Wyniki wyszukiwania - Biblioteka Nauki

1

LES numerical study on n-hexane injection in a compression ignition engine

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Kercheva B. , Kapusta Ł. J. , Teodorczyk A.

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tom Vol. 34 nr 2

155--167

EN

The aim of the study was the comparison of different approaches to modeling the injection process in a heavy duty compression ignition engine. The conducted numerical investigation concerned n-hexane direct injection into the engine combustion chamber. Simulations were performed using AVL Fire software, a CFD (Computational Fluid Dynamics) code based on the control volume method. In order to achieve engine conditions, computational model was built basing on piston and cylinder geometry of a real engine and the mesh deformation was defined according to crank mechanism dimensions of the engine. In presented simulations for modeling dispersed phase the Lagrangian approach was used. For capturing the turbulent patterns present in the flow, the Large Eddy Simulation (LES) approach was used. Three different nozzle outflow conditions were compared. In the simplest case, constant flow rate was defined. In the second one, linear stage of increase and decrease of flow rate was defined, and in the third one – the most advanced – data collected during previously done in-injector cavitating flow simulations were used to define the flow parameters on the nozzle outlet. Calculated results for all cases were analyzed and compared. The focus was on the initial stage of the spray. The results show that the way of defining parameters at the outlet influences not only the initial stage of the spray but the whole process.

2

Numerical simulations of n-heptane spray in high pressure and temperature environments

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Smuga W. , Kapusta Ł. J. , Teodorczyk A.

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tom Vol. 97, nr 1

1--6

EN

In this study n-heptane spray in supercritical environments was simulated using commercial CFD (Computational Fluid Dynamic) software AVL Fire. The numerical results were analyzed in terms of global spray parameter, and spray penetration. The results obtained were compared with experimental data available at Sandia National Laboratories. N-heptane spray simulations were performed in the same conditions as in the Sandia experiments. The goal of the study was to assess whether the Lagrangian approach performs well in engine relevant conditions in terms of spray global parameters. Not included in this assessment was the influence of supercritical mixing on liquid-gas interphase. The major element was the potential for practical application of the commercial CFD code in terms of properly representing global spray parameters and thus mixture formation in supercritical conditions, which is one of the core aspects in whole engine process simulation. The key part of the study was mesh optimization. Therefore, the influence of mesh density on both the accuracy of calculations and the calculation time was determined, taking into consideration detailed experimental data as initial conditions for the subsequent calculations. This served as a basis to select the optimal mesh with regard to both accuracy of the results obtained and time duration of the calculations. As a determinant of accuracy, the difference within a range of evaporated fuel stream was used. Using selected mesh the set of numerical calculations were performed and the results were compared with experimental ones taken from the literature. Several spray parameters were compared: spray tip penetration, temperature of the gaseous phase and mixture fraction in the gaseous phase. The numerical results were very consistent in respect of spray tip penetration. The other parameters were influenced by specific features of the Lagrangian approach. Nevertheless the results obtained showed that the Lagrangian approach may be used for engine relevant conditions.

3

Symulacje numeryczne spalania n-heptanu w komorze o stałej objętości

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Kapusta Ł. J. , Teodorczyk A. , Drabik M.

Archiwum Spalania

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2011

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tom Vol. 11, nr 1-2

89-101

PL

W pracy zostały przedstawione wyniki symulacji komputerowych spalania n-heptanu w komorze o stałej objętości. Komora o kształcie sferycznym miała średnicę 100 mm. Do symulacji zostało wykorzystane oprogramowanie Fire firmy AVL. W rozpatrywanych przypadkach paliwo przed zapłonem było wymieszane z powietrzem. Wskaźnik stechiometrii mieszanki palnej (zdefiniowany jako odwrotność współczynnika nadmiaru powietrza) wynosił 0,8; 1 i 1,2. Temperatura początkowa mieszanki palnej we wszystkich przypadkach wynosiła 373 K natomiast wartości ciśnienia początkowego wyniosły 1 MPa oraz 2,5 MPa. Analizowanymi parametrami procesu spalania były głównie: temperatura, oraz propagacja płomienia. Uzyskane wyniki porównano z literaturowymi wynikami eksperymentalnymi przeprowadzonymi dla takich samych warunków początkowych.

EN

The paper presents the results of a numerical simulations of n-heptane combustion process in a constant volume vessel. Spherically shaped vessel had diameter of 100 mm. Simulations were done using AVL Fire software. In all investigated cases fuel was homogenized with air. Equivalence ratio of a flammable mixture was of 0.8, 1 and 1.2. The initial temperature of the mixture was in all investigated cases of 373 K. The initial pressure was of l MPa and 2.5 MPa. The analyzed parameters were mainly temperature and flame propagation. Numerical results were compared with literature data obtained for the same initial conditions

4

Jet and droplet breakup modelling approaches

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Kapusta Ł. J. , Jaworski P. , Kowalski J.

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tom Vol. 22, No. 3

83--90

EN

Three-dimensional computational fluid dynamics (CFD) plays important role in engines development. The mixture formation in a direct-injection piston engines poses a huge challenge in successful simulations of the engine processes. It is due to the fact that the spray as a two-phase flow complicates the computational process. Moreover, this multiphase flow is not uniform. Three main zones, depending on the distance from the nozzle exit are visible when a liquid is injected. Very dense so called “thick” in a direct vicinity of the injector hole, than “thin” as a result of pri-mary breakup downstream the injector and finally in the certain distance from the injector appears “very thin” region as a result of secondary breakup. It is important to take into account that the liquid phase in various regimes behaves differently and is under influence of different phenomena. The modelling approach needs to take in to consideration all those elements. This paper focuses on presentation of the theory and numerical models for primary and secondary breakup phenomena. The primary breakup is a process that results from a combination of three mechanisms: turbu-lence within liquid phase, implosion of cavitation’s bubbles and aerodynamic forces acting on a liquid jet. Secondary breakup regime occurs mainly due to the aerodynamic interactions between the liquid and the gaseous phase.

5

SCR systems for NOx reduction in heavy duty vehicles

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Jaworski P. , Kapusta Ł. J. , Jarosiński S. , Ziółkowski A. , Cortes Capetillo A. , Grzywnowicz R.

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tom Vol. 22, No. 4

139--146

EN

Air pollution has become an important worldwide problem. The European Commission credits road and water transport as the major source of NOx pollution, and of being responsible for around 50% of the total air pollution in urban areas. In Poland, around 45% of the country NOx emissions are attributed to transportation. During the last decade, the use of SCR technologies have gained popularity as a method for NOx reduction, the technology is widely considered as one of the solutions for road transport emissions. SCR technology had previously been employed in stationary plants, maritime transportation and other installations using combustion processes in which exhaust conditions are easier to control. The advance on the technology led to the introduction of the first heavy-duty vehicle with an SCR system into the market in 2004. New technologies and applications are constantly appearing, for example, SCR exhaust gas cleaning systems for reciprocating engines are still under development and compression ignition engines can be found in a number of different applications. The technology still needs to be studied and improved as constant problems and knowledge is required in issues such as urea injection, crystallization and NOx reduction efficiency. Moreover, the designs intended for heavy duty vehicles need to meet vehicle limitations and EURO emissions restrictions. This paper presents a review of the different SCR system designs derived from the various factors and regulations in the automotive industry, which have influenced the technology, along with a parametric study of a proprietary SCR system for heavy-duty application.