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Studying a large number of scenarios is necessary to consider the uncertainty inherent to the energy transition. In addition, the integration of intermittent renewable energy sources requires complex energy system models. Typical days clustering is a commonly used technique to ensure the computational tractability of energy system optimisation models, while keeping an hourly time step. Its capability to accurately approximate the full-year time series with a reduced number of days has been demonstrated (i.e., a priori evaluation). However, its impact on the results of the energy system model (i.e., a posteriori evaluation) is rarely studied and was never studied on a multi-regional whole-energy system. To address this issue, the multi-regional whole-energy system optimisation model, EnergyScope Multi-Cells, is used to optimise the design and operation of multiple interconnected regions. It is applied to nine diverse cases with different numbers of typical days. A bottom-up a posteriori metric, the design error, is developed and analysed in these cases to find trade-offs between the accuracy and the computational cost of the model. Using 10 typical days divides the computational time by 8.6 to 23.8, according to the case, and ensures a design error below 17%. In all cases studied, the time series error is a good prediction of the design error. Hence, this a priori metric can be used to select the number of typical days for a new case study without running the energy system optimisation model. [ABSTRACT FROM AUTHOR]

Abstract In most Rapid Compression Machine (RCM) operations, it is sought to have a homogeneous temperature field inside the core region of the reaction chamber so that the adiabatic core assumption may be appropriately applied. Pistons with crevice on their side have shown to be effective in producing a uniform temperature field at the end of the compression. Although the efficiency of the crevice to produce a homogeneous environment is highly dependent on the operational conditions (pressure, temperature, gases composition, compression time, etc.), crevice designs are seldom adapted to the intended experiments. This is problematic as there are potentially many experiments which do not respect the conditions to obtain a uniform temperature field required to correctly interpret the data. Actually, no method other than CFD simulations has been proposed to this day to validate a specific crevice design, which is in practice most often an obstacle to the systematic validation of crevices. The model proposed in this study aims to fill this gap in allowing to check if a crevice design yields a homogeneous temperature field in the considered operational conditions. It is observed that as soon as a critical mass is transported from the chamber to the crevice, the crevice fulfills its role and guarantees the temperature homogeneity of the core region. The two key findings of the present work are therefore to be able to predict this critical mass for any possible configuration, and to propose an easy method to assess whether a specific crevice volume ensures this critical mass to be effectively sucked from the chamber. The whole process proposed in this study could then be applied as a certification of crevice design prior to any RCM experimental campaign. [ABSTRACT FROM AUTHOR]

Highlights • Novel methodology to directly use unscrubbed biomass syngas in piston engines. • Demonstration of EGR as an efficient control parameter for HCCI engines operated with synthetic syngas. • For syngas combustion, EGR has mainly a thermal effect rather than chemical kinetic effect. • The study spans a large range of conditions and improve by 30% the IMEP. Abstract In combined heat and power plants operated with biomass syngas, the removal of condensible tars is a necessary but expensive step (up to one third of the installation and maintenance costs). This step is required because the syngas has to be cooled down to avoid knocking in the spark ignition engines traditionally used in such plants. To remove the tar condensation problem, we developed an alternative system based on an Homogeneous Charge Compression Ignition (HCCI) engine operated at intake temperatures above the tar dew point. To address the challenge of power derating of such engine setups, the current paper focuses on the application of Exhaust Gas Recirculation (EGR) as a control parameter that would indirectly allow the improvement of the engine performance. Based on a conservative estimate of tar dew points, HCCI combustion was studied at an intake temperature of 250 °C using synthetic biomass syngas and synthetic EGR on a mono-cylinder HCCI engine operated at 1000 RPM. The effects of charge dilution, thermal and kinetic damping due to the EGR gases were also analysed to understand their main effects. The use of EGR successfully increased the maximum achievable Indicated Mean Effective Pressure from 2.5 bar at EGR = 0% up to 3.3 bar at EGR = 25%, through damping the maximum pressure rise rate and allowing higher equivalence ratios. [ABSTRACT FROM AUTHOR]

