Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCalculation of the Minimum Ignition Energy based on the ignition delay time
90
0
0.0
(
0
)
Added by
Nils Erland L. Haugen
Publication date
2011
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
The Minimum Ignition Energy (MIE) of an initially Gaussian temperature profile is found both by Direct Numerical Simulations (DNS) and from a new novel model. The model is based on solving the heat diffusion equation in zero dimensions for a Gaussian velocity distribution. The chemistry is taken into account through the ignition delay time, which is required as input to the model. The model results reproduce the DNS results very well for the Hydrogen mixture investigated. Furthermore, the effect of ignition source dimensionality is explored, and it is shown that for compact ignition kernels there is a strong effect on dimensionality. Here, three, two and one dimensional ignition sources represent a spherical kernel, a long spark and an ignition sheet, respectively.
rate research
Read More
Auto-ignition process of stoichiometric mixture of methane-air is investigated using detailed chemical kinetics in a single-zone combustion chamber. Effect of initial temperature on start of combustion (SOC). The Arrhenius expression for the specific reaction rate are calculated and auto-ignition was evaluated based on the species fractions and sensitivity analysis. Our results suggest that the SOC is directly related to initial temperature and the auto-ignition will not occur if the initial temperature low enough.
The present study addresses the role of molecular non-equilibrium effects in thermal ignition problems. We consider a single binary reaction of the form A+B -> C+C. Molecular dynamics calculations were performed for activation energies ranging between RT and 7.5RT and heat release of 2.5RT and 10RT. The evolution of up to 10,000 particles was calculated as the system undergoes a thermal ignition at constant volume. Ensemble averages of 100 calculations for each parameter set permitted to determine the ignition delay, along with a measure of the stochasticity of the process. A well behaved convergence to large system sizes is also demonstrated. The ignition delay calculations were compared with those obtained at the continuum level using rates derived from kinetic theory: the standard rate assuming that the distribution of the speed of the particles is the Maxwell-Boltzmann distribution, and the perturbed rates by Prigogine and Xhrouet [1] for an isothermal system, and Prigogine and Mahieu [2] for an energy releasing reaction, obtained by the Chapman-Enskog perturbation procedure. The molecular results were found in very good agreement with the latter at low temperatures, confirming that non-equilibrium effects promote the formation of energetic particles, that serve as seeds for subsequent reaction events: i.e., hot spots. This effect was found to lower the ignition delay by up to 30%. At high temperatures, the ignition delay obtained from the standard equilibrium rate was found to be up to 60% longer than the molecular calculations. This effect is due to the rapidity of the reactive collisions that do not allow the system to equilibrate. For this regime, none of the perturbation solutions obtained by the Chapman-Enskog procedure were valid. This study thus shows the importance of non-equilibrium effects in thermal ignition problems, for most temperatures of practical interest.
Relativistic fluid dynamics and the theory of relativistic detonation fronts are used to estimate the space-time dynamics of the burning of the D-T fuel in Laser driven pellet fusion experiments. The initial High foot heating of the fuel makes the compressed target transparent to radiation, and then a rapid ignition pulse can penetrate and heat up the whole target to supercritical temperatures in a short time, so that most of the interior of the target ignites almost simultaneously and instabilities will have no time to develop. In these relativistic, radiation dominated processes both the interior, time-like burning front and the surrounding space-like part of the front will be stable against Rayleigh-Taylor instabilities. To achieve this rapid, volume ignition the pulse heating up the target to supercritical temperature should provide the required energy in less than ~ 10 ps.
In this Article, we study the hydrodynamics and burn of the thermonuclear fuel in inertial confinement fusion pellets at the ion kinetic level. The analysis is based on a two-velocity-scale Vlasov-Fokker-Planck kinetic model that is specially tailored to treat fusion products (suprathermal {alpha}-particles) in a self-consistent manner with the thermal bulk. The model assumes spherical symmetry in configuration space and axial symmetry in velocity space around the mean flow velocity. Compared to fluid simulations where a multi-group diffusion scheme is applied to model {alpha} transport, the full ion-kinetic approach reveals significant non-local effects on the transport of energetic $alpha$-particles. This has a direct impact on hydrodynamic spatial profiles during combustion: the hot spot reactivity is reduced, while the inner dense fuel layers are preheated by the escaping {alpha}-suprathermal particles, which are transported farther out of the hot spot. We show how the kinetic transport enhancement of fusion products leads to a significant reduction of the fusion yield.
The free energy profile of a reaction can be estimated in a molecular-dynamics approach by imposing a mechanical constraint along a reaction coordinate (RC). Many recent studies have shown that the temperature can greatly influence the path followed by the reactants. Here, we propose a practical way to construct the minimum energy path directly on the free energy surface (FES) at a given temperature. First, we follow the blue-moon ensemble method to derive the expression of the free energy gradient for a given RC. These derivatives are then used to find the actual minimum energy reaction path at finite temperature, in a way similar to the Intrinsic Reaction Path of Fukui on the potential energy surface [K Fukui J. Phys. Chem. 74, 4161 (1970)]. Once the path is know, one can calculate the free energy profile using thermodynamic integration. We also show that the mass-metric correction cancels for many types of constraints, making the procedure easy to use. Finally, the minimum free energy path at 300 K for the addition of the 1,1-dichlorocarbene to ethylene is compared with a path based on a simple one-dimensional reaction coordinate. A comparison is also given with the reaction path at 0 K.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
