Effects of turbulence-chemistry interactions on auto-ignition and flame structure for n-dodecane spray combustion

The Engine Combustion Network (ECN) spray A under diesel engine conditions is investigated with a non-adiabatic 5D Flamelet Generated Manifolds (FGM) model with the consideration of detailed chemical kinetic mechanisms. The enthalpy deficit due to droplet vapourisation is considered by employing an additional controlling parameter in the FGM library. In this FGM model, ß-PDF is used for the PDF integration over the control variable space. Validation results in non-reacting conditions indicate relatively good agreement between the predicted and experimental data in terms of liquid and vapour penetrations and mixture fraction spatial distribution. In reacting conditions, the effects of variance of mixture fraction and progress variable were examined. The ignition delay time and the quasi-steady flame structure are both affected by the variances. The variance of mixture fraction delays the ignition process and the variance of progress variable accelerates it. For mixture fraction, the ignition process is quicker at any stage in the case of neglecting variance. While things are more complex for progress variable, the ignition process is advanced in the case of neglecting variance at early times, but surpassed by the case of ß-PDF later and until auto-ignition. When variance of mixture fraction is considered, the OH mass fraction shows a wide spatial distribution. While if not, a very thin flame is observed with a higher peak in OH, and a very large lift-off length. The variance of progress variable has little impact on the global flame structure, but makes the flame lift-off length much shorter. This study confirms the general observation, that the variance of mixture fraction is of higher importance in high temperature non-premixed combustion, however, we found that the variance of progress variable is far from negligible.This work was supported by Major Research Plan of the National Natural Sci-ence Foundation of China (No. 91541205); National Natural Science Foundation of China [grant numbers 51876140]; the project of National Key R&D Program of China (2017YFE0102800); This project has also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sk lodowska-Curie grant agreement No. 713673. Ambrus Both has received financial support through the ”la Caixa” INPhINIT Fellowship Grant for Doctoral studies at Spanish Research Centres of Excellence, ”la Caixa” Banking Foundation, Barcelona, Spain.Peer ReviewedPostprint (author's final draft

LES/FGM investigation of ignition and flame structure in a gasoline partially premixed combustion engine

This paper presents a joint numerical and experimental study of the ignition process and flame structures in a gasoline partially premixed combustion (PPC) engine. The numerical simulation is based on a five-dimension Flamelet-Generated Manifold (5D-FGM) tabulation approach and large eddy simulation (LES). The spray and combustion process in an optical PPC engine fueled with a primary reference fuel (70% iso-octane, 30% n-heptane by volume) are investigated using the combustion model along with laser diagnostic experiments. Different combustion modes, as well as the dominant chemical species and elementary reactions involved in the PPC engines, are identified and visualized using Chemical Explosive Mode Analysis (CEMA). The results from the LES-FGM model agree well with the experiments regarding the onset of ignition, peak heat release rate and in-cylinder pressure. The LES-FGM model performs even better than a finite-rate chemistry model that integrates the full-set of chemical kinetic mechanism in the simulation, given that the FGM model is computationally more efficient. The results show that the ignition mode plays a dominant role in the entire combustion process. The diffusion flame mode is identified in a thin layer between the ultra fuel-lean unburned mixture and the hot burned gas region that contains combustion intermediates such as CO. The diffusion flame mode contributes to a maximum of 27% of the total heat release in the later stage of combustion, and it becomes vital for the oxidation of relatively fuel-lean mixtures

Conceptual model description of the double injection strategy applied to the gasoline partially premixed compression ignition combustion concept with spark assistance

