Influence of laser ignition on characteristics of an engine for hydrogen enriched CNG and iso-octane usage

The study has focused on determining the laser plug effects on engine characteristics and the laser plug usage results have compared with spark plug usage. The laser ignition technique is a type of new ignition technique and an important solution that can make combustion systems more efficient. The testing of an engine with a laser plug is the novelty of the study and the tests were carried out with reference to equivalence ratio and plug power ranges. The behaviors of the engine at full load were examined so experimentally for both ignition techniques at hydrogen enriched CNG and iso-octane mixture usage. The tests were carried out for variations of 0.4–2.0 equivalence ratio and 20–120 W plug power. A mixture that 90% iso-octane and 10% HCNG in mass was used at two ignition modes in tests for 3300 rpm maximum engine torque speed. Also, the flame formation and propagation for both ignition techniques were detected via a high-speed camera. The tests have shown the laser ignition leads to more energy consumption in the rich mixture conditions and also, less energy is required in the lean conditions. The laser ignition discharge has extended the engine's lean combustion limits via a small energy input at the tests. The high-speed camera images have shown that the laser ignition reduces the Kernel flame formation and propagation time. The laser ignition technique was produced less NO_x than the conventional spark ignition method.     

Low concentration CO gas sensor constructed from MoS2 nanosheets dispersed SnO2 nanoparticles at room temperature under UV light

In consideration of the different electron structure-associated physical properties and internal sensing merits of MoS₂ and SnO₂, this work reports a nanocomposite with unique structure of MoS₂ nanosheets dispersed SnO₂ nanoparticles. The sensing performance of MoS₂/SnO₂ sensor toward low concentration CO was investigated at room temperature under the UV light illumination. It was found that MoS₂/SnO₂ sensor shows improved CO gas response (R ~ 4.97 at 40 ppm CO) compared with pure SnO₂ (R ~ 3.27 at 40 ppm CO), which is due to the unique structure and the formation of heterostructure between MoS₂ and SnO₂. Moreover, the fabricated sensor also exhibits fast response and recovery time (43 s/36 s). The sensor provides a potential platform for monitoring CO gas at room temperature.     

Electrochemical characteristics of limiting current sensors with LSM-YSZ and LSM-CGO-YSZ composite electrodes

Limiting current gas sensors with Pt electrodes are widely used to detect gaseous species, such as O₂, CO, HC, and NO_x, from exhaust gases generated by the incomplete combustion of fossil fuels. In this study, aperture-type limiting current sensors were fabricated based on La_0.8Sr_0.2MnO₃ (LSM)–yttria-stabilized zirconia (YSZ) and LSM–Gd_0.1Ce_0.9O_2-d (CGO)–YSZ composites. The potential of these composites as alternative electrodes for O₂ and CO sensing was evaluated. The composite electrodes exhibited current–voltage curves that are typical for limiting current sensors. LSM–CGO–YSZ registered higher limiting current values than those of the commercial Pt and LSM–YSZ electrodes in O₂ and CO atmospheres. The formation of a resistive secondary La₂Zr₂O₇ phase at the LSM/YSZ interface of LSM–YSZ deteriorates the electrochemical reaction and increases the polarization resistance of the electrode in the CO environment. The addition of CGO prevented the formation of the secondary phase, which lowered the ohmic and polarization resistances of LSM–CGO–YSZ compared to that of the LSM–YSZ composite. However, increasing the CGO concentration from 10 to 40 wt% weakened the adhesion of LSM and reduced the triple phase boundaries, which increased the electrode polarization resistance in both O₂ and CO atmospheres.     

The catalytic activity of the Pr2Zr2−xFexO7±δ system for the CO oxidation reaction

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO₂, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr₂Zr_2−xFe_xO_7±δ (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO₂ sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction.     

