Performance of a conventional diesel aftertreatment system used in a medium-duty multi-cylinder dual-mode dual-fuel engine

[EN] Dual-mode dual-fuel combustion stands as one of the promising techniques to allow the dual-fuel operation along the whole engine map. This concept relies on using different combustion strategies as reactivity controlled compression ignition up to medium load, then migrating to diffusive dual-fuel combustion to reach full load. With this strategy, it is possible to obtain sensible reductions in NOx and soot while providing improvements in fuel consumption and CO2 emissions. However, the excessive quantities of HC and CO together with the low exhaust temperature can compromise the diesel oxidation catalyst (DOC) efficiency. In addition, the diffusive dual-fuel combustion applied at high engine load produces considerable soot amounts that should be reduced within the diesel particulate filter (DPF). Based on these facts, this work intends to evaluate the efficiency of a commercial aftertreatment system (DOC¿+¿DPF) while operating in dual-mode dual-fuel combustion. Additionally, fundamental studies where developed to understand the impact of the combination of fuels on the exhaust hydrocarbon species. First, the DOC performance was evaluated at steady-state and transient conditions under different operating conditions fulfilling the EUVI NOx and soot limits. In parallel, the different engine-out hydrocarbon species were measured by means of a Fourier-transform infrared spectroscopy (FTIR) gas analyzer. Finally, the passive and active regeneration processes were assessed by means of different methodologies aiming to evaluate the low NOx-low soot interaction and the capability of the active regeneration in dual-fuel dual-mode (DMDF) operating conditions. The DOC results showed an improper conversion efficiency at low load operating condition, where the exhaust temperature is low. By contrast, the thermal inertia at transient conditions allowed to improve the DOC behavior at low load, reaching DOC-out emissions one order of magnitude lower than those from the steady-state tests. Concerning the DPF, it was demonstrated that the low concentration of NOx and soot produced during the combustion does not lead to sensible changes in the NO2/NOx ratio before and after the DPF, indicating a low level/absence of passive regeneration. In the case of the active regeneration, both conventional diesel combustion (CDC) and DMDF operating conditions can obtain satisfactory reduction in the total soot trapped, being the increase in the exhaust temperature consequence of the HC and CO conversion the supporting mechanism for the active regeneration in the DMDF concept.The authors thanks VOLVO Group Trucks Technology and ARAMCO Overseas Company for supporting this research. The authors also acknowledge FEDER and Spanish Ministerio de Economía y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R).García Martínez, A.; Monsalve-Serrano, J.; Villalta-Lara, D.; Lago-Sari, R. (2019). Performance of a conventional diesel aftertreatment system used in a medium-duty multi-cylinder dual-mode dual-fuel engine. Energy Conversion and Management. 184:327-337. https://doi.org/10.1016/j.enconman.2019.01.069S32733718

Octane number influence on combustion and performance parameters in a Dual-Mode Dual-Fuel engine

[EN] Low temperature combustion stands as a promising alternative to realize low soot and NOx emissions while achieving fuel consumption benefits compared to the conventional diesel combustion. Nonetheless, its applicability is limited to narrow zones inside the engine map, reducing the potential benefits on a real driving case. In this scenario, the use of dual-mode dual-fuel combustion stands as an alternative to cover engine conditions up to full load, avoiding the constraints of the fully premixed combustion whenever is needed. This combustion concept is strongly influenced by the characteristics of the fuels that are used to create the charge stratification during the engine operation. The current research aims to evaluate the influence of the low reactivity fuel octane number on the combustion process and the average performance and emissions results. Additionally, the best octane number was determined by means of a merit function evaluation. Octane values of 100, 92.5, 87.5, 85 and 80 were obtained by blending iso-octane and heptane. Their performance was assessed in a medium-duty multi-cylinder platform at different representative operating conditions. The results suggest that fuels with octane number lower than 92.5 have a low impact at low load conditions. However, as load is increased, the high reactivity of the low research octane number fuels leads to early combustion processes, demanding settings modifications to avoid the appearance of excessive pressure gradients. As a consequence of these modifications, the fuel consumption and soot emissions increase. In general, RONs from 92.5 to 87.5 are less penalized, presenting the best merit function values, and therefore being the best fuels to be used in the hardware under investigation.The authors thanks VOLVO Group Trucks Technology and ARAMCO Overseas Company for supporting this research. The authors also acknowledge FEDER and Spanish Ministerio de Economía y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R) and the Universitat Politècnica de València for partially supporting this research through Convocatoria de ayudas a Primeros Proyectos de Investigación (PAID-06-18).García Martínez, A.; Monsalve-Serrano, J.; Villalta-Lara, D.; Lago-Sari, R. (2019). Octane number influence on combustion and performance parameters in a Dual-Mode Dual-Fuel engine. Fuel. 258:1-11. https://doi.org/10.1016/j.fuel.2019.116140S11125

