Search

International audience; The influence of equal channel angular pressing (ECAP) on the corrosion fatigue behaviour of an Al-Mg-Si alloy was studied. Preliminary fatigue tests in air showed an increase in fatigue lifetime for ECAP samples, as compared to as-received samples, related to the ECAP-induced grain refinement. After pre-corrosion, the fatigue lifetime was lower for ECAP samples than for as-received samples, because the fragmentation of coarse intermetallics during ECAP led to an increase in the density of corrosion defects.C orrosion fatigue tests demonstrated a synergy between cyclic mechanical loading and corrosion processes for all samples; a deleterious effect of ECAP was also noted.

Outdoor air pollution is an increasing public health burden. Fine particulate matter (PM2.5) is a pollutant of major concern for human health, and it also affects the climate and ecosystems. Understanding and quantifying emission sources and their impact on particulate air pollution is critical for improving global health and for informing climate action. Poor air quality across the globe disproportionately affects middle- and lower-income countries. Delhi, the capital of India, is one of the most populated and polluted megacities in the world, where in 2017 almost 12,000 premature deaths were attributed to outdoor air pollution. My thesis aims to advance our understanding of outdoor air pollution in Delhi megacity, with a focus on the impact of on-road transport emissions on surface levels of PM2.5 and its implications for air quality policymaking. To do this, I use a combination of a state of the art regional atmospheric chemistry transport model, recently developed local emissions inventories, and sensitivity analysis techniques. In the first research chapter I use the WRF-Chem atmospheric chemical transport model to understand the regional influence on air quality over Delhi. As part of this work, I characterise seasonal anthropogenic, pyrogenic, and biogenic influences on fine particulate matter and one of its main constituents, organic aerosol (OA), over the Indo-Gangetic Plain (IGP). My results show that anthropogenic emissions influence the magnitude and distribution of PM2.5 and OA throughout the year, especially over cities including Delhi, while pyrogenic emissions from crop residues burning result in localized contributions over the central and upper parts of IGP in all non-monsoonal seasons, with the highest impact during the post-monsoon season that correspond to the post-harvest season in the agricultural calendar. Biogenic emissions play an important role in the magnitude and distribution of PM2.5 and OA during the monsoon season, particularly over the lower IGP. In all seasons mean values of PM2.5 still exceed the recommended levels, indicating that air pollution is a year-round problem. In the second research chapter I develop the WRF-Chem model used in my first chapter to include local emission inventories, in order to quantify the contribution of the on-road transport sector to surface PM2.5 over Delhi during the highly polluted post-monsoon season. This contribution is compared to the contributions of other local (within Delhi) and regional (within the National Capital Region, NCR) anthropogenic sectors. My results show that emissions from the local transport sector contribute typically less than 10% to daily mean PM2.5 values over Delhi, rising to 17% when regional transport sources are included. The contribution from the local transport sector is largest (18%) during the evening traffic peak. The total transport impact is dominated by contributions from twoand three-wheelers (50%) and heavy-duty vehicles (30%). The largest individual contributions to daily mean PM2.5 values are found to be from regional power and industry (14%) and domestic (11%) sectors. In the third research chapter I drive the WRF-Chem model with future transport emissions scenarios to investigate the potential impact of electric and clean-fuel vehicles on surface PM2.5 and ozone (O3) over Delhi for two contrasting seasons, pre-monsoon and post-monsoon. My results show that the conversion of diesel vehicles to compressed natural gas (CNG) brings a greater reduction in PM2.5 concentrations than the full electrification of two- and three-wheelers. However, the maximum reduction of daily mean PM2.5 concentrations for all scenarios is within 5% compared to baseline values for both seasons. Electrification of two- and three-wheelers increases average 8-hour daily maximum (MDA8) ozone (1.3-3.5% in pre-monsoon 5-13% in post-monsoon) compared to baseline values. On the other hand, conversion of all diesel vehicles to CNG reduces MDA8 O3 in both seasons (by 2.3-5.3% in pre-monsoon and by 1-1.5% in post-monsoon) compared to baseline values. In conclusion, the findings of my thesis highlight different factors that can be relevant for designing effective policies to meet PM2.5 air quality standards over Delhi megacity, with a focus on mitigating the impact from the on-road transport sector. First, air quality over Delhi is strongly influenced by regional and seasonal pollution sources from the IGP. As such, effective mitigation of PM2.5 pollution over Delhi will require a range of regional and state-level policies. In particular, cooperative mitigation strategies between the Delhi megacity and the broader NCR is needed if PM2.5 pollution is to be reduced. Second, two-and three-wheelers and heavy-duty vehicles dominate on-road transport impact on PM2.5, thus emissions reductions from these vehicles should be given priority, both within Delhi and in the NCR. Third, cleaner mobility plans of electrification of two- and threewheelers should be accompanied by diesel vehicles conversion to compressed natural gas, to limit ozone pollution increase and further reduce PM2.5 concentrations. This also highlights the importance of coordinated control of PM2.5 and other pollutants such as O3 when considering emission control strategies for transport over Delhi.