To face climate changes and energy dependency, governments encourage their industries and communities to increase the share of renewable energy (RE). However, the RE production is mostly inflexible. The risk of unmatching electricity market grows. Tools such as power plant flexibility, import/export, demand side management, storage and RE curtailment are developed to handle this problem. This study focuses on the energy storage mix required for the energy of the electricity system to high RE shares. An hour based model is developed in order to optimise the renewable energy and storage assets by maximising the energy return on investment (EROI) while respecting power fluxes constraints. The model is used to quantify the storage needs for the energy transition of Belgium. An in-depth analysis is performed for four scenarios. Depending on the RE deployment and nuclear share, EROI between 5 and 10.5 are obtained. Large scale storage is required as soon as the energy mix has more than 30% of RE. With more than 75% of RE, power to gas becomes unavoidable. This study highlights that curtailment can be limited to less than 5% of RE production. These values are the result of the optimum between increasing storage, RE capacity and curtailment. [ABSTRACT FROM AUTHOR]

Abstract: Numerous industrial applications dedicated to the conversion of biomass into heat and power include a pyrolysis step conducted under severe thermal conditions (heating rates of 103…105 K s−1 and maximum temperatures higher than 1000 K). While pyrolysis might not be the central phenomenon of the considered processes, it is often an essential input for the other steps to be modelled, for instance the successive oxidation of the pyrolysis volatiles in combustion applications. Two competitive, multi-component pyrolysis mechanisms have been compared to low (1 K s−1) and high (103 K s−1) heating rate experimental results. One of them features a characterization of the emitted gaseous species. It was found that both mechanisms reasonably agree with measurements at low heating rate, and that they diverge at higher heating rates, none of them being able to reasonably fit the experimental data. The observed discrepancies have been studied and modifications have been proposed for the most comprehensive mechanism. The resulting scheme has been combined with a two-dimensional physical model of a single particle that is necessary for problems that cannot be considered as thermally thin. The resulting model is a powerful predicting tool for the emitted species yields from a pyrolysing particle, even in high temperature applications. [Copyright &y& Elsevier]

Different scenarios at different scales must be studied to help define long term policies to decarbonate our societies. In this work, we analyse the Belgian energy system in 2035 for different carbon emission targets, and accounting for electricity, heat, and mobility. To achieve this objective, we applied the EnergyScope Typical Days open source model, which optimises both the investment and the operation strategy of a complete energy system for a target year. The model includes 96 technologies and 24 resources that have to supply, hourly, the heat, electricity, mobility, and non-energy demands. In line with other research, we identify and quantify, with a merit order, different technological steps of the energy transition. The lack of endogenous resources in Belgium is highlighted and estimated at 275.6 TWh/y. It becomes obvious that additional potentials shall be obtained by importing renewable fuels and/or electricity, deploying geothermal energy, etc. Aside from a reduction of the energy demand, a mix of solutions is shown to be, by far, the most cost effective to reach low carbon emissions. [ABSTRACT FROM AUTHOR]

The Energy Return On Investment (EROI) is a recognised indicator for assessing the relevance of an energy project in terms of net energy delivered to society. For woody biomass divergences remain on the right methodology to assess the EROI leading to large variations in the published estimates. This article presents an in‐depth discussion about the EROI of woody biomass in three different forms: woodchips, pellets and liquid fuels. The conceptualisation of EROI is further developed to reach a consistent definition for biomass post‐processed fuels. It considers, on top of the external energy investments, the grey energy associated with the energy used to enrich the fuel. With the proposed methodology, all woodchips have an EROI of the same order of magnitude, between 20 and 37, depending on forestry types, operations and machineries. For secondary residues, the first estimate is 170 if, as co‐products, no energy investment is allocated to the forestry operations and transport. On the basis of a mass allocation for forestry operations and transport, the EROI for secondary residues becomes of the same order of magnitude as that for wood chips. Woodchips can be further post‐processed into pellets or liquid fuels. Pellets have an EROI of 4–7 if the heat is externally supplied and 8–23 if internally supplied (self‐consumption of part of the raw material). Liquid fuels derived from primary wood and residues through gasification and Fischer‐Tropsch synthesis have an EROI between 4 and 16. Fuel enhancement with hydrogen (Power & Biomass to Liquids) impacts negatively the EROI due to the low EROI of hydrogen produced from renewable electricity. However, these fuels offer other advantages such as improved carbon efficiency. A correct estimate of EROI for forestry biomass, as proposed in this work, is a necessary dimension in assessing the suitability of a project. [ABSTRACT FROM AUTHOR]

