Thermodynamic analysis of combustion and pollutants formation in a synthesis gas spark ignited engine

V magistrski nalogi je predstavljena zasnova merilne proge ter ključne predelave, ki so potrebne za ustrezno krmiljenje ter termodinamsko in emisijsko analizo delovanja 4-valjnega motorja z notranjim zgorevanjem in prisilnim vžigom ob uporabi sinteznega plina. Na podlagi izvedenih meritev, v točkah primernih za uporabo v kogeneracijskem postrojenju, so opravljene analize globalnih termodinamskih parametrov, koncentracij onesnažil v izpušnih plinih, cikličnih in valjnih variacij, samovžiga ter termodinamska analiza procesa zgorevanja. Analizirani parametri so primerjani s parametri dobljenimi ob uporabi zemeljskega plina. Na podlagi analiz rezultatov se ugotovi, da ob uporabi sinteznega plina: - ostane izkoristek v primeru delovanja s stehiometrično zmesjo enak ob zgodnejšem proženju prisilnega vžiga, sicer pa rahlo pade, - izpusti dušikovih oksidov in nezgorelih ogljikovodikov se zmanjšajo za najmanj en red velikosti, izpusti ogljikovega monoksida in delcev pa nekoliko manj, - do pojava samovžiga ne pride, - proces zgorevanja se podaljša za najmanj 15%, - ciklične variacije postanejo manj izrazite, njihova pojavnost pa se zaradi drugačnih tlačnih razmer v sesalnem zbiralniku spremeni.This dissertation presents a measurement system assembly alongside necessary key modifications required to properly control and analyze the thermodynamics of combustion and pollutant formation in a four-cylinder spark ignited synthesis gas fuelled internal combustion engine. Based on measurements carried out, several analysis of key phenomena have been performed, namely: global thermodynamic parameters, concentration of pollutants in exhaust, thermodynamic aspects of combustion, knock behavior, cycle to cycle and cylinder to cylinder variations. The analyzed parameters are addressed in comparison with ones acquired when natural gas was used as fuel instead of synthesis gas. Based on results of analyzed phenomena, we can sum up the key findings as: - when working with stoichiometric mixture the efficiency remains the same if we retard the ignition, otherwise it falls slightly, - emissions of nitric oxides and THC decrease by at least one order magnitude, while emissions of carbon monoxide and particles fall by a bit less, - knocking or any other form of spontaneous combustion does not occur, - combustion duration is prolonged by at least 15%, - cycle to cycle variations become less pronounced and their presence alone is changed due to different pressure conditions within the intake manifold

Termodinamsko osnovan model gorivnih celic s protonsko izmenjevalno membrano z znižano dimenzionalnostjo za opazovanje in nadzor z virtualnimi tipali