Performance of limestone-based sorbent for sorption-enhanced gasification in dual interconnected fluidized bed reactors

A possibility to carry out sorption-enhanced gasification (SEG) is represented by its integration with the calcium looping concept in dual interconnected fluidized beds (DIFB). This article is focused on the sorbent CO₂ uptake performance and attrition/fragmentation tendency when operating conditions simulating those of a DIFB-SEG process are adopted. Experiments were carried out on a commercial Italian limestone in a laboratory-scale DIFB reactor. Carbonation was carried out in a range of test conditions, including variable temperature (600–700°C) and absence/presence of steam (10% by volume); CO₂ concentration was set at 10% by volume. The characterization is extended by investigating the behavior of preprocessed DIFB-SEG samples on impact fragmentation tests, conducted in an ex situ apparatus. Tests were carried out for impact velocities in the range 17–45 m/s. Results were discussed considering both the impact velocity value and the operating conditions under which the sample was preprocessed in the fluidized bed.     

Numerical modelling of rotating packed beds used for CO2 capture processes: A review

Over the last decades, renewable and clean energy sources are being rigorously adopted along with carbon capture technologies to tackle the increasing carbon dioxide (CO₂) concentration level in the environment. CO₂ capture is a quintessential option for tackling global warming issues. In this context, the present paper has reviewed the process intensification equipment called a rotating packed bed (RPB), which is highly industry applicable due to high gravity (HiGee) force. This facilitates strong mass transfer characteristics, a compact design, and low energy consumption. In this review, the current research scenario of RPBs using numerical, computational fluid dynamics (CFD), and mathematical modelling, along with different machine learning approaches in the CO₂ capture process, has been reviewed. The different geometry designs, hydrodynamic characteristics, performance parameters, research methods, and their effects on CO₂ removal efficiency have been discussed. Furthermore, the latest experimental studies are also summarized, especially in the absorption and adsorption domain. Finally, recommendations have been given to support the RPBs in different industrial and commercial applications of CO₂ removal.     

Preparation of Mo2C by the temperature-programmed reaction between h-MoO3 and CO

In the work, the temperature-programmed reaction (TPR) between hexagonal-shaped h-MoO₃ and high-purity CO under different heating rates was investigated in order to prepare Mo₂C. Various technologies such as TG-DTA-DTG, XRD, FESEM, FT-IR and Raman spectrum as well as the thermodynamic calculation were adopted to analyze the experimental data. The results showed that the physically adsorbed water on the sample surface, the residual ammonium and coordinated water in the internal structure of h-MoO₃ were successively released as the temperature increased, and then α-MoO₃ and Mo₄O₁₁ were formed when the temperature arrived at around 791 K. Upon further increasing the temperature, the reduction process occurred and MoO₂ will be generated. Thereafter, the carburization reaction was taken place and the subsequent reaction pathways were significantly different at lower and higher heating rates: at lower heating rates (8 and 12 K/min), the carburization process of MoO₂ to Mo₂C followed MoO₂→MoO₂+Mo₂C→Mo₂C + Mo→Mo₂C; while at higher heating rates (16 and 20 K/min), the reaction pathways followed MoO₂→MoO₂+Mo₂C→MoO₂+Mo₂C + Mo + MoO_xC_y→Mo→Mo₂C, single-phase metallic Mo can be generated. The work also discovered that the as-prepared Mo₂C always kept the same platelet-shaped morphology as that of the newly-formed MoO₂; while due to the removal of oxygen and the decrease of molar volume during the transformation process, the as-prepared Mo₂C exhibited a rougher and more porous morphological structure.     

