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Brake particle emissions number (PN) and mass (PM) of a light-duty hybrid-electric vehicle have been assessed under realistic driving patterns on a chassis dynamometer. Therefore, the front-right disc brake was enclosed in a specifically designed casing featuring controlled high scavenging air ventilation. The WLTC cycle was chosen for most measurements. Different scavenging flow rates have been tested assessing their influence on the measured particles as well as on the temperature of the braking friction partners. Particle transport efficiencies have been assessed revealing scavenging flow rates with losses below 10%. During the performed cycle, most brake particle emissions occurred during braking. There were also isolated emission peaks during periods with no brakes in use, especially during vehicle accelerations. Sequential WLTC cycles showed a continuous decrease in the measured PN and PM emissions; however, size-number and size-mass distributions have been very similar. The measured PN emission factors (>23 nm) at the right front wheel over the WLTC cycle lie at 5.0 × 1010 1/km, whereas the PM emission factor lies at 3.71 mg/km for PM < 12 µm and 1.58 mg/km for PM < 2.5 µm. These values need to roughly triple in order to obtain the brake particle emission of all four brakes and wheels of the entire vehicle. Thus, the brake PN emissions factors have been in the same order of magnitude as the tailpipe PN of a Euro 6 light-duty vehicle equipped with a particle filter. Finally, differences between brake particle emissions in hybrid and all-electric operating modes have been assessed by a series of specific measurements, demonstrating the potential of all-electric vehicle operation in reducing brake particles by a factor of two. [ABSTRACT FROM AUTHOR]

Fast fillings of hydrogen vehicles require proper control of the temperature to ensure the integrity of the storage tanks. This study presents an analysis of heat transfer during filling of a hydrogen tank. A conjugate heat transfer based on energy balance is introduced. The numerical model is validated against fast filling experiments of hydrogen in a Type IV tank by comparing the gas temperature evolution. The impact of filling parameters, such as initial temperature, inlet nozzle diameter and filling time is then assessed. For the considered Type IV tank, the results show that both a higher and lower tank shell thermal conductivity results in lower inner wall peak temperatures. The presented model provides an analytical description of the temperature evolution in the gas and in the tank shell, and is thus a useful tool to explore a broad range of parameters, e.g., to determine new hydrogen filling protocols. • An analytical model is developed to predict the tank shell temperature distribution. • The analytical model is validated against experimental results. • The influence of filling parameters on the tank wall peak temperature is assessed. • The tank materials heat diffusivity is the critical parameter for fast fillings. [ABSTRACT FROM AUTHOR]

The present work focuses on a detailed analysis of new and used braking friction partners (discs and pads) in order to provide a comprehensive characterization of the source of the airborne particles formed during braking. Scanning electron microscopy (SEM) combined with energy dispersive X-Ray analysis (EDX) was applied to investigate the new brake disc and new and used brake pad components of a passenger vehicle. The pads include at least 21 different substances, involving carbonaceous particles, oxides, sulfides, sulfates and silicates of Al, Si, K, Ca, Ti, Fe, Zr, Sn, less Mg, Ba, Na and, rarely, Bi and Zn, as well as K-titanate. Aramid and phenolic resin are also present, enriched toward the metal interface. The size of the pad constituents extends over a very wide range, from hundreds of µm to a few µm, and goes down to hundreds of nm and, rarely, tens of nanometers. Carbonaceous particles with sizes down to a few tens of nanometers occupy ca. 16% of the total of the pad constituents. Abundant Zr-bearing phases, as well as various other phases involving S, Ca, Mg, Si, Ti and, to a lower extent, Ba and Fe in different combinations, constitute the pad main matrix. [ABSTRACT FROM AUTHOR]

Methane abatement remains a challenge in aftertreatment systems of natural gas engines, currently under discussion in combination with synthetic methane. In this study, Pt/Rh and Pd/Rh-based three-way catalysts are investigated under various transient conditions because transients between O2 excess (lean) and O2-poor (rich) conditions can significantly enhance methane abatement. At mid to high temperatures, transitions from rich to lean feed yield higher rates of methane direct oxidation under lean conditions with the Pt/Rh catalyst, compared to the Pd/Rh catalyst. Both catalysts are able to trigger methane steam reforming (SR) after transitions from lean to rich feed. The SR reaction leads to increased H2 and NH3 formation. However, SR deactivates much faster in the Pt/Rh catalyst. At low temperature, the Pt/Rh catalyst is more active for SR. Results from an additional Pd-only catalyst confirm that Rh is essential for NOx conversion and high N2 selectivity. The distinct characteristics of Pt, Pd and Rh demonstrate the benefits obtained from the combination of the three platinum group metals. The potential of the Pt/Pd/Rh catalyst is proved to be significant throughout the complete engine map. Under optimized lean/rich oscillatory conditions, the Pt/Pd/Rh catalyst yields more than 95% methane conversion under almost all conditions while maintaining efficient abatement of all other pollutants. [ABSTRACT FROM AUTHOR]

