Mixing layer ignition of hydrogen

A theoretical analysis is given for the high-temperature ignition in a laminar mixing layer between hydrogen and air at the high temperatures characteristic of supersonic combustión. We analyze the most important practical case where the temperature of the air stream is higher than that of the hydrogen stream. In this case, the chemical reactions responsible for ignition occur in the air side of the mixing layer, where the mixture is lean. A simplified reduced mechanism is found to describe the ignition process. The radicáis OH and H follow the steady-state approximation while the radical O is the chain branching species following an autocatalytic reaction with moderately large activation energy. Numerical results of the governing equations for large valúes of the activation energy are presented and from a symplified analysis, we obtain a closed form solution of the ignition distance as a function of the physicochemical parameters

Efficiency at maximum power output for an engine with a passive piston

Efficiency at maximum power (MP) output for an engine with a passive piston without mechanical controls between two reservoirs is theoretically studied. We enclose a hard core gas partitioned by a massive piston in a temperature-controlled container and analyze the efficiency at MP under a heating and cooling protocol without controlling the pressure acting on the piston from outside. We find the following three results: (i) The efficiency at MP for a dilute gas is close to the Chambadal-Novikov-Curzon-Ahlborn (CNCA) efficiency if we can ignore the side wall friction and the loss of energy between a gas particle and the piston, while (ii) the efficiency for a moderately dense gas becomes smaller than the CNCA efficiency even when the temperature difference of reservoirs is small. (iii) Introducing the Onsager matrix for an engine with a passive piston, we verify that the tight coupling condition for the matrix of the dilute gas is satisfied, while that of the moderately dense gas is not satisfied because of the inevitable heat leak. We confirm the validity of these results using the molecular dynamics simulation and introducing an effective mean-field-like model which we call stochastic mean field model.Comment: 24 pages, 13 figure

Modeling of a Torch and Calculations of Heat Transfer in Furnaces, Fire Boxes, Combustion Chambers. Part I. Calculations of Radiation from Solids and Gas Volumes by the Laws of Radiation from Solid Bodies

Through the 20th century scientists, researches made many attempts to solve important complex scientific problem. The solution to the problem was to derive analytical expressions, formulas for calculating heat radiation from gas volumes, torches on heating surfaces. However, the formulas were not derived in the 20 th century. At the beginning of the 21st century the author of this article disclosed the laws for heat radiation from cylinder gas volumes. On the basis of the scientific disclosure the problem was solved, analytical equations for calculating heat transfer in torch furnaces, steam boiler boxes, combustion chambers of gas-turbine installations were obtained. To assess the scientific disclosure and its present and future roles, the analysis of methods for calculating heat transfer in furnaces, fire boxes, combustion chambers was performed

High temperature combustion: Approaching equilibrium using nuclear networks

A method for integrating the chemical equations associated with nuclear combustion at high temperature is presented and extensively checked. Following the idea of E. M\"uller, the feedback between nuclear rates and temperature was taken into account by simultaneously computing molar fraction changes and temperature response in the same matrix. The resulting algorithm is very stable and efficient at calculating nuclear combustion in explosive scenarios, especially in those situations where the reacting material manages to climb to the nuclear statistical equilibrium regime. The numerical scheme may be useful not only for those who carry out hydrodynamical simulations of explosive events, but also as a tool to investigate the properties of a nuclear system approaching equilibrium through a variety of thermodynamical trajectories.Comment: 31 pages, 11 figures, accepted for publication in the ApJ

Acoustic timescale characterization of hot spot detonability

Premixed reactive mixtures of fuel and oxidizer often contain regions of higher temperature. These regions of raised temperature are generally called hot spots and have been shown to be the autoignition center in reactive mixtures. Linear temperature gradients and thermal stratification are often used to characterize their behavior. In this work, hot spots are modeled as a linear temperature gradient adjacent to a constant temperature plateau. This approach retains the simplicity of a linear temperature gradient, but captures the effects of a local temperature maximum of finite size. A one-step Arrhenius reaction for H2-Air is used to model the reactive mixture. A one dimensional model is considered first to characterize hot spot behavior based on the relation between how quickly the fuel reacts (excitation time) and the time it takes for fluid motion to be induced (acoustic time). Plateaus of three different initial sizes spanning two orders of magnitude are simulated. Each length corresponds to a different ratio of excitation time to acoustic time or acoustic timescale ratio. It is shown that ratios less than unity react at nearly isochoric conditions while ratios greater than unity react at nearly isobaric conditions. It is demonstrated that the gasdynamic response is characterized by the a priori prescribed hot spot acoustic timescale ratio. Based upon this ratio, it is shown that the plateau can have either a substantial or negligible impact on the reaction of a surrounding temperature gradient. This is explored further as the slope of the temperature gradient is varied. Plateaus with a particular acoustic timescale ratio are shown to facilitate detonation formation inside gradients that would otherwise not detonate. This 1-D model is extended to two dimensions with symmetric and asymmetric plateau regions, modeled using both rectangular and elliptical geometries. Even with clear differences in behavior between one and two dimensions, the hot spot acoustic timescale ratio is shown to characterize the 2-D gasdynamic response. The relationship between one and two dimensions is explored using asymmetric plateau regions. It is shown that 1-D behavior is recovered over a finite time. Furthermore, the duration of this 1-D behavior is directly related to the asymmetry of the plateau