Supplemental Digital Content is available in the text., Background: Hutchinson-Gilford progeria syndrome (HGPS) is a rare disorder characterized by premature aging and death mainly because of myocardial infarction, stroke, or heart failure. The disease is provoked by progerin, a variant of lamin A expressed in most differentiated cells. Patients look healthy at birth, and symptoms typically emerge in the first or second year of life. Assessing the reversibility of progerin-induced damage and the relative contribution of specific cell types is critical to determining the potential benefits of late treatment and to developing new therapies. Methods: We used CRISPR-Cas9 technology to generate LmnaHGPSrev/HGPSrev (HGPSrev) mice engineered to ubiquitously express progerin while lacking lamin A and allowing progerin suppression and lamin A restoration in a time- and cell type–specific manner on Cre recombinase activation. We characterized the phenotype of HGPSrev mice and crossed them with Cre transgenic lines to assess the effects of suppressing progerin and restoring lamin A ubiquitously at different disease stages as well as specifically in vascular smooth muscle cells and cardiomyocytes. Results: Like patients with HGPS, HGPSrev mice appear healthy at birth and progressively develop HGPS symptoms, including failure to thrive, lipodystrophy, vascular smooth muscle cell loss, vascular fibrosis, electrocardiographic anomalies, and precocious death (median lifespan of 15 months versus 26 months in wild-type controls, P

The term open-air factor (OAF) was coined following microbiological research in the 1960s and 1970s which established that rural air had powerful germicidal properties and attributed this to Criegee intermediates formed in the reaction of ozone with alkenes. We have re-evaluated those early experiments applying the current state of knowledge of ozone–alkene reactions. Contrary to previous speculation, neither Criegee intermediates nor the HO radicals formed in their decomposition are directly responsible for the germicidal activity attributed to the OAF. We identify other potential candidates, which are formed in ozone–alkene reactions and have known (and likely) germicidal properties, but the compounds responsible for the OAF remain a mystery. There has been very little research into the OAF since the 1970s, and this effect seems to have been largely forgotten. In this opinion piece we remind the community of the germicidal open-air factor. Given the current global pandemic spread by an airborne pathogen, understanding the natural germicidal effects of ambient air, solving the mystery of the open-air factor and determining how this effect can be used to improve human welfare should be a high priority for the atmospheric science community.

International audience; Abstract. This article, the eighth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers the gas-phase thermal and photochemical reactions of organic species with four, or more, carbon atoms (≥ C4) available on the IUPAC website in 2021, including thermal reactions of closed-shell organic species with HO and NO3 radicals and their photolysis. The present work is a continuation of volume II (Atkinson et al., 2006), with new reactions and updated data sheets for reactions of HO (77 reactions) and NO3 (36 reactions) with ≥ C4 organics, including alkanes, alkenes, dienes, aromatics, oxygenated, organic nitrates and nitro compounds in addition to photochemical processes for nine species. The article consists of a summary table (Table 1), containing the recommended kinetic parameters for the evaluated reactions, and a supplement containing the data sheets, which provide information upon which recommendations are made.

This article, the seventh in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers an extension of the gas-phase and photochemical reactions related to Criegee intermediates previously published in Atmospheric Chemistry and Physics (ACP) in 2006 and implemented on the IUPAC website up to 2020. The article consists of an introduction, description of laboratory measurements, a discussion of rate coefficients for reactions of O3 with alkenes producing Criegee intermediates, rate coefficients of unimolecular and bimolecular reactions and photochemical data for reactions of Criegee intermediates, and an overview of the atmospheric chemistry of Criegee intermediates. Summary tables of the recommended kinetic and mechanistic parameters for the evaluated reactions are provided. Data sheets summarizing information upon which the recommendations are based are given in two files, provided as a Supplement to this article.