About 30% of the fuel energy is lost in combustion engines to the exhaust gas. New development of thermoelectric materials allows to partly recuperating the lost heat. New Half-Heusler materials using only low-priced elements show promising performances for heat conversion in the temperature range of a vehicle exhaust. An investigation of the installation of Half-Heusler-based thermoelectric generators at the manifold and after the exhaust after-treatment system (ATS) of 4 light duty vehicles (2 gasolines and 2 diesels) has been made. Gas temperatures at the manifold and after the ATS were simulated based on measured data. These reach 800 °C and 600 °C respectively during a typical driving cycle. During the WLTC, an average of 100 W of electricity can be generated at the manifold and 30 W after the ATS, without adding specific heat transfer enhancing devices in the exhaust pipe. The geometric dimensions of the TEGs must be adapted in order to match the optimal thermal resistance according to their location in the exhaust and the vehicle type (differing heat flows and temperatures) to recuperate an optimal amount of energy. [ABSTRACT FROM AUTHOR]

This study presents an investigation of the heat transfer characteristics of the urea-water spray (UWS) impingement on a stainless steel plate under typical diesel exhaust flow conditions. The rear side temperature of the spray-impinged plate has been measured by infrared thermography with high temporal and spatial resolution. The spray impinged side temperature and heat flux distributions have been computed by solving the 3D inverse heat conduction in the plate with the sequential function specification method. Measurements show that the instantaneous plate temperature determines the heat transferred during the spray impingement. Based on the plate temperature, different regimes (film boiling, transition boiling and nucleate boiling) have been identified. At high plate temperatures, film boiling and Leidenfrost effect are prevailing and the heat transferred from the plate to the liquid is low. With decreasing plate temperatures, the critical heat flux regime is approached and the heat transferred increases substantially. At lower plate temperatures, nucleate boiling occurs limiting the heat transferred to low values. The critical heat flux and temperature found for UWS are reported and in good agreement with the trend in previous studies for water. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction with urea-derived ammonia is the method of choice for NOx abatement in diesel engine exhaust. Pressure-driven or air-assisted atomization of aqueous urea are the main methods taken into consideration and greatly determine urea decomposition, mixture formation and SCR performance. This experimental study compares the spray behavior of two commercially available urea water solution injectors under various cross-flows. Shadow imaging and planar Mie scattering captured the spray phenomenology, while phase Doppler anemometry provided droplet sizes and velocities. Distributions of urea and decomposition products were determined from samples by high pressure liquid chromatography. Fourier-transform infrared spectroscopy measurements downstream of a catalyst provided ammonia distributions as well as NOx reduction characteristics. Pressure-driven urea-distributions are shown to be governed by the extensive volume fraction in the largest droplets. These are affected only slightly by the flow and their impingement is of primary interest. This resulted in poor mixture formation across all flow conditions. In contrast, distribution of the smaller droplets created by air-assisted atomization depends mostly on the turbulence and vorticity induced by the injector air-flow. Uniformity was excellent under low flow conditions but reduced at higher cross-flows. Urea and consequent non-uniform ammonia distribution led to inherent NOx conversion deficiency and NH 3 -slip. For identical overall NH 3 /NOx ratios in the feed the pressure-driven injector results in lower NOx conversion and higher NH 3 -slip in respect to the air-assisted injector. [ABSTRACT FROM AUTHOR]

