to the major particle-type classes consisting of fresh sea salt with organics or processed sea salt containing dust and sulfur with organics. Ice nucleation experiments show IMF events at temperatures as low as 231 K, including the subsaturated regime. DIN events were observed at lower temperatures of 210 to 231 K. IMF and DIN observations were analyzed with regard to activated INP fraction, ice-nucleation active site (INAS) densities, and a water activity-based immersion freezing model (ABIFM) yielding heterogeneous ice nucleation rate coefficients. Observed IMF and DIN events of ice formation and corresponding derived freezing rates demonstrate that the marine boundary layer aerosol particles can serve as INPs under typical mixed-phase and cirrus cloud conditions. The derived IMF and DIN parameterizations allow for implementation in cloud and climate models to evaluate predictive effects of atmospheric ice crystal formation.

Relating Metabolism Suppression and Nucleation Probability During Supercooled Biopreservation.

Aqueous supercooling provides a method by which to preserve biological matter at subfreezing temperatures without the deleterious effects of ice formation. The extended longevity of the preserved biologic is a direct result of a reduction in the rate of metabolism with decreasing temperature. However, because the nucleation of ice from a supercooled solution is a stochastic process, supercooled preservation carries the risk of random ice nucleation. Theoretical supercooled biopreservation research to date has largely treated these biological and thermophysical phenomena separately. Here, we apply a statistical model of stochastic ice nucleation to demonstrate how the possible reduction in metabolic rate is inherently related to supercooling stability (i.e., the likelihood of ice nucleation). We develop a quantitative approach by which to weigh supercooling stability versus potential metabolic reduction, and further show how the stability-metabolism relationship varies with system size for two assumed modes of nucleation. Ultimately, this study presents a generalizable framework for the informed design of supercooled biopreservation protocols that considers both phase transformation kinetics and biochemical or biophysical kinetics.

Characterization of condensation on nanostructured surfaces and associated thermal hydraulics using a thermal lattice Boltzmann method

The dynamics of the condensation process on nanostructured surfaces can be modulated substantially by tuning the surface architecture. Present study uses the mesoscopic framework of lattice Boltzmann method (LBM) to explore the role of surface morphology and cold spot temperature in determining the visual state of the condensate droplet, mode of nucleation, and associated rates of energy and mass interactions. A multiple relaxation time-(MRT)-based LBM solver, coupled with pseudopotential model, has been developed to simulate a rectangular domain of saturated vapor, housing a cold spot on the bottom rough surface. Superhydrophobicity has been achieved for certain combinations of surface parameters, with the intercolumn spacing being the most influential one. Gradual increase in the spacing modifies the nucleation mode from top through side to bottom, while the droplet changes from Cassie to Wenzel state. The Cassie drop in top nucleation mode exhibits the largest contact angle and least rate of surface heat transfer. Both types of Wenzel drops display large rate of condensation and two peaks in heat transfer, along with very short nucleation time in comparison with Cassie drops. Couple of phase diagrams have been developed combining all four scenarios of condensation predicted by the present model. One important novelty of the present study is the consideration of nonisothermal condition within LB structure. Enhancement in the degree of subcooling at the cold spot encourages greater condensation and Cassie-to-Wenzel transition.

Waste cooking oil biodiesel and petroleum diesel soot from diesel bus: A comparison of morphology, nanostructure, functional group composition and oxidation reactivity

Biodiesel is one of carbon neutral fuels for diesel engine and waste cooking oil (WCO) would be the most viable source for biodiesel production in China. This paper studied the micromorphology, nanostructure, surface functional group composition, and oxidation activity characteristics of particles emitted from a China V bus fueled by pure WCO biodiesel and petroleum diesel, respectively. Compared with petroleum diesel, the results showed that particle mass (PM) and particle number (PN) of WCO biodiesel decreased by 38.66% and 38.12%, respectively, while the proportion of nucleation mode particles increased by about 10%. The soot particles of WCO biodiesel have higher disordered nanostructure, smaller primary particle size and fringe length, larger fringe separation distance and tortuosity, and lower graphitization degree than those of petroleum diesel. Moreover, the oxygen-containing surface functional groups content and carbon atom hybrid ratio of soot particles of WCO biodiesel were higher than those of petroleum diesel under the same oxidation temperature. And then the activation energy of soot particles from WCO biodiesel which contained more lattice defect structures was 38.43 kJ/mol, 37.8% lower than petroleum diesel, which is easier to be oxidized.