This doctoral thesis focuses on modeling and predicting fuel cell performance and degradation. Firstly, a reduced dimensionality model is developed, improving predictability in low current density regions and allowing for efficient determination of fuel cell intrinsic parameters, which can with developed model-based design of experiments methodology be efficiently determined with reduced experimental effort. Furthermore, novel mechanistic-based liquid water model is developed, that addresses critical aspects such as flooding, phase change, and two-phase transport in all fuel cell regions. When applied to the existing and newly developed 1D+1D system-level model, it provides a comprehensive understanding of liquid water dynamics, particularly in channels, catalyst, and gas diffusion layers. With real-time readiness and excellent agreement with experimental data, this model demonstrates its applicability in practical scenarios. Additionally, an integrated modelling framework considers causal chain of intertwined degradation mechanisms, providing comprehensive predictions for fuel cell degradation by addressing membrane aging, catalyst layer degradation, platinum migration, and peroxide formation, this framework enhances the understanding of degradation processes. Lastly developed modelling frameworks is used to develop distributed parameter model-based observer algorithm that makes possible, for the first time, to identify spatially resolved two-phase internal states of the fuel cell based only on adequate voltage and current traces.Doktorsko delo obravnava modeliranje in napovedovanje delovanja in degradacije gorivnih celic (GC). V njem je predstavljen razvoj modela z zmanjšano dimenzionalnostjo, ki izboljša napovednost v območjih z nizko gostoto toka in omogoča učinkovito določanje intrinzičnih parametrov GC, ki jih je mogoče z razvito metodologijo modelsko osnovanega načrtovanja eksperimentov učinkovito določiti z zmanjšanim eksperimentalnim naporom. Dodatno je bil razvit nov mehanistično osnovan model tekoče vode, ki obravnava kritične pojave, kot so poplavljanje, sprememba faze in dvofazni transport v vseh domenah GC. Zaradi svoje modelske osnove se lahko uporablja tako z obstoječimi modeli kot tudi z novo razvitim sistemskim 1D+1D modelom in omogoča celovito razumevanje dinamike tekoče vode, zlasti v kanalih, katalizatorju in plasteh za difuzijo plinov. Z odličnim ujemanjem z eksperimentalnimi podatki in z zmožnostjo izračunavanja hitreje od realnega časa, model dokazuje svojo uporabnost v praktičnih aplikacijah. Dodatno je bil implementiran tudi modelski okvir, ki upošteva vzročno verigo prepletenih degradacijskih mehanizmov in zagotavlja celovite napovedi z obravnavo staranja membrane, degradacije plasti katalizatorja, migracije platine in nastajanja vodikovega peroksida ter tako omogoča poglobljen uvid v degradacijo GC. Razviti modelski okviri so bili nazadnje uporabljeni za razvoj prostorsko razločenega virtualnega tipala, ki prvič omogoča identifikacijo prostorsko razločenih dvofaznih notranjih stanj GC samo na podlagi ustreznih signalov napetosti in toka

Hybrid methodology for efficient on the fly (re)parametrization of proton exchange membrane fuel cells electrochemical model for diagnostics and control applications

Successful parametrization and re-parametrization of the models used in PEMFC observer applications is instrumental to assure ideal control of the system. To increase ease of parametrisation and accuracy of parameter determination, this paper presents framework of twin analytical ansatzes for modelling PEMFC response in time and frequency domains sharing same set of calibration parameters. Owing to thermodynamically consistent modelling basis of the twin models, which are based on electrochemical model with state-of-the-art extrapolation capabilities and replication of the experimental data with one set of calibration parameters, they are valid in all current density regions. Furthermore, unique sharing of the calibration parameters enables unprecedented enrichment of the dataset that can be used to determine values of model\u27s calibration parameters with higher certainty or enhances identification of individual calibration parameters that are otherwise harder to be uniquely determined. Additionally, proposed hybrid methodology also enables a significant reduction in the measurement time and enable re-parametrization on the fly

Methodology for evaluation of contributions of Ostwald ripening and particle agglomeration to growth of catalyst particles in PEM fuel cells

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

Closed-form formulation of the thermodynamically consistent electrochemical model considering electrochemical co-oxidation of CO and H [sub] 2 for simulating solid oxide fuel cells

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

Predictive virtual modelling framework for performance and platinum degradation modelling of high temperature PEM fuel cells

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

Predictive system-level modeling framework for transient operation and cathode platinum degradation of high temperature proton exchange membrane fuel cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are a promising and emerging technology, which enable highly efficient, low-emission, small-scale electricity and heat generation. The simultaneous reduction in production costs and prolongation of service life are considered as major challenges toward their wider market adoption, which calls for the application of predictive virtual tools during their development process. To present significant progress in the addressed area, this paper introduces an innovative real-time capable system-level modeling framework based on the following: (a) a mechanistic spatially and temporally resolved model of HT-PEMFC operation, and (b) a degradation modeling framework based on interacting individual cathode platinum degradation mechanisms. Additional innovative contributions arise from a consistent consideration of the varying particle size distribution in the transient fuel cell operating regime. The degradation modeling framework interactively considers the carbon and platinum oxidation phenomena, and platinum dissolution, redeposition, detachment, and agglomerationhence, covering the entire causal chain of these phenomena. Presented results confirm capability of the modeling framework to accurately simulate the platinum particle size redistribution. Results clearly indicate more pronounced platinum particle growth towards the end of the channel since humidity is the main precursor of oxidation reactions. In addition, innovative modeling framework elucidate contributions of agglomeration, which is more pronounced at voltage cycling, and Ostwald ripening, which is more pronounced at higher voltages, to the platinum particles growth. These functionalities position the proposed modeling framework as a beyond state-of-the-art tool for model-supported development of the advanced clean energy conversion technologies

