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We discover presence of chemical inductive effects in phase separating ion intercalation energy storage materials, specifically in lithium iron phosphate (LFP) and also lithium titanate oxide (LTO). These materials features fast (de)intercalation and slow diffusion relaxation phenomena which are prerequisites for observing such inductive effects. Presented finding is supported by the mechanistic model and analytical reasoning indicating that all equilibrium states that lay inside the miscibility gap of the phase separating material exhibit strong inductive response in the low frequency part of spectrum. We also explain why such inductive effects are not observed outside the miscibility gap. This letter presents the first mechanistic reasoning of previously reported electrode level experimental observation of inductance during impedance measurements at low currents., 21 pages, 7 figures

Capillary tube models frequently rely on friction factor correlations, which are functions of the Reynolds number, and the tube's relative surface roughness. However, this study shows that explicitly correlating the friction factor with the relative surface roughness is unnecessary, at least when the latter is lower than 0.0025. To test this a correlation was fitted directly onto friction factor measurements obtained in an adiabatic flow of R600a, through nine capillary tubes from three manufacturers. The friction factor was correlated exclusively as a function of the Reynolds number, meaning that the impacts of the relative surface roughnesses on the friction factor were averaged, and included only implicitly. This correlation, and an existing correlation, which allows the specification of the relative surface roughness, were then implemented in a capillary tube model. The accuracy of the capillary tube model, using either the developed or existing correlation was then evaluated by comparing the results to experimental data. No significant decrease in the accuracy of the model was observed when the relative surface roughnesses, ranging from 0.0012 to 0.0025, were not individually specified for each capillary tube. To further verify this, the procedure was repeated on a larger database of friction factor and mass flow rate measurements, which also consisted of data from independent studies. Similar conclusions were drawn, as the average accuracy of the model differed only by 1 to 3% among different studies, and not always in favor of the correlation where the relative surface roughnesses could be specified.

Optimal control of liquid water dynamics plays an instrumental role in achieving optimised performance and prolonged lifetime of PEM Fuel Cells (PEMFC). Tackling these challenges calls for precise on-line monitoring and control tools such as coupled virtual observers taking into consideration also liquid water dynamics. The latter proves to be especially challenging to model due to varying retention and removal rates of liquid and gaseous water depending on the operating conditions thus representing a longstanding knowledge gap. To fill this gap, this contribution presents derivation of a 1D+1D system level physically motivated two-phase model of PEMFC, which enables consistent treatment of liquid water dynamics on the system level in all seven most influential regions of the PEMFC, namely membrane, anode and cathode channels, GDLs, and catalyst layers, while exhibiting real-time readiness with real-time factor of 0.0449. The model is extensively tested on single-cell data, which consists of five sets of experiments with different operating regimes and durations. Overall results exhibit good agreement with experimental data in all of the performed tests with R$^2$ factors larger than 0.95. Newly developed features of the model enable its use in development of advanced control methodologies and hardware-in-the-loop as well as digital twin applications.

The performance of lithium-ion batteries (LIBs) relies on the characteristics of the cathode material, including both intentionally applied coatings and naturally formed surface layers or binder adhesion. This study investigated the influence of the ion-permeable surface fraction, distribution, and characteristics of the coating on the performance of a lithium iron phosphate (LFP) electrode material. We developed an extended Newman-type half-cell model and examined the impact of coating parameters on the galvanostatic discharge curves of the LFP electrode material. The study found that the ion-permeable surface fraction has a significant influence on the diffusion and charge transfer characteristics of the electrode material. A decrease in the ion-permeable surface fraction leads to a decrease in the measured diffusion coefficients and to an increase in the overall coating resistance of the electrode material. Interestingly, the distribution of the ion-permeable surface also plays a role in the diffusion characteristics, with a coarsely dispersed coating resulting in lower diffusion coefficients. Additionally, the coating characteristics significantly affect the polarization and capacity of the electrode material at different C-rates. The model was used to approximate the experimental discharge curves of the LFP-based composite electrodes with two different compositions, and the simulated data showed satisfactory agreement with the experiment. Thus, we believe that the developed model and its further extension will be useful in numerical simulations that aim to facilitate the search for optimal compositions.

Achieving efficient solid oxide fuel cell operation and simultaneous prevention of degradation effects calls for the development of precise on-line monitoring and control tools based on predictive, computationally fast models. The originality of the proposed modelling approach originates from the hypothesis that the innovative derivation procedure enables the development of a thermodynamically consistent multi-species electrochemical model that considers the electrochemical co-oxidation of carbon monoxide and hydrogen in a closed-form. The latter is achieved by coupling the equations for anodic reaction rates with the equation for anodic potential. Furthermore, the newly derived model is capable of accommodating the diffusive transport of gaseous species through the gas diffusion layer, yielding a computationally efficient quasi-one-dimensional model. This resolves a persistent knowledge gap, as the proposed modelling approach enables the modelling of multi-species fuels in a closed form, resulting in very high computational efficiency, and thus enable the model’s real-time capability. Multiple validation steps against polarisation curves with different fuel mixtures confirm the capability of the newly developed model to replicate experimental data. Furthermore, the presented results confirm the capability of the model to accurately simulate outside the calibrated variation space under different operating conditions and reformate mixtures. These functionalities position the proposed model as a beyond state-of-the-art tool for model supported development and control applications.