The use of creviced pistons in Rapid Compression Machines (RCMs) has proven to be very efficient in making the temperature homogeneous inside the reaction chamber but has the disadvantage of inducing an unintended mass transfer from the reaction chamber to the crevice, especially during the preliminary heat release of two-stage ignition processes. Aiming to mitigate this mass transfer, the technique of ‘crevice containment’ (CC) has been proposed. It consists of a physical separation between the reaction chamber and the crevice region that is engaged at the end of the compression, physically preventing any mass transfer between both parts of the geometry. In order to numerically assess this novel design concept across a broader range of conditions than previously investigated, reactive simulations using detailed chemical kinetic mechanisms are performed for n-heptane and iso-octane mixtures. It is found that for compressed temperatures outside of the NTC (negative temperature coefficient) region, the CC approach is very effective in suppressing the influence of the crevice mass transfer and thus increases the validity of the widely-used 0-D model based on the adiabatic core assumption. Still, for most of the temperature cases inside the NTC region, ignition appears to be prematurely initiated in the residual vortex region formed after the seal engagement, possibly inducing very significant differences with the 0-D model. The benefits of eliminating the post-compression crevice mass transfer appear to be counter-balanced by effects that have not been previously identified. [ABSTRACT FROM AUTHOR]

Looking ahead to 2050 many countries intend to utilise wind as a prominent energy source. Predicting a realistic maximum yield of onshore and offshore wind will play a key role in establishing what technology mix can be achieved, specifying investment needs and designing policy. Historically, studies of wind resources have however differed in their incorporation of physical limits, land availability and economic constraints, resulting in a wide range of harvesting potentials. To obtain a more reliable estimate, physical and economic limits must be taken into account. We use a grid-cell approach to assess the theoretical wind potential in all geographic locations by considering technological and land-use constraints. An analysis is then performed where the Energy Return on Investment (EROI) of the wind potential is evaluated. Finally, a top-down limitation on kinetic energy available in the atmospheric boundary layer is imposed. With these constraints wind farm designs are optimized in order to maximize the net energy flux. We find that the global wind potential is substantially lower than previously established when both physical limits and a high cut-off EROI > 10 is applied. Several countries’ potentials are below what is needed according to 100% renewable energy studies. [ABSTRACT FROM AUTHOR]

For decentralized power generation in West Africa, gas from a small biomass gasification unit can be used as the main fuel in a dual-fuel engine with diesel as the pilot fuel. To study the combustion in this type of engine (Lister Petter), experiments were conducted with a surrogate gas composed of liquefied petroleum gas and nitrogen (LPGN2), the energy context of which is similar to that of syngas. The tests were conducted at different loads and for different diesel substitution rates. The combustion analysis showed that the LPGN2 mixture had an overall behaviour similar to neat diesel, while the pressure peaks were lower in dual-fuel mode. The results also indicated a longer ignition delay and a pronounced diffusive combustion phase leading to a lower indicated mean effective pressure with gas. The fuel efficiencies remained low in both mono- and dual-fuel operation. The relative instability of the combustion in dual-fuel mode gave rise to an increase in the coefficient of variation (COVIMEP). Compared to neat diesel, the engine running at low loads in dual-fuel mode showed higher emission levels of CO, a slight reduction of 2.5% of CO2 and a substantial decrease of 73% for nitrogen oxides. [ABSTRACT FROM AUTHOR]

