Modeling detonation waves in nitromethane

Menikoff, Ralph; Shaw, M. S.

doi:10.1016/j.combustflame.2011.05.009

Cited by 34 publications

(39 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Figure 3 shows the time evolution of the spatial extent of the dynamically formed hotspots for different pore sizes by tracking the amount of material in the simulation cell above 1700 K. In all cases studied there is an initial sudden rise in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the hot spot area due to the collision of the ejected material with the downstream wall of the pore. The overall behavior described thus far is fairly consistent with current understanding of hot spot formation from continuum modelling and experiments 13,15,23,24,36,[39][40][41] . An important distinction is the initial temperature spike and local non-equilibrium state at short times, which continuum models suppress through limited resolution, artificial viscosity and equilibrated equations of state.…”

Section: Dynamical Hot Spot Formationsupporting

confidence: 81%

“…Such defects are presumed to be the dominant initiation sites in this class of materials and most initiation models include some ad hoc representation of their physical response [9][10][11] . Continuum models have been used to analyze the hot spot initiation process, but these necessarily make assumptions regarding reaction kinetics, local equilibration and materials properties that are not well-known under the conditions of interest 7,[12][13][14][15]36,[39][40][41] .…”

mentioning

confidence: 99%

See 1 more Smart Citation

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

et al. 2015

View full text Add to dashboard Cite

We use molecular dynamics simulations to describe the chemical reactions following shockinduced collapse of cylindrical pores in the high-energy density material RDX. For shocks with particle velocities of 2km/s we find that the collapse of a 40nm diameter pore leads to a deflagration wave. Molecular collisions during the collapse lead to ultra-fast, multi-step chemical reactions that occur under non-equilibrium conditions. Exothermic products formed during these first few picoseconds prevent the nanoscale hotspot from quenching. Within 30ps, a local deflagration wave develops; it propagates at 0.25km/s and consists of an ultra-thin reaction zone of only ~5nm, thus involving large temperature and composition gradients. Contrary to the assumptions in current models, a static thermal hotspot matching the dynamical one in size and thermodynamic conditions fails to produce a deflagration wave indicating the importance of nonequilibrium loading in the criticality of nanoscale hot spots. These results provide insight into the initiation of reactive decomposition. TOC GRAPHICS

show abstract

Section: Dynamical Hot Spot Formationsupporting

confidence: 81%

mentioning

confidence: 99%

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

et al. 2015

View full text Add to dashboard Cite

show abstract

“…As Menikoff and Shaw pointed out, the choice of EoS and reaction rate model is crucial for an accurate modeling of detonation waves in NM. 68 Using the same Cochran-Chan EoS (Eqs. [2][3][4] to govern the reactant and products of liquid NM does not adequately describe the physics in the reaction zone and the subsequent flow expansion.…”

Section: E Simulation Results Vs Experimental Datamentioning

confidence: 99%

Meso-resolved simulations of shock-to-detonation transition in nitromethane with air-filled cavities

Michael

Ioannou

et al. 2019

Journal of Applied Physics

View full text Add to dashboard Cite

Two-dimensional, meso-resolved numerical simulations are performed to investigate the complete shock-to-detonation transition (SDT) process in a mixture of liquid nitromethane (NM) and air-filled, circular cavities. The shock-induced initiation behaviors resulting from the cases with neat NM, NM with an array of regularly spaced cavities, and NM with randomly distributed cavities are examined. For the case with randomly distributed cavities, hundreds of cavities are explicitly resolved in the simulations using a diffuse-interface approach to treat two immiscible fluids and GPUenabled parallel computing. Without invoking any empirically calibrated, phenomenological models, the reaction rate in the simulations is governed by Arrhenius kinetics. For the cases with neat NM, the resulting SDT process features a superdetonation that evolves from a thermal explosion after a delay following the passage of the incident shock wave and eventually catches up with the leading shock front. For the cases wherein mesoscale heterogeneities are explicitly considered, a gradual SDT process is captured. These two distinct initiation behaviors for neat NM and heterogeneous NM mixtures agree with experimental findings. Via examining the global reaction rate of the mixture, a unique time scale characterizing the SDT process, i.e., the overtake time, is measured for each simulation. For an input shock pressure less than approximately 9.4 GPa, the overtake time resulting from a heterogeneous mixture is shorter than that for neat NM. This sensitizing effect is more pronounced for lower input shock pressures. A random distribution of cavities is found to be more effective in enhancing the SDT process than a regular array of cavities. Statistical analysis on the meso-resolved simulation data provides more insights into the mechanism of energy release underlying the SDT process. Possible directions towards a quantitatively better agreement between the experimental and meso-resolved simulation results are discussed. arXiv:1905.05727v2 [physics.comp-ph]

