Growing global concern over the impact of carbon emissions has spurred many nations to aim to achieve net-zero carbon emissions within the 2030 to 2050 timeframe. A significant contributor to these emissions is the transport sector, responsible for a substantial 23% of total carbon emissions, with heavy-duty (HD) transport accounting for 40% of this cumulative figure. This study explores waste heat recovery (WHR) via the utilization of multiple working fluids in closed and open Joule cycles from the exhaust gas of the Volvo D13 truck engine operating on the European Stationary Cycle (ESC). Furthermore, this paper investigates the potential for recovering heat from the gases in the exhaust gas recirculation (EGR) circuit and examines the impact of pressure drops within the heat exchangers on the WHR process. The design and analysis of these cycles are executed using Aspen Plus, complemented by a one-dimensional D13 engine simulation model in GT-suite to provide the essential exhaust and EGR properties. This study also aims to offer more insight into the viability of pursuing WHR for truck applications using the Joule cycle.

The development of novel and economical methods to improve carbon capture from point sources is critical in alleviating global warming and climate change concerns. Cryogenic carbon capture (CCC) remains one of the prominent technologies, currently being studied as a viable replacement for other known conventional industrial technologies such as chemical sorption using amines. Though previous works began research on the main thermal properties of the deposited frost on a solid surface, the in-depth study of the CO2 frosting (desublimation) phenomena and the factors affecting the rate of frosting becomes a significant area of research that has not been fully understood. This study presents measurements of the desublimation rate on a coin under atmospheric conditions. These measurements aid to calculate the CO2 capture efficiency and enables the validation of the modelling efforts, which were relying on the thermophysical properties, heat, mass transport fluxes and their influences. The frost distribution and its characteristics are also discussed in this study. A fixed CO2 concentration of 16.2 % wt in the flue gas was used in all the experiments. Results show that the desublimation rate on the solid coin is faster in the first few minutes of the experiments. Precooling the inlet flue gas significantly influences the rate of frosting on the solid coin surface. Since temperature difference is the main driving force for CO2 frosting, the difference between the pre-cooling and coin temperatures determines the rate of desublimation, frost thickness, and distribution with time.

Autothermal reforming (ATR) is an important technology for hydrogen production from natural gas, where soot formation deserves particular attention as it may cause catalyst poisoning. The typical configuration of ATR reactors is that of an inverse diffusion flame (IDF). In this study, soot formation near ATR condi-tions is investigated experimentally and numerically, focusing on the effects of pressure and CO2 dilution in IDFs with pressure reaching 5 bar. The fuel stream consists of methane diluted with CO2 or N2. The mole fraction of O2 in the oxidant stream is 70%. Polycyclic aromatic hydrocarbons (PAHs) and soot vol -ume fraction are measured by the planar laser-induced fluorescence (PLIF) and planar laser-induced in-candesce (PLII) methods. High-fidelity simulations with a detailed soot aerosol model are also performed, and an empirical reactive soot inception model is proposed. A comparison of the results shows that the soot behavior is well predicted by the empirical reactive inception model but not fully captured by the physical inception model based on irreversible dimerization, demonstrating the importance of radical in-volvement in the soot inception process. Both measurements and predictions show a linear relationship between peak soot volume fraction and pressure, which can be explained by the linear increase of PAH molar concentration with pressure. Simulation analysis indicates that the dimer adsorption and HACA mechanism have a similar quantitative contribution to the soot growth. The CO2 shows stronger suppres-sion effects in soot formation at the investigated pressures compared to N2. The contributions of chemical and thermal effects to soot suppression are numerically analyzed and the results indicate that the chem-ical effect of CO2 is mainly due to the removal of H radicals through the reaction CO2 + H & RARR; CO + OH, providing a soot suppression contribution of two times larger compared to the thermal one.& COPY; 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Arrays of vertical parallel wires ('wetted wires') are a promising alternative to industrial columns such as spray, tray, or packed columns. Yet, further research is required to optimize their performance and com-petitiveness against packed columns. This work investigates the maximum wire density using the min-imum pitch (center-to-center wire distance). Results show that the pitch can be smaller than two millimeters, which is significantly less than the minimum pitches recommended in the literature. Results are discussed for liquid flow rates, wire diameters, and counter-current gas velocities. The min-imum pitch is often less than the diameter of the drops due to a bead-passing phenomenon. An analytical model illustrates the pressure drop characteristics of wetted-wire columns compared to existing pack-ings. This model shows that wetted-wire columns including those with small pitches have very low pres-sure drops. However, this model also shows that packing factors do not adequately describe wetted-wire columns. This implies that gas-side fluid dynamics of wetted-wire columns are fundamentally different from the gas-side fluid dynamics of packed columns. (c) 2023 Elsevier Ltd. All rights reserved.