The injection process of urea–watersolution determinesinitial conditions for reactions and catalysis and is fundamentallyresponsible for optimal operation of selective catalytic reduction(SCR) systems. In this study, injection and spray atomization characteristicsof a pressure driven injector were investigated in varying crossflowconditions using shadow imaging, Mie scattering, and particle imagevelocimetry (PIV). Spray angle and tip propagation are described.Processed images characterize spray density and mass distribution.Velocity fields from PIV analyses indicate the entrainment of dropletsin the spray. This is shown to be primarily dependent on the injectionmomentum ratio, in accordance with previous literature. The presenceof a vortex pair is clearly evidenced at low gas flow momentums. Resultsindicate that fluid mechanic differences between the spray and gasflow are insufficient to induce substantial secondary breakup andinteract extensively with the bulk of the spray. Spray wall impingementremains unavoidable; therefore, sufficient mixing lengths or devicesare required for urea decomposition. [ABSTRACT FROM AUTHOR]

Abstract: The reactivity of soot at different sites of the exhaust after-treatment system of a diesel engine (upstream and downstream of the diesel oxidation catalyst (DOC), downstream of the diesel particulate filter (DPF), as well as inside the DPF) was investigated on the basis of morphology and structure of primary soot particles by high resolution transmission electron microscopy (HRTEM). The results indicate that combustion-formed soot particles are susceptible to further transformations of their morphology within the exhaust system. The same primary soot particles can possess both oxidation-promoting and oxidation-inhibiting morphological features, the particle cores being highly reactive. Most reactivity-promoting features are encountered in pre-DOC and post-DOC primary particles, suggesting that soot can be more easily oxidised before it enters the DPF. The residence time of soot in the DPF contributes to modification of its reactivity by affecting size distribution and nanostructure of primary particles. Partial NO2 oxidation and high temperatures during active regeneration modify the morphology of outer particle shells, thus rendering post-DOC and post-DPF primary soot particles less reactive in this respect. Primary soot particles that pass through the DPF and reach the atmosphere are characterised by the highest graphitisation degree and sizes larger than those entering the DPF. Complementary Near-Edge X-ray Absorption Fine Structure (NEXAFS) analyses proved not as relevant regarding soot reactivity but indicate higher chemical inhomogeneity of pre-DOC than of post-DOC and post-DPF soot and high contents of carboxyl carbon in post-DPF particles. [Copyright &y& Elsevier]

Remote Emission Sensing (RES) is a measurement method based on absorption spectroscopy for the determination of pollutant concentrations. The absorption of the exhaust plume of a vehicle is measured from the roadside without intervention by means of a light/laser barrier during a short measurement (∼0.5 s) and concentration ratios of pollutants (e.g., NO x to CO 2 ) are estimated. Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations of exhaust plumes in vehicle wakes are performed using the k- ω SST turbulence model with focus on pollutant dispersion. The simulation setup has been validated by a comparison with experimentally obtained drag coefficients. The resulting concentration fields represent the pollutants available for measurements by a RES device. The influence of the characteristics of the RES device on the measurement is assessed. In addition, investigations involve several environmental and vehicle related parameters. The results demonstrate that due to strong turbulence, mixing is enhanced and the exhaust plumes rapidly disperse in the near vehicle wakes. Results show that emission characteristics of a vehicle are contained downstream for approximately half the vehicle length, regardless of different vehicle configurations, driving and ambient parameters. Further downstream dispersion of pollutants results in concentrations that are less than 1 / 100 of the pollutant concentration in the vehicle's exhaust tailpipe implying that RES devices have to measure at a high sampling frequency. Therefore, reliable determination of the concentration ratios of pollutant at high vehicle velocities requires the RES device to operate in the order of 1000 Hz sampling frequency. Ultimately, the numerical simulations not only help to understand exhaust plume dispersion, but provide a very useful tool to minimize RES uncertainties. [ABSTRACT FROM AUTHOR]