Sustainable Aviation Fuel (SAF) has become an important measure in the aviation industry’s efforts to mitigate carbon emissions and reduce their overall environmental impacts. However, commercial usage is relatively stunted due to a plethora of drawbacks in the production process and economic feasibility of the fuel. In this study, the currently accepted technologies for producing synthetic jet fuels under the American Society for Testing Material (ASTM D7566) standard specification for aviation turbine fuel are reviewed. The emphasis is placed in terms of their reactions, type of catalysts used for the conversion pathways of Fisher-Tropsch (FT), Hydroprocessed Esters and Fatty Acids (HEFA) and Alcohol-to-Jet (ATJ), and the use of biomass resources as feedstock. The advancement in the production process and physicochemical properties of the uncertified biojet fuels are reviewed and discussed. Generally, Co- and Fe-based catalysts are commonly used for the FT process, while bimetallic catalysts consisting of Pt, Pd, Ni and Mo have shown excellent activities and selectivities for the HEFA process. For the ATJ process, zeolites such as HZSM-5, beta and SAPO have shown remarkable ethanol dehydration efficiency, while TiO2 and ferrierite have been studied for the combined iso-butanol dehydration and oligomerisation processes. Fundamental factors influencing the reaction efficiency including the feedstock properties, reaction conditions, catalytic reusability and catalyst supports are discussed. Finally, the key challenges and prospects for biojet fuel commercialisation are addressed.

To support the ongoing energy transition and minimize the environmental footprint of combustion related technologies, the paper presents a novel approach for combustion control in gas turbines and burners. It relies on spatially targeted injection of inert components in the spray core where existent concepts fail to deliver the desired dilution rate and are unable to fully govern the spatial distribution of heat release rates. Combustion process control is thus possible by actively adjusting the composition and mass flow of spatially selective introduction of inert species in the spray, optionally combined with classic, external exhaust gas recirculation, leading to an ultimate fuel-flexible concept which is capable of adjustments to heterogeneous fuels, their reactivity and physical properties. The proof of concept is demonstrated in a gas turbine combustion chamber first by investigating the isolated effects of spatially selective injection of inert species, its comparison to external exhaust gas recirculation and a combination of both. The results confirm the superiority of the approach as spatially selective mixture inertization is capable of 7% reduction of NO emissions with merely 3% increase of CO emissions and even 9% reduction of PM emissions. Furthermore, the concept proved transferrable together with all its benefits to combustion cycles with external exhaust gas recirculation. In this case, the 63% reduction of NO emissions with no observed CO penalty is possible. Simultaneous exploitation of spatially selective inertization, as well as external exhaust gas recirculation forms a fully controllable concept - spatially selective dilution control (SSDC), which enables extensive adjustability of dilution rates throughout the spray core and primary zone of combustion chamber. Compared to baseline case, such approach was proved to simultaneously reduce CO, NO and PM emissions normalized to fuel thermal power for 39%, 63% and 91%, respectively. The confirmation of applicability of the novel approach and its potential to influence the local conditions is opening a series of possible uses, either as an original design feature for future fuel-flexible systems or as a retrofit approach in existent combustion systems.

The state of health of polyfluorinated sulfonic-acid ionomer membranes (e.g. Nafion®) in low-temperature proton exchange membrane fuel cells (LT-PEMFCs) is negatively influenced by degradation phenomena occurring during their operation. As a consequence, the performance and durability of the membrane are decreased. In this article, we focus on simulating and predicting chemical membrane degradation phenomena using a holistic zero-dimensional kinetic framework. The knowledge of chemical degradation mechanisms is widely spread. We have collected and evaluated an extensive set of chemical mechanisms to achieve a holistic approach. This yields a set of 23 coupled chemical equations, which provide the whole cause and effect chain of chemical degradation in LT-PEMFCs (based on the Fenton reaction between Fe2+ and H2O2via the attack of hydroxyl radicals on the membrane, loss of ionomer moieties and emission of fluoride). Our kinetic framework allows the reproduction of experimentally accessible data such as fluoride emission rates and concentrations of ionomer moieties (from both in situ and ex situ tests). We present an approach, which allows estimations of the membrane lifetime based on fluoride emission rates. In addition, we outline the demetallation of Fe-N-C catalysts as a source of additional harmful iron species, which accelerate chemical membrane degradation. To demonstrate the expandability and versatility of the kinetic framework, a set of five chemical equations describing the radical scavenging properties of cerium agents is coupled to the main framework and its influence on membrane degradation is analysed. An automated solving routine for the system of coupled chemical equations on the basis of the chemical kinetic simulation tool COPASI has been developed and is freely accessible online ().

System level simulations, which are gaining on importance in the product concept design process and in the Hardware-in-the-Loop (HiL) applications, require models that feature high level of accuracy, high level of prediction capability and short computational times. This paper presents an innovative mechanistic quasi 3D model capable of real time computation of steady state and transient fuel cell operation. This model relies on a hybrid 3D analytic-numerical model (HAN) approach, which models species transport by taking 1D numerical model for pipe gas-flow and superimposing onto it a 2D analytic solution for concentration and velocity distribution in the plane perpendicular to the gas-flow. The main innovative contribution of this paper comprises a significant mathematical reduction of the previously published HAN approach to a computationally optimized approach featuring a minimal amount of computational points yielding a real-time capable model (denoted HAN-RT), which complies with 1kHz HiL constraints while retaining HAN's quasi 3D nature. Presented results confirm that the computationally optimized HAN-RT model displays real-time capabilities at sampling rates above 1 kHz while producing results that agree very well with spatially resolved results generated by the 3D multiphase CFD tool and with the experimental results of steady state and transient fuel cell operation.