Fuel sensitivity effects on dual-mode dual-fuel combustion operation for different octane numbers

[EN] The dual-mode dual-fuel combustion is a promising combustion concept to achieve the required emissions and carbon dioxide reductions imposed by the next emissions standards. Nonetheless, since the combustion concept relies on the reactivity of two different fuels (diesel and gasoline), the fuel formulation requirements are stricter. This work investigates the effects of the low reactivity fuel sensitivity for different octane numbers at different operating conditions representative of the combustion regimes found inside the dual-mode dual-fuel engine map. For this, experimental evaluations were performed using fuels with research octane number 92.5 and 80 and different sensitivities (0, 5 and the maximum one achievable for each fuel). The combustion development was assessed by means of the heat release rate characterization. Moreover, numerical simulations in a constant volume homogeneous reactor were used to explore and understand the impact of the different fuels on the ignition delay time. The results suggest that the sensitivity increase affects the different research octane number fuels in a different way. For the fuel with research octane number 92.5, the sensitivity variation increases the experimental ignition delay, impairing the combustion process and increasing the fuel consumption. In the case of the fuel with research octane number 80, the sensitivity increase does not affect the combustion development. This was justified by the numerical investigation, which points to a wider temperature range where the sensitivity does not affect the final ignition delay for research octane number 80. Moreover, generally, the ignition delay times for research octane number 80 considering the experimental gasoline fraction used are half than those of research octane number 92.5. At full load conditions, the trend is inverted, where the experimental ignition delay for research octane number 80 is affected by the sensitivity whilst research octane number 92.5 presents only modifications after the combustion start.The authors thanks ARAMCO Overseas Company and VOLVO Group Trucks Technology for supporting this research. The authors also acknowledge FEDER and Spanish Ministerio de Economía y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R), and the Universitat Politècnica de València for partially supporting this research through Convocatoria de ayudas a Primeros Proyectos de Investigación (PAID-06-18).García Martínez, A.; Monsalve-Serrano, J.; Villalta-Lara, D.; Lago-Sari, R. (2019). Fuel sensitivity effects on dual-mode dual-fuel combustion operation for different octane numbers. Energy Conversion and Management. 201:1-13. https://doi.org/10.1016/j.enconman.2019.112137S11320

Actualización do censo de lobos do norte de Galicia. Valoración crítica sobre metodoloxía e resultados do censo da Xunta de Galicia de 2021-2022

O presente artigo presenta os resultados obtidos nunha nova estima dos grupos reprodutores de lobo presentes no norte de Galicia. O traballo de campo foi efectuado os anos 2021 e 2022, de maneira que se actualiza o censo que se abordara en anos anteriores (2019 e 2020). Os resultados obtidos compáranse cos contidos no resume do censo oficial do lobo presentado pola Xunta de Galicia e relativo aos anos 2021-2022. A análise dos resultados do censo oficial e a súa comparativa cos obtidos no presente traballo confirman unha subestima no primeiro de entre un 27.7 e un 43.4 % dos grupos reprodutores existentes nos case 3000 km2 da área de estudo. Finalmente, preséntase unha valoración crítica da metodoloxía aplicada no censo oficial, que explicaría as deficiencias observadas nos resultados

Potential of e-Fischer Tropsch diesel and oxymethyl-ether (OMEx) as fuels for the dual-mode dual-fuel concept