Abstract: Multi-scale analytical investigations of particulate matter (soot and ash) of two loaded diesel particulate filters (DPF) from (a) a truck (DPF1) and (b) a passenger car (DPF2) reveal the following: in DPF1 (without fuel-borne additives), soot aggregates form an approximately 130–270μm thick, homogeneous porous cake with pronounced orientation. Soot aggregates consist of 15–30nm large individual particles exhibiting relatively mature internal nanostructures, however, far from being graphite. Ash aggregates largely accumulate at the outlet part of DPF1, while minor amounts are deposited directly on the channel walls all along the filter length. They consist of crystalline phases with individual particles of sizes down to the nanoscale range. Chemically, the ash consists mainly of Mg, S, Ca, Zn and P, elements encountered in lubricating oil additives. In the passenger car DPF2 (with fuel-borne additives), soot aggregates form an approximately 200–500μm thick, inhomogeneous porous cake consisting of several superposed layers corresponding to different soot generations. The largest part of the soot cake is composed of unburned, oriented soot aggregates left behind despite repeated regenerations, while a small part constitutes a loose layer with randomly oriented aggregates, which was deposited last and has not seen any regeneration. Fe-oxide particles of micro- to nano-scale sizes, originating from the fuel-borne additive, are often dispersed within the part of the soot cake composed of the unburned soot leftovers. The individual soot nanoparticles in DPF2 are approximately 15–40nm large and generally less mature than in the truck DPF1. The presence of soot leftovers in DPF2 indicates that the addition of fuel-borne material does not fully compensate for the temperatures needed for complete soot removal. Ash in DPF2 is filling up more than half of the filter volume (at the downstream part) and is dominated by Fe-oxide aggregates, due to the Fe-based fuel-borne additive, but otherwise its chemical composition reflects compounds of lubricating oil additives. [Copyright &y& Elsevier]

• Significantly improved methane conversion with targeted lean/rich oscillations. • Characteristic 'W' shape methane concentration profiles during oscillations. • Analysis of different reaction regimes over the 'W' shape. • Reaction regimes linked to catalyst oxidation state and adsorbed species. Methane (CH 4) has the prospective of becoming one of the major energy carriers for heavy-duty mobility, but its catalytic abatement remains a challenge. CH 4 abatement reaction pathways were analyzed using targeted periodic lean/rich oscillations, which resulted in higher CH 4 conversion than under static conditions. At both the lean-to-rich and rich-to-lean transitions of such oscillations, local maxima of CH 4 concentration were followed by local minima during each lean and rich phase. The CH 4 concentration profile during one oscillation displayed a 'W' shape. Four reaction regimes were identified corresponding to the four sections of the characteristic concentration shape. Entering the rich phase, Steam reforming (SR) started, which was then hampered by the formation of carbonaceous species and CO interaction with the catalytic surface. By entering the lean phase, SR is again enhanced as more active sites became available due to oxygen related reactions. However, increasing chemisorbed oxygen slowed down the oxidation of CH 4. The transition between the consecutive regimes was linked to changes of the active Ce3+ coverage ratio, which plays an important role in SR reaction. Similar 'W' shapes were observed under various oscillation conditions and at different measurement points along the catalyst axis. The CH 4 concentration profile was found to shift downwards with decreasing oscillation frequencies until a frequency threshold, which is marked by the equivalence of oscillation rich/lean phase length and the time needed to completely deplete/replenish the Oxygen storage capacity (OSC). The conversion characteristics were reproduced by numerical simulations, which revealed the spatial distribution of reactions in the catalyst under these dynamic conditions. Optimal overall CH 4 conversion was reached for an even distribution of SR along the catalyst. [ABSTRACT FROM AUTHOR]