Energy crops on marginal lands are seen as an interesting option to increase biomass contribution to the primary energy mix. However, in the literature there is currently a lack of integrated assessments of margin land availability, energy crop production potential and supply chain optimisation. Assessing the potential and the cost of these resources in a given region is therefore a difficult task. This work also emphasises the importance on a clear definition and discussion about marginal lands and the related ethical issues embedded in the concept to ensure positive societal impacts of the results. This study proposes a methodology to estimate and analyse, in terms of economic costs, the potential of miscanthus grown on marginal lands from the production to the final point of use. Different datasets are assembled and a supply chain optimisation model is developed to minimize the total cost of the system. Miscanthus is used as a representative energy crop for the Belgian and French case studies. High temperature heat demand is considered as final use. The miscanthus can be traded by truck either in the form of chips or pellets. The results show that the miscanthus on marginal lands could supply high temperature heat up to 38 TWh in France and 1.4 TWh in Belgium with an average cost of around 50 €/t. The different sensitivity analyses showed that the yield variation has the strongest influence on the final cost, together with the distances and the cost of production of miscanthus. The main pattern observed is the local consumption of miscanthus chips and export of the surplus (if any) to the neighbouring regions. Pellets are only of marginal interest for France and are never observed for Belgium. Distances and availability of sufficient feedstocks are the two main parameters impacting the production of pellets. [ABSTRACT FROM AUTHOR]

The aim of the study is to analyze the effect of ethanol in rich benzene flame, to observe the influence of this oxygenated species and to understand the kinetics of ethanol in the benzene combustion. Two premixed rich benzene/oxygen/argon (11.5% C6H6, 43.2% O2, 45.3% Ar) and benzene/ethanol/oxygen/argon (10.7% C6H6, 2.1% C2H5OH, 43.2% O2, 44.0% Ar) flat flames are stabilized at low pressure (45 mbar) on a burner with the same equivalence ratio of 2.0. Identification and monitoring of signal intensity profiles of species within the flames are carried out using molecular beam mass spectrometry (M.B.M.S.). The substitution of some C6H6 by C2H5OH is responsible for a reduction of the maximum concentrations of main intermediate species such as C2H2, C4H2, C4H4 and C5H6. The UCL mechanism is extended to heavier hydrocarbons, tested against these flames to check its validity and used to underline the effect of ethanol on soot precursors formation. It contains 1028 elementary reactions and 184 chemical species. [ABSTRACT FROM AUTHOR]

Due to the imperative nature of addressing climate change, the energy transition is currently underway, prompting the recognition of its urgency. Energy system optimisation models have emerged as crucial tools to assist policymakers in formulating laws and regulations that facilitate the transition towards carbon neutrality. While numerous models have been developed to explore various scenarios and define long-term objectives, only a few models focus on optimising the specific pathway to achieve these objectives. Many existing models lack the necessary time resolution to capture the integration of intermittent renewable energies; or are not open-source, creating a challenge in terms of transparency and reproducibility. This paper introduces EnergyScope Pathway, an open-source and documented model that addresses these limitations. It specifically optimises investment strategies for the whole-energy system over a 30-year period, or more, and optimising its hourly operation. This approach allows for a comprehensive evaluation of the effective integration of intermittent renewable energy sources. The model has a concise and efficient formulation, enabling its execution on personal laptops within approximately 15 min. By applying the model to the case study of Belgium, which presents challenges due to limited potential for renewable energy, we illustrate the importance of four pillars: energy efficiency, renewable energies, sector coupling, electrification and imports. The result pave the way to a new and incremental tool to support decision makers. In comparison to non open-source models, we verified the model's results with similar studies and found consistency in terms of technico-economic estimations. • Linear formulation of an optimisation model to represent a whole energy system transition pathway with an hourly resolution. • Short computational time, 15 min on a personal laptop • Quantify the pillars of the transition: efficiency, renewable energies and sector coupling. • Offers a new and incremental tool to support decision-makers in the energy transition. • Comparison of different approach to represent the transition. [ABSTRACT FROM AUTHOR]