[EN] The dual-mode dual-fuel combustion strategy allows operating over the entire engine map by implementing a diffusive dual-fuel combustion at high engine loads. This requires increasing the amount of exhaust gas re-circulation to control the NOx emissions, which penalizes the soot levels. At these conditions, the use of nonsooting fuels as the e-Fischer Tropsch Diesel (e-FT) and oxymethylene dimethyl ethers (OMEx) could be a potential way to avoid the NOx-soot trade-off. The experimental results acquired in a compression ignition multi-cylinder medium-duty engine evidence that the higher oxygen content of OMEx allows reducing the soot emissions at high loads to near zero levels, while e-FT promotes a soot reduction of around 20% as compared to diesel. Nonetheless, the low lower heating value of OMEx leads to excessive injection durations, enlarging the combustion process and increasing the fuel consumption around 1.3-7.2% and 1.4-5.3% as compared to diesel and e-FT, respectively, depending on the engine load. Finally, the well to wheel analysis confirms the potential in reducing the carbon dioxide footprint of OMEx (14.8-69%) and e-FT (0.3-38.5%) compared to diesel, as they can be synthetized via direct air capture as a source of carbon and using renewable energy.The authors thanks VOLVO Group Trucks Technology and Aramco Overseas Company for supporting this research. The authors also acknowledge FEDER and the Spanish Ministerio de Economia y Competitividad for partially supporting this research through the TRANCO project (TRA2017-87694-R), and the Universitat Politecnica de Valencia for partially supporting this research through Convocatoria de ayudas a Primeros Proyectos de Investigacion (PAID-06-18)García Martínez, A.; Monsalve-Serrano, J.; Villalta-Lara, D.; Lago-Sari, R.; Gordillo Zavaleta, V.; Gaillard, P. (2019). Potential of e-Fischer Tropsch diesel and oxymethyl-ether (OMEx) as fuels for the dual-mode dual-fuel concept. Applied Energy. 253:1-10. https://doi.org/10.1016/j.apenergy.2019.113622S11025

Influence of Multiple Conformations and Paths on Rate Constants and Product Branching Ratios. Thermal Decomposition of 1-Propanol Radicals

The potential energy surface involved in the thermal decomposition of 1-propanol radicals was investigated in detail using automated codes (tsscds2018 and Q2DTor). From the predicted elementary reactions, a relevant reaction network was constructed to study the decomposition at temperatures in the range 1000–2000 K. Specifically, this relevant network comprises 18 conformational reaction channels (CRCs), which in general exhibit a large wealth of conformers of reactants and transition states. Rate constants for all the CRCs were calculated using two approaches within the formulation of variational transition-state theory (VTST), as incorporated in the TheRa program. The simplest, one-well (1W) approach considers only the most stable conformer of the reactant and that of the transition state. In the second, more accurate approach, contributions from all the reactant and transition-state conformers are taken into account using the multipath (MP) formulation of VTST. In addition, kinetic Monte Carlo (KMC) simulations were performed to compute product branching ratios. The results show significant differences between the values of the rate constants calculated with the two VTST approaches. In addition, the KMC simulations carried out with the two sets of rate constants indicate that, depending on the radical considered as reactant, the 1W and the MP approaches may display different qualitative pictures of the whole decomposition processThis work was partially supported by the Consellería de Cultura, Educación e Ordenación Universitaria e da Consellería de Economía, Emprego e Industria (Axuda para Consolidación e Estructuración de unidades de investigación competitivas do Sistema Universitario de Galicia, Xunta de Galicia ED431C 2017/17 & Centro singular de investigación de Galicia acreditación 2016-2019, ED431G/09), the Ministerio de Economía y Competitividad of Spain (Research Grant No CTQ2014-58617-R), and the European Regional Development Fund (ERDF). D.F.-C. also thanks Xunta de Galicia for financial support through a postdoctoral grant. The authors thank “Centro de Supercomputación de Galicia (CESGA)” for the use of their computational facilitiesS

Pedicle myiasis by Lucilia caesar (Diptera, Calliphoridae): an emerging disease in roe deer from north-western Spain

A total of 35 male roe deer (Capreolus capreolus) from Lugo province (north-western Spain) were examined for pedicle myiasis between 2020 and 2022. All these animals had died by different causes and were examined or preserved just after their death to avoid post-mortem infestations. After external and internal head inspection, five animals were diagnosed with severe myiasis at the basis of the antlers (14.29%; 95% confidence interval = 5.38–31.04). All the affected bucks presented a cutaneous wound (1.5–15 cm in diameter) around the pedicles with extensive tissue destruction, exposition of frontal and parietal bones, and massive infestation by dipteran larvae (2–12 mm long). Four of five roe deer showed whitish egg clusters adhered to the basis of the antlers. Moreover, in one animal, six larvae had penetrated the cranial cavity, and in two of them larvae were also found in the nasopharyngeal cavity. All the cases were recorded in summer (May–August). Morphological identification and subsequent molecular confirmation revealed that all animals were infested by different larval stages of Lucilia caesar (Diptera: Calliphoridae). This study represents the first report of pedicle myiasis in Spain. Since this disease is reported sporadically, the detection of five cases in a short period of time suggests an increase in the incidence of this myiasisS

