Stochastics theory of log-periodic patterns

We introduce an analytical model based on birth-death clustering processes to help understanding the empirical log-periodic corrections to power-law scaling and the finite-time singularity as reported in several domains including rupture, earthquakes, world population and financial systems. In our stochastics theory log-periodicities are a consequence of transient clusters induced by an entropy-like term that may reflect the amount of cooperative information carried by the state of a large system of different species. The clustering completion rates for the system are assumed to be given by a simple linear death process. The singularity at t_{o} is derived in terms of birth-death clustering coefficients.Comment: LaTeX, 1 ps figure - To appear J. Phys. A: Math & Ge

Modeling HCCI using CFD and Detailed Chemistry with Experimental Validation and a Focus on CO Emissions

Multi-zone CFD simulations with detailed kinetics were used to model engine experiments performed on a diesel engine that was converted for single cylinder, HCCI operation, here using iso-octane as the fuel. The modeling goals were to validate the method (multi-zone combustion modeling) and the reaction mechanism (LLNL 857 species iso-octane), both of which performed very well. The purpose of this paper is to document the validation findings and to set the ground work for further analysis of the results by first looking at CO emissions characteristics with varying equivalence ratio

Operating range extension of RCCI combustion concept from low to full load in a heavy-duty engine

Fuel reactivity controlled compression ignition (RCCI) concept has arisen as a solution to control premixed combustion (PCI) strategies, which avoids soot and NOx formation by promoting a lean air fuel mixture and low temperature combustion. Thus, this study is focused on investigating the effects of different engine operating variables over combustion, to be able to suggest suitable strategies for extending the RCCI operation from low to full load, in a HD single-cylinder research engine. Different strategies are implemented at low, medium and high load, varying fuel and air reactivity, by means of parametrical studies. Performance and emissions results are analyzed combining engine testing with 3D-CFD modeling. Based on those results, an overlimit function is used to select the best engine settings for each operating point. Finally, engine emissions and performance results from that RCCI operation are compared with conventional Diesel combustion (CDC). Results suggest that double injection strategies should be used for RCCI operation from low to mid load. However, from high to full load operation, single injection strategies should be used, mainly to avoid excessive in-cylinder pressure gradients. In addition, it is confirmed the suitability of RCCI combustion to overcome the soot NOx trade-off characteristic of CDC, from 6 to 24 bar of BMEP, while improving fuel consumption.The authors would like to recognize the technical support from VOLVO Group Trucks Technology and to express their gratitude to CONVERGENT SCIENCE Inc. and IGNITE3D Engineer-ing GmbH for their kind support for performing the CFD calculations using CONVERGE software. In addition, thank the Spanish Ministry of Economy and Competitiveness for the financial support through Eduardo Belarte's grant (BES-2011-047073). The authors would also like to thank Gabriel Alcantarilla for the management of the facility and his assistance in data acquisition.Molina Alcaide, SA.; García Martínez, A.; Pastor Enguídanos, JM.; Belarte Mañes, E.; Balloul, I. (2015). Operating range extension of RCCI combustion concept from low to full load in a heavy-duty engine. Applied Energy. 143:211-227. https://doi.org/10.1016/j.apenergy.2015.01.035S21122714

Numerical simulations for evaluating the impact of advanced insulation coatings on H2 additivated gasoline lean combustion in a turbocharged

[EN] This paper presents a numerical methodology based on Computational Fluid Dynamics (CFD) simulations to understand the physics of heat losses through the cylinder walls coated with different materials, taking into account other important factors such as surface roughness and near wall flow velocity in a turbocharged spark-ignited (SI) engine. Engine closed cycle simulations have been performed to estimate the thermodynamic evolution of the charge inside the cylinder and therefore, to evaluate the effect of roughness on heat transfer and combustion at real operating conditions. The model has been validated by using experimental data for two different steady-state operation conditions of a fully instrumented engine. In general, the maximum rate of heat release is reduced as the roughness is increased. Observed trends indicate that the heat transfer variation is mainly caused by changes in the combustion process due to the surface roughness, rather than to the effects of the coating material properties/characteristics (the increase of the effective contact area, porosity, etc.). Lastly, the comparison between uncoated and coated engine have shown that maximal gains around 5% in heat loss could be achieved, with very limited efficiency improvement, whereas the knock tendency increases.J. Gomez-Soriano is partially supported through the Programa de Apoyo para la Investigation y Desarrollo (PAID) of Universitat Politecnica de Valencia [Grant No. FPI-S2-2016-1353].Broatch, A.; Olmeda, P.; Margot, X.; Gómez-Soriano, J. (2019). Numerical simulations for evaluating the impact of advanced insulation coatings on H2 additivated gasoline lean combustion in a turbocharged. Applied Thermal Engineering. 148:674-683. https://doi.org/10.1016/j.applthermaleng.2018.11.106S67468314

Evapotranspiration and simulation of soil water movement in small area vegetation

In Greece, crops are frequently cultivated in small isolated areas in close proximity to roads and bare soils and therefore evapotranspiration is affected by local advection. Under these circumstances, oasis effect conditions are present and evapotranspiration is higher than what is expected. In this paper, the evapotranspiration and soil water dynamics of a cotton crop cultivated in small areas under the oasis effect is studied. To this end, two isolated free-drainage lysimeters cultivated with cotton in the year 2007 were used. Soil moisture of the soil profile of both the lysimeters was monitored with two capacitance water content probes. The soil water balance method was used to estimate crop evapotranspiration and corresponding crop coefficients in one of the two lysimeters. These coefficients were 75% larger than the FAO-56 crop coefficients at the mid-season stage. The FAO-56 and the derived crop coefficients were used for the simulation of the water dynamics in the second lysimeter by the SWBACROS model. The derived crop coefficients for these conditions produced much better results than the FAO-56 crop coefficients. The results were improved when crop coefficient value equal to 2.5 was used for the mid-season stage