Preheating technology is widely used to improve the emission or efficiency of combustors, such as diesel engines and gasifiers operating at high pressures. Soot is an unwanted by-product, but its formation is unavoidable in high-pressure diffusion combustion. In this study, the effect of preheating temperature on polycyclic aromatic hydrocarbon (PAH) and soot formation in methane/air co-flow flames was comprehensively investigated in the pressure range of 1-5 bar. The temperature of inlet gas ranges from 295 K to 573 K. The soot, PAH, and OH* concentrations were obtained using planar laser-induced incandescence, planar laser induced fluorescence, and chemiluminescence techniques, respectively. The experimental results reveal that soot and PAH formation is greatly enhanced at higher pressure or with a higher preheating temperature of inlet gas. At a fixed preheating temperature, the peak/integrated soot volume fraction follows a power law with pressure. As pressure increases, the enhancement of soot formation by preheating temperature is suppressed. As the preheating temperature is raised from 295 K to 573 K, the integrated soot volume fraction is increased by 33.7 times at 1.5 bar, but the difference narrows to 2.3 times at 5 bar. OH* signal increases with preheating temperature at 1 bar, but the difference becomes indistinguishable at higher pressure. Further, the experimental results were utilized to evaluate the soot modeling, PAH and soot formation under experimental conditions are examined using four different kinetic mechanisms. While the soot trend along different pressure and preheating temperature is qualitatively captured, the quantitative predictions vary depending on the mechanisms. Specifically, KAUST and Narayanaswamy-Blanquart-Pitsch (NBP) mechanisms overpredict the soot volume fraction while DRL and AppelBockhorn-Frenklach (ABF) mechanisms underpredicts the soot volume fraction. In terms of the PAH spatial distribution, only DRL and ABF mechanisms show the ability to capture the experimental observations, that is the peak PAH appears in the flame centerline. The reaction pathway analysis indicates both fuel-pyrolysis chemistry and PAH growth chemistry should be accounted for the discrepancy.

Desublimation of CO2 from a point source through direct contact with a cryogenic liquid is a promising approach to capture carbon. This study presents the results of a 3D numerical model of the desublimation process of CO2 onto a solid surface. Due to its high triple point pressure (~5.2 bar), CO2 converts to solid directly from the gas phase (i.e., desublimates) if cooled sufficiently at around atmospheric pressure. Desublimation phenomena on the surface has been modeled using a user-defined function (UDF) based on the diffusion boundary layer model implemented in CONVERGE. Preliminary work on the development of a 3D CO2 desublimation model is presented here with two different test cases: one with a single isothermal, solid, spherical surface; and the other with multiple solid isothermal spheres stacked vertically. The results show that the rate of desublimation is dependent on the number of spheres in the domain, the concentration of the point source, and the temperature of the spherical surface. The resulting decrease in the local molar concentration of CO2 between the surface of the static sphere and the immediate gas phase in the domain suggests desublimation. This was supported by the temperature difference at the same points in the domain. The numerical formulation of the desublimation model is validated analytically through the solid-vapor equations of state and the energy, mass, and species balance. The developed model will be used in future assessment of the desublimation-based cryogenic carbon capture system, post-experimental validation.

Catalyst degradation due to soot formation is one of the main issues in the autothermal reforming (ATR) process, which is widely regarded as the future technology for hydrogen production from natural gas. In this work, soot formation under conditions similar to ATR was systematically investigated, focusing specifically on the effects of pressure on soot formation in inverse diffusion flames (IDFs) under oxygen rich conditions. Methane was diluted with carbon dioxide; the oxygen content in the oxidizer stream varied from 55 to 70%-by-mol. Polycyclic aromatic hydrocarbon (PAH) and soot concentrations in the flames were measured by laser-induced fluorescence (LIF) and laser-induced incandescence (LII) respectively. Flame images showed that, as the pressure increased, the luminous region of the IDFs moved downward to mask the blue reaction region, and the flames became narrower. The degree of flame narrowing in the IDFs was milder than normal diffusion flames (NDFs). LIF measurements showed that increasing the pressure promoted PAH formation, which also subsequently promoted soot formation. Both PAH and soot formation increased linearly with pressure. The linear relationship was different from that of the NDFs. Flame simulations suggested that the promotion of soot formation with pressure was largely driven by PAH adsorption. Under the conditions of this study, lowering the oxygen content promotes soot formation in the IDFs. The results of this work contribute to the understanding of soot formation in IDFs at elevated pressures and the optimization of the ATR process.