Characterizing combustion performance and PM emissions of an aviation compression ignition engine by fueling RP-3 kerosene and RP-3/pentanol blends

General aviation (GA) aircraft generally driven by aviation piston engines (APE) are currently experiencing promising growth globally. To relieve the fossil fuel scarce, the application of alternative fuels was extensively encouraged for green GA development. This study aims to investigate the suitability of using aviation kerosene rocket propellant 3 (RP-3) and its pentanol blends (by 30% volume fraction) in an aviation compression ignition (CI) engine, by comparing their combustion performance and emission characteristics differences under various injection timings with baseline diesel. The major combustion parameters including the in-cylinder pressure, heat release rate, ignition delay, combustion duration, indicated thermal efficiency (ITE), and indicated specific fuel consumption (ISFC) were evaluated as the crank angle (CA) 50 swept from 9 to 15° crank angle after top dead center (ATDC). The ITE of RP-3/Pentanol blends presented to be higher than those of diesel by 4.2%−5.0%, and pure RP-3 by 2.6%−3.4%. The improved ITE of the blended fuel is due to the longest ignition delay and the shortest combustion duration under all the CA50. Moreover, the particulate matter (PM) emissions with the number concentration, geometric mean diameter (GMD), size-resolved distribution characteristics were quantitatively analyzed for all the test fuels. RP-3/Pentanol dramatically reduced the number-based PM, by over 50% and two magnitudes of order lower than those of RP-3 and diesel, respectively. Improved PM emissions from the alcohol blends intensively was caused by the better premixing and evaporating states with subsequent homogeneous combustion. Additionally, the PM emissions of the three fuels exhibited different sensitivities to the varied injection timings. With the retardance of injection timings, the PM declined apparently for diesel and RP-3 due to prolonged ignition delay and decreased in-cylinder temperature, but remained nearly unchanged for RP-3/Pentanol because of the growth of nucleation mode PM.

Origins of plastic shock waves in single-crystal Cu

We investigate shock wave propagation in single-crystal Cu with large-scale molecular dynamics simulations. Plastic shock waves propagate via dislocation nucleation or growth. With decreasing particle velocity, a remarkable drop in plastic shock wave velocity relative to the linear shock velocity–particle velocity relation is observed in the elastic–plastic two-wave regime for different loading directions. This reduction can be attributed to the changes in the mechanisms of plastic shock wave generation/propagation, from the dislocation nucleation-dominant mode, to the alternating nucleation and growth mode, and to the growth-dominant mode. For weak shocks, the plastic shock advances at the speed of the growth of existing dislocations (below the maximum elastic shock wave speed), considerably slower than the dislocation nucleation front for strong shocks (above the maximum elastic shock wave speed).

Measurement of Sub-23 nm Particles Emitted from PFI/DI SI Engine Fueled with Oxygenated Fuels: A Comparison between Conventional and Novel Methodologies

This study focuses on the measurement of sub-23 nm particles emitted from a small DI/PFI spark ignition engine through conventional techniques and innovative systems. Measurements were performed with well-known systems, such as the EEPS coupled to a PMP-compliant sample conditioning device. Moreover, a novel instrument developed within the European project Sureal-23, the advanced HM-DMA, capable of operating with a simplified conditioning setup was used. The engine was fueled with ethanol, both pure and in blend at 30% v/v. The effects of fuel on the particle emissions were analyzed at different operating conditions. The results highlighted that a larger fraction of emissions consists of particles smaller than 23 nm, and their number changes according to the fuel, injection strategy and operating condition. A significant effect of the sampling system conditions was observed reveling the inception of nucleation mode particles or the condensation of the volatiles onto existing particles depending on the combination fuel/injection strategy. Different trends were noted at certain operating conditions between the results from the EEPS and the advanced HM-DMA ascribable to the different measurement principle and to the dilution system.