Coal combustion

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Experimental investigations on combustion and emission behaviour during oxy-coal combustion

Experimental investigations on combustion and emission behaviour during oxy-coal combustion

Most techno-economic reviews are based on the comparison of oxy-fuel technology with air-blown combustion or post combustion scrubbing. The comparisons vary significantly in cost as costs vary between countries and the basis of calculation. Capture of carbon dioxide from an existing large refinery power station boiler by conversion to oxygen firing with flue gas recirculation however has been reported to be feasible, and could be based on proven equipments [Wil01, Yam05, Zhe01]. Furthermore, an air-fired furnace could be converted to oxy-fuel operation without changes in the costly steam pressure parts and without loss of duty [Wil01]. Also, the flue gas volume exiting the boiler, downstream the recycle flue gas take off point during oxy-coal combustion is reduced by almost 70% relative to air-blown combustion, thus minimising the additional processing or treatment costs necessary to prepare a CO 2 rich
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Modeling of particle-radiation-interaction for the numerical simulation of coal combustion

Modeling of particle-radiation-interaction for the numerical simulation of coal combustion

by Manickavasagam and Mengüç [84]. The authors also applied the extinction method with KBr pellets and presented polynomial approximations for the values obtained. From their analysis of the results they concluded that a spectrally constant refractive index n does not affect the accuracy of the extinction efficiency, whereas, for the small wavelength range, it is desirable to account for the spectral variation of both n and k when scattering efficiency is calculated. They also observed a dominant role of particle size when radiative properties were determined. Refractive indices obtained by Foster and Howarth differ from the results of Manickavasagam and Mengüç, especially for larger wavelengths, where the value of the absorptive index, k, determined by Foster and Howarth is approximately four times larger. Im and Ahluwalia [61] summarized data on optical properties of coal combustion particles and noted uncertainties in the scarce data of char particles, but did not attempt to assess the influence of these uncertainties on modeling of radiative heat transfer.
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Large eddy simulation of pulverised coal combustion

Large eddy simulation of pulverised coal combustion

The scope of this chapter is to present a comprehensive overview of the employed Pulverised Coal Combustion ( PCC)-LES model. This includes presenting the gas- phase transport equations, fundamental coal particle equations, and the applied sub-model equations for closure. These equations are derived from the fundamen- tal equation presented in section 3.1 using the approach discussed in chapter 4. In general, equations are presented as implemented within the framework of Open- FOAM, which might in some cases deviate from the standard representation found in the literature. OpenFOAM, acronym for Open source Field Operation And Ma- nipulation, is a collection of software written in C++ under the GNU General Pub- lic License ( GPL) version 3. The purpose of OpenFOAM is to provide libraries and solvers for fluid mechanic problems including combustion. Furthermore, Coal- FOAM is an in-house solver, developed over the course of this research project and based on the standard coalChemistryFoam solver of OpenFOAM v2.4.x. The Coal- FOAM solver extends the coalChemistryFoam by several features, like a particle dispersion model for LES, cf. Bini and Jones (2008), an LES-TCI model, cf. Hu et al. (2006), and the coal pyrolysis model of Richards and Fletcher (2016). A dis- cussion of OpenFOAM and CoalFOAM and corresponding implementations can be found in appendix B and C.
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Experimental and numerical investigation of flameless pulverised coal combustion

Experimental and numerical investigation of flameless pulverised coal combustion

For each setting, three images from different axial positions are shown. From the first setting on the left to the last setting on the right, the inlet velocity of the combustion air is decreased successively. In the first two experiments, nitrogen was used as coal carrier whereas the latter two experiments were carried out with air as carrier. It becomes evident, that in the case with air as carrier the reaction zone is localised around the coal jet. When nitrogen is used, hardly any reaction zone can be determined in the burner vicinity. Only very faintly the coal jet can be distinguished from the background. For flameless combustion of gas, Mancini et al. [104] identified it as a key feature that ignition only occurs upon mixing with the oxidiser jet. By using an inert carrier gas for the coal, this characteristic can be adapted to pulverised coal combustion. This finding is also in line with the reburning experiments by Hardy and Kordylewski [66] presented in the previous chapter as well as experiments on combustion of sawdust injected with air and CO 2 into a MILD combustion furnace carried out by Shim et al. [144].
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Ecological evaluation of the pulverized coal combustion in HTAC technology