• A novel grid-cell approach to estimate global solar energy potential. • Solar potentials constrained by land-use, technology conversion and net energy. • A new solar-to-electric efficiency parametrization for CSP power plants. • Power plants design optimised by maximising the Energy Return on Investment. • Solar potential is established between 1089 and 165 EJ/year at EROImin from 5 to 9. The amount of energy striking the earth's surface in one hour is higher than global annual societies energy use, yet the fraction of incoming solar radiation that can be harvested is significantly constrained. A global grid-cell methodology was adopted to assess the available global solar energy potential taking into account four constraints: land-use, solar irradiation, solar-to-electric technology, and net energy. Net energy is the amount of energy that is delivered to end-users, after subtraction of the energy inputs needed for capital infrastructure and operation. Both photovoltaic and concentrated solar power technologies are considered. The resulting constrained solar potential worldwide was estimated at 1098 exajoules per year, of which 98%, 75%, and only 15% can be extracted if the system needs to deliver an energy return on energy invested set at 5, 7.5, and 9, respectively. The resulting global solar potential is substantially lower than most previous estimates. Depending on how high the energy return needs to be relative to the energy investment needed to maintain a sustainable society, the achievable potential will be significantly constrained. The effect is especially significant in lower solar radiation regions. The European Union holds only 2% of the global solar net energy potential. [ABSTRACT FROM AUTHOR]

• Novel open-source model for long-term energy planning. • Multi-sector modelling: electricity, heat and mobility. • Optimization of design and operation for a target future year. • Suitable for scenarios with high penetration rates of renewables and storage. • Computational efficiency: hourly time resolution using typical days. The transition towards more sustainable, fossil-free energy systems is interlinked with a high penetration of stochastic renewables, such as wind and solar. Integrating these new energy resources and technologies will lead to profound structural changes in energy systems, such as an increasing need for storage and a radical electrification of the heating and mobility sectors. To capture the increasing complexity of such future energy systems, new flexible and open-source optimization modelling tools are needed. This paper presents EnergyScope TD, a novel open-source model for the strategic energy planning of urban and regional energy systems. Compared to other existing energy models, which are often proprietary, computationally expensive and mostly focused on the electricity sector, EnergyScope TD optimises both the investment and operating strategy of an entire energy system (including electricity, heating and mobility). Additionally, its hourly resolution (using typical days) makes the model suitable for the integration of intermittent renewables, and its concise mathematical formulation and computational efficiency are appropriate for uncertainty applications. We present the linear programming model, detailing its formulation, and we apply it to a real-world case study to discuss advantages and disadvantages in comparison to other modelling frameworks. In particular, we model the national energy system of Switzerland to evaluate a 50% renewable energy scenario. [ABSTRACT FROM AUTHOR]

The biophysical foundations of socio-economic systems are underrepresented in the vast majority of macroeconomic models. This lack is particularly troublesome when considering the links between energy, matter and the economy in the context of the energy transition. As a remedy, we present here a biophysical stock-flow consistent macroeconomic model calibrated at the global scale, that combines detailed bottom-up estimates for the high capital intensity of renewable energies and the decreasing energy return on investment (EROI) of fossil fuels. We find that the completion of a global energy transition scenario compatible with the 1.5 °C objective of the Paris Agreement leads to a decrease of the system's EROI and to high investment share, employment and inflation trends, characteristic of a "war economy". Our results further indicate that a slower growth rate eases the transition, and call for further work on post-growth scenarios studies. • We present a global biophysical stock-flow consistent macroeconomic model. • This model contains detailed bottom-up estimates for the EROI of energy resources. • An energy transition scenario compatible with the Paris Agreement is assessed. • Trends in investment share and inflation are characteristic of a "war economy". • A slower growth rate eases the transition, calling for further post-growth studies.. [ABSTRACT FROM AUTHOR]

