The formation of internal diesel injector deposits (IDIDs) in heavy-duty engines is a growing problem as engine technology becomes more advanced while fuel blends become more diverse, posing new challenges for mixing and compatibility. IDIDs have a variety of causes that can be challenging to pinpoint due to the number of factors involved, such as engine operation effects, fuel types, fuel additives, and fuel contamination. The aims of this study were to characterize IDIDs formed in an injector from an engine operating on a biofuel blend contaminated with coolant, gain a deeper understanding of the underlying formation mechanisms, and identify potential markers of coolant contamination in failed field injectors. In this study, a failed injector from the field was examined that was known to have fuel contamination from coolant. Laboratory experiments using the thermal deposit test (TDT) were carried out to generate deposits from a test fuel spiked with coolant. The laboratory and field deposits were characterized and compared using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared attenuated reflectance spectroscopy (FTIR-ATR), and pyrolysis combined with gas chromatography (Py GC-MS). The results indicate that the deposits generated in the TDT were found to be primarily composed of sodium carboxylates originating from the organic acid technology additives in the coolant. The deposits were found to have structures with similarities to grease soaps, oleogels, or paraffin wax, suggesting that similar formation mechanisms may be involved. In contrast, the field injector deposits consisted of three distinct types: a cracked layer composed of sulfate salts and metal carboxylates, a globular cluster layer consisting of metal carboxylates, and particulate deposits that differ from the surroundings. The high proportion of sodium carboxylates in the globular cluster deposits was the key similarity to the laboratory deposits. In addition to the high sodium content, particulate deposits containing silicon and aluminum or aluminum and nitrogen were identified as potential markers of coolant contamination in IDIDs.

This study presents a comprehensive investigation into CO<inf>2</inf> absorption in a pilot-scale, multi-nozzle spray tower operating under industrial conditions. Through the integration of pilot-scale experimentation and reactive CFD modeling, this work advances the quantitative understanding of coupled hydrodynamic behavior and mass transfer phenomena in conditions representative of full-scale operations. A modular carbon capture unit was built and deployed at a Swedish waste-to-energy facility to experimentally investigate gas–liquid flow behavior and CO<inf>2</inf> absorption performance using a 15 wt% NaOH solution as the absorbent. The experimental data provided the basis for validating a reactive Euler–Lagrange multiphase CFD model, which elucidated gas–liquid interactions, including droplet dispersion, turbulent flow structures, mixing, and interphase mass transfer. Sensitivity analyses across a range of gas (50–200 m³/h) and liquid flow rates demonstrate how operating conditions influence droplet trajectories, residence time, and CO<inf>2</inf> absorption efficiency. Flow segmentation identifies two distinct zones where turbulence and recirculation enhance mixing and mass transfer, with side gas inlet configurations providing more effective radial mixing compared to axial inlet designs. Results demonstrate that tuning the liquid-to-gas (L/G) ratio, droplet characteristics, and gas inlet design significantly influences CO<inf>2</inf> capture, offering practical guidance for the next generation of spray-based carbon capture systems. The study investigated L/G ratios ranging from 2.3 to 7.0 kg/kg and examined the effects of droplet sizes between 200 and 3000 μm, observing that droplets predominantly in the lower size range exhibited improved dispersion and extended residence times, which are favorable for effective CO<inf>2</inf> absorption. The findings provide a direct basis for optimizing hydrodynamics and scaling spray tower absorbers for effective CO<inf>2</inf> capture in real-world systems.

This study investigates the CO<inf>2</inf> absorption performance of sodium hydroxide (NaOH) and monoethanolamine (MEA) solutions in a spray column under various operational conditions. The effects of gas flow rate (1.25–5.19 L/min), CO<inf>2</inf> concentration (10–40 vol%), solvent concentration (2.5–7.5 wt percent (wt.%) for NaOH; 5–25 wt% for MEA), solvent volume (0.5–1.5 L), and temperature (303–323 K) were systematically analyzed. The results show that NaOH achieves a maximum absorption efficiency of 95 % at 5 wt% concentration and the lowest gas flow rate. In comparison, MEA requires a higher concentration of 15 wt% to reach 96 % efficiency under the same conditions. Raising gas flow from 1.25 to 5.19 L/min reduced efficiency to 47 % (NaOH, 5 wt%) and 45 % (MEA, 15 wt%). Increasing solvent temperature from 303 to 323 K significantly improved MEA performance at 3.00 L/min (≈75 %→83 %), while NaOH remained ≳95 % at 1.25 L/min with minor sensitivity. These results show that, in spray columns, high capture can be achieved with relatively low solvent concentrations, implicating lower regeneration energy, reduced solvent degradation, and lower operating costs while clearly delineating operating windows for NaOH vs. MEA.

