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Journal ArticleDOI

Effect of piston bowl shape on the in-cylinder flow characteristics of IC engines

14 Jun 2014-Journal of Mechanical Science and Technology (Korean Society of Steel Construction)-Vol. 28, Iss: 6, pp 2377-2384
TL;DR: In this article, numerical simulation of the in-cylinder flow for internal combustion (IC) engine with different bowl shapes has been performed, and the results of these simulations aid in the improved understanding of the effect of intake and compression process of piston geometry on the internal combustion flow.
Abstract: Numerical simulation of the in-cylinder flow for internal combustion (IC) engine with different bowl shapes has been performed. The LES models are applied to a piston-cylinder assembly with a stationary valve and a harmonically moving piston. Gas motion inside the engine cylinder determines the thermal efficiency of an IC engine, and combustion chamber geometry affects the performance of the IC engine. Comparison of the flow characteristics inside the engine cylinder equipped with different piston geometries shows that the squish flow affects the turbulence generation process near the top dead center during compression stroke. The A-type combustion chamber with reentrant shape is shown to have higher radial velocity and turbulence intensity in the piston bowl compared with other types. Results of these simulations aid in the improved understanding of the effect of intake and compression process of piston geometry on the in-cylinder flow. The detailed flow characteristics inside the in-cylinder for different piston bowl shapes can offer basic guidelines to improve the combustion process.
Citations
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Journal ArticleDOI
TL;DR: In this article, the cavitation phenomenon inside micro- and minichannel configurations was numerically investigated at different upstream pressures varying from 1 to 15 MPa, and the effect of energy associated with turbulence was investigated using wall shear stress, turbulence kinetic energy and mean velocity at various locations of the micro/minichannels.
Abstract: The cavitation phenomenon inside micro- and minichannel configurations was numerically investigated. The simulations for each channel were performed at different upstream pressures varying from 1 to 15 MPa. Two microchannel configurations with inner diameters of 152 and 254 μm and two minichannel configurations with inner diameters of 504 and 762 μm were simulated. To validate the numerical approach, micro-jet impingement from a microchannel with an inner diameter of 152 μm was first simulated at different Reynolds numbers. Then, the mixture model was used to model the multiphase flow inside the channels. The results of this study present major differences in the cavitating flows between the micro- and miniscale channels and show that the pressure profile and vapor phase distribution exhibit different features. The static pressure drops to negative values (tensile stress) in microchannels, while the minimum static pressure in minichannels is found to be equal to vapor saturation pressure, and higher velocity magnitudes especially at the outlet are visible in the microchannels. It is shown that for higher upstream pressures, the cavitating flow extends over the length of the micro/minichannel, thereby increasing the possibility of collapse at the outlet. The effect of energy associated with turbulence was investigated at high Reynolds numbers for both micro/minichannels and its impact was analyzed using wall shear stress, turbulence kinetic energy and mean velocity at various locations of the micro/minichannels.

19 citations

Journal ArticleDOI
10 Jul 2017-Energies
TL;DR: In this article, an experimental study was conducted to investigate the effect of the structure of the induction flow on the characteristics of early flames in a lean-stratified and lean-homogeneous charge combustion of compressed natural gas (CNG) fuel in a direct injection (DI) engine at different engine speeds.
Abstract: An experimental study was conducted to investigate the effect of the structure of the induction flow on the characteristics of early flames in a lean-stratified and lean-homogeneous charge combustion of compressed natural gas (CNG) fuel in a direct injection (DI) engine at different engine speeds. The engine speed was varied at 1500 rpm, 1800 rpm and 2100 rpm, and the ignition timing was set at a 38.5° crank angle (CA) after top dead center (TDC) for all conditions. The engine was operated in a partial-load mode and a homogeneous air/fuel charge was achieved by injecting the fuel early (before the intake valve closure), while late injection during the compression stroke was used to produce a stratified charge. Different induction flow structures were obtained by adjusting the swirl control valves (SCV). Using an endoscopic intensified CCD (ICCD) camera, flame images were captured and analyzed. Code was developed to analyze the level of distortion of the flame and its wrinkledness, displacement and position relative to the spark center, as well as the flame growth rate. The results showed a higher flame growth rate with the flame kernel in the homogeneous charge, compared to the stratified combustion case. In the stratified charge combustion scenario, the 10° SCV closure (medium-tumble) resulted in a higher early flame growth rate, whereas a homogeneous charge combustion (characterized by strong swirl) resulted in the highest rate of flame growth.

8 citations


Cites background from "Effect of piston bowl shape on the ..."

  • ...The intake flow structure is further modified and broken down into small-scale eddies in the compression stroke, with the piston shape and chamber design influencing the turbulence decay rate in the cylinder [2,3]....