To explore the influence of fuel injection strategy on the combustion process, the Computational Fluid Dynamics (CFD) simulations were performed, and simulation results were validated against the experimental data measured at different rail pressures and injection timings. The experiments were conducted on a diesel engine equipped with an advanced injection system that allows full control over the injection parameters. To model the combustion process of EN590 diesel fuel, two different approaches were used: the General Gas Phase Reactions (GGPR) approach and the 3-zones Extended Coherent Flame Model (ECFM-3Z+). The calculated results, such as mean pressure and rate of heat release, were validated against experimental data in operating points with different injection parameters in order to prove the validity of spray and combustion sub-models. At the higher injected pressure, GGPR model showed better prediction capability in the premixed phase of combustion process, compared to the ECFM-3Z+ model. Nevertheless, in the rate-controlled phase of combustion process, ECFM-3Z+ model shows stronger diffusion of temperature field, due to the more detailed consideration of combustion diffusion phenomena in the ECFM-3Z+ governing equations. Furthermore, the results show that the rail pressure has a lower impact on the combustion process for injection timing after the Top Dead Centre (TDC). Both, single and multi-injection cases are found to be in a good agreement with the experimental data, while the GGPR approach was found to be suitable only for combustion delay determination and ECFM-3Z+ also for the entire combustion process.

Commonly applied 3D CFD models lack suitable combustion description of fuels with complex composition, such as encountered in wastewater sludge specific applications. This significantly influences their prediction capability, in particular when used in small, confined combustion volumes. To tackle this challenge, it is necessary to introduce detailed chemical kinetic models for specifically tailored fuel surrogates, which ensure physically accurate description of local thermodynamic conditions and heat release rates. However, necessity to increase the level of detail of models needs to be balanced by their computational expenses to preserve their applicability when solving real engineering problems. With an aim to fill this gap, the present study significantly extends the existing surrogate model methods for applications in small-scale systems to include also reduced combustion kinetic mechanisms. The innovative extension applies Simulation Error Minimization Connectivity Method and involves tailoring of kinetic mechanisms to variable thermodynamic conditions and variable surrogate compositions, specific to sewage sludge combustion. Suitability of the proposed approach is confirmed with the 3-D CFD simulations maintaining similar level of accuracy within the design space of reduced mechanisms as well as in off-design conditions, while maintaining sufficient flexibility to adapt to different types and compositions of the sludge. Thereby, reduction of the in-model applied detailed ethanol and propene mechanisms from 47 and 71 species down to 33 and 34 species, respectively, was demonstrated together with linearly dependent decrease in computational time. The proposed model extension and resulting surrogate combustion model thus for the first time offer an efficient tool for affordable and accurate virtual design of small-scale combustion systems using fuels with complex chemical composition.

The degradation of the catalyst layer represents one of the main limiting factors in a wider adoption of fuel cells. The identification of the contributions of different mechanisms of catalyst degradation, namely the Ostwald ripening and particle agglomeration, is an important step in the development of mitigation strategies for increasing fuel cell reliability and prolonging its life time. In this paper, the degradation phenomena in high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) are analyzed using a physically-based model of fuel cell operation and catalyst degradation, describing carbon corrosion, platinum dissolution and consequent growth of catalyst particles. The model results indicate significantly different time dependence of catalyst particle growth resulting from different mechanisms: linear growth in the case of particle agglomeration and root-like time dependence for the Ostwald ripening. Based on these results, a new analytic method is proposed, performed by the fitting of a test root-function to the time profile of the particle size growth and using best-fit parameters to identify the prevailing growth mechanism. Using this method on a particle growth time trace deduced from in situ cyclic voltammetry measurement during HT-PEMFC degradation, we are able to identify the agglomeration as the main mechanism of catalyst particle grow.

The limited durability of hydrogen fuel cells is one of the main obstacles in their wider adoption as a clean alternative technology for small scale electricity production. The Ostwald ripening of catalyst material is recognized as one of the main unavoidable degradation processes deteriorating the fuel cell performance and shortening its lifetime. The paper systematically studies how the modeling approach towards the electrochemically driven Ostwald ripening in the fuel cell catalyst differs from the classical diffusion driven models and highlights how these differences affect the resulting evolution of particle size distribution. At moderately low electric potential, root-law growth of mean particle size is observed with linear relation between mean particle size and standard deviation of particle size distribution, similar to Lifshitz-Slyozov-Wagner theory, but with broader and less skewed distribution. In case of high electric potential, rapid particle growth regime is observed and qualitatively described by redeposition of platinum from a highly oversaturated solution, revealing the deficiencies of the existing platinum degradation models at describing the Ostwald ripening in the fuel cells at high electric potentials. Several improvements to the established models of platinum degradation in fuel cell catalysts are proposed, aimed at better description of the diffusion processes involved in particle growth due to Ostwald ripening.