Ecological evaluation of the pulverized coal combustion in HTAC technology

the remaining 10% through the thermal route. The experiment on MILD coal combustion under high pressure (3 bar) conditions was carried out by Heil et al. [127] and modeled by Erfurth et al. [128] using the CFD FLUENT code. Three dimensional steady-state simulations of a 1/6-sector of the furnace were performed for lignites and bituminous coals. Standard sub-models implemented in the FLUENT code were used; the Eddy Dissipation Concept with two global reactions for turbulence- chemistry interaction modeling and P1 or Discrete Ordinates models for radiation. A Lagrangian description for the solid phase was used. Very simple empirical sub-models were used for devolatilization (constant rates) and char burnout (diffusion- kinetics limited). This simple mathematical model was able to predict well the flow field and the recirculation inside the combustion chamber. The temperatures were over- predicted in comparison with the experimental data while the species concentrations differed substantially from the measured values. Needs for detailed sub-models for devolatilization and char burnout became apparent.
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The implementation of circular economy concept in the Polish coal combustion products sector: Selected problems

The implementation of circular economy concept in the Polish coal combustion products sector: Selected problems

3.2.1. Examples of CCP using in particular sectors of the Polish economy Concrete production: fluid ash generated by power stations is used as a stabilizer of natural soils or ashes and ash-slag mixtures (conventional) or as a binder component. Fluid ash is primarily used by mines as a raw material for the so-called ‘PKW aggregate’, the main component of which is the coal slate. This aggregate is used in the construction of roads. Fluid ash is particularly important in road engineering, and it can be used to produce aggregates in the lower layers of the road. In the concrete production process, various types of aggregates are used, containing several components in the form of ash, cement, water and concrete additives. If we use ash (but in relatively small quantities, the larger cannot be due to technological standards), it can replace much more expensive cement (a ton of cement costs about 120 PLN, while a ton of ash - about 20 PLN). In this case, you can save about 7-11 PLN on the cubic meter of the produced concrete. This shows the cost analysis of one cubic meter of concrete produced below:
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A theoretical analysis of single coal particle behavior during spontaneous devolatilization and combustion

A theoretical analysis of single coal particle behavior during spontaneous devolatilization and combustion

In few last decades, extensive research has been carried out in development of comprehensive computer models for better performance of coal in many industrial applications. However, the processes occurring during coal combustion and their interaction, especially in devolatilization, are scarcely understood. Although, as mentioned in section 1.1, the ideal situations of either nonvolatile char combustion or devolatilization in an inert atmosphere are inconsistent with practical situation, there has been only few research works in this field. The objective of this work has been to systematically analyze coal devolatilization, the radiation and convection effect over combustion, internal conduction within coal particle, and the reaction rates in circumstances where highly reactive gases are starting to come in contact with coal particle. Special emphasis has been placed on modeling and understanding the physical and chemical processes and their interaction which dominate the burning phenomenon. The modeling concept is similar to that of liquid droplet combustion except that volatiles emitted from the coal particle which has a constant diameter during devolatilization unlike droplet burning. Moreover, the data incongruity existing in estimation of kinetic coefficients for gasification of coke by CO 2 has shown a need to perform experimental investigation.
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The effect of char kinetics on the combustion of pulverized coal under oxyfuel conditions