Power generation from biomass gasification through the use of spark ignition engines requires the cooling of the biomass syngas to avoid knock. This cooling leads to the condensation of tar impurities, which foul and clog up critical process components leading to significant maintenance issues and costs. Conventionally, tar related problems are addressed by optimizing the gasification process along with developing tar purification systems, both of which result in increased investment and maintenance costs. A novel method is being developed at the Université catholique de Louvain, where the entire process, from the exit of the biomass gasifier to the combustion of tar loaded impure syngas in an internal combustion engine, is carried out at a temperature of 250 ° C, thereby avoiding tar condensation and its consequent problems. A Homogeneous Charge Compression Ignition (HCCI) engine is utilized for such a high intake temperature operation. This paper describes the first experiments with an impure and hot biomass syngas, produced from a two-stage gasifier, which is burned in a HCCI engine without the intermediate cooling and tar purification steps. The objective of the experiment was to test the stability of the engine in response to the naturally occurring random variations in the syngas composition. The experiments were carried out over a continuous period of 24 h. Indicated efficiencies of 33%–39% and IMEP around 2.5 bar were observed while the emissions of NO x were relatively high, probably due to the presence of ammonia in the syngas. The implementation of a closed control loop, with the combustion phasing as the feedback parameter and the fueling rate as the controlled parameter, ensured a stable operation over the experimental duration. [ABSTRACT FROM AUTHOR]

Accurate temperature measurements in reactive combustion systems are crucial for kinetic and heat transfer studies. Intrusive temperature measurement methods, such as thermocouples, are still widely used in experimental combustion research applications. Thin wire customized type B thermocouples, (Pt Rh6%-Pt Rh30%), coated with BeO (Beryllium oxide) - Y 2 O 3 (Yttrium oxide) anti-catalytic ceramic, are used in this study to measure the flame temperature at low pressure of three H 2 /CH 4 /CO-air flat flames at different equivalence ratios. In the range 500–1700 K, the measured flame temperatures are corrected for radiation losses with two different well-known approaches, the experimental electrical compensation method (ECM) and the numerical heat transfer correction method (HTM). Both methods are applied to the measured flame temperatures, and their performance and limits are assessed, highlighting the primary sources of uncertainties. This work aims to shed light on the crucial issues related to the temperature correction methods primarily used in the experimental combustion diagnostic. A strategy to reduce the uncertainties of the two methods is proposed and applied to the measured temperature flames. The propagation of the errors on the main parameters involved in the numerical correction method is carried out to estimate the final uncertainty of the corrected gas temperatures. Finally, a new approach is proposed to quantify the error incurred by neglecting conductive heat transfer between the thermocouple bead and the connecting thermocouple wires. [ABSTRACT FROM AUTHOR]

The microstructures of six sawdust packings, three fresh and three dried, are studied by using three-dimensional X-ray microtomography data. Packings are highly disordered and are considered as porous media resulting from a stochastic process. To describe the packings, three categories of properties are defined and exploited. They are all based on the phase indicator function. The first set gives information about the geometry of the packings. The second set covers morphological parameters linked with the particles and the pores of the packings. The third set describes the connectedness of the porosity, i.e. the topology of the packings. Fresh and dried sawdust packings are compared based on the three sets of properties. The packing topology is the same for dry and wet sawdust. Dry packings have a slightly larger porosity than wet packings, by about 4%. The pore diameters are also larger in dry packings, by about a factor 2. But the specific surfaces are smaller for dry packings, by about 30%. Finally, while the sawdust particles are anisotropic, all categories of parameters show that beds are isotropic. [ABSTRACT FROM AUTHOR]

Abstract: In the context of a hypothetic hydrogen based economy, ammonia has been suggested as a potential alternative to liquid fossil fuels for spark ignition (SI) engines. However, its use requires a detail understanding of its combustion characteristics, particularly the comprehension of the unavoidable thermal and fuel nitrogen oxides formation. This study presents the elaboration of an improved ammonia combustion mechanism validated for the flame structure prediction of ammonia, hydrogen, oxygen, argon flames investigated at several low pressures and for various conditions of equivalence ratio and of initial hydrogen content. The improved kinetic model is then reduced in order to be used in a complete SI engine numerical simulation. The comparison of the predictions of these mechanisms for the same ammonia flame structure is presented. The reduced mechanism contains 80 elementary reactions and 19 chemical species and allows a better understanding of the complete nitrogen oxides formation pathways. [Copyright &y& Elsevier]