• Methane conversion pathway is analyzed in engine exhaust and model gas reactor. • CH 4 conversion efficiency is more than fivefold higher in transient than in steady. • In steady states, direct oxidation is the only CH4 conversion pathway. • Transient high conversion is due to activation of steam reforming. • Methane steam reforming diminishes with time due to surface carbonaceous species. Methane abatement pathways in Pd/Rh three-way catalysts have been investigated in three scales ranging from a vehicle application size catalyst, a model gas reactor and the catalyst in powder form. A special test rig was designed for the investigation of vehicle size catalysts, allowing sampling along the catalyst at discrete spatial locations, which are subject to different feed compositions. Dependent on the history of chemical environment of the catalyst, significant differences in methane conversion rate at identical feed have been identified. At steady state methane conversion rate was low and the reaction pathway was identified as limited to only direct oxidation by oxygen. Following a rich-to-lean transition, the catalyst exhibited more than 8 times higher methane conversion rates compared to steady state. The high methane conversion rates have been identified and attributed to the activation of methane steam reforming (SR) related to transient reduction of ceria. Methane SR efficiency decreased with time and the conversion rate finally converged to steady state levels. The findings were validated using a model gas reactor enabling analysis under well-defined feed compositions. The deactivation of SR was further analyzed with infrared spectroscopy (DRIFTS). Evidences from DRIFTS measurements showed that the deactivation was linked to the formation of carbonaceous species on the catalyst surface, most likely carbonates. The coherent results from engine exhaust analysis, model gas reactor and DRIFTS study give important insights in the activation and deactivation of methane reaction pathways. The results of this study suggest that catalyst formulation and operation strategies of methane conversion should focus on the stimulation of SR and the maintenance of catalyst activity towards SR through targeted periodic lean/rich transitions. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has the potential to revolutionize engineering because of its advantages in the product development phase. The revolution consists in the new approach of components' design by function and no longer by manufacturability. This is the motivation driving authors to design and realize by additive manufacturing a new catalyst support for automotive exhausts which is no longer constrained by the industrial manufacturing methods and thus allows an optimized flow of the exhaust gasses. This work presents a new class of periodic cellular ceramic substrates. To authors' knowledge this is the first time such kind of structures are employed in the automotive field. After a review the different ceramic AM techniques which are currently utilized in the production of highly complex ceramic architectures, the most suited one was selected and several samples were produced by AM. They were finally characterized via microscopic analysis (SEM, CT) compression tests revealing the best printing configuration for their mechanical behavior. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation of the heat transfer characteristics of the spray/wall interaction in diesel selective catalytic reduction (SCR) systems. The work was performed with a commercial 3-Hole pressure-driven injector dosing into a flow channel under typical diesel exhaust flow conditions. Infrared thermography captured the surface temperature of the wall around the impingement area with high temporal and spatial resolution. The resulting temperatures have been used for assessing the heat extracted from the wall. Phase Doppler Anemometry (PDA) was applied to measure the droplet sizes and velocities prior to the wall impingement, providing information on the kinetic properties of the impinging droplets. Based on these, the influence of the gas flow conditions on the heat transfer characteristics is deduced. The spray impingement leads to a substantial and rapid temperature drop on the wall, resulting in a maximum heat flux of several MW/m 2 during the injection duration. The spray cooling effect decreases with increasing exhaust gas flow rate due to the increased entrainment of spray droplets in the flow prior to impingement. Increase in gas flow temperature affects the heat transfer by increasing the wall temperature. At lower wall temperatures, the principal spray/wall interaction regime is deposition. With increasing wall temperature, there is a shift to rebound and thermal breakup. The shorter contact times in the rebound and thermal breakup regimes result in decreased spray/wall heat transfer. [ABSTRACT FROM AUTHOR]

Modern direct injection gasoline engines (GDI) generate considerably higher soot particulate matter (PM) emissions than conventional, port fuel gasoline, as well as diesel cars with particle filter. Soot PM generated by a typical state-of-the-art GDI (Euro VI) vehicle during two standard international driving cycles (NEDC, WLTC), as well as during a short experimental sub-cycle was investigated by electron microscopy. The study reveals primary particles between ∼4–55 nm in diameter, the majority being < 20 nm during all driven cycles; sub-20 nm particles are more abundant in the more dynamic WLTC. Monodisperse agglomerates made of small (<20 nm), medium (∼25 nm) and large (∼35 nm) primary particles are distinguished; they usually form parts of polydisperse agglomerates but also occur as distinct entities. The particle groups of different sizes are probably derived under diverse operating conditions, the larger ones being likely associated with the cold start phase. This inference is supported by simultaneously ran FMPS measurements, which reveal in addition that the cold start phase seems to account for ∼25% of the particle agglomerate emissions of the entire cycle. All particles, especially the medium and large fractions, exhibit low degrees of crystallinity indicating relatively high reactivity. The predominance of sub-20 nm primary particles render GDI soot PM potentially hazardous to human health, especially considering the higher surface and surface/volume ratio compared to larger particles of the same total volume. The engine operating parameters seem to be of prime importance for the resulting morphological features of soot. [ABSTRACT FROM AUTHOR]

Foam based catalytic converters have the potential to decrease cold-start emissions in automotive applications due to their low thermal inertia and excellent mass and heat transfer properties. A 3D CFD model of a foam based catalytic converter is proposed and employed here to simulate cold-start transients. The modeled phenomena include conjugate heat transfer, finite rate washcoat diffusion and detailed multi-step chemistry of CO oxidation over Pt. The simulation results confirm that foam based catalytic reactors have potentially lower cold start emissions compared to honeycomb reactors. Cumulative emissions decrease with increasing foam porosity, decreasing pore diameter and decreasing effective axial solid conductivity. The effects of inflow velocity, inflow CO mass fraction and washcoat surface area (Pt loading) on cold start emissions are discussed in detail. The effects of foam properties and inflow conditions on cumulative emissions are summarized with a correlation that matches the results of the pore scale simulations. [ABSTRACT FROM AUTHOR]