Uniform Si-Infused UiO-66 as a Robust Catalyst Host for Efficient CO2 Hydrogenation to Methanol

Due to the weak nature of organic coordination bonds, metal–organic frameworks (MOFs) can hardly retain their intrinsic physicochemical properties and structural integrity when functioning in harsh heterogeneous reactions. Herein, a post-synthetic strategy to reinforce the MOF structure by inserting siliceous linkers inside is proposed, according to which a Si-infused UiO-66 (s-UiO-66) with well-developed porosity and exceptional thermal/structural stability is fabricated. This monodispersed Si-infused matrix with enlarged nanopores is then utilized as the catalyst host, and is highly conductive to confining ultrafine CuO nanoparticles with uniform dispersion. Targeting CO₂ hydrogenation to methanol reaction, the Cu-loaded s-UiO-66 (CuO/s-UiO-66) delivers a remarkable and efficient methanol production rate outperforming other Cu/ZrO₂-based catalysts and the commercial catalyst. Moreover, the robust structure of CuO/s-UiO-66 prevents both copper phase and host material from aggregation during the catalyst preparation procedure and the reaction. In addition to material-oriented studies, in situ characterization techniques are employed to identify the active Cu component and key intermediates formed during the CO₂ hydrogenation reaction, separately. It is envisioned that this Si infusion strategy can be applied to construct stable host materials with boundary-defined structures from the pristine MOFs for broadened applications under extreme circumstances.     

Electrosynthesized CuMgAl Layered Double Hydroxides as New Catalysts for the Electrochemical Reduction of CO2

In this study, new nanostructured CuMgAl Layered Double Hydroxide (LDH) based materials are synthesized on a 4 cm² sized carbonaceous gas diffusion membrane. By means of microscopic and spectroscopic techniques, the catalysts are thoroughly investigated, revealing the presence of several species within the same material. By a one-step, reproducible potentiodynamic deposition it is possible to obtain a composite with an intimate contact between a ternary CuMgAl LDH and Cu⁰/Cu₂O species. The catalyst compositions are investigated by varying: the molar ratio between the total amount of bivalent cations and Al³⁺, the amount of loading, and the molar ratios among the three cations in the electrolyte. Each electrocatalyst has been evaluated based on the catalytic performances toward the electrochemical CO₂ reduction to CH₃COOH at −0.4 V versus reversible hydrogen electrode  in liquid phase. The optimized catalyst, that is, CuMgAl 2:1:1 LDH exhibits a productivity of 2.0 mmol_CH3COOH g_cat⁻¹ h⁻¹. This result shows the beneficial effects of combining a material like the LDHs, alkaline in nature, and thus with a great affinity to CO₂, with Cu⁰/Cu⁺ species, which couples the increase of carbon sources availability at the electrode with a redox mediator capable to convert CO₂ into a C₂ product.     

Structure of Na Species in Promoted CaO-Based Sorbents and Their Effect on the Rate and Extent of the CO2 Uptake

To advance CaO-based CO₂ sorbents it is crucial to understand how their structural parameters control the cyclic CO₂ uptake. Here, CaO-based sorbents with varying ratios of Na₂CO₃:CaCO₃ are synthesized via mechanochemical activation of a mixture of Na₂CO₃ and CaCO₃ to investigate the effect of sodium species on the structure, morphology, carbonation rate and cyclic CO₂ uptake of the CO₂ sorbents. The addition of Na₂CO₃ in the range of 0.1–0.2 mol% improves the CO₂ uptake by up to 80% after 10 cycles when compared to ball-milled bare CaCO₃, while for Na₂CO₃ loadings >0.3 mol% the cyclic CO₂ uptake decreases by more than 40%. Energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy, X-ray absorption spectroscopy (XAS), and ²³Na MAS NMR, reveal that in sorbents with Na₂CO₃ contents <0.3 mol% Na exists in highly distributed, noncrystalline [Na₂Ca(CO₃)₂] units. These species stabilize the surface area of the sorbent in pores of diameters >100 nm, and enhance the diffusion of CO₂ through CaCO₃. For Na₂CO₃ contents >0.3 mol%, the accelerated deactivation of the sorbents via sintering is related to the formation of crystalline Na₂Ca(CO₃)₂ and the high mobility of Na.