Degradation of proton exchange membrane in low-temperature fuel cells represents one of the main limiting factors for wider adoption of this clean, carbon emission free energy device. In combination with mechanical degradation caused by membrane swelling and shrinkage during water content change, chemical degradation of the membrane is considered to be the main mechanism leading to loss of membrane conductivity, membrane thinning and eventual pinhole formation. Chemical degradation is caused by the attack of reactive radical species on the perfluorinated polymer chains of the membrane, which are formed in Fenton reaction between hydrogen peroxide and ions of transition metals, which are inevitably present in the membrane in small traces. Since the metal ions are recycled in Fenton reactions, the rate of chemical degradation is mainly determined by the production of hydrogen peroxide, formed as a side product to water in reaction between oxygen and protons in the fuel cell. [1] The source of hydrogen peroxide production in low-temperature fuel cells have long been debated in scientific literature. On one hand, the abundance of oxygen in the cathode suggest that the production takes place there, but high local electric potential strongly promotes 4-electron reaction, forming water, over 2-electron reaction required for production of hydrogen peroxide [2]. The conditions in the anode are reversed, low electric potential is well suited for peroxide production, but the concentration of oxygen, present in the anode due to diffusion through the membrane, is in general expected to be quite low, making it a rate limiting factor for the peroxide production in the anode. The last possible source of hydrogen peroxide is closely related to the degradation of platinum (Pt) catalyst in the cathode. When Pt catalyst nanoparticles dissolve due to high local electric potential on the cathode, part of the dissolved ions diffuses into the membrane, where it is reduced by counter-diffusing hydrogen from the anode. These Pt particles in the membrane, the so-called Pt band, serve as a catalyst for the reaction between diffusing oxygen from cathode and hydrogen in anode. Since these particles are not electrically connected to either anode or cathode, their electric potential is determined by the rates of oxygen reduction and hydrogen oxidation on their surface, which result in production of water and potentially also hydrogen peroxide. The complex interplay between the processes determining the peroxide production, explained above, suggest that different sources of peroxide might be relevant in different fuel cell operation conditions and at different states of health of the fuel cell. To explore this question quantitatively, we propose a mathematical model of peroxide production which describes physical and electrochemical processes for hydrogen peroxide production in fuel cell catalysts and the membrane, relevant for hydrogen peroxide production: oxygen and hydrogen diffusion in the membrane, electrochemical oxygen reduction in the cathode, anode and on Pt band inside membrane, hydrogen oxidation on Pt band and electric charging of Pt particles in the band due to electrochemical reactions on their surface. To provide realistic internal states of the fuel cell during operation, the model is coupled with advanced spatially and temporally resolved model of the fuel cell operation. [3] Preliminary results of the model indicate that main source of peroxide production depends on the fuel cell operating conditions. In fresh fuel cell, where Pt band in membrane is not yet formed, low current densities and high fuel cell voltages promote the peroxide formation mainly on the anode from the diffused oxygen, while at high current densities the electric potential on the cathode is low enough to allow for significant peroxide production there, outweighing the production on the anode. The formation of the Pt band shifts the production of peroxide from anode to the Pt particles in the band, since large amount of the oxygen is consumed there and therefore its diffusion to the anode is reduced. The results indicate that the question of where the peroxide is formed cannot be resolved by a single answer and that the use of sufficiently complex models, coupling physical and electrochemical processes in different fuel cell components, are required to properly manage fuel cell operation in order to avoid or at least mitigate its detrimental effects of chemical membrane degradation. [1] Frühwirt, P., Kregar, A., Törring, J. T., Katrašnik, T., Gescheidt, G. (2020). Physical Chemistry Chemical Physics, 22(10), 5647–5666. [2] Sethuraman, V. A., Weidner, J. W., Haug, A. T., Motupally, S., Protsailo, L. V. (2008). Journal of The Electrochemical Society, 155(1), B50. [3] Kregar, A., Tavčar, G., Kravos, A., Katrašnik, T. (2020). Applied Energy, 263(March), 114547.

The first EU Renewable Energy Directive (RED) served as an effective push for world-wide research efforts on biofuels and bioliquids, i.e. liquid fuels for energy purposes other than for transport, including electricity, heating, and cooling, which are produced from biomass. In December 2018 the new RED II was published in the Official Journal of the European Union. Therefore, it is now the right time to provide a comprehensive overview of achievements and practices that were developed within the current perspective. To comply with this objective, the present study focuses on a comprehensive and systematic technical evaluation of all key aspects of the different distributed energy generation pathways using bioliquids in reciprocating engines and micro gas turbines that were overseen by these EU actions. Methodologically, the study originates from the analyses of feedstock and fuel processing technologies, which decisively influence fuel properties. The study systematically and holistically highlights the utilisation of these bioliquids in terms of fuel property specific challenges, required engine adaptations, and equipment durability, culminating in analyses of engine performance and emissions. In addition, innovative proposals and future opportunities for further technical improvements in the whole production-consumption cycle are presented, thus serving as a guideline for upcoming research and development activities in the fast-growing area of bioliquids. Additionally, the paper systematically addresses opportunities for the utilisation of waste streams, emerging from the ever increasing circular use of materials and resources. With this, the present review provides the sorely needed link between past efforts, oriented towards the exploitation of bio-based resources for power generation, and the very recent zero-waste oriented society that will require a realistic exploitation plan for residuals originating from intensive material looping.