To address energy transition in the immediate future, synthetic energy carriers are among the most promising options for decarbonization due to their capability to store renewable energy in the long term and rely on existing infrastructure. Methane, as a substitute for natural gas, can be produced at high purity through sorption-enhanced processes. These processes are discontinuous, they require sorbent regeneration once saturation is reached. Therefore, optimal operation of these complex systems requires the control of many time-dependent variables. In this framework, the rapid analyses that can be carried out via dynamic mathematical models could be greatly beneficial in lowering costs at the design stage. In this study, a model of a sorption-enhanced methanation system was developed and validated with experimental data. The proposed model allows the dynamic behavior of the process to be captured during production and sorbent regeneration. Insights into the process show the behavior of the sorbent bed while retaining water, demonstrating how the bed saturation occurs and how to effectively exploit it. The model potential was assessed by analyzing the alternating operation of two reactors for continuous production. The importance of bed drying was underlined to ensure the enhancement of the reaction and maximize the conversion. [ABSTRACT FROM AUTHOR]

Many countries worldwide have introduced a limit for solid particles larger than 23 nm for the type approval of vehicles before their circulation in the market. However, for some vehicles, in particular for port fuel injection engines (gasoline and gas engines) a high fraction of particles resides below 23 nm. For this reason, a methodology for counting solid particles larger than 10 nm was developed in the Particle Measurement Programme (PMP) group of the United Nations Economic Commission for Europe (UNECE). There are no studies assessing the reproducibility of the new methodology across different laboratories. In this study we compared the reproducibility of the new 10 nm methodology to the current 23 nm methodology. A light-duty gasoline direct injection vehicle and two reference solid particle number measurement systems were circulated in seven European and two Asian laboratories which were also measuring with their own systems fulfilling the current 23 nm methodology. The hot and cold start emission of the vehicle covered a range of 1 to 15 × 1012 #/km with the ratio of sub-23 nm particles to the >23 nm emissions being 10–50%. In most cases the differences between the three measurement systems were ±10%. In general, the reproducibility of the new methodology was at the same levels (around 14%) as with the current methodology (on average 17%). [ABSTRACT FROM AUTHOR]

Investigation of soot and ash particulate matter deposited in diesel particulate filters (DPFs) operating with biofuel (B100) and diesel (pure diesel: B0 and diesel/biofuel blend: B20) by means of optical microscopy, scanning electron microscopy, and high resolution transmission electron microscopy (HRTEM) reveals the following: the rapeseed methyl ester biofuel used for this study contributes to ash production, mainly of Ca-S- and P-bearing compounds ranging in size between 50 and 300 nm. Smaller ash particles are less common and build aggregates. Ash is deposited on the inlet DPF surface, the inlet channel walls, and in B100-DPF at the plugged ends of inlet channels. The presence of Fe-Cr-Ni fragments, down to tens of nanometers in size within the ash is attributed to engine wear. Pt particles (50-400 nm large) within the ash indicate that the diesel oxidation catalyst (DOC) upstream of the DPF shows aging effects. Radial cracks on the coating layer of the DOC confirm this assumption. The B100-DPF contains significantly less soot than B20 and B0. Based on the generally accepted view that soot reactivity correlates with the nanostructure of its primary particles, the length and curvature of graphene sheets from biofuel- and diesel-derived soot were measured and computed on the basis of HRTEM images. The results show that biofuel-derived soot can be more easily oxidized than diesel soot, not only during early formation but also during and after considerable particle growth. Differences in the graphene sheet separation distance, degree of crystalline order and size of primary soot particles between the two fuel types are in line with this inference. [ABSTRACT FROM AUTHOR]

Open cell foams are considered promising catalytic substrates providing high surface area and a tortuous structure resulting in enhanced mass transfer characteristics. CFD analysis, recently, has focused in pointing structures with favourable reactivity-flow resistance characteristics. In order to reduce the geometrical complexity and computational efforts, foams have been modelled as regular (polyhedric) open cell structures. In this study a comprehensive comparison of real foams with equivalent Kelvin cell lattices is performed in CFD. Therefore 4 typical foams (two ceramic and two metallic) have been chosen. Geometric properties have been accessed with Micro-Tomography scans. Randomised Kelvin cell lattices have been generated matching porosity and specific surface area of the scanned real foams. Geometric, momentum and mass transfer characteristics of real foams and Kelvin cell lattices are analysed with CFD. Kelvin cell lattices showed similar behaviour in respect to their real foam equivalents, had though clearly better reactivity-pressure drop trade-offs. Based on the results presented best performances as a catalyst can be expected by 3D printed, additive manufactured, high porosity polyhedric structures. [ABSTRACT FROM AUTHOR]