Sustainable design methods and tools abound, but their implementation in practice remains marginal. This article brings together results from previous literature reviews and analyses of sustainable design methods and tools, as well as input from design researchers and professional practitioners to identify the needs and gaps in the area. It results in a shared vision of how sustainable design methods and tools can be more tightly integrated into mainstream product design and development, as well as the current state of practice and research in relation to four central questions: What are the needs and values of industry regarding sustainable design? What improvements in sustainable design methods and tools would most drive industry forward? How should researchers move forwardwith developingmore useful sustainable designmethods and tools? Howcan sustainable design be more effectively integrated into industry? A roadmap for the international sustainable design research community is proposed with descriptions of short-, medium-, and long-term tasks for addressing each question. The purpose is to support collective progress and discussions on method and tool development and adoption, and to enablemore tangible success inmainstreaming sustainable design practices in industry. © 2020 by the authors. open access

In the present work, a 5-component gasoline surrogate chemical kinetic mechanism has been developed and validated. The first novelty of this mechanism is that a recently advanced H2/O2/CO/C1 detailed sub-mechanism is adopted for accurately predicting the laminar flame speeds over a wide range of operating conditions and a recently advanced C2-C3 detailed sub-mechanism is used due to its potential benefits on accurate flame propagation simulation in order to overcome the drawbacks in the original decoupling methodology. The second novelty of this mechanism is that the sub-mechanisms of propyne and allene which are important for soot formation from non-aromatics have been improved significantly. For each of the five gasoline surrogate components (iso-octane, n-heptane, iso-hexane, 1-hexene, and toluene) a skeletal sub-mechanism, which determines the simulation of ignition delay times, is constructed for species C4-Cn. The five skeletal sub-mechanisms are coupled with the new C2-C3 and H2/O2/CO/C1 detailed sub-mechanisms. Together with a reduced NOx (oxides of nitrogen) sub-mechanism, the 5-component gasoline surrogate chemical kinetic mechanism has 214 species and 1233 reactions, which are feasible currently for CFD simulation of gasoline engine combustion, emissions, and knock. The new H2/O2/CO/C1 and C2-C3 detailed sub-mechanisms were validated with selected experimental data of ignition delay times, laminar flame speeds, and important species profiles in the literature. The reaction rate constants of the five skeletal sub-mechanisms were optimized in this work to match available experimental data of either pure fuels or fuel blends, including real gasoline fuels. The validation results show that the prediction accuracy of the 5-component gasoline surrogate chemical kinetic mechanism of the present work can be less than 5% for various fuel blends under a pressure range of 1.0 80.0 bar, a temperature range of 300 1260 K, and an equivalence ratio range of 0.5 2.5. This work was partially funded by a URP (University Research Program) of Ford Motor Company. Shiyou Yang of Ford thanks Dr. Chitral Naik of Reaction Design (now ANSYS) for help in using the CHEMKIN-PRO software, also SY thanks Dr. Snehasish Panigrahy of National University of Ireland-Galway for implementing the latest propyne detailed sub-mechanism into MCCh v2.0 mechanism and providing the experimental data for validation. James Yi, Steven Wooldridge, Brad VanDerWege, Claudia Iyer, Foo-Chern Ting, and Cindy Zhou of Ford Motor Company are thanked for helpful discussions and suggestions. peer-reviewed

An Al-Mg-Si aluminium alloy was shaped by using a two-pass equal-channel angular pressing (ECAP) process. This led to fragmentation of the coarse Fe-rich intermetallics (IMCs), a decrease in grain size and an increase in the high angle grain boundary (HAGB) density, with overconcentration of HAGBs around the IMCs. Corrosion tests in NaCl solution showed that, before and after ECAP, only pitting corrosion occurred. However, for ECAP samples, pits were more numerous due to the fragmentation of the IMCs; they were also larger and less deep, their propagation being strongly influenced by the presence of very small grains around the IMCs.