New combustion concepts applied to Compression Ignition engines are focused on achieve low temperature combustion together with a lean mixture distribution by allowing extra time from the end of injection to the start of combustion. Recently, the use of gasoline in a Compression Ignition engine under PPC conditions has been demonstrated as a suitable technique to achieve this extra mixing time, however the concept has also demonstrated difficulties under low load conditions using gasoline with octane number up to 95. The use of spark assistance with single injection operation has been found to be an appropriate way to improve the combustion control, providing both temporal and spatial control over the combustion process. The current paper details the influence of the double injection strategy on the Spark Assisted Partially Premixed Combustion concept compared with the single injection strategy. For this purpose, a reference combustion cycle for both injection strategies is compared in terms of the main parameters derived from the in-cylinder pressure signal as well as OH* and natural luminosity images acquired from the single-cylinder transparent engine. The cylinder head used along the research has been modified including a spark plug. In addition, a detailed analysis of the air/fuel mixing process has been developed by means of a 1-D in-house spray model.The authors would like to thank General Motors for supporting this research.Benajes Calvo, JV.; Molina Alcaide, SA.; García Martínez, A.; Monsalve Serrano, J.; Durrett, R. (2014). Conceptual model description of the double injection strategy applied to the gasoline partially premixed compression ignition combustion concept with spark assistance. Applied Energy. 129:1-9. doi:10.1016/j.apenergy.2014.04.093S1912

Study of the short-term quality of life of patients with esophageal cancer after inflatable videoassisted mediastinoscopic transhiatal esophagectomy

ObjectiveTo compare the short-term outcomes and postoperative quality of life in patients with esophageal cancer between inflatable videoasisted mediastinoscopic transhiatal esophagectomy (IVMTE) and minimally invasive Mckeown esophagectomy (MIME), and to evaluate the value of IVMTE in the surgical treatment of esophageal cancer.MethodsA prospective, nonrandomized study was adopted. A total of 60 esophageal cancer patients after IVMTE and MIME December 2019 to January 2022 were included. Among them, 30 patients underwent IVMTE and 30 patients underwent MIME. Shortterm outcomes (including the operation time, intraoperative blood loss, postoperative drainage 3 days, total postoperative tube time, postoperative hospital stay, number and number of thoracic lymph node dissection stations, postoperative complications and so on), postoperative quality of life, [including Quality of Life Core Questionnaire (QLQ-C30) and the esophageal site-specific module (QLQ-OES18)] were compared between the 2 groups.ResultsThe operation time, intraoperative blood loss, postoperative drainage volume and total postoperative intubation time in IVMTE group were significantly lower than those in MIME group (P < 0.05). A total of 22 patients had postoperative complications, including 7 patients in IVMTE group (23.3%) and 15 patients in MIME group (50.0%). There was significant difference between the two groups (P = 0.032). The physical function, role function, cognitive function, emotional function and social function and the overall health status in the IVMTE group were higher than those in the MIME group at all time points after operation, while the areas of fatigue, nausea, vomiting and pain symptoms in the MIME group were lower than those in the MIME group at all time points after operation.ConclusionIVMTE is a feasible and safe alternative to MIME. Therefore, when the case is appropriate, IVMTE should be given priority, which is conducive to postoperative recovery and improve the quality of life of patients after operation

An investigation on RCCI combustion in a heavy duty diesel engine using in-cylinder blending of diesel and gasoline fuels

An experimental and numerical study has been carried out to understand mixing and auto-ignition processes in RCCI combustion conditions, using gasoline and diesel as low and high reactivity fuels, respectively. Three parametrical studies have been developed using a heavy duty compression ignition engine equipped with a direct injector and a port fuel injector, to be able to vary the in-cylinder fuel blending ratio. Besides, a detailed analysis in terms of air/fuel mixing process has also been performed by means of a 1-D spray model. It is found that combustion starts with the auto-ignition of the diesel injection and the air and gasoline entrained. Then, the temperature and pressure raise starts the flame propagation across the lean diesel and gasoline zones of the combustion chamber. As the Diesel/Gasoline fuel ratio is reduced, the ignition delay increases extending the mixing time and the first combustion stage gets lowered while the second one is enhanced. The advance of the diesel injection timing enlarges the mentioned effects over the combustion process. With respect to conventional neat diesel combustion, a slight reduction in terms of NOx and a very important reduction in terms of soot were achieved with the RCCI combustion.The authors would like to thank VOLVO Group Trucks Technology for supporting this research.Benajes Calvo, JV.; Molina Alcaide, SA.; García Martínez, A.; Belarte Mañes, E.; Vanvolsem, M. (2014). An investigation on RCCI combustion in a heavy duty diesel engine using in-cylinder blending of diesel and gasoline fuels. Applied Thermal Engineering. 63(1):66-76. doi:10.1016/j.applthermaleng.2013.10.052S667663