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Journal ArticleDOI
TL;DR: In this article , the effects of different bowl geometries which have the wall guided fuel injection were compared with the standard combustion chamber geometry of a single-cylinder, air-cooled, and direct-injection diesel engine.
Abstract: This paper has included the effects of different bowl geometries which has the wall guided fuel injection. Bowl geometries, which affect in-cylinder air flows, have a great influence on the change of mixture formation. Also, the region where the fuel hits in the bowl affects all engine parameters. In this presented numeric study, the standard combustion chamber geometry of a single-cylinder, air-cooled, and direct-injection diesel engine is compared with the designed new combustion chamber. Four different rotation angles (0°, 7.5°, 10°, and 15°) were determined for the new combustion chamber geometry and compared with the standard geometry. The three-dimensionally modeled bowl geometries in 3D Computational Fluid Dynamics simulation were examined in terms of in-cylinder pressure and temperature, instantaneous and cumulative heat release rate, exhaust emissions (NO, soot, CO, and CO 2 ), temperature/spray, and equivalence ratio/spray at different CA’s. The effects of the different rotation angles of the designed new bowl geometry on both the air movement and the region where the fuel hits were investigated for the engine parameters. When the results obtained are examined, maximum in-cylinder pressures for standard combustion chamber, new combustion chamber 1, new combustion chamber 2, new combustion chamber 3, and new combustion chamber 4 geometries were obtained 79.5, 75.2, 78, 78.1, and 78 bar respectively, and the maximum in-cylinder temperatures were found 1766, 1742, 1805, 1817, and 1818 K, respectively. According to the results obtained from the numerical analysis, CO, CO 2 , and soot emissions decreased while NO emissions increased in the new combustion chamber, compared to the standard combustion chamber. Examined the spray distributions in bowl, it was seen that the fuel sprays distributed more homogeneously and flame propagates which is spread throughout the chamber in the new combustion chamber type, which improved the mixture formation. The wall guided fuel flow in the novel designed chamber geometries beneficial to turbulence kinetic energy, spray distribution, emissions.
References
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Journal ArticleDOI
TL;DR: In this article, an extended period numerical integration of a baroclinic primitive equation model has been made for the simulation and the study of the dynamics of the atmosphere's general circulation, and the solution corresponding to external gravitational propagation is filtered by requiring the vertically integrated divergence to vanish identically.
Abstract: An extended period numerical integration of a baroclinic primitive equation model has been made for the simulation and the study of the dynamics of the atmosphere's general circulation. The solution corresponding to external gravitational propagation is filtered by requiring the vertically integrated divergence to vanish identically. The vertical structure permits as dependent variables the horizontal wind at two internal levels and a single temperature, with the static stability entering as a parameter. The incoming radiation is a function of latitude only corresponding to the annual mean, and the outgoing radiation is taken to be a function of the local temperature. With the requirement for thermal equilibrium, the domain mean temperature is specified as a parameter. The role of condensation is taken into account only as it effectively reduces the static stability. All other external sources and sinks of heat are assumed to balance each other locally, and are thus omitted. The kinematics are th...

12,952 citations

Journal ArticleDOI
TL;DR: In this article, a new eddy viscosity model is presented which alleviates many of the drawbacks of the existing subgrid-scale stress models, such as the inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes.
Abstract: One major drawback of the eddy viscosity subgrid‐scale stress models used in large‐eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid‐scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid‐scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near‐wall region of a turbulent boundary layer. The results of large‐eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.

6,747 citations

Journal ArticleDOI
TL;DR: Germano et al. as discussed by the authors generalized the dynamic subgrid-scale (SGS) model for the large eddy simulation (LES) of compressible flows and transport of a scalar.
Abstract: The dynamic subgrid-scale (SGS) model of Germano et al. (1991) is generalized for the large eddy simulation (LES) of compressible flows and transport of a scalar. The model was applied to the LES of decaying isotropic turbulence, and the results are in excellent agreement with experimental data and direct numerical simulations. The expression for the SGS turbulent Prandtl number was evaluated using direct numerical simulation (DNS) data in isotropic turbulence, homogeneous shear flow, and turbulent channel flow. The qualitative behavior of the model for turbulent Prandtl number and its dependence on molecular Prandtl number, direction of scalar gradient, and distance from the wall are in accordance with the total turbulent Prandtl number from the DNS data.

1,588 citations

Journal ArticleDOI
TL;DR: In this paper, five types of models applied to HCCI engine modelling are discussed in the present paper, and specific strategies for diesel-fuelled, gasoline-fined, and other alternative fuelled combustion are also discussed.

1,068 citations


"Effect of piston bowl shape on the ..." refers background in this paper

  • ...Homogeneous charge compression ignition (HCCI) entails thoroughly mixing fuel and air before combustion starts; the mixture automatically ignites as a result of the temperature increase in the compression stroke [2]....

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Journal ArticleDOI
TL;DR: In this article, three-dimensional flow calculations of the intake and compression stroke of a four-valve direct-injection Diesel engine have been carried out with different combustion chambers.

195 citations