International audience

We present a digital, freely available, searchable, and evaluated compilation of rate coefficients for the gas-phase reactions of organic compounds with OH, Cl, and NO3 radicals and with O3. Although other compilations of many of these data exist, many are out of date, most have limited scope, and all are difficult to search and to load completely into a digitized form. This compilation uses results of previous reviews, though many recommendations are updated to incorporate new or omitted data or address errors, and includes recommendations on many reactions that have not been reviewed previously. The database, which incorporates over 50 years of measurements, consists of a total of 2765 recommended bimolecular rate coefficients for the reactions of 1357 organic substances with OH, 709 with Cl, 310 with O3, and 389 with NO3, and is much larger than previous compilations. Many compound types are present in this database, including naturally occurring chemicals formed in or emitted to the atmosphere and anthropogenic compounds such as halocarbons and their degradation products. Recommendations are made for rate coefficients at 298 K and, where possible, the temperature dependences over the entire range of the available data. The primary motivation behind this project has been to provide a large and thoroughly evaluated training dataset for the development of structure–activity relationships (SARs), whose reliability depends fundamentally upon the availability of high-quality experimental data. However, there are other potential applications of this work, such as research related to atmospheric lifetimes and fates of organic compounds, or modelling gas-phase reactions of organics in various environments. This database is freely accessible at https://doi.org/10.25326/36 (McGillen et al., 2019).

This paper presents an experimental study into the flow behaviour of lubricant in a reciprocating contact simulating a piston ring–cylinder liner pair. The aim was to understand the effects of cavitation, starvation and surface texture, as well as the interaction between these, in order to improve automotive engine performance. A custom-built test rig was used, in which a section of piston ring is loaded against a reciprocating, laser-textured, fused silica pad representing the liner. A fluorescence microscope focusses through the silica specimen onto the contact in order to image the distribution of dyed oil. Tests were performed using a range of texture geometries and orientations, under starved and fully-flooded lubrication conditions, with measurements being compared against those from a non-textured reference. Under limited oil supply conditions, the non-textured reciprocating contact sweeps oil towards the reversal points (TDC and BDC), leading to starvation and increased friction. This issue is alleviated by the presence of surface texturing, with each pocket transferring oil from the inlet to the outlet of the contact as it passes; the result being 33% lower friction and oil distributed evenly over the liner surface. Even under fully flooded conditions, starvation is shown to occur following each reversal, as the change in sliding direction causes the cavitated outlet to become the oil-deprived inlet. This proof of cavitation-reversal-starvation, which occurs for up to the first 5% of the stroke length, depending on the lubricant’s viscosity, corresponds to regions of high wear, measured in this study and on actual cylinder liners reported in the literature. This process is also counteracted by the presence of surface texture, with each pocket depositing oil into the cavitated region prior to reversal. Fluorescence data also provides insights into other mechanisms with which different textures geometries control friction. Grooves oriented parallel to sliding direction increase friction as they appear to connect the high pressure inlet with the low pressure outlet, leading to oil film collapse. Grooves oriented transverse to sliding direction produce localised cavitation inside each pocket, which supports the theory that texture draws lubricant into the contact through the ‘inlet suction’ mechanism. These findings can aid texture design by showing how pockets can be used in practice to simultaneously control oil consumption, and reduce friction and wear along the stroke. It should be noted that the lubricant transport mechanisms described above should also result from other types of depressions, such those produced by porous coatings (provided they are smaller than the contact area).

This paper presents a comparison between the results from numerical modelling and experiments to shed light on the mechanisms by which surface texture can reduce friction when applied to an automotive cylinder liner. In this configuration, textured features move relative to the piston-liner conjunction and to account for this our approach is to focus on the transient friction response to individual pockets as they pass through, and then leave, the sliding contact. The numerical approach is based on the averaged Reynolds’ equation with the Patir & Cheng's flow factors and the p-θ Elrod-Adams mass-conserving cavitation model. The contact pressures that arise from the asperity interactions are solved simultaneously to the fluid flow solution using the Greenwood and Tripp method. The experimental data is produced using a pin-on-disc set up, in which laser textured pockets have been applied to the disc specimen. Under certain conditions in the mixed and boundary lubrication regimes, both model and experimental results show i ) an increase in friction as the pocket enters the contact, followed by ii ) a sharp decrease as the pocket leaves the contact, and then iii ) a gradual decay back to the pre-entrainment value. From the evidence obtained for the first time from the proposed combined modelling and experimental investigation conducted under carefully controlled conditions, we suggest that these three stages occur due to the following mechanisms: i ) a reduction in fluid pressure due to the increased inlet gap, ii ) inlet suction as the cavitated fluid within the pocket draws lubricant into the contact, and iii ) film thickness decay as oil is squeezed out of the contact. The interplay of these three mechanisms is shown to control the response of micro-textured surfaces under all lubrication regimes.