Spray towers have proven to be efficient in capturing gases and vapours, finding widespread use across various applications including CO₂ capture. As there is scarce reference material regarding spray tower performances with different flow configurations other than the conventional counter-current flow, as well as the use of substitute solvents to MEA, there is a need to study different configurations and setup designs, including different placements of gas and liquid inlets in the absorber tower, to find the optimal configuration. In this study, the capture of CO₂ from a CO₂/N₂ mixture using unpromoted potassium carbonate as the absorbent in a lab-scale spray tower was experimentally measured in four different flow configurations over a wide range of operating conditions, including gas and liquid flow rates, CO₂ concentration, K₂CO₃ concentration and solvent temperature. Among four different configurations, the two sides co-current configuration, with gas nozzles positioned on opposite sides of the column and liquid coming from above, was found to be the most effective setup for enhancing CO₂ capture efficiency by promoting better mixing and contact between gas and liquid.

 To reduce carbon emissions in heavy-duty transportation, renewable fuels like biodiesel and hydrotreated vegetable oil are increasingly blended with fossil fuels as drop-in alternatives. However, these blends can lead to issues such as the formation of insoluble materials, or soft particles, within the fuel system. These precipitates, composed of inorganic salts and organic aggregates, cause filter clogging, nozzle fouling, and internal injector deposits, negatively impacting engine performance, increasing fuel consumption, and causing drivability issues. This study investigates internal injector deposits through an accelerated laboratory thermal test, replicating the deposits observed in injectors from heavy-duty vehicles. The goal is to understand the chemistry behind these deposits and explore the formation of inorganic salts, such as calcium crystals, and soft particle deposits. Temperature plays a critical role in deposit formation, influencing both morphology and composition. FTIR-ATR and SEM-EDX analyses reveal that metal carboxylates form between 100 ◦C and 170 ◦C, while calcium sulfate crystals form above 170 ◦C. The test successfully replicates the characteristics of real-world deposits, with findings suggesting that calcium sulfate deposits primarily form in the presence of engine oil contaminants. This points to engine oil leakage as a significant factor in the formation of internal diesel injector deposits (IDIDs). This research highlights the value of laboratory testing as a cost-effective alternative to engine tests for studying deposit formation in drop-in fuel systems. 

Oxidation catalysts can greatly improve the regeneration efficiency of diesel particulate filters (DPF) by providing sufficient levels of NO₂ for low-temperature soot oxidation. As for other automotive catalysts, catalyzed DPFs are subject to aging effects, resulting in decreased performance of the NO oxidation reaction. The life span of DPFs generally only considers the elevated back pressure as a consequence of the accumulation of ash. However, with reduced catalytic activity and impaired functionality of the regeneration process there is a risk of premature replacement of the catalyzed DPF or accumulation of soot above critical levels. In this study, a new exhaust aftertreatment system has been developed to accommodate laboratory-scale catalysts and DPFs for testing with full-size heavy-duty engines. The modified exhaust aftertreatment set-up was used together with a rig for accelerated soot and ash loading to assess the impact of catalyst aging on regeneration performance under real conditions. Experiments were conducted with and without diesel oxidation catalyst to limit or increase the concentration of NO₂. It could be demonstrated that the impaired catalytic activity can have a significant impact on the regeneration process. With a limited upstream concentration of NO₂ fed to the catalyzed DPF, a temperature increase from about 390 °C to 450 °C was required to initiate the oxidation of soot. Furthermore, an overall lower oxidation rate was observed. With the addition of a diesel oxidation catalyst, resulting in elevated upstream concentrations of NO₂, the effect of aging could be partially mitigated leading to more comparable soot oxidation rates with a temperature difference of 30 °C for soot ignition. These results highlight the importance of the catalytic activity for the functionality of the system, which should be considered for future catalyzed DPF design and regeneration strategies.

Generally, agriculture activities represent the main economic income of rural areas, and during these, huge amounts of biomass are generated. This biomass is considered as garbage due to its high storage cost. However, energy and added-value products can be recovered from biomass. Within this context, açai stems and cocoa husks were collected from different rural areas of Bolivia due to their high importance in the local and international markets as two of the most available products of the country. The preliminary study will contribute in the field of green energy recovery and resource management. Thus, in this study, both residues were tested as renewable feedstocks for the generation of added-value products from pyrolysis at 500 °C for 30 min. Açai stems were found to be more suitable to biochar based with yields up to 49.1% ± 2.4%, but also for biogas production (33.9% ± 2.0%). Cocoa husk was also found to be more suitable for biochar production (38.1% ± 1.7%) but also for bio-oils (33.6% ± 17.6%). Both resulting biochars had basic pH (between 10 and 12) and low density (287.2 kg/m³ and 401.7 kg/m³). Additionally, the lack of heavy metals on the surface makes both biochar products good candidates for soil amendment applications. Furthermore, the bio-oil composition is complex and varied, and products such as Maltol, 2-methyl furane, and D-allose have direct applications in the food industry. Moreover, the presence of phenolic compounds and hydrocarbons with more than five carbons in the structure makes the obtained bio-oils suitable for upgrading processes for biofuel production. Finally, the obtained biogases can be applied for local electricity generation, or to reduce the energy requirements for the pyrolysis reactor. Graphical Abstract: (Figure presented.)