The effect of char kinetics on the combustion of pulverized coal under oxyfuel conditions

ence of CO2 on chemical reactivity (both at the char surface and in the surrounding gas phase) and the ability to predict combustion in various char combustion regimes. The CFD software employed in this work is the open source CFD software OpenFOAM, version 2.1 . The only other published investi- gation of coal combustion using OpenFOAM to the author's knowl- edge is Yamamoto et al. [103], who studied the effect of Large eddy simulation (LES) for coal combustion with air. The solver application employed in that study relied on many in-house extensions, so the methods presented there cannot be transferred directly to this work. The solver application and the models presented here involve various changes and extensions of the software code, from source terms in the governing equations to pressure velocity coupling and additional models. The following chapters intend to describe and validate these changes and to document the remaining model equa- tions. Where possible, the original literature sources for the latter are identified.
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An LCA study of an electricity coal supply chain

An LCA study of an electricity coal supply chain

Hauschild, Alting & editors, 1997), EDIP 2003 (Dreyer, Niemann & Hauschild, 2003), IMPACT 2002+ (Jolliet, Margni, Charles, Humbert, Payet, Rebitzer et al., 2003), Ecological Scarcity (UBP Method) (Frischknecht, Steiner & Jungbluth, 2009) and so on. However, the shortcomings of these methods are that most indicators, normalization factors and weighting factors are based on the data of Netherlands, Denmark, and the European Union. Because these normalization factor and weighting factors depend on the actual conditions of a particular country or region, they cannot be used to process the data of the Chinese electricity coal supply chain. Thus, this paper uses Chinese normalization factors and weighting factors given by the Environment Research Center in Chinese Academy of Science and Technical University of Denmark (Yang, Cheng & Wang, 2002). Table 13 illustrates that in the electricity coal supply chain, the biggest environmental impact of waste gas emissions is GWP, followed by EP, POCP, AP and ODP.
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Phase-out of 'coal to power' in an ETS

Phase-out of 'coal to power' in an ETS

projected changes in primary energy from fossil energy resources in 2030 relative to 2010. Averaged across these pathways, the change required in primary energy from coal, gas, and oil is about minus 71 %, plus 6 %, and plus 8 %, respectively. To date, many countries produce a large share of their electricity from coal. In the EU, about 21.5 % of the fossil energy resources used for generating electricity are still coal resources (Agora Energiewende and Sandbag 2017, p. 7), and many EU citizens and environmental groups are concerned about their governments’ reluctance towards, or too slow pace of, phasing out coal. The impression we get from the intensive public discussion about phasing out coal-based electricity generation is that there are policymakers, media and even economists without a clear understanding what the impact of the phase-out policy is when implemented in the prevailing regulatory framework of the EU, which is characterized by the interaction of the climate policies at Union and national level. Our paper aims to identify the distortions such phase-out policies generate on the markets for electricity and permits and it assesses the resulting impact on the countries’ welfare.
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Testing supply-side climate policies for the global steam coal market: Can they curb coal consumption?

Testing supply-side climate policies for the global steam coal market: Can they curb coal consumption?

4.1 Remaining coal reserves in operating mines Due to individual assessment methods, prevailing complexity of measurement and measurement errors, as well as a political component, estimates of reserves and resources are hard to obtain and prone to substantial uncertainty. While there exists an international code for fossil fuel energy and mineral reserves and resources classification (UN 2013), it is not broadly used. Rather the code developed by the Joint Ore Reserve Committee (JORC 2012) is more and more commonly applied by companies, also outside its original Australasian scope. Based on various sources, BGR (2015) provides a comprehensive list of resource and reserves estimates for 81 countries. According to BGR (2015, 43), hard coal reserves totaled 699 Gt in 2014. A more in-depth, country-by-country analysis is available from the World Energy Council (2013) which reports a similar value of 691 Gt of proved recoverable reserves of anthracite, other bituminous and sub-bituminous coal by end of 2011. Thurber and Morse (2015) and Osborne (2013), both provide a selected number of country case studies providing estimates of recoverable reserves and resources. The NGO “coalswarm” 11 provides an incomplete list of mining operations in a limited number of countries. Commercial providers like “IntierraRMG” 12 or “Mining Atlas” 13 advertise to provide a comprehensive data set on operating mines
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Geophysical Investigation of Wuda Coal Mining Area, Inner Mongolia: Electromagnetics and Magnetics for Coal Fire Detection