Hybrid methodology for parametrisation of proton exchange membrane fuel cell model for diagnostics and control applications

Electrochemical impedance spectroscopy (EIS) is a very powerful tool for the diagnosis and characterisation of fuell cells (FC). However, there is still a lack of physico-chemically consistent models that include parameters with a clear physical meaning and can be related to intrinsic parameters of FC. To fill this knowledge gap, this paper presents a novel, mechanistically-based and computationally-efficient FC modeling framework for time and frequency domain simulations. Furthermore, the model consistently handles forward and backward reactions, ensuring its validity at all current densities. These features enable the development of a hybrid methodology for parameterising the FC model in both domains, resulting in unprecedented accuracy in determining the internal states around which the EIS perturbation is applied. Furthermore, innovative modeling framework incorporates a 1D analytical solution of FC impedance that for the first time accounts for both electrodes, the membrane and individual effects of the electrodes coupled to the respective GDL and channel, all significantly impacting the accuracy of the model. This was confirmed by state-of-the-art reproduction of experimental data with R$^2$ values exceeding 0.965 for data not used in the parameterisation. The presented modeling framework thus provides a modelling basis for observer functionalities beyond the state-of-the-art

Educational scale-bridging approach towards modelling of electric potential, electrochemical reactions, and species transport in PEM fuel cell

The use of hydrogen fuel cells as a mobile source of electricity could prove key to the future decarbonisation of heavy-duty road and marine transportation. Due to the complex interplay of various physicochemical processes in fuel cells, further development of these devices will depend on concerted efforts by researchers from various fields, who often lack in-depth knowledge of different aspects of fuel cell operation. These knowledge gaps can be filled by information that is scattered in a wide range of literature, but is rarely covered in a concise and condensed manner. To address this issue, we propose an educational-scale-bridging approach towards the modelling of most relevant processes in the fuel cell that aims to adequately describe the causal relations between the processes involved in fuel cell operation. The derivation of the model equations provides an intuitive understanding of the electric and chemical potentials acting on protons at the microscopic level and relates this knowledge to the terminology commonly used in fuel cell research, such as catalyst electric overpotential and internal membrane resistance. The results of the model agreed well with the experimental data, indicating that the proposed simple mathematical description is sufficient for an intuitive understanding of fuel cell operation

Operational stability of a spark ignition engine fuelled by low H2 content synthesis gas

The paper focuses on the implementation of a comprehensive and robust optimization procedure for a synthesis gas fired four-cylinder, spark ignited, 2.2 L industrial engine used in combined heat and power applications. Innovatively designed workflow is for the first time incorporating also a thorough operational stability analysis for evaluation of the engine operation durability while using off-design fuels. Design constraints of the engine operational space are set after in depth investigation of knock phenomena, cycle to cycle variations, emission formation phenomena and engine performance parameters. These are derived from experimental data, obtained from the engine, equipped with newly designed components. Throughout the paper, results obtained with synthesis gas are benchmarked to natural gas. With significant emphasis laid on analysis of lean operation conditions, as a measure to reduce environmental footprint of energy generation, a newly proposed optimum operation points reveal a possibility to obtain TA-Luft and EPA emission limits already with stoichiometric mixture. This allows to achieve a remarkably low power de-rating factor of only 16.5% and omission of any aftertreatment system. Therefore, findings of this study represent a significant improvement of current control strategies and enable further increase in specific power and thus economic attractiveness of distributed power generation techniques at enhanced durability while using low-carbon and renewable fuels