The Goat as a Risk Factor for Parasitic Infections in Ovine Flocks

Small ruminants in northwestern Spain are frequently managed in mixed flocks. Sheep–goat joint management has not been considered a risk factor for parasite infection, so the main objective of this study was to establish if mixed management with goats supposes a risk factor for parasitic infections in ovine flocks. Two thousand and ninety-three sheep were sampled from 74 commercial meat ovine flocks for diagnostic of the main parasites. Goat contact was a risk factor for sheep to be infected by protostrongylids, Dictyocaulus filaria, gastrointestinal nematodes and Eimeria spp. In contrast, Moniezia, Fasciola hepatica, Dicrocoelium dendriticum and Paramphistomidae prevalences were not influenced. Sheep–goat mixed management can be considered as a risk factor, since goats would act as a source of pasture contamination for interspecific parasites (protostrongylids, Dictyocaulus filaria and gastrointestinal nematodes). In relation to host-specific parasites, such as Eimeria spp., goats cannot be considered as a source for sheep, but competition for food and spaces between both small ungulates can suppose a reduced grazing area to sheep, provoking high environmental contamination and stress that facilitate their infection. Future epidemiological studies for parasitic infections in small ruminants should consider sheep–goat mixed management as a possible risk factor to be included in multivariate analysesThis work was supported by a program for consolidating and structuring competitive research groups (ED431D 2019/04, Xunta de Galicia, Spain)S

Cardiorespiratory nematodes and co-infections with gastrointestinal parasites in new arrivals at dog and cat shelters in north-western Spain

Metastrongyloid and trichuroid cardiorespiratory nematodes of dogs and cats are considered emergent in several European countries, and an increase in the number and extent of endemic foci has been described. Since data on their prevalence are limited in this continent, faecal samples from new arrivals (365 dogs and 65 cats) at two animal shelters in North-western Spain were analysed using both floatation and Baermann techniques. In order to confirm the microscopic identification of Metastrongylidae first stage larvae, molecular characterization based on the sequence of the ITS-2 was performed. The possible influence of some variables such as the species, sex and age of the animals and the co-infection with other gastrointestinal parasites on the prevalence of cardiorespiratory nematodes was analysed. The most prevalent metastrongylid was Aelurostrongylus abstrusus (15.4%) followed by Angiostrongylus vasorum (4.1%) and Crenosoma vulpis (1.1%). Regarding trichuroids, Eucoleus aerophilus and/or Eucoleus boehmi eggs were detected in 28 dogs (7.7%) and four cats (6.2%). Almost all animals positive to cardiorespiratory nematodes (86.8%) were co-infected with gastrointestinal parasites. The prevalence of Metastrongylidae and respiratory trichuroids was significantly higher in dogs co-infected with Taenia spp. and Toxocara canis or Giardia duodenalis and Sarcocystis spp., respectively. In cats, a significant higher prevalence of Metastrongylidae nematodes was found in animals co-infected with Toxocara cati. Our results reveal that cardiorespiratory nematodes are common in companion animals from north-western Spain, showing higher prevalences than those previously reported from this country. This investigation represents the first report of C. vulpis, E. aerophilus and E. boehmi in dogs from Spain. The identification of a number of zoonotic parasites is of public health concern. Our results indicate that these nematodes should be included in the differential diagnosis of dogs and cats from north-western Spain showing respiratory or cardiac clinical signsThis research was funded by the Program for consolidating and structuring competitive research groups (ED431C 2019/04, Xunta de Galicia, Spain)S

The Age-Related Cryptosporidium Species Distribution in Asymptomatic Cattle from North-Western Spain

An age-related distribution of Cryptosporidium species has been reported in cattle, with C. parvum being predominant in suckling calves, C. bovis and C. ryanae being predominant in post-weaned calves and C. andersoni being predominant in adults. However, variants to this pattern have recently been reported. Thus, fecal samples (n = 594) from asymptomatic cattle were collected in north-western Spain. Animals were classified as 2 years (G5). Cryptosporidium detection and species identification were performed by SSU rRNA PCR. Individual Cryptosporidium prevalence was 16.7%; it significantly decreased with age. Cryptosporidium parvum was predominant in G1 and C. bovis was predominant in the rest of the age classes; C. bovis and C. ryanae were especially prevalent in G2 and G3. Cryptosporidium occultus was not found in suckling calves. Finally, C. andersoni and C. xiaoi were occasionally detected in G5. The presence of C. parvum in all age classes implies significant animal and public health concerns. The predominance of C. bovis in cattle older than 1 month supports the idea that the age-related pattern of Cryptosporidium species described in cattle is not fully consistent, and thus further studies are still needed to identify those factors determining the species distributionThis research was funded by Ministerio de Ciencia e Innovación (Spain), grant number AGL2016-76034-P and by Xunta de Galicia (Spain), grant number 2017-PG117S