The oil and gas industry operates by reciprocating natural gas engines which must comply with regulated emission standards for hazardous air pollutants, including NOx, CO, and volatile organic compounds (VOCs). These pollutants are regulated by Environmental Protection Agency, and each engine is regularly tested for compliance with national emission standards. A general emissions control strategy in combustion engines is to control the air-to-fuel ratio. However, stationary reciprocating engines, especially two-stroke engines, rarely have any mechanisms to control air and fuel parameters at various operating conditions. This article discusses a novel air management system that is invented to control the air-to-fuel ratio for a large bore two-stroke naturally aspirated gas engine, that is, AJAX™ brand model number 2802. The method can also be used for other engines with the same working principle. This novel air management system has been developed through comprehensive computational analyses of the gas exchange process inside the engine and is presented here. Pilot tests have also been conducted to validate the computational model results. The results show that this air management system can significantly reduce the engine emissions to the standard level at various operating conditions, including partial loads and speeds. In the case of VOCs emissions, up to a 75% reduction is observed.

In an earlier publication [1] the authors compared numerical predictions of the mean cylinder pressure of diesel and dual-fuel combustion, to that of measured pressure data from a medium speed, large-bore engine. In these earlier comparisons, measured data from a flush-mounted in-cylinder pressure transducer showed notable and repeatable pressure oscillations which were not evident in the mean cylinder pressure predictions from CFD. In this paper, the authors present a methodology for predicting and reporting the local cylinder pressure consistent with that of a measurement location. Such predictions for large-bore, medium-speed engine operation demonstrate pressure oscillations in accordance with those measured. The temporal occurrences of notable pressure oscillations were during the start of combustion and around the time of maximum cylinder pressure. With appropriate resolutions in time steps and mesh sizes, the local cell static pressure predicted for the transducer location showed oscillations in both diesel and dual-fuel combustion modes which agreed with those observed in the experimental data. Fast Fourier Transform (FFT) analysis on both experimental and calculated pressure traces revealed that the CFD predictions successfully captured both the amplitude and frequency range of the oscillations. Resolving propagating pressure waves with the smaller time steps and grid sizes necessary to achieve these results required a significant increase in computer resources.

This research used resources of the KAUST Supercomputing Laboratory located at King Abdullah University of Science and Technology, Saudi Arabia. Components of this work were supported by the U.S. Department of Energy, Vehicle Technologies Office.

The co-combustion of pulverised coal and biomass is increasingly being used for environmental reasons, and a number of computational fluid dynamic investigations are being undertaken to understand the details of the combustion process. These investigations assume that the particle flow entering the burner is uniformly distributed across the burner mouth or inlet. In this paper, this assumption is examined for an industrial burner by numerically simulating the fuel particle flows in the tube leading to the burner mouth. While there is evidence of maldistribution of the particles at the burner mouth, it is concluded from the flame data that this effect does not significantly influence the combustion flame in the furnace for the cases investigated.

This paper investigates the potential benefits, as well as limitations, of using the LES technique to predict the combustion efficiency, emissions and temperatures of wake-stabilised flares. LES calculations have been performed for two jet-to-cross-flow momentum flux ratios, with the results being compared with experimental data, where available, and with predictions of a closed RANS model using a second-moment turbulence closure. The flame fragmentation and the secondary flame zone attached to the release pipe at high jet-to-cross-flow momentum flux ratios, and their influence on the evolution of the counter-rotating vortex pair found in such flames, are discussed in detail, with realistic predictions being produced by the LES. The global mixing characteristics and the combustion efficiency of such flames are also compared with available data with reasonable agreement found. In all cases, LES predictions are found to be superior to equivalent RANS results, although the extra computational effort required in predicting species concentrations and flare efficiencies, in particular, may not be warranted.