The potential of RCCI concept to meet EURO VI NOx limitation and ultra-low soot emissions in a heavy-duty engine over the whole engine map

This work investigates the potential of RCCI concept to achieve ultra-low NOx and soot emissions over a wide range of engine speed and loads. For this purpose, a detailed experimental methodology has been defined and applied in a heavy-duty single-cylinder engine fueled with diesel and gasoline. In addition, to assess the influence of the engine compression ratio on RCCI capabilities two different compression ratios, 14.4:1 and 11:1, have been tested. Results suggest that a low compression ratio allows to fulfill all the self-imposed constraints (maximum cylinder pressure rise rate of 25 bar/CAD, NOx < 0.4 g/kW h and soot* < 0.01 g/kW h) from idle to full load and engine speeds from 900 to 1800 rpm. However, the use of higher compression ratio requires a delayed injection strategy to avoid excessive knocking levels, which results in unacceptable soot emissions at loads higher than 50%, even when gasoline fractions around 90% are used.The authors would like to acknowledge VOLVO Group Trucks Technology for supporting this research and to express their gratitude to Spanish economy and competitiveness ministry for partially funding this research under the project HiReCo TRA2014-58870-R.Benajes Calvo, JV.; Pastor Soriano, JV.; García Martínez, A.; Monsalve Serrano, J. (2015). The potential of RCCI concept to meet EURO VI NOx limitation and ultra-low soot emissions in a heavy-duty engine over the whole engine map. Fuel. 159:952-961. https://doi.org/10.1016/j.fuel.2015.07.064S95296115

Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels

This work investigates the effects of the direct injection timing and blending ratio on RCCI performance and engine-out emissions at different engine loads using four low reactivity fuels: E10-95, E10-98, E20-95 and E85 (port fuel injected) and keeping constant the same high reactivity fuel: diesel B7, (direct injected). The experiments were conducted using a heavy-duty single-cylinder research diesel engine adapted for dual-fuel operation. All the tests were carried out at 1200 rpm. To assess the blending ratio effect, the total energy delivered to the cylinder coming from the low reactivity fuel was kept constant for the different fuel blends investigated by adjusting the low reactivity fuel mass as required in each case. In addition, a detailed analysis of the air/fuel mixing process has been developed by means of a 1-D in-house developed spray model. Results suggest that notable higher diesel amount is required to achieve a stable combustion using E85. This fact leads to higher NOx levels and unacceptable ringing intensity. By contrast, EURO VI NOx and soot levels are fulfilled with E20-95, E10-98 and E10-95. Finally, the higher reactivity of E10-95 results in a significant reduction in CO and HC emissions, mainly at low load.The authors acknowledge VOLVO Group Trucks Technology and TOTAL for supporting this research.Benajes Calvo, JV.; Molina, S.; García Martínez, A.; Monsalve Serrano, J. (2015). Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels. Energy Conversion and Management. 99:193-209. doi:10.1016/j.enconman.2015.04.046S1932099

An investigation of partially premixed compression ignition combustion using gasoline and spark assistance

