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Aplikace chlazené recirkulace výfukových plynů u moderních zážehových motorů
(Vysoké učení technické v Brně. Fakulta strojního inženýrství, ) Bazala, Jiří; Píštěk, Václav; Bauer, František; Tůma, Jiří
systémů chlazeného EGR (recirkulace výfukových plynů), vodního vstřikování a jejich kombinace. Pro tento účel byl na základě měření zkalibrován simulační model spalovacího zážehového motoru. Na tomto modelu byl prověřen vliv externího chlazeného EGR systému na klíčové parametry motoru jako je účinnost, měrná spotřeba paliva, výkon a jiné. Zde se dospělo k závěru, že systém EGR má z hlediska poměru dosažených výsledků a komplexnosti nevyhovující parametry. Proto byl na modelu prověřen model i vodního vstřikování a porovnán právě se systémem EGR. Model motoru s vodním vstřikováním byl vyhodnocen jako výhodnější. Proto se rozhodlo, že se prostředky k ověření výsledků investují do experimentálního vozidla s vodním vstřikováním a dojde ke srovnání výsledků simulačního modelu a experimentálního měření. Jako budoucí nejvhodnější kombinace vzhledem ke sledovaným parametrům se jeví použití jak systému EGR, tak vodního vstřikování a ideálně s možností zapalování směsi v předkomůrce.
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Improving the strength of -TCP scaffolds produced by Digital Light Processing using two-step sintering
(ELSEVIER SCI LTD, 2024-04-01) Paredes Sánchez, Claudia Isabel; Roleček, Jakub; Miranda, Pedro
Digital Light Processing is combined with two-step sintering to obtain bioactive scaffolds with improved strength and mechanical isotropy. Highly loaded photosensitive suspensions were prepared from beta-TCP powder to create scaffolds consisting of interpenetrating struts with two different designs. Two sintering methods were used: conventional sintering (CS) and two-step sintering (2SS). The latter resulted in a microstructure with uniformly shaped grains and reduced porosity. Their compressive strength was determined by uniaxial testing under two different load configurations, with the force applied parallel or perpendicular to the building plane of the scaffolds. Design optimisation and fine-tuning of the sintering process helped in reducing the presence of interlayer defects and minimise the shear-dominated fractures. Isotropic fracture behaviour was achieved, with similar central values of the Weibull distribution (49 +/- 1 MPa vs. 51 +/- 1 MPa) along both testing directions, showing a great potential for their use in load-bearing bone tissue engineering applications.
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A precise asymptotic description of half-linear differential equations
(WILEY-V C H VERLAG GMBH, 2024-04-08) Řehák, Pavel
We study asymptotic behavior of solutions of nonoscillatory second-order half-linear differential equations. We give (in some sense optimal) conditions that guarantee generalized regular variation of all solutions, where no sign condition on the potential is assumed. For all of these solutions, we establish precise asymptotic formulas, where positive as well as negative potential is considered. We examine, as consequences, also equations with regularly varying coefficients, or with the coefficients viewed as perturbations of exponentials, or the equations under certain critical (double roots) settings. We make also asymptotic analysis of Poincare-Perron solutions. Many of our results are new even in the linear case.
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Grasping the behavior of magnetorheological fluids in gradient pinch mode via microscopic imaging
(AIP Publishing, 2024-04-03) Kubík, Michal; Žáček, Jiří; Goldasz, Janusz; Nečas, David; Sedlačík, Michal; Blahuta, Jiří; Bańkosz, Wojciech; Sapinski, Bogdan
Magnetorheological (MR) fluids are suspensions of micrometer-sized ferromagnetic particles in a carrier fluid, which react to magnetic fields. The fluids can be operated in several fundamental modes. Contrary to the other modes, the rheology and microstructure formation of the MR fluid in the gradient pinch mode have been studied to a far lesser extent. The magnetic field distribution in the flow channel is intentionally made non-uniform. It is hypothesized that the Venturi-like contraction is achieved via fluid property changes, leading to a unique behavior and the presence of a pseudo-orifice. The main goal is to investigate the presence of the Venturi-like contraction effect in the fluid by means of optical imaging and hydraulic measurements. To accomplish the goal, a unique test rig has been developed including a fluorescence microscope and MR valve prototype. The Venturi-like contraction hypothesis was confirmed. The results indicate that the effective flow channel size decreases by 92% at the maximum magnetic flux applied. This has a direct impact on the flow characteristics of the MR valve. The variation of the pressure–flow rate curve slope with magnetic field was demonstrated. The results provide valuable information for understanding the rheology and microstructure formation mechanism in MR fluids in the pinch mode.
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Separation of Cellulose fromWastewater and Valorisation via Pyrolysis: A Case Study in the Czech Republic
(MDPI, 2024-04-05) Djordjevićová, Denisa; Miino, Marco Carnevale; Raček, Jakub; Chorazy, Tomáš; Hlavínek, Petr; Vranayová, Zuzana
Currently, the recovery of resources from urban wastewater (WW) represents a priority. On this topic, the potential recovery of cellulose for its subsequent reuse in different sectors is gaining interest. In this work, a large-size conventional wastewater treatment plant (WWTP) was selected as a case study. A preliminary mechanical treatment was used, with the aim of separating, quantifying, and characterizing cellulose in WW. The results suggest that the per-capita production of dry primary cellulosic sludge (D-PCS) is equal to 1.46 ± 0.13 kgD-PCS PE1 y1, with an average calorific value of 21.04 MJ kg1DM. Cellulosic fibres have an average length of >100 µm and a thickness of 2–5 µm. The D-PCS was subsequently treated via medium-temperature pyrolysis; a total of 29.5% of the initial D-PCS was converted into pyrolyzed primary cellulosic sludge (P-PCS) and only 26% into pyrolytic gas. More than 44.5% of the dried cellulose can be converted into pyrolytic oil. Moreover, three different scenarios of recovery have been considered, and the impact of cellulose separation in terms of COD fluxes entering the WWTP and potential energy recovery has been studied. The results suggested that, in this case study, the potential separation of the primary cellulosic sludge from the influent water flux would have no significant impact on COD load entering the biological treatments and biogas production in the anaerobic digestion of the secondary sludge.