Abstract: The increased use of alcohols in internal combustion engines has driven the attention to formaldehyde emissions. Yet the experimental database on formaldehyde flames is limited. The experimental structures of two formaldehyde flames have been investigated at low pressure (30mbar) using a molecular beam sampling coupled with a mass spectrometer. The initial compositions are for the lean flame (ϕ =0.22): 18% CH2O and 82% O2, and for the stoichiometric one (ϕ =1.09): 17.7% CH2O, 16.3% O2 and 66.0% Ar. A kinetic model, previously elaborated, has been improved by building a complete submechanism taking into account the formation and consumption of species involved in the formaldehyde combustion. The improved mechanism contains 107 chemical species and 568 reactions in order to simulate these two formaldehyde flames accurately. The reliability of this kinetic model has also been tested in ethanol and acetaldehyde flames. This allows the extension of its validity range. [Copyright &y& Elsevier]

Large-eddy simulation (LES) with regular explicit filtering is investigated. The filtered-scale stress due to the explicit filtering is here partially reconstructed using the tensor-diffusivity model: It provides for backscatter along the stretching direction(s), and for global dissipation, both also attributes of the exact filtered-scale stress. The necessary LES truncations (grid and numerical method) are responsible for an additional subgrid-scale stress. A natural mixed model is then the tensor-diffusivity model supplemented by a dynamic Smagorinsky term. This model is reviewed, together with useful connections to other models, and is tested against direct numerical simulation (DNS) of turbulent isotropic decay starting with Re[sub λ]=90 (thus moderate Reynolds number): LES started from a 256[sup 3] DNS truncated to 64[sup 3] and Gaussian filtered. The tensor-diffusivity part is first tested alone; the mixed model is tested next. Diagnostics include energy decay, enstrophy decay, and energy spectra. After an initial transient of the dynamic procedure (observed with all models), the mixed model is found to produce good results. However, despite expectations based on favorable a priori tests, the results are similar to those obtained when using the dynamic Smagorinsky model alone in LES without explicit filtering. Nevertheless, the dynamic mixed model appears as a good compromise between partial reconstruction of the filtered-scale stress and modeling of the truncations effects (incomplete reconstruction and subgrid-scale effects). More challenging 48[sup 3] LES are also done: Again, the results of both approaches are found to be similar. The dynamic mixed model is also tested on the turbulent channel flow at Re[sub τ]=395. The tensor-diffusivity part must be damped close to the wall in order to avoid instabilities. Diagnostics are mean profiles of velocity, stress, dissipation, and reconstructed Reynolds stresses. The velocity profile obtaine... [ABSTRACT FROM AUTHOR]

Coke oven gas (COG) is a valuable by-product of coke-making process, due to its high H 2 content and calorific value. The potential exploitation of COG as an energy carrier requires a proper characterization of its kinetic behavior. Moreover, the residual presence of aromatic compounds in COG can potentially affect both its combustion efficiency and pollutant emissions. In this work, the chemical effect of benzene addition (up to 1.12% by vol.) to H 2 /CH 4 /CO mixtures, representative of COG, is assessed. Flame structure and speciation are extensively investigated through a combined experimental and modeling study, carried out in low-pressure (7.5 kPa) premixed laminar flames. Different equivalence ratios (0.8, 1.0, 1.2) are considered, with air as oxidant and a constant cold-gas velocity. It is found that NO formation progressively increases with the amount of benzene at all the investigated equivalence ratios, and such increase mostly occurs at the flame front region. Through a detailed kinetic analysis, it is found that benzene addition increases the NO formation in the H 2 /CH 4 /CO/C 6 H 6 flames. This is mainly due to the enhancement of the prompt and thermal NO routes. The kinetic study allowed to identify the sources of the interactions between benzene oxidation and prompt NO chemistry, ultimately involving the ketenyl radical (HCCO) and acetylene (C 2 H 2). This results in an increase of singlet CH 2 (CH 2 (S)) and CH 2 with consequent modification of CH profile, via HCCO→CH 2 (S)→CH 2 →CH and C 2 H 2 →CH 2 →CH routes. As a result, the higher available CH radical enhances NO formation through the established prompt mechanism, coherently with the experimental results. [ABSTRACT FROM AUTHOR]

