Lattice Boltzmann method for direct numerical simulation of turbulent flows

We present three-dimensional direct numerical simulations (DNS) of the Kida vortex flow, a prototypical turbulent flow, using a novel high-order lattice Boltzmann (LB) model. Extensive comparisons of various global and local statistical quantities obtained with an incompressible-flow spectral element solver are reported. It is demonstrated that the LB method is a promising alternative for DNS as it quantitatively captures all the computed statistics of fluid turbulenc

Study of ignition delay time and generalization of auto-ignition for PRFs in a RCEM by means of natural chemiluminescence

An investigation of the effects of contour conditions and fuel properties on ignition delay time under Homogeneous Charge Compression Ignition (HCCI) conditions is presented in this study. A parametric variation of initial temperature, intake pressure, compression ratio, oxygen concentration and equivalence ratio has been carried out for Primary Reference Fuels (PRFs) in a Rapid Compression Expansion Machine (RCEM) while applying the optical technique of natural chemiluminescence along with a photo-multiplier. Additionally, the ignition delay time has been calculated from the pressure rise rate and also corresponding numerical simulations with CHEMKIN have been done. The results show that the ignition delay times from the chemical kinetic mechanisms agree with the trends obtained from the experiments. Moreover, the same mechanism proved to yield consistent results for both fuels at a wide range of conditions. On the other hand, the results from natural chemiluminescence also showed agreement with the ignition delay from the pressure signals. A 310 nm interference filter was used in order to detect the chemiluminescence of the OH* radical. In fact, the maximum area and peak intensity of the chemiluminescence measured during the combustion showed that the process of auto-ignition is generalized in the whole chamber. Moreover, the correlation of peak intensity, maximum area and ignition delay time demonstrated that natural chemiluminescence can also be used to calculate ignition delay times under different operating conditions. Finally, the area of chemiluminescence was proved to be more dependant on the fuel and ignition delay time than on the operating conditions. (C) 2015 Elsevier Ltd. All rights reserved.The authors would like to thank different members of the LAV team of the ETH-Zurich for their contribution to this work. The authors are grateful to the Universitat Politecnica de Valencia for financing the Ph.D. studies of Vera-Tudela (FPI SP1 Grant 30/05/2012) and his stay at ETH-Zurich (grant 30/12/2014). Finally, the authors would like to thank the Spanish Ministry of Education for financing the Ph.D. studies of Lopez-Pintor (Grant FPU13/02329) and his stay at ETH-Zurich (Grant EST14/00626).Desantes Fernández, JM.; García Oliver, JM.; Vera-Tudela-Fajardo, WM.; López Pintor, D.; Schneider, B.; Boulouchos, K. (2016). Study of ignition delay time and generalization of auto-ignition for PRFs in a RCEM by means of natural chemiluminescence. Energy Conversion and Management. 111:217-228. https://doi.org/10.1016/j.enconman.2015.12.052S21722811

Study of the auto-ignition phenomenon of PRFs under HCCI conditions in a RCEM by means of spectroscopy

An investigation of the effects of contour conditions and fuel properties on the auto-ignition and combustion process under HCCI conditions is presented in this study. A parametric variation of initial temperature, intake pressure, compression ratio, oxygen concentration and equivalence ratio has been carried out for Primary Reference Fuels in a Rapid Compression Expansion Machine while applying spectroscopy. The results have also been contrasted with natural chemiluminescence measurements. Additionally, the experiments have been simulated in CHEMKIN and the results derived from the optical techniques have been compared with the results from the chemical kinetics of the process, validating the chemical kinetic mechanism and an additional sub-model of excited OH . Two different scenarios can be seen according to the results from the spectrograph. For very lean or very low-temperature combustions no peak of OH is seen at 310 nm of wavelength, proving that the luminosity came from the CO continuum rather than from the OH . However, for more intense combustions (richer equivalence ratios, higher temperatures or lower EGR rates) spectrography shows a clear peak of OH that has much longer time of life than the corresponding to the CO continuum. The main chemical reaction that causes this two scenarios has been identified as H þ HO2 ) 2OH. The increase of relevance of this reaction at high combustion temperatures causes a higher OH accumulation, which leads to a brighter OH emission. Finally, for low temperature combustions the CO continuum out-shines the OH radiation so the light emitted by this radical cannot be detected by means of natural chemiluminescence. 201The authors would like to thank different members of the LAV team of the ETH-Zurich for their contribution to this work. The authors are grateful to the Universitat Politecnica de Valencia for financing the Ph.D. studies of W. Vera-Tudela (FPI SP1 grant 30/05/2012) and his stay at ETH-Zurich (grant 30/12/2014). Finally, the authors would like to thank the Spanish Ministry of Education for financing the Ph.D. studies of Dario Lopez-Pintor (grant FPU13/02329) and his stay at ETH-Zurich (grant EST14/00626).Desantes Fernández, JM.; García Oliver, JM.; Vera-Tudela-Fajardo, WM.; López Pintor, D.; Schneider, B.; Boulouchos, K. (2016). Study of the auto-ignition phenomenon of PRFs under HCCI conditions in a RCEM by means of spectroscopy. Applied Energy. 179:389-400. https://doi.org/10.1016/j.apenergy.2016.06.134S38940017