Geophysical Investigation of Wuda Coal Mining Area, Inner Mongolia: Electromagnetics and Magnetics for Coal Fire Detection

TEM measurements were conducted across FZs and at single locations of a FZ. A num- ber of 65 transient electromagnetic soundings on 12 profile lines were performed using the Geonics PROTEM47 system. Those across the well investigated FZ 8 (Figure 2) – one of the 20 or so FZs in Wuda Coal Mining Area – are discussed in this paper. The spacing of the TEM sites was adapted to the terrain. A loop size of 50 m x 50 m was chosen for most sites in inloop configuration, where the receiver coil is placed in the center of the transmitter loop. Models for each site were created from the data obtained without a-priori information, using an iterative Marquardt algorithm (Weidelt 1984) to determine resistivities (Rho) and depths of model layers.
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Combustion noise: modeling and prediction

Combustion noise: modeling and prediction

To avoid many of the difficulties mentioned above in the development of a theory of combustion noise, Strahle [20, 21] was the first to employ Lighthill’s Acoustic-Analogy method to identify the combustion- noise source term by recasting the governing equations in a certain form. Since Strahle’s early work, this approach has gained a good deal of popularity. The Acoustic-Analogy formulation was originally developed by Lighthill [22, 23] in the early 1950s for the identification of the sources of jet noise and as a framework to describe its propagation to the far field. For turbulence-generated jet noise, Lighthill [22, 23] showed that the source in the Acoustic-Analogy theory is a quadropole. He also established his celebrated U 8 velocity-scaling law for jet noise by means of this method. However, during the intervening years between then and now, high quality narrow band, hot and cold jet noise data at different Mach numbers became available. As a result, more and more discrepancies between the jet-noise quadrupole theory and experimental measurements became known. About a decade ago, based on extensive experimental data, Tam et al. [24] proposed a two-source jet-noise model to replace the quadrupole representation. They showed, using single far-field microphone data, two far-field microphone cross-correlation data and jet-turbulence far-field microphone correlation data, that high-speed jet noise actually consists of two components. These two noise components are generated by the fine scale turbulence and the large turbulence structures of the jet flow. They also provided far-field data that were at variance with Lighthill’s velocity-scaling law. Their data show clearly that the velocity exponent is not eight. It depends on the direction of radiation and the jet temperature. For a temperature ratio 2.7 jet, the velocity exponent is around 6.5 to 7.5 in the sideline direction and around 9 for inlet angles larger than 130 degrees.
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Large Eddy Simulation of Mixing and Combustion in Combustion Systems under Non-adiabatic Conditions

Large Eddy Simulation of Mixing and Combustion in Combustion Systems under Non-adiabatic Conditions

In the literature many works are available on reduction methods for chemistry. The classical approach for reducing the chemical reaction mechanism by reducing to a single step reaction between fuel and oxidizer forming the products; was proposed by Zeldovich and Frank-Kamentzki [231]. The necessary Arrhenius law reactions rates for reactions involved in these reaction mechanisms are fitted with the experimental data/detailed simulations to avoid the complexity to derive from the elementary kinetic data [221]. This limits the insight provided by these one step mechanisms to only the overall analysis, by ignoring many crucial physical phenomenon that takes place during the combustion. Therefore, more sophisticated reduction techniques incorporate additional chemical kinetic details. The very small time scales of combustion chemistry allow decoupling combustion chemistry from other processes with larger time scales. The most of the reduction strategies are based on this assumption. This can be achieved systematically via steady-state or partial-equilibrium [150, 151]. The reduction strategies cannot be achieved by following universal principle. Thus they cannot be automated. One need to understand chemical kinetics involved in detail to reduce them typically below 10 reaction steps, thus reduced mechanisms are specific to the selected applications. The reduction mechanisms in recent times are becoming very popular industrially. But as the stringent emission norms demand the capturing and retaining of in detail thermo-chemical information new methods were evolving. Maas and Pope [129] proposed Intrinsic Low-Dimensional Manifolds (ILDM) considering combustion as a movement along a trajectory through composition space. These trajectories are rapidly evolved to form low-dimensional manifolds starting from different initial conditions taking advantage of different time scales present in the combustion process. The slowest time scales govern the movement and thereby it reaches the chemical equilibrium. The manifold can be identified automatically by an Eigen value analysis of the Jacobean of the detailed mechanism. This results in the possibility of tabulation of chemical system as a function of a few reaction progress variables (RPV) across the manifold. Typically, a progress variable a combination of two species mass fractions, namely the mass fractions of CO 2
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Challenges of coal transitions : a comparative study on the status quo and future prospects of coal mining and coal use in Indonesia, Colombia and Viet Nam