In order to determine a material's hydrogen storage potential, capacity measurements must be robust, reproducible, and accurate. Commonly, research reports focus on the gravimetric capacity, and often times the volumetric capacity is not reported. Determining volumetric capacities is not as straight-forward, especially for amorphous materials. This is the first study to compare measurement reproducibility across laboratories for excess and total volumetric hydrogen sorption capacities based on the packing volume. The use of consistent measurement protocols, common analysis, and figure of merits for reporting data in this study, enable the comparison of the results for two different materials. Importantly, the results show good agreement for excess gravimetric capacities amongst the laboratories. Irreproducibility for excess and total volumetric capacities is attributed to real differences in the measured packing volume of the material.

International audience; Gasoline soot nanoparticles (SNPs) were studied by performing in situ compression tests on individual nanoparticles inside a transmission electron microscope. After consecutive compressions, the SNPs exhibited an elasto-plastic behavior, and an increasing trend in Young's modulus and hardness values. Molecular dynamics were used to simulate compression cycles, the results of which confirmed the observations made during the experiments. The simulations were used to investigate how the different structural components of the nanoparticles affect their elastic and plastic response. By comparing the behavior of gasoline and diesel SNPs under compression, differences were observed both experimentally and in the simulations: the former were found to be more elastic and less prone to become hard under compression compared to the latter.

From the earliest observations of ozone in the lower atmosphere in the 19th century, both measurement methods and the portion of the globe observed have evolved and changed. These methods have different uncertainties and biases, and the data records differ with respect to coverage (space and time), information content, and representativeness. In this study, various ozone measurement methods and ozone datasets are reviewed and selected for inclusion in the historical record of background ozone levels, based on relationship of the measurement technique to the modern UV absorption standard, absence of interfering pollutants, representativeness of the well-mixed boundary layer and expert judgement of their credibility. There are significant uncertainties with the 19th and early 20th-century measurements related to interference of other gases. Spectroscopic methods applied before 1960 have likely underestimated ozone by as much as 11% at the surface and by about 24% in the free troposphere, due to the use of differing ozone absorption coefficients. There is no unambiguous evidence in the measurement record back to 1896 that typical mid-latitude background surface ozone values were below about 20 nmol mol–1, but there is robust evidence for increases in the temperate and polar regions of the northern hemisphere of 30–70%, with large uncertainty, between the period of historic observations, 1896–1975, and the modern period (1990–2014). Independent historical observations from balloons and aircraft indicate similar changes in the free troposphere. Changes in the southern hemisphere are much less. Regional representativeness of the available observations remains a potential source of large errors, which are difficult to quantify. The great majority of validation and intercomparison studies of free tropospheric ozone measurement methods use ECC ozonesondes as reference. Compared to UV-absorption measurements they show a modest (~1–5% ±5%) high bias in the troposphere, but no evidence of a change with time. Umkehr, lidar, and FTIR methods all show modest low biases relative to ECCs, and so, using ECC sondes as a transfer standard, all appear to agree to within one standard deviation with the modern UV-absorption standard. Other sonde types show an increase of 5–20% in sensitivity to tropospheric ozone from 1970–1995. Biases and standard deviations of satellite retrieval comparisons are often 2–3 times larger than those of other free tropospheric measurements. The lack of information on temporal changes of bias for satellite measurements of tropospheric ozone is an area of concern for long-term trend studies.