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are a promising and emerging technology that allow for highly efficient low emission small scale electricity and heat generation. Simultaneous reduction of production costs and prolongation of the service life is considered as a significant challenge towards their wider market adoptions, which calls for application of predictive virtual tools during the development process of HT-PEMFC systems. To present a significant progress in the addressed area, this paper presents an innovative modelling framework based on: a) mechanistically based spatially and temporally resolved HT-PEMFC performance model and b) modular degradation modelling framework based on interacting partial platinum degradation mechanisms. Proposed innovative tool chain thus allows for - compared to the current state of the art – more efficient and systematic model supported design of FCs and in-depth understanding of cause and effect chain from FC operation to its degradation. This merit of the proposed modelling framework arises from systematic reflection of FC control parameters in operational parameters of the FC, which are inputs to degradation modelling framework that considers in an interacting manner carbon and Pt oxidation phenomena and Pt dissolution, redeposition, detachment and agglomeration phenomena thereby adequately modelling the causal chain.

The presented paper focuses on the combustion analysis of a highly oxygenated, viscous and economically viable fuel in an internal combustion micro gas turbine. Results suggest that environmental benefits in terms of NOx emissions and PM emissions are significant as concentrations of both species are reduced. Based on the analysis presented in the study, altered local air-fuel ratio suppresses NOx formation and PM formation resulting in 10-fold lower PM emission than same experimental apparatus with diesel fuel. The study further analyses and identifies three key mechanisms that are responsible for this reduction: altered oxygen profile during mixture preparation, prevention of soot precursors formation and promotion of soot oxidation reactions. The influence of tested fuel is also perceivable through higher CO and THC emissions. Parametric analysis within the selected experimental space suggests that operational parameters of the micro gas turbine can be adjusted to reduce concentrations of these two species without negatively affecting other pollutants. Significant benefits of the fuel in terms of environmental impact indicate that further investigation and development of this approach might provide a new alternative energy source for stationary use as well as for mobility in sectors where heavy duty gas turbines are used as prime movers.

Models of Li-ion batteries addressing a particular scale—from atomistic to continuum—have reached a certain level of maturity. Meanwhile, consistent multi-scale modelling approaches are still in their infancy despite their large potential to boost the accuracy and prediction capability of Li-ion battery models. As an answer to this challenge, the paper presents an advanced quasi-3D model of the active electrode material that tackles one of the main deficiencies of the porous-electrode theory (PET) based models which arises from a poor representation of the electrode topology. It is hypothesised that there exists a quasi-3D modelling representation of the active electrode material that adequately virtually replicates intra primary particle Li-distribution and features significantly shorter computational times compared to models featuring a fully 3D meshed electrode topology, which enables its full integration into the porous electrode model. An advanced quasi-3D model is constructed by the integration of the concentration and the chemical potential in each primary particle across its volume and by the introduction of the permeability parameter at the interfaces. Besides compatibility with PET and acceptable computational times, the model also exhibits results that are in good agreement with measured lithium concentration profiles inside secondary particles published in literature.

The use of mathematical modelling for describing the degradation of platinum-based carbon-supported catalysts (Pt/C) in PEMFC plays a crucial role in the development of new materials and mitigation strategies as well as in the improved understanding of individual degradation mechanisms and their relation to the operational conditions. In this work we present the first physically based model of Pt/C catalyst degradation that fully covers the effects of temperature on detrimental electrochemical reactions, consequent platinum particles dissolution, detachment and agglomeration, and the resulting loss of electrochemical surface area. The model is verified on the results of six accelerated stress tests performed on an industrial benchmark catalyst at various temperatures and potential cycling windows. The model is capable of reproducing the results of all experiments using the same set of model parameters, compatible with DFT calculations for energy barriers of similar electrochemical reactions as well as with the parameters of existing degradation models, which confirms its plausibility. According to the model results, the dissolution and subsequent redeposition of platinum is strongly affected by the temperature and represents the main mechanism of particle growth at temperatures below 60 °C, with carbon corrosion induced detachment and agglomeration playing only a minor role in particle growth.

In the presented study, low temperature combustion was established with a direct injection of diesel fuel being a representative of high reactivity fuels and tire pyrolysis oil being a representative of low reactivity fuels. Tire pyrolysis oil was tested as a potential waste derived fuel for low temperature combustion, as it features diesel-like physical properties and lower cetane number compared to diesel fuel. The goal of this study was determination of suitable injection strategies and exhaust gas recirculation rates to explore potentials of both fuels in reducing emissions in low temperature combustion modes. It was demonstrated that relatively small changes in the engine control strategy possess the potential to significantly improve nitrogen oxide/particulate matter trade-off with minor effect on engine efficiency. In addition, low temperature combustion was for the first time successfully demonstrated with tire pyrolysis oil fuel, however, it was shown that lower reactivity of the fuel is by itself not sufficient to improve nitrogen oxide/ soot trade-off compared to the diesel fuel as entire spectra of fuel properties play an important role in improving nitrogen oxide/soot trade-off. This study thus establishes relations between different engine control strategies, intake manifold pressure and exhaust gas recirculation rate on engine thermodynamic parameters and engine-out emissions while utilizing innovative waste derived fuel that have not yet been analysed in similar combustion concepts.