Challenges of coal transitions : a comparative study on the status quo and future prospects of coal mining and coal use in Indonesia, Colombia and Viet Nam

With respect to the question how climate mitigation will impact on the economy of coal producing countries, one important issue is whether reducing emission from coal directly implies reduced coal use or to which degree emission reductions could be achieved by carbon capture and storage (CCS). Ever since the IPCC’s Special Report on carbon capture and storage (CCS) in 2005, there has been hope that CCS could in future make a substantial contribution to reducing CO 2 emissions from the power sector (IPCC 2005). However, 14 years later there are only two large-scale projects operational in the power sector (Global CCS Institute 2018). So a solid proof that the concept works not only as a tech- nical theory but in terms of being technically, economically, and socially viable to be deployed at com- mercial scale is still missing. Barriers to technology diffusion are technology costs, lack of acceptance in some countries and storage limitations leading to a slow uptake of the technology (Gaede and Mead- owcroft 2016). In consequence the various climate mitigation scenarios include very different shares of CCS (Bui et al. 2018). So on an optimistic note, CCS may help to reach climate targets quicker, beside its possible role to reduce emissions from industry and/or to achieve negative emissions through com- bining the combustion of bio-energy with CCS (BECCS). Quick advances in the development and em- ployment of CCS technologies may to some degree increase the "burnable" amount of coal. However, the IPCC special report on 1.5°C states on this issue: "the use of CCS would allow the electricity genera-
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Flashback prevention in lean-premixed hydrogen combustion

Flashback prevention in lean-premixed hydrogen combustion

As discussed in the previous section, swirl is imposed on the flow in order to achieve fuel–air mixing and create a central recirculation zone that provides low flow velocities for flame anchoring. Between a swirl number too low for the occurrence of VB and a swirl number so high, that it requires an unaffordable pressure loss, a certain margin for swirl number variation exists. In case of incomplete mixing, the high flame temperatures associated to rich pockets of hydrogen would lead to increased NOx emissions. This poses an argument in favor of a high swirl number for hydrogen combustion. An argument in favor of a lower swirl number is the reported increased FB resistance. Sayad et al. [ 53 ] reported a significantly extended operational range when decreasing the swirl number from S = 0.66 to S = 0.53 for a generic swirl burner operating on syn gases containing up to 80 vol.-% hydrogen. With decreasing swirl number, the swirling jet opening angle downstream of the mixing tube outlet was also reduced. This reduction in jet opening angle was previously reported by Terhaar et al. [ 70 ] and Reichel et al. [ 2 ] to also occur when the swirl number was reduced due to increasing injection rates of a non-swirling central air jet. Similar to the swirl number reduction of Sayad et al., the non-swirling air jet also increased FB resistance. This is reasonable, since a decreasing jet discharge angle reduces the area consumed by the mixture downstream of the mixing tube and leads to higher axial velocities.
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Supercontinuum Absorption Spectroscopy for Combustion Diagnostics

