General overview of the stochastic approach for turbulent non-uniform combustion is described. The stochastic approach combined with a CFD calculation with the conventional turbulence model is discussed. At each point in a turbulent flow field, the variation of some scalar-variables are statistically described by the joint probability density function (joint-PDF), and the velocity is expressed using a conventional turbulence model. The transport equation of this joint-PDF is calculated by a finite-difference method in convection and turbulent diffusion and by the stochastic model in molecular mixing. In addition, simulation results using this stochastic approach are presented for the mixing process in a high-speed jet and the combustion process in a natural gas HCCI engine.
A series calculation method from injector nozzle internal flow to in-cylinder combustion in diesel engines has been developed. In this study, the calculation results of in-cylinder pressure, heat release rate, and NO concentration are compared with experimental results for conventional combustion conditions as well as an advanced combustion condition, which combines a high exhaust gas recirculation (EGR) rate, high boost pressure, and high pressure injection. The calculated pressure and heat release rate histories are in reasonable agreement with those of experiments, but the NO concentration is underestimated especially on the higher EGR rate condition. Therefore, the investigation for improving the quantitative accuracy of NO concentration is performed. The probability density function (PDF) method is one way to estimate the accurate mean reaction rate containing the reaction rate fluctuation by turbulence. In this study, the PDF method only applied for NO calculation is developed to balance the calculation accuracy and the computational cost. The result shows that the reaction rate fluctuation, on NO formation, has a small effect on conventional combustion conditions, but increases with decreasing combustion temperature.
In this article multi-state stochastic cellular automata is considered which is suitable to apply for forest fire models. Specifically, we discuss the value of the critical face, below which the probability that propagative substances spread infinitely is zero, on a special case as for the state transitions. Furthermore, we introduce the transition rate change for some cells as an input on the square lattice to prevent spreading substances, and propose a feedback control framework to prevent spreading with probability 1 by using the critical face.
In Japan, energy-related CO2 emissions were around one thousand and seventy nine million tons in 2009. CO2 emissions from electric utilities accounted for 32 % of the total CO2 emissions. So, low carbon technologies are indispensable to the reduction of energy-related CO2 from electric utilities. In this paper, I would like to introduce the present and future aspects of low carbon technologies in thermal power generation in Japan.
Quantum chemical calculations were performed to investigate the mechanism for the low-temperature oxidation of ethylbenzenes and propylbenzenes. The equilibrium constant for the reaction between R + O2 ⇔ RO2 in the alkylbenzene system was found to be dependent on the position of O2 in RO2 relative to the aromatic ring. The activation energies and the pre-exponential factors for the isomerization reactions of RO2 were also calculated using the transition state theories based on the calculated structures predicted by the density functional theory. It was confirmed that (1, 3) H-atom migration in the alkyl side chain or O2-adduct formation played the key roles on the isomerization reactions of RO2 at relatively lower temperature range. At higher temperature HO2 formation is dominant for all reaction systems. The subsequent reactions of O2-adduct complex in the ethylbenzene system were also searched and the possible roles on the pathway of the benzene-ring cleavage reaction from the O2-adduct complex were suggested.
The unsteady 3-D numerical simulation was done in order to clarify the influence of ignition position on high-speed flame propagation phenomenon along a line vortex. The distance between the vortex center line and the ignition position was changed from D = 0 mm to D = 7 mm, while the vortex diameter was fixed at d = 2 mm. In the 3-D visualization, the shapes of flame and vortex line ware considerably different depending on D. Only when the high-speed flame propagation along the vortex occurred, the helical vortex line (the vortex filament solitons) was observed near the flame top. In the 1-D analysis along the vortex line, the peaks of curvature of the vortex line (the vortex filament solitons) were observed at the locations of large temperature gradient (the flames), and the vortex filament solitons and the flames propagated together along the vortex line. Due to these results, the validity of vortex driving mechanism of high-speed flame propagation phenomenon was reconfirmed. Finally, in the analysis of flame propagation speed, the steady maximum speeds reached about 11-12 m/s in all cases of D. However, the startup time of flame propagation depended on D sensitively, and the earliest startup was obtained at D = 0.8 mm, and not at D = 0 mm. Thus, it was found that the optimum ignition position for rapid startup of flame propagation existed, and such a result was explained by using the vortex driving mechanism.