The combustion of a viscous biofuel, liquefied wood (LW) produced via solvolysis of lignocellulosic biomass in acidified glycols, has been studied in a small gas turbine rig. The test rig includes a modified injection line which is compatible with acidic, viscous biofuels allowing fuel preheating and two pilot injectors, and a re-designed combustion chamber. The link between fuel properties and combustion performance of liquefied wood is investigated by burning the biofuel at different blending ratios with ethanol. Exhaust emissions have been compared to reference measurements with diesel fuel and ethanol. Combustion analysis is supported by the investigation of the engine operating parameters and the main emission species at different electrical loads. The experimental study reveals that it is possible to establish efficient operation of the micro gas turbine while utilizing liquefied wood-ethanol blends with high share of liquefied wood.

On-road exhaust emissions of a Euro 5 factory bi-fuel CNG/gasoline light-duty vehicle equipped with the TWC were assessed considering the Real Driving Emissions (RDE) guidelines. The vehicle was equipped with a Portable Emission Measurement System (PEMS) that enabled the measurement of THC, CO, NOx, CO2, and CH4. With respect to the characteristics of the vehicle, the appropriate Worldwide Harmonized Light-Duty Vehicle Test Cycles (WLTC) were selected and based on the requirements of the RDE legislation a suitable route was conceived. In addition to the moderate RDE-based route, an extended RDE-based route was also determined. The vehicle was driven along each defined route twice, once with each individual fuel option and with a fully warm vehicle. RDE routes feature a multitude of new driving patterns that are significantly different to those encountered in the NEDC. However, as these driving patterns can greatly influence the cumulative emissions an insight in to local time trace phenomena is crucial to understand, reason and to possibly reduce the cumulative emissions. Original contributions of this paper comprise analyses of the RDE-LDV local time resolved driving emissions phenomena of a CNG-powered vehicle that are benchmarked against the ones measured under the use of gasoline in the same vehicle and under similar operating conditions to reason emission trends through driving patterns and powertrain parameters and exposing the strong cold-start independent interference of CO and N2O infrared absorption bands in the non-dispersive infrared (NDIR) analyzer. The paper provides experimental evidence on this interference, which significantly influences on the readings of CO emissions. The paper further provides hypotheses why CO and N2O interference is more pronounced when using CNG in LDVs and supports these hypotheses by PEMS tests. The study reveals that the vehicle's NOx real-world emission values of both conceived RDE-based routes when using both fuels are within Euro 5 and type-approval limits. Additionally, the THC and the NMHC emissions of both RDE-based routes using both fuels are within the Euro 5 limits indicating reasonable CH4 emissions. Notable increases above the type-approval and Euro 5 limits appeared in the CO emissions profile when using gasoline, while the CO2 emissions profile expectedly also exceeded the type-approval specifications.

Multi-scale and multi-domain mathematical models capable of modelling main electrochemical reactions, side reactions and heat generation can reduce the time and cost of lithium-ion battery development and deployment, since these processes decisively influence performance, durability and safety of batteries. Experimental evidences clearly indicate the importance of the interplay between electric and thermal boundary conditions, cell design and applied materials, side reactions as well as safety implications of batteries, which are not yet captured to a sufficient level by simulations models. As an answer to this challenge, the paper presents an advanced multi-scale battery modelling framework that can be seamlessly integrated into multi-domain models. The key hypothesis is that nanoscopic transport phenomena and resulting heat generation decisively influence the entire chain of mechanisms that can lead to the outbreak of the thermal runaway. This is confirmed by developing a multi-scale battery modelling framework that is based on the continuous modelling approach featuring more consistent virtual representation of the electrode topology and incorporating the coupled chain of models for heat generations and side reactions. As a result, the battery modelling framework intuitively yet insightfully elucidates the entire chain of phenomena from electric and thermal boundary conditions, over cell design and properties of applied materials to solid electrolyte interphase growth, its decomposition and subsequent side reactions at the anode, cathode and the electrolyte that lead to the thermal runaway. One of key results comprises multi-level main and side reaction driven heat transfer cross-talk between the anode and the cathode. Therefore, the presented advanced multi-scale battery modelling framework represents a contribution to the advanced virtual development of batteries thereby contributing to tailoring battery design to a specific application.

Finding alternative value-added usage for glycerol is imperative as existing uses are inadequate due to the vast excesses of glycerol generated mainly as a result of increased biodiesel production. This paper explores a mid-term, cost-efficient, technically viable utilisation in power generation applications and exposes the nature of its combustion. Blended with methanol to avoid the heat loss and fuel coking problems associated with preheating, glycerol was combusted in a model swirl-stabilised gas turbine burner utilising a standard pressure-swirl injector for fuel atomisation. Stable flames resulting from the tested blends – 70/30 and 50/50 combinations of methanol/glycerol by volume – were achieved over an equivalence ratio (ER) range between 0.29 and 0.51. The upper and lower limits of stable operating ER for the 70/30 case were accompanied by significant flame lift-off from the nozzle exit orifice – a phenomenon that was not pronounced in the 50/50 case. Also, the temporal variation of CH* species integral intensity suggested a reduction in the fluctuation of heat release rate, hence better flame stability, as ER increased for both blends. Overall, the 50/50 case showed greater flame stability compared with the 70/30 case based on the CH* chemiluminescence data and spectral analysis by means of fast Fourier transform.