International audience; Peroxy radicals (HO 2 and RO 2 ) are key species in atmospheric chemistry, which together with the hydroxyl radical (OH), are involved in oxidation processes leading to the formation of secondary pollutants such as ozone and organic aerosols. Monitoring these short-lived species during intensive field campaigns and comparing the measured concentrations to box model simulations allow assessing the reliability of chemical mechanisms implemented in atmospheric models. However, ambient measurements of peroxy radicals are still considered challenging and only a few techniques have been used for field measurements. Three complementary instruments capable of ambient measurements of pe roxy radicals have been deployed together at the HELIOS atmospheric simulation chamber (Orléans, France) in October 2018. These instruments rely on the PEroxy Radical Chemical Amplification (PERCA), Laser Induced Fluorescence-Fluorescent Assay by Gas Expansion (LIF-FAGE), and Chemical Ionisation Mass Spectrometry (CIMS) techniques. Several chamber experiments have been conducted under dark and irradiated conditions, including oxidation experiments of dihydrogen, methane, pentene, isoprene, and α-pinene. In this presentation, the agreement between the different instruments will be discussed in the light of supporting measurements of volatile organic compounds and inorganic species (O3, NO, NO2), photolysis frequencies, as well as box modelling of the chamber chemistry.

This work employs a combination of pressure trace analysis, high-speed optical measurements and laser-based techniques for the assessment of the effects of various post-injection schemes on the soot reduction potential in an optical single-cylinder light-duty diesel engine. The engine was operated under a multiple injection scheme of two pilot and one main injection, typical of a partially premixed combustion mode, at the lower end of the load and engine speed range (ca 2.0 bar IMEP at 1200 r/min). Experiments considering the influence of the post-injection fuel amount (up to 15% of the total fuel quantity per cycle) and the post-injection timing within the expansion stroke (5, 10 and 15 CAD aTDC), under a constant total fuel mass per cycle, have been conducted. Findings were analysed via means of pressure trace and apparent rate of heat transfer analyses, as well as a series of optical diagnostic techniques, namely, high-speed flame natural luminosity imaging, CH*, C∗2 and OH* line-of-sight chemiluminescence, as well as planar laser-induced incandescence measurements at 31 and 50 CAD aTDC. The combination of post-injection fuel amount and timing has substantial effects on charge reactivity and soot oxidation potential. The analysis reveals that an amount of fuel (7% of the total fuel mass per cycle) injected more than 10 CAD after the main combustion event leads to higher levels of soot emissions, while a larger amount of fuel (15% of the total fuel mass) injected 5 CAD after the main combustion event appears to have a beneficial effect on the soot oxidation processes. Overall, results indicate that a post-injection scheme close to the main combustion phasing could reduce soot levels and improve engine performance, that is, higher IMEP levels at the same fuel consumption rates, although it could increase engine noise.

The aim of this study is to gain insights into the interactions between laser-textured surface pockets and friction and wear behaviour of an automotive piston-liner pairing. To do this, a recently developed, reciprocating, test apparatus was used to conduct wear tests under highly loaded conditions. Fused silica specimens with a range of pocket geometries were rubbed against a convex steel pad and the resulting friction and wear data were compared with those from a non-textured specimen. Contact conditions were set to remove the influence of initial surface roughness on texture behaviour. These tests showed that, as the specimen become worn and surface roughness increases, the contact progresses further into the mixed and boundary regime. This leads to a significant improvement in the relative performance of the textured specimens, showing reductions in friction of up to 70%, compared with the non-texture case. This is consistent with previous results that have shown texture to have the effect of boosting film thickness in the mixed lubrication regime. Surface texture was also shown to reduce the volume of wear, by up to 69% (corresponding to a change in wear coefficient from 2.67e−4 to 0.81e−4 [mm3/N m]). Another, important, finding is that both friction and wear reduce monotonically as the sum of the pocket volumes along the stroke increases. This may aid texture design, since it means that individual pocket width and depth values can largely be ignored, so long as the overall volume is maximised. The only exception to this trend is when the pockets are larger than the contact area. In this case, friction increases due to a collapse of the lubricant film, while wear reduction remains unaffected – a discrepancy which may suggest that pockets reduce wear and friction via separate mechanisms.