Nowadays the automotive scientific community and companies are focusing part of their efforts on the investigation of new combustion modes in Compression Ignition (Cl) engines, mainly based on the use of locally lean air fuel mixtures. This characteristic, combined with exhaust gas recirculation, provides low combustion temperatures that reduce pollutant formation. However these combustion concepts have some shortcomings, related to combustion phasing control and combustion stability under the light load engine operating range which must be overcome. The aim of this work is focused on the study of the integration of phasing and cycle-to-cycle repeatability control by means of an ignition spark plug system in a CI engine working under partially premixed charge (PPC) in order to overcome the lack of combustion stability in light load conditions when very low fuel reactivity is used. To achieve this objective, experimental tests have been carried out in a single cylinder optical engine combining broadband luminosity images with cylinder pressure derived heat release rate analysis. Research results reveals the spark assistance as a proper methodology to provide temporal and spatial control over the combustion process solving the lack of cycle to cycle control on the highly premixed compression ignition modes overall in light loads with high octane number (ON) fuels. Additionally, different stages have been identified in the combustion mode. The process starts with the spark discharge, which produces a flame kernel around the spark plug that later evolves to a premixed flame front. This premixed flame front heats unburned mixture and progresses into an auto-ignition combustion that burns out the rest of the charge with higher light intensity and finally an extinction of combustion process. Finally, the effect of injected fuel mass on the combustion mode has been also tested. An increase in the injected fuel mass has a positive effect on the assistance of the spark in the combustion process for both, combustion stability and cycle to cycle control. (C) 2013 Elsevier Ltd. All rights reserved.The authors would like to thank General Motors for supporting this research.Benajes Calvo, JV.; García Martínez, A.; Doménech Llopis, V.; Durret, R. (2013). An investigation of partially premixed compression ignition combustion using gasoline and spark assistance. Applied Thermal Engineering. 52(2):468-477. doi:10.1016/j.applthermaleng.2012.12.025S46847752

An experimental investigation on the influence of piston bowl geometry on RCCI performance and emissions in a heavy-duty engine

This experimental work investigates the effects of piston bowl geometry on RCCI performance and emissions at low, medium and high engine loads. For this purpose three different piston bowl geometries with compression ratio 14.4:1 have been evaluated using single and double injection strategies. The experiments were conducted in a heavy-duty single-cylinder engine adapted for dual fuel operation. All the tests were carried out at 1200 rev/min. Results suggest that piston geometry has great impact on combustion development at low load conditions, more so when single injection strategies are used. It terms of emissions, it was proved that the three geometries enables ultra-low NOx and soot emissions at low and medium load when using double injection strategies. By contrast, unacceptable emissions were measured at high load taking into account EURO VI limitations. Finally, the application of a mathematical function considering certain self-imposed constraints suggested that the more suitable piston geometry for RCCI operation is the stepped one, which has a modified transition from the center to the squish region and reduced piston surface area than the stock geometry.The authors acknowledge VOLVO Group Trucks Technology for supporting this research.Benajes Calvo, JV.; Pastor Soriano, JV.; García Martínez, A.; Monsalve Serrano, J. (2015). An experimental investigation on the influence of piston bowl geometry on RCCI performance and emissions in a heavy-duty engine. Energy Conversion and Management. 103:1019-1030. doi:10.1016/j.enconman.2015.07.047S1019103010

Self-powered on-line ion concentration monitor in water transportation driven by triboelectric nanogenerator

The final publication is available at Elsevier via https://doi.org/10.1016/j.nanoen.2019.05.029. © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Ion concentration in water is a key criterion for evaluating water quality. In this work, we developed a self-powered on-line ion concentration monitor in water transportation based on impedance matching effect of triboelectric nanogenerator (TENG). A rotary disc-shaped TENG (RD-TENG) and an ion concentration sensor were fabricated based on the industrial printed circuit board (PCB) technology. Flowing water in the pipeline acts as the energy source to drive the RD-TENG and generate an open-circuit (Voc) of 210 V. The ion concentration sensor exhibits a nearly pure resistance characteristic under the alternating current (AC) signal with the frequency below 500 Hz, corresponding to the rotation speed of 250 rpm for the RD-TENG. The impedance matching relationship between the RD-TENG and the ion concentration sensor was experimentally studied and applied to elucidate the sensing mechanism. Finally, a self-powered sensing system integrated with an alarm circuit was assembled which exhibits excellent responsibility and high sensitivity. The change of ion concentration with only 1 × 10−5 mol/L can light up an alarm LED.Natural Science and Engineering Research CouncilCanada Research ChairsNational Natural Science Foundation of China, no. 61804103National Key R&D Program of China, no. 2017YFA0205002Natural Science Foundation of the Jiangsu Higher Education Institutions of China, no. 18KJA535001, no. 14KJB150020Natural Science Foundation of Jiangsu Province of China, no. BK20170343, no. BK20180242China Postdoctoral Science Foundation, no. 2017M610346Collaborative Innovation Center of Suzhou Nano Science & TechnologyPriority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)111 Projec