The paper presents an innovative mechanistically based spray model intended for use in mixture-controlled-combustion models. The primary objective of the spray model is to predict masses of fuel within selected limits of excess air ratios during and after the end of injection. The model is based on a 0D non-vaporizing and non-reacting modelling framework to ensure short computational times. These assumptions represent clear simplifications compared to the real transient spray propagation phenomena in reacting turbulent flows. However, from the study, it is concluded that the modelling framework is capable of attaining an adequate level of predictability for system-level applications. The model is capable of predicting spray detachment from the nozzle after the end of injection. This feature is crucial for plausible prediction of masses within selected excess air ratios. The spray model is also capable of determining the fuel mass reaching the wall. In addition, the spray modelling framework is capable of considering injection rate-shaping and evaluating its impact on predicted masses of fuel within selected limits of excess air ratios. The spray model is successfully validated against experimental data for varying injection parameters and ambient densities, demonstrating its reliability and applicability.

To further expand the knowledge base on the use of innovative fuels in the micro gas turbines, this paper provides insight into interrelation between specific fuel properties and their impact on combustion and emission formation phenomena in micro gas turbines for stationary power generation as well as their impact on material corrosion and deposit formation. The objective of this study is to identify potential issues that can be related to specific fuel properties and to propose counter measures for achieving stable, durable, efficient and low emission operation of the micro gas turbine while utilizing advanced/innovative fuels. This is done by coupling combustion and emission formation analyses to analyses of material degradation and degradation of component functionality while interpreting them through fuel-specific properties. To ensure sufficiently broad range of fuel properties to demonstrate the applicability of the method, two different fuels with significantly different properties are analysed, i.e. tire pyrolysis oil and liquefied wood. It is shown that extent of required micro gas turbine adaptations strongly correlates with deviations of the fuel properties from those of the baseline fuel. Through the study, these adaptations are supported by in-depth analyses of impacts of fuel properties on different components, parameters and subsystems and their quantification. This holistic approach is further used to propose methodologies and innovative approaches for constraining a design space of micro gas turbine to successfully utilize wide spectra of alternative/innovative fuels.

Prevention and diminution in effects of degradation phenomena under highly dynamic operation of proton exchange membrane fuel cells (PEMFC), while retaining sufficiently high efficiency and performance of the system, are considered significant obstacles toward their wider use in transport applications. Overcoming these obstacles calls for precise on-line monitoring and control tools such as coupled observers, which enable combined performance and service life optimizations. Models used in these applications should feature low computational effort, good extrapolation capabilities and should be easy to parametrize. The first requirement, which is obvious for on-line applications, in frequently in contradiction to the last two, which are heavily intertwined. Good extrapolation capabilities of the model significantly reduce the size of experimental data sets needed for successful parametrization, thus enabling the parametrization on small data sets, while retaining higher accuracy outside of trained variation space. This rationale motivates the use of the computationally-fast reduced-dimensionality electrochemical models e.g. [1, 2], featuring a more profound mechanistic basis; thus, exhibiting better prediction capability of the model. To present significant progress in the aforementioned area, this contribution presents framework of computationally-fast electrochemical models that can be parametrized whether on experimental data from polarization curves or on data obtained by electrochemical impedance spectroscopy (EIS). This hybrid methodology consists of interchangeable thermodynamically consistent reduced-dimensionality electrochemical model for PEMFC [2] and newly developed analytical physical model for impedance spectra with the same set of calibration parameters. The latter is developed by applying electrochemical ansatzes for the cathode and anode reactions derived in [2] on the proposed modelling approach used for calculation of the cathode catalyst layer impedance in the inspiring work of Kulikovsky [3]. Profound modelling basis using the same set of calibration parameters enable enhanced identification of individual calibration parameters that are otherwise harder to be uniquely determined [4] on one hand, and enable parametrization of the model from either of the two separate measurements in time and frequency domains on the other. Enhanced identifiability of calibration parameters using proposed hybrid methodology is especially pronounced in the case of parameters describing anodic and cathodic reaction rates and their activation energies, which are extremely hard to be uniquely determined based on the experimental data consisting of polarization curves only, due to coupling of their information with other calibration parameters. Additionally, proposed hybrid methodology also enables a significant reduction in the measurement time in the case of experimental data obtained by EIS, allowing the low frequency regions, where the transport phenomena could be otherwise characterized, to be omitted due to already uniquely determined calibration parameters from polarization curve measurements. Furthermore, to reduce the necessary amount of experiments for successful parametrization of the model even further, the optimal design of experiments (DoE) is used, based on D-optimal criterion applied onto Fisher information matrix. To assess developed hybrid methodology calibration parameters, obtained by means of minimizing penalty function value with differential evolution algorithm on EIS data, are used for validation against polarization curves measured at the same RuL (remaining useful life). Furthermore, to confirm applicability of the methodology, the same procedure is also used for calibration on the measured polarization curves and validation on the EIS experimental data. Small discrepancy between the values of the root-mean-square errors show plausibility of the proposed hybrid methodology. On the other hand, Fisher information analysis is performed to assess increment in the information about individual calibration parameter when each experimental point from EIS data set is added to experimental space used for parametrization. Results of this joint analysis offer unique insight into the information that data set obtained with the EIS measurements possess about individual calibration parameter in the individual frequency interval and intuitively confirm the results obtained by application of the optimal DoE for a synthetic space of EIS measurements. The latter extremely reduces experimental workload needed for successful calibration of the model in comparison with the full factorial. Innovative hybrid methodology of the measurements in time and frequency domains can thus be used for achieving reduced costs and efforts in initial parametrization and during operation in re-parametrization procedures of the modelling framework for virtual observers. References: [1] A. A. Kulikovsky, J. Electrochem. Soc., 2014, 161, F263 https://doi.org/10.1149/2.028403jes [2] A. Kravos, D. Ritzberger, G. Tavcar, C. Hametner, S. Jakubek, T. Katrasnik, Journal of Power Sources, 454, 2020, 227930, https://doi.org/10.1016/j.jpowsour.2020.227930 [3] A.A. Kulikovsky, Electrochimica Acta, 147, 2014, 773-777, https://doi.org/10.1016/j.electacta.2014.09.145 [4] A. Kravos, D. Ritzberger, G. Tavcar, C. Hametner, S. Jakubek, T. Katrasnik, EFC19, 8th European Fuel Cell, Piero Lunghi Conference, Naples, 9-11 December, 2019. ENEA, 2019, 303-304, https://www.europeanfuelcell.it/media/book_of_proceedings_EFC19.pdf