Production of synthetic methane as a substitute for natural gas has been widely discussed as a means of long-term energy storage with the potential of CO 2 neutrality. While the maximum conversion of catalytic CO 2 methanation is limited by the highly exothermic and pressure-dependent nature of the Sabatier reaction, high conversion at low pressure could be achieved at laboratory scale through sorption enhancement. The transient nature of this process requires new reactor designs and process engineering for large-scale reactors. We investigated pellet bed reactors from a process and reactor engineering perspective, particularly in the context of upscaling. Our results show that heat generation in the reactor remains a major challenge for process performance and product purity. The bed temperature is coupled with the water adsorption capacity of the catalyst, which in turn affects the reactor capacity. Consequently, this has an impact on the dynamics of the coupled adsorption and reaction front with implications for the design of larger reactors. The results provide a comprehensive understanding of the process and a guide for reactor engineering. • Reactor temperature affects yield and quality for sorption-enhanced CO 2 methanation. • Continuous conversion affects water-saturated sections by increasing temperature. • Thermal and flow design are key parameters for upscaling and process intensification. • Comprehensive dataset of material and process parameters for reactor design. • Simple model supports reactor scale-up and process scheduling. [ABSTRACT FROM AUTHOR]

This study presents a joint experimental and numerical investigation of a spray used in selective catalytic NOx reduction (SCR) after-treatment systems for Diesel engine exhaust gases. The focus lies on the impingement conditions and distribution and mixing mechanisms of the spray in cross-flowing exhaust gases. These aspects are vital to system performance but still not well described. A pressure-driven SCR injector is characterized in an optically accessible flow test rig at different temperatures and mass flow rates representative of Diesel engine exhaust gas conditions by means of Mie scattering and Phase Doppler Anemometry (PDA). The effects of cross-flow velocity and temperature on spray structure, droplet size and velocity distributions are assessed resulting in a comprehensive characterization of the spray. Results show that the dense spray core, with droplets up to 200 μm, only moderately reduces in density as smaller droplets are entrained at high exhaust flows. Wall impingement conditions however vary substantially as impingement angles are shallower at higher cross-flow velocities. A detailed assessment of the numerical model is presented and validation is carried out at different measurement locations of interest. The predicted droplet size distributions and velocities follow the observed trends and impingement angles as well as spray film areas on the channel floor are also in agreement with the experimental data. The validated model is subsequently used to numerically study the mixing dynamics. The findings suggest that at low cross-flow conditions two counter-rotating kidney vortices are formed which entrain reflected droplets of the spray impinging on the channel floor, which leads to improved mixing. Vapor concentrations increase close to the side walls and reflected droplets lead to film-formation on the side walls. At higher cross-flow velocities, vortex formation is not evident and spray-wall interaction is less pronounced – impairing mixing and leading to a reduction in concentration uniformity at down-stream locations. Film formation and high vapor concentrations are restricted to the bottom channel centerline. [ABSTRACT FROM AUTHOR]

Foam based catalytic converters are a promising alternative to the established honeycomb reactors for treatment of pollutants in automotive applications. They provide excellent mass transfer properties at reasonable pressure drop and have the potential to achieve high conversion at smaller external dimensions. The goal of this work is to determine the relative importance of washcoat diffusion resistance in foam based reactors. Catalytic oxidation of CO over Pt is computationally simulated with a volume averaged model. Based on micro-kinetic modelling and the resulting resolution of the reaction-diffusion processes inside the washcoat, the simulations provide a comprehensive picture of the chemistry and transport processes. Washcoat diffusion resistances in foams – although often considered negligible – are shown to be at least as important as in honeycomb converters, due to the higher external mass transfer coefficients in foams. The computations show a reduction in conversion with respect to the limit of infinitely fast kinetics of 46% for the foam-based reactor after catalytic light-off. The impact of washcoat diffusion resistance on conversion decreases with increasing surface area of the washcoat. An increase in pore size of the washcoat leads to improved conversion. [ABSTRACT FROM AUTHOR]