Compared to Reynolds averaged Navier–Stokes (RANS)-based combustion modeling, the large eddy simulation (LES) technique has recently emerged as a more accurate and very adaptable technique in terms of handling complex turbulent interactions in combustion modeling problems. In this article, application of the LES-based combustion modeling technique and the validation of models in non-premixed and premixed situations are considered. Two well-defined experimental configurations where high-quality data are available for validation are considered as case studies to demonstrate the methods, accuracy, and capability of the LES combustion modeling technique as a predictive tool. The large eddy simulation technique for modeling flow and turbulence is based on the solution of governing equations for continuity and momentum in a structured Cartesian grid arrangement. A Smagorinsky eddy viscosity model with a localized dynamic procedure is used as the subgrid-scale turbulence model. A swirl flame is considered as the non-premixed combustion application. For non-premixed combustion modeling a conserved scalar mixture fraction-based steady laminar flamelet model is used. A radiation model incorporating the discrete transfer method is also included in the non-premixed swirl flame calculations. For premixed combustion where the application considered here is flame propagation in a confined explosion chamber, a model based on dynamic flame surface density is used. It is shown that in both cases LES-based combustion models perform remarkably well and results agree well with the experimental data.

Recent national and international emission legislations to reduce emissions of carbon dioxide are forcing power generation industries using coal to look at various alternatives, such as biomass and especially by co-firing techniques. Biomass is transported to the burners either mixed with the primary fuel, in general, coal, or used in dedicated pipelines. In both cases, transportation of biomass is difficult due to its composition, size, shape and physical behaviour in comparison to the transportation of coal. This study considers experimental measurements for biomass particle transportation in a pipeline with a transverse elbow and compares the results with those using computation fluid dynamic (CFD) techniques. Various materials: flour, willow, wood, bark and a mixture of flour and willow, have been considered in the present investigation. The experimental work was performed using the dynamic changes in the electrostatic charges of biomass particles in conjunction with correlation signal processing techniques. The CFD simulations were performed by considering the effects of gravity, non-spherical drag (based on estimated shape factor), detailed information of the particle distribution, particle wall collisions and particle–particle interactions. Good quantitative and qualitative agreement was obtained between the CFD simulations and the experimental data. It is concluded that particle–particle interactions are of less importance if the mass loading ratio of particles to air is less than 0.03.

Operational issues, such as slagging, fouling and corrosion of boilers during co-firing are yet to be fully understood. A numerical slagging index (NSI) to predict the slagging potential of coals and coal blends has been developed by some of the present authors, and this has been successfully validated with some Australian bituminous coals. In this paper, the NSI has been modified in order to predict the slagging potential of coal and biomass blends. The modified slagging index (MSI) considers the effects of the ash properties, the ash content and the heating values of the individual fuels in predicting the slagging potential of each blend. The results of the MSI predictions on coal/sewage sludge and coal/saw-dust blends produce a very good correlation with the reported experimental data. It has been observed that the ash content and the composition of the ash in the blends can be used to predict the behaviour of the ash mixture according to the proportional weights of the individual fuels. (C) 2012 Elsevier Ltd. All rights reserved.

The propagation of transient, turbulent premixed flames in a vented explosion chamber in the presence of a series of obstacles is numerically investigated by a dynamic formulation for the Flame Surface Density (FSD) with the Large Eddy Simulations (LES) technique. The chemistry is modelled by a one-step overall reaction, which simulates the reaction of a stoichiometric propane-air mixture. The FSD modelling in the reaction rate model is numerically employed with two different sub-grid scale (SGS) models. The first one is based on an empirical correlation of the SGS velocity fluctuations and the second one is based on similarity ideas involved in solving the wrinkled flame front considered as a fractal surface. The numerical predictions are analyzed and compared against an algebraic, simple FSD model together with experimental data. The calculations show that the dynamic FSD models provide superior results as compared with the algebraic FSD model. The comparisons demonstrate the importance of the contributions from the unresolved FSD and provide good agreement with experimental data for the flame structure, overpressure, and burning velocities.

The co-firing of pulverised coal/biomass in power generation plants is receiving considerable attention due to its influence in reducing all forms of emissions. Unlike coal, milled biomass, such as straw, may contain large particles of different sizes and shapes, which can have an impact on the combustion characteristics and emissions. Computational fluid dynamics (CFD) is often used to understand the influence of large biomass particles in a furnace. However, most CFD sub-models simplify heat transfer effects within the particles during combustion. In this paper a particle heat-up model, which considers the influence of thermal gradients within large biomass particles, is applied to a co-firing coal/biomass simulation in a tangentially fired furnace with up to 12% thermal biomass loading. Different sizes of biomass particles of non-spherical shape and their impact on the combustion behavior have been investigated. The influence of the particle size and shape distribution on the combustion characteristics and emissions was found to be significant. The computed results were found to be in good agreement with the experimental data.