Applying surface texture to piston liners may provide an effective means of controlling friction and hence improving engine efficiency. However, little is understood about the mechanisms by which pockets affect friction, primarily because of a lack of reliable experimental measurements. To address this, the influence of surface texture on film thickness and friction force was measured simultaneously in a convergent-divergent bearing, under conditions that closely replicate an automotive piston ring-liner conjunction. Film thicknesses were measured using a modified version of the ultra-thin film optical interferometry approach, enabling film thicknesses

The present work investigates the effect of the injection dwell time and injection pressure on soot reduction potential in an optical single-cylinder light-duty diesel engine. The engine operated under a double-injection scheme under low load and low engine speed conditions. The conducted experiments considered two different dwell times for three different injection pressures. The fuel quantity of the main injection was adjusted to maintain the same indicated mean effective pressure (IMEP) value among all cases considered. Findings were analyzed via means of pressure trace and apparent heat release rate (AHRR) analyses, as well as a series of optical diagnostics techniques, namely high-speed imaging and planar laser-induced incandescence (pLII). The combination of dwell time and injection pressure substantially affects charge reactivity and soot oxidation potential. The analysis suggests that a shorter dwell time combined with a higher injection pressure can lead to an enhanced potential for engine-out particulate reduction by creating an in-cylinder environment that promotes soot oxidation. Overall, results indicate that a close-coupled pilot and main injection scheme can reduce soot levels, albeit while increasing specific fuel consumption by up to 12% to maintain the same engine power output levels.

International audience; Incomplete fuel burning inside an internal combustion engine results in the creation of soot in the form of nanoparticles. Some of these soot nanoparticles (SNP) become adsorbed into the lubricating oil film present on the cylinder walls, which adversely affects the tribological performance of the lubricant. In order to better understand the mechanisms underlying the wear caused by SNPs, it is important to understand the behavior of SNPs and to characterize potential changes in their mechanical properties (e.g. hardness) caused by (or during) mechanical stress. In this study, the behavior of individual SNPs originating from diesel engines was studied under compression. The experiments were performed in a transmission electron microscope using a nanoindentation device. The nanoparticles exhibited elasto-plastic behavior in response to consecutive compression cycles. From the experimental data, the Young's modulus and hardness of the SNPs were calculated. The Young's modulus and hardness of the nanoparticles increased with the number of compression cycles. Using an electron energy loss spectroscopy technique, it was shown that the sp(2)/sp(3) ratio within the compressed nanoparticle decreases, which is suggested to be the cause of the increase in elasticity and hardness. In order to corroborate the experimental findings, molecular dynamics simulations of a model SNP were performed. The SNP model was constructed using carbon and hydrogen atoms with morphology and composition comparable to those observed in the experiment. The model SNP was subjected to repeated compressions between two virtual rigid walls. During the simulation, the nanoparticle exhibited elasto-plastic behavior like that in the experiments. The results of the simulations confirm that the increase in the elastic modulus and hardness is associated with a decrease in the sp(2/)sp(3) ratio.

International audience; It is hard to overstate the importance of oxygenated organiccompounds in atmospheric chemistry. Oxygenated organiccompounds are emitted into the atmosphere from natural andman-made sources, and they are formed in the atmosphere asoxidation products of all hydrocarbons present in theatmosphere. Oxygenated volatile organic compounds(OVOCs) are generally more reactive than the alkanes fromwhich they are derived. OVOCs play an active role in thesequence of chemical reactions responsible for troposphericozone formation in both polluted and remote environments.

The work investigates the effect of various post-injection strategies on the flame patterns in a Ricardo Hydra optical single-cylinder, light-duty diesel engine, operated in a partially premixed combustion mode, under low load (IMEP: ca. 2.3 bar), low speed (1200 rpm) conditions. The effect of post-injection fuel amount (12% and 24% of the total fuel quantity per cycle) and post-injection timing (0, 5, 10 deg aTDC) are investigated via pressure trace analysis and optical measurements. Flame propagation is captured by means of high-speed flame natural luminosity imaging and of CH*, C2*, and OH* line-of-sight chemiluminescence measurements. Results suggest that post-injections suppress mixture reactivity but enhance oxidation, and that a larger amount of fuel and/or later post-injection, leads to higher levels of natural luminosity, indicating possible higher soot-out emissions, while post-injection close to the main combustion event appears to have a beneficial effect on the soot oxidation processes.