Wind and solar energies present a time and space disparity that generally leads to a mismatch between the demand and the supply. To harvest their maximum potentials, one of the main challenges is the storage and transport of these energies. This challenge can be tackled by electrofuels, such as hydrogen, methane, and methanol. They offer three main advantages: compatibility with existing distribution networks or technologies of conversion, economical storage solution for high capacity, and ability to couple sectors (i.e., electricity to transport, to heat, or to industry). However, the level of contribution of electric-energy carriers is unknown. To assess their role in the future, we used whole-energy system modelling (EnergyScope Typical Days) to study the case of Belgium in 2050. This model is multi-energy and multi-sector. It optimises the design of the overall system to minimise its costs and emissions. Such a model relies on many parameters (e.g., price of natural gas, efficiency of heat pump) to represent as closely as possible the future energy system. However, these parameters can be highly uncertain, especially for long-term planning. Consequently, this work uses the polynomial chaos expansion method to integrate a global sensitivity analysis in order to highlight the influence of the parameters on the total cost of the system. The outcome of this analysis points out that, compared to the deterministic cost-optimum situation, the system cost, accounting for uncertainties, becomes higher (+17%) and twice more uncertain at carbon neutrality and that electrofuels are a major contribution to the uncertainty (up to 53% in the variation of the costs) due to their importance in the energy system and their high uncertainties, their higher price, and uncertainty. [ABSTRACT FROM AUTHOR]

Air quality is a growing concern worldwide because of its impacts on both the environment and the human health. The road transport sector is a major contributor to this poor air quality. To reduce the emission of particulate matter, all diesel passenger cars were equipped with diesel particulate filters since the EURO5b emission standard. Unfortunately, these filters can be damaged or intentionally removed during the lifetime of a vehicle. This work presents the particle number emission factors for EURO5 and EURO6 diesel passenger cars, based on the measurements of 757 vehicles. These measurements were performed at low idle, which shows a high correlation to particle number emission factors obtained during homologation cycles or real-driving emission measurements. The results show that the average Particle Number (PN) emission factors are highly impacted by high emitters present in the fleet and that the mileage has a significant impact on the PN emission factors. Finally, the estimated PN emission factors based on low idle measurements were higher by a factor 5.6 for EURO5a, 2.5 for EURO5b and 5.5 for EURO6, compared to their respective HBEFA (Handbook Emission Factors for Road, Transport) emission factors. • Particle number measurements on 757 diesel passenger cars from the field, homologated according to the EURO5 and EURO6 emission standards. • Fleet average emission factors are strongly increased due to the presence of high emitters. • The Handbook Emission Factors for Road Transport strongly underestimates the particle number emission factors of the tested fleet. • Mileage has a significant impact on the particle number emissions. [ABSTRACT FROM AUTHOR]

Increasing the biodiesel content of diesel fuels is encouraged because of its reduced carbon footprint. Pure rapeseed methyl ester (RME)and used cooking oil methyl ester (UCOME) are characterised by well-to-tank greenhouse gas (GHG) reductions of 54% and 88% compared to pure B0 petrodiesel, respectively. Captive fleets such as public transport buses could benefit from these GHG reductions by increasing the biodiesel content of their fuel because they have a consequent yearly fuel consumption. The aim of this paper is to compare on-road tailpipe emissions of a diesel bus when increasing the biodiesel concentration in the fuel. The tests were carried out on a standard city bus belonging to the Euro V EEV emission standard that was equipped with a portable emission measurement system measuring NO, NO2, PN, CO and CO2 at the tailpipe. The bus followed the SORT which is representative of urban bus driving. The heavy urban on-road measurements indicated increased NOx emissions (24–26%), decreased PN emissions (43–45%) and slightly decreasing CO emissions for B30 RME and UCOME compared to B7. A measurement uncertainty analysis showed that the CO emissions were less reliable. Similar conclusions were drawn for the easy urban on-road bus emission measurements with smaller differences between B7 and B30 RME and UCOME. [ABSTRACT FROM AUTHOR]