Supercontinuum Absorption Spectroscopy for Combustion Diagnostics

As with all new diagnostic techniques, a thorough and detailed application of the technique combined with different validations are required. To perform this important step with SCLAS, several systems were chosen, that offer unique challenges as well as possibilities for SCLAS to offer additional insights compared to other diagnostic systems. For the following chapter two systems were investigated in detail, since these systems show the advantages of SCLAS most clearly and are representative for all systems tested. The first case is gas cell measurements that allow the evaluation of SCLAS under controlled conditions with a reasonable parameter range. The focus in this experiment was on the characteristics of SCLAS in multi-parameter high- pressure environments combined with multi-species situations, as well as higher concentrations of species. The second experiment focuses on high-temperatures as well as combustion related issues. For this test case the Wolfhard Parker burner (WHP, details about the burner will be given later in this chapter, [23, 131–133]) was chosen due to its extensive database of reference measurements available in combination with temperatures up to 2000 K (up to 1400 K in the investigated regions of the flame). Since SCLAS is an absorption-based line of sight (LOS) technique, it is necessary for a system under investigation to provide homogeneous conditions along the relevant absorption path, which the WHP burner is especially designed to ensure. The gas cell measurements will be presented first, since they provide additional insights to the implemented evaluation and data processing algorithms, while the second part focusses on the WHP burner trials. Both trials are followed by a discussion of the achieved performance and uncertainty. It has to be kept in mind, that during the development of SCLAS, the system was continuously improved. These validation trials are therefore among the first performed measurements with SCLAS.
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Indirect Combustion Noise Generation in Gas Turbines

Indirect Combustion Noise Generation in Gas Turbines

The paper investigates the indirect combustion noise, which is generated during the acceleration of the convected entropy nonuniformities of the combustion products in the outlet nozzle of the combustion chamber. The generation mechanism of the indirect noise is proven experimentally and through numerical simulation. Probe microphones and fast thermocouple probes were used to measure pressure and temperature fluctuations. The generation of indirect noise is verified via the phase relationship between thermocouple and microphone signals. The flow field in the combustion chamber is simulated by means of an unsteady RANS computation. Self excited oscillations are used for the computation of the direct and indirect noise generation of the combustion chamber. Since the related frequencies are low and the corresponding scales much larger than the turbulent scales, a CAA-method is employed for both the propagation of sound waves as well as entropy perturbations. It is shown that the CAA method is capable to describe the acoustical properties of the combustion system found in the experiments when the URANS simulation is used as input. The experimental results also show that indirect combustion noise may contain high frequency noise contributions, which are generally attributed to turbine noise.
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HF Combustion Instability - Research Activities in Germany

HF Combustion Instability - Research Activities in Germany

Research activities aim at a better understanding of the underlying mechanisms of combustion instability. This understanding is important to develop the engineering capabilities towards predictive analyses. Furthermore, such understanding can help to transfer the existing design parameters to new designs or new propellants combinations. Methane - Oxygen, for example, has recently moved into the focus of European space activities and the European heritage on this propellant combination is limited. For traditional propellant combinations, like H2-O2, kerosene or hypergolic propellants, there are several guidelines for the design of rocket engines also with respect to HF in order to minimize the risk. Apart from other factors, these guidelines involve the estimation of the frequencies both of the combustion chamber and injection system. These analyses are well known and have been conducted for years. The combustion chamber usually is approximated as cylindrical volume and analytical solutions are used. Injection systems are characterized by 1D acoustic models and can be described in a fairly straightforward mannar. Approaches like this, however, are still quite limited in their fidelity. The flame source term, for example, is reduced to an n-tau term [4].
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Modes Reconstruction of Hybrid Combustion Flame

Modes Reconstruction of Hybrid Combustion Flame

Optical investigations of hybrid combustion flame are essential to better understand their combustion mechanism. Therefore, combustion tests using para ffin-based fuels and gaseous oxygen (GOX) were performed in the framework of this research. The combustion flame was analyzed with two decomposi- tion methods, which give a low-dimensional representation of the complex flow structures and identify the main combustion phenomena. To prove the reliability of this analysis, a modes reconstruction has been performed. The results show that the output of the reconstruction provides a good representation of the original combustion video frames. This means that the low-dimensional modes representation is able to efficiently and correctly describe the main combustion phenomena in the combustion chamber.
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