In recent years, interest in reducing friction in internal combustion engines has grown significantly. This has mainly been due to stricter regulatory standards, with emission targets set as low as 95g of CO2/km from 2020 onwards. As a result, motor vehicle manufacturers have been focusing investment on energy efficient technologies with the aim of reducing fuel consumption. As part of this drive, the reduction of friction between the piston rings and cylinder liners is gaining considerable attention. A potentially effective way of doing this is to apply laser texturing to piston liner surfaces. However, little is understood about the mechanisms by which pockets affect friction, primarily because of the lack of reliable experimental measurements. In this study, the influence of surface texture on film thickness and friction force was measured simultaneously in a convergent-divergent bearing under different lubrication regimes, closely replicating an automotive piston ring-bore conjunction. This was achieved using a reciprocating sliding test rig, designed to control all operating parameters with a high degree of accuracy. Various pocket shapes were assessed in order to understand the beneficial or detrimental effects of surface texture under various operating conditions. This showed unequivocally that pockets are able to reduce friction in the mixed regime and increase friction under full film conditions. After the optimum pocket shape had been determined, various spatial parameters (depth, breadth, separation) were tested, under different lubrication regimes, in order to characterise the influence of geometry. A key finding here is that optimum pocket geometry varies along the length of the stroke. Next, film thickness was measured using a modified version of the ultra-thin film optical interferometry approach. The results here agreed with the friction data by showing how pockets increase film thickness in the mixed and boundary regime and decrease film thickness in the full film regime. Furthermore, through transient measurements, a number of insights into mechanisms by which surface texture reduce or increase friction were obtained. In addition, cavitation in the ring-liner pairing was investigated, as well as various aspects of pocket behaviour, such as orientation, location relative to reversal and the influence of steady state versus transient sliding. Finally, wear tests were conducted under highly loaded conditions which led to an understanding of the interactions between laser surface texture and wear behaviour. Open Access

International audience

Recent experiments have shown that automotive piston-liner friction may be reduced by up to 50 % if the surface of the liner is laser textured with certain configurations of micro-pockets. It is important to model this behavior to understand and optimize the friction reduction mechanisms that are occurring. However, until now, very few models that predict the lubrication performance of textured surfaces have been successfully validated against experimental data. This is because of the requirement for them to: (1) reproduce experimental configurations with a certain degree of fidelity, (2) conserve mass properly, and (3) account for transient, boundary lubrication conditions. To address this, the current paper presents a comparison between the results from a numerical model, which fulfils these criteria, and an experimental test rig operating under the same conditions. The mathematical modeling is based on the averaged Reynolds’ equation with Patir and Cheng’s flow factors and the p − θ Elrod–Adams mass-conserving cavitation model. Simultaneously to the fluid flow solution, the contact pressures that arise from the asperity interactions are also included into the calculations through the well-known stochastic Greenwood and Tripp model for rough contacts. The experimental data is produced using a reciprocating tribometer, whose contact conditions are closely controlled and accurately mimic those found in an automotive piston–liner conjunction. Data is presented in terms of friction force versus stroke angle, and the similarities and differences between the model and experiment are discussed.

The aim of this thesis is to investigate ways to reduce soot emission from compression ignition engines by investigating the combustion processes within the diesel engine. The approach is to include computational and experimental work. In order to investigate the trade-off between the amount and stratification of the premixing and the consequent rate of pressure rise, and in particular the effects of changing the autoignition properties of the fuel blend, a multizone code capable of representing the ignition of a premixed charge consequent on multiple injection of fuel is presented. As part of this investigation, this thesis began the process of looking into the potential of gasoline fuel. Experimentally, investigations of soot distribution were carried out in an optically-accessed single cylinder “Hydra” engine. The soot was visualized using high speed imaging and laser induced incandescence in the optical engine to look at the effect of injection pressure on combustion luminosity and soot distribution. An extensive parametric study was carried out on the Hydra engine to look at the effect of engine load, injection timing and pressure, number of injections, intake temperature and combustion phasing. High speed imaging was carried out to measure injection tip penetration and soot luminosity as a function injection pressure. The combustion luminosity was studied, with proper orthogonal decomposition (POD) analysis, at different injection pressures. It was found that increase of injection pressure decreases combustion luminosity. The technique of laser induced incandescence (LII) was used to visualize the soot. As a preliminary to the use of the LII in the engine, fundamental work on the technique itself was carried out at Heriot-Watt University to isolate the radiative emission component of heat loss from the soot and measure the complex refractive index of soot. Results on soot particle sizes were compared to scanning electron micrograph of the soot collected. The LII measurement was found to be much larger, due to the high signal to noise ratio and the bias towards detection of larger particles. The investigation also showed that the soot agglomerates could undergo micro-explosions on being exposed to laser irradiance. It is speculated that the soot molecules become ionized and mutually repel each other. Open Access