Low-temperature soot oxidation in catalytic diesel particulate filters (DPF) is important for maintaining high efficiency of heavy-duty vehicles. This can be achieved by coating DPFs with an oxidation catalyst. In this work, catalytic DPFs have been collected from real-world operating heavy-duty vehicles for assessment of their catalytic activity and subsequent characterization. Testing of catalytic activity revealed the diminishing nitric oxide (NO) oxidation of the aged catalysts. The apparent reaction rates showed that the number of available catalytic sites decreased with mileage explaining the loss in activity. Characterization of the samples showed a decreasing surface area as well as an accumulation of metals and poisonous elements. An important finding from SEM-EDS analysis is the evident accumulation of phosphorus and sulfur in the washcoat in the absence of other ash-related elements, potentially explaining the decreased activity.

 In recent years, deposit formation in fuel systems for heavy-duty engines, using drop-in fuels, have become increasingly common. Drop-in fuels are particularly appealing because they are compatible with existing engines, allowing for higher proportions of alternative fuels to be blended with conventional fuels. However, the precipitation of insoluble substances from drop-in fuels can result in fuel filter clogging and the formation of internal injector deposits, leading to higher fuel consumption and issues with engine drivability. The precise reasons behind the formation of these deposits in the fuel system remain unclear, with factors such as operating conditions, fuel quality, and fuel contamination all suggested as potential contributors. In order to reproduce and study the formation of internal injector deposits, for heavy-duty engines under controlled conditions and to facilitate a more precise comparison to field trials, a novel injector test rig has been developed. This newly constructed, non-firing rig includes the main components of heavy-duty vehicle engines and uses an electric motor to simulate the revolutions per minute of an engine. A tailored run cycle has been developed to enable the continuous monitoring of injector performance during the deposit formation process, as well as to meticulously mimic the actual operations of a real engine. The deposits formed on injectors during the rig tests were analyzed using scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and pyrolysis connected to gas chromatography-mass spectroscopy (Py GC-MS). This work presents the outcome of the analysis of injector deposits using the test rig, and compares these findings with deposits gathered from field operations. The deposits obtained from the injector test rig were found to be similar in terms of deposit location, composition, and microstructure, with both sets of deposits containing metal carboxylates and derivatives of engine oil additives. These similarities demonstrate that the test rig effectively reproduces the formation of injector deposits observed in real-world conditions. 

 The formation of deposits in the fuel systems of heavy- duty engines, using drop-in fuels, has been reported in recent years. Drop-in fuels are of interest because they allow higher levels of alternative fuels to be blended with conventional fuels that are ompatible with today’s engines. The precipitation of insolubles in the drop-in fuel can lead to clogging of fuel filters and internal injector deposits, resulting in increased fuel consumption and engine drivability problems. The possible mechanisms for the formation of the deposits in the fuel system are not yet fully understood. Several explanations such as operating conditions, fuel quality and contamination have been reported. To investigate injector deposit formation, several screening laboratory test methods have been developed to avoid the use of more costly and complex engine testing. To further evaluate and understand the formation of internal injector deposits in heavy-duty engines, a thermal laboratory test method has been developed. The test method is called Thermal Deposits Test (TDT) and it is inspired by Jet Fuel Thermal Oxidation Test (JFTOT) method. This test unit can be used to study in applications where a fluid is in contact with a hot surface. The method uses common laboratory hardware and readily available off-the-shelf parts, making it inexpensive to build and very flexible to operate. Deposits are collected on a metal foil, which makes it easier to analyze. This paper describes the construction of the apparatus and its performance. Experimental tests with diesel fuel, doped with soap-type soft particles, which contain typical particles that can form deposits, are performed, and compared with JFTOT results. Analytical techniques, such as Scanning Electron Microscopy with Energy Dispersive X-Ray, Fouriertransform Infrared Spectroscopy, and Pyrolysis coupled with Gas Chromatography-Mass Spectroscopy and Ellipsometry were used. Conclusions about the performance of the doped fuel are drawn from the test. Future plans are to study the mechanisms behind the formation of internal diesel injector deposits.