Open-cell foams are increasingly gaining attention as catalytic substrates due to their promising properties of high porosity, high specific surface and tortuous structure resulting in enhanced gas–wall interactions. However, due to the foam complex structure and variability of properties, the published data do not clarify weather true advantages of ceramic foam based catalytic converters can be expected; high gas–wall interactions may result to increased flow resistance. In the present work, foams are modelled as Kelvin Cells and compared to honeycombs, the state of the art catalyst substrates, in the controlled environment of numerical simulations. A CFD analysis has been performed assuming a mass transfer limited regime and imposing infinitive fast chemistry at the catalytic surface. Our results show that open-cell structures compared to honeycombs have higher mass transfer properties at moderate to high flow rates ( u > 2 m / s ), allowing more compact reactors. Moreover they can achieve the same conversion with a significantly lower surface, saving an equivalent fraction of noble metal. In order to have the same conversion to pressure drop trade off, foam porosity has to be much higher compared to honeycombs. [ABSTRACT FROM AUTHOR]

Abstract: Pore-scale simulations of transport phenomena in foam based catalytic converters are highly desirable due to their intrinsic accuracy in describing the involved physics. Unfortunately, such computations are prohibitively time consuming and costly. Here we combine a detailed pore-scale characterization with a volume average description of an open-cell foam based catalytic converter. The resulting volume averaged model is accurate and more than three orders of magnitude more efficient in terms of computational time, compared to direct pore scale simulations. This makes simulations of the related complex phenomena tractable, providing a highly flexible and powerful tool for parametric studies of open-cell foams. The volume-averaged model is validated with a pore-scale simulation of a full-scale catalytic converter used for automotive exhaust gas treatment. Fast chemistry is assumed and the heat released by the chemical reaction in combination with conjugate heat transfer is considered. We show that the conversion to pressure drop trade-off improves with increasing foam porosity and the heat release of the reaction significantly affects the pressure drop across the reactor. The simulations show non-uniform surface temperatures which are attributed to the non-unity Lewis number of the mass transfer limiting species. The model predictions agree well with experimental measurements of pressure drop and Sherwood number in open-cell foams. [Copyright &y& Elsevier]

Open cell foams are attractive materials for various industrial applications, but building accurate universal correlations is challenging due to their great geometrical complexity. Momentum and mass transfer of a randomly packed Kelvin cell structures are numerically investigated. Porosity, ε, Kelvin cell size, PPI, and inflow velocity, u, are systematically varied for a total of 120 simulations. Correlations for geometrical and transfer properties are discussed. The analogy based on the generalized Lévêque equation (Martin, 2002) between mass and momentum transfer is evaluated and it is qualitatively in agreement with the results of Incera Garrido et al. (2008) on ceramic foams. [ABSTRACT FROM AUTHOR]

A model Pd-only three-way catalyst has been subjected to simulated driving conditions of natural gas and gasoline operation in an operando reactor cell for X-ray absorption spectroscopy that included alternated, but longer than real oscillations, rich and lean periods and a high temperature surge (850–900°C). The X-ray absorption near edge structure (XANES) spectra indicated that metallic palladium is observed in the whole temperature range investigated (up to 900°C) and irrespective of the air/fuel ratio. In both natural gas and gasoline cycles, the XANES data show that the PdO reduced in the rich periods cannot be restored in the lean periods. With this background, activity for methane abatement in the high temperature regime is greatly affected by the oxidation state of palladium rather than by the change of air/fuel ratio. In the case of propene oxidation, while Pd also remains predominantly in the reduced state, activity is dictated by the oxygen concentration in the feedstock. Comparison between the two hydrocarbons demonstrates that the oxidation state of Pd may be responsible for observed methane emissions under realistic operating circumstances. Moreover, the experiments demonstrate that reduced Pd may be continuously present during operation in agreement with observations on real catalytic converters. Although this may be the average oxidation state of Pd, more advanced probes are certainly necessary to capture variations of oxidation state under the fast oscillatory conditions needed to imitate real operation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gasoline–ethanol fuel blends result in additional mechanical and ash burden for TWCs. [•] Oxidation of unburned hydrocarbons and reduction of NOx decreases. [•] Catalyst ash layer of CNGs have loose ‘sieve’ structure. [•] CNG fuel results in high HCs consisting almost entirely of CH4 after catalyst. [•] Ash from lube oil does not affect catalysts with CNG fuel. [Copyright &y& Elsevier]