show abstract

“…In this work, the parameters have been calibrated and validated for the range of pressures arising in the problem at hand, but adjustment might be needed if other regimes are considered. Moreover, it should be noted that multi-step models exist, such as, for example, the two-stage model by Kipp and Nunziato [20] developed for simultaneous modelling ignition and detonation regimes, as well as second-order single-step models, as used, for example, by Menikoff and Shaw [21], and they might have a quantitative effect on the temperature evolution.…”

Section: Reaction Rates For Nitromethanementioning

confidence: 99%

“…Some reaction is also seen in the FHS and in the region that is traversed by the BCSW and the waves emanating from the lobes. After the ignition (stages [21][22], the fuel continues burning until it reaches the threshold of λ = 0.01, where no more fuel is considered to be available for burning.…”

Section: Evolution Along Constant Latitude Linesmentioning

confidence: 99%

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

Michael

Nikiforakis

2018

Shock Waves

View full text Add to dashboard Cite

This work is concerned with the effect of cavity collapse in non-ideal explosives as a means of controlling their sensitivity. The main objective is to understand the origin of localised temperature peaks (hot spots) which play a leading order role at the early stages of ignition. To this end, we perform two-and three-dimensional numerical simulations of shock-induced single gas-cavity collapse in liquid nitromethane. Ignition is the result of a complex interplay between fluid dynamics and exothermic chemical reaction.In the first part of this work, we focused on the hydrodynamic effects in the collapse process by switching off the reaction terms in the mathematical formulation. In this part, we reinstate the reactive terms and study the collapse of the cavity in the presence of chemical reactions. By using a multi-phase formulation which overcomes current challenges of cavity collapse modelling in reactive media, we account for the large density difference across the material interface without generating spurious temperature peaks, thus allowing the use of a temperature-based reaction rate law. The mathematical and physical models are validated against experimental and analytic data. In Part I, we demonstrated that, compared to experiments, the generated hot spots have a more complex topological structure and that additional hot spots arise in regions away from the cavity centreline. Here, we extend this by identifying which of the previously determined hightemperature regions in fact lead to ignition and comment on the reactive strength and reaction growth rate in the distinct hot spots. We demonstrate and quantify the sensitisation of nitromethane by the collapse of the isolated cavity by comparing the ignition times of nitromethane due to cavity collapse and the ignition time of the neat material. The ignition in both the centreline hot spots and the hot spots generated by Mach stems occurs in less than half the ignition time of the neat material. We compare two-and three-dimensional simulations to examine the change in topology, temperatures, and reactive strength of the hot spots by the third dimension. It is apparent that belated ignition times can be avoided by the use of three-dimensional simulations. The effect of the chemical reactions on the topology and strength of the hot spots in the timescales considered is also studied, in a comparison between inert and reactive simulations where maximum temperature fields and their growth rates are examined.

show abstract

Modeling detonation waves in nitromethane

Cited by 34 publications

References 24 publications

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

Meso-resolved simulations of shock-to-detonation transition in nitromethane with air-filled cavities

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

Contact Info

Product

Resources

About