Low temperature fuel cells with perfluorinated proton exchange membrane (LT-PEMFC) are recognized as one of the most promising technologies for clean electricity production in automotive sector. Despite significant progress in their efficiency and reliability, the degradation of fuel cells still remains an important issue, significantly hindering their wider market adoption. Degradation processes can to some extent be avoided by the use of new, more durable materials and components, but also by properly managing the fuel cell operation and thus avoiding the conditions in which the fuel cell degradation is most pronounced. Fast and reliable computational models of fuel cell operation and degradation are crucial for efficient development of such mitigation strategies. The catalyst layer and the membrane are the components recognized as being most susceptible to degradation phenomena. In the catalyst layer, high temperature, electric potential and relative humidity lead to electrochemical corrosion of carbon support and dissolution of the catalyst, most commonly being platinum or platinum-based binary alloy. Dissolved platinum, diffusing into the membrane, plays an important role in its chemical and consequent mechanical degradation. The platinum particles in the membrane serve as the catalyst for hydrogen peroxide formation from crossover fluxes of hydrogen and oxygen, while the presence of transition metal ions, such as copper or cobalt, originating from the binary catalyst dissolution, initiate the decay of hydrogen peroxide into various radical species via Fenton-like reactions [1]. The radical’s attack on the perfluorinated chains and sulphonic groups leads to a reduction of membrane conductivity, thinning of the membrane and consequent increase in its susceptibility to mechanical degradation, caused by the swelling and shrinking of the membrane due to the changes in its humidity, which can result in formation of cracks and pinholes in the membrane. To properly model the entire causal chain of chemical membrane degradation, several individual processes mentioned above need to be coupled into a unified model. To achieve this, we present a physically based spatially and temporally resolved model of fuel cell operation, providing the detailed picture of species concentration and electric potential distribution in the fuel cell [2], coupled with innovative model of hydrogen peroxide formation, diffusion and decay into reactive radicals, causing the chemical degradation of the membrane. The model describes the electrochemical dissolution of binary alloy catalyst, its diffusion into the membrane and the formation of so-called Pt band. The hydrogen peroxide production is modeled by including both its formation in the catalyst layers and inside the Pt band by consistently taking into account the cross-over fluxes of reactants and local electric potential across the membrane [3]. The rate of radical formation (.H, .OH, .OOH) via Fenton-like reactions is modeled by considering the concentration of transition metal ions, originating from electrochemical dissolution of binary alloy catalyst and their diffusion into the membrane. The chemical degradation due to reactive radical’s attack on the membrane is described by recently developed 0-D reactor approach [4]. The output of the model is a detailed spatially and temporally resolved profile of chemical groups concentration in the membrane, which enables the calculation of changes in both membrane thickness and proton conductivity. The results, indicating most pronounced membrane degradation in vicinity of Pt band, are compatible with the Raman measurements of chemical group concentrations in the aged membrane [5]. Furthermore, the testing of the model on long-term degradation experiments is used to identify the optimal fuel cell operating conditions in which the durability of the fuel cell membrane is maximized. [1] Strlič M, Kolar J, Šelih VS, Kočar D, Pihlar B. A comparative study of several transition metals in fenton-like reaction systems at circum-neutral pH, Acta Chim Slov 2003;50:619–32. [2] Tavčar G, Katrašnik T. A Real Time Capable Quasi 3D System Level Model of PEM Fuel Cells, Fuel Cells 2020;20:17–32. [3] Burlatsky SF, Gummalla M, Atrazhev V V., Dmitriev D V., Kuzminyh NY, Erikhman NS. The Dynamics of Platinum Precipitation in an Ion Exchange Membrane, J Electrochem Soc 2011;158:B322. [4] Frühwirt P, Kregar A, Törring JT, Katrašnik T, Gescheidt G. Holistic approach to chemical degradation of Nafion membranes in fuel cells: modelling and predictions, Phys Chem Chem Phys 2020;22:5647–66. [5] Ohma A, Yamamoto S, Shinohara K. Membrane degradation mechanism during open-circuit voltage hold test. J Power Sources 2008;182:39–47. Figure 1