Shock tube study of n-decane ignition at low pressures

Ignition delay times for n-decane/O2/Ar mixtures were measured behind reflected shock waves using endwall pressure and CH＊ emission measurements in a heated shock tube. The initial postshock conditions cover pressures of 0.09-0.26 MPa, temperatures of 1 227-1 536 K, and oxygen mole fractions of 3.9%-20.7% with an equivalence ratio of 1.0. The correlation formula of ignition delay dependence on pressure, temperature, and oxygen mole fraction was obtained. The current data are in good agreement with available low-pressure experimental data, and they are then compared with the prediction of a kinetic mechanism. The current measurements extend the kinetic modeling targets for the n-decane combustion at low pressures.

Radiation Hydrodynamic Simulations in the Planar Scheme for the Fundamental Studies of Shock Ignition

As a fundamental and crucial research topic in the direct-driven inertial confinement fusion（ICF）,especially for shock ignition（SI）,investigation on the laser coupling with planar lowZ targets is beneficial for deep physical comprehension at the primary phase of SI.The production of the intense shock and the shock coalescence in the multi-layer targets,driven by the 3ω intense laser（351 nm the wavelength）,were studied in detail with the 1D and 2D radiation hydrodynamic simulations.It was inferred that the 1D simulation would overrate the shock velocity and the ablation pressure of the spike;the coalescence time and the velocity of the coalescence shock depended evidently on the pulse shape and the start time of the spike.The present study can also provide a semi-quantitative reference for the design of the SI decomposition experiments on the Shenguang-III prototype laser facility.

Hot-electron deposition and implosion mechanisms within electron shock ignition

A hot-electron driven scheme can be more effective than a laser-driven scheme within suitable hot-electron energy and target density. In our one-dimensional (1D) radiation hydrodynamic simulations, 20× pressure enhancement was achieved when the ignitor laser spike was replaced with a 60-keV hot-electron spike in a shock ignition target designed for the National Ignition Facility (NIF), which can lead to greater shell velocity. Higher hot-spot pressure at the deceleration phase was obtained owing to the greater shell velocity. More cold shell material is ablated into the hot spot, and it benefits the increases of the hot-spot pressure. Higher gain and a wider ignition window can be observed in the hot-electron-driven shock ignition.

Observation and modelling of stimulated Raman scattering driven by an optically smoothed laser beam in experimental conditions relevant for shock ignition

We report results and modelling of an experiment performed at the Target Area West Vulcan laser facility,aimed at investigating laser±plasma interaction in conditions that are of interest for the shock ignition scheme in inertial confinement fusion(ICF),that is,laser intensity higher than 10^(16) W/cm^(2) impinging on a hot(T>1 keV),inhomogeneous and long scalelength pre-formed plasma.Measurements show a significant stimulated Raman scattering(SRS)backscattering(;%-20%of laser energy)driven at low plasma densities and no signatures of two-plasmon decay(TPD)/SRS driven at the quarter critical density region.Results are satisfactorily reproduced by an analytical model accounting for the convective SRS growth in independent laser speckles,in conditions where the reflectivity is dominated by the contribution from the most intense speckles,where SRS becomes saturated.Analytical and kinetic simulations well reproduce the onset of SRS at low plasma densities in a regime strongly affected by non-linear Landau damping and by filamentation of the most intense laser speckles.The absence of TPD/SRS at higher densities is explained by pump depletion and plasma smoothing driven by filamentation.The prevalence of laser coupling in the low-density profile justifies the low temperature measured for hot electrons(7-12 keV),which is well reproduced by numerical simulations.

Experimental research of air-throttling ignition for a scramjet at Ma 6.5

An experimental investigation on ignition characteristics with air-throttling in an ethylene-fueled scramjet under flight Ma 6.5 conditions was conducted.The dynamic process of air-throttling ignition was explored systematically.The influences of throttling parameters,i.e.,throttling mass rate and duration,were investigated.When the throttling mass rate was 45% of the inflow mass rate,ambient ethylene could be ignited reliably.The delay time from ignition to throttling was about 45–55 ms.There was a threshold of throttling duration under a certain throttling mass rate.It was shorter than 100 ms when the throttling mass rate was 45%.While a 45%throttling mass rate would make the shock train propagate upstream to the isolator entry in about10–15 ms,four lower throttling mass rates were tested,including 30%,25%,20%,and 10%.All of these throttling mass rates could ignite ethylene.However,combustion performances varied with them.A higher throttling mass rate made more ethylene combust and produced higher wall pressure.Through these experiments,some aspects of the relationships between ignition,flame stabilization,combustion efficiency,and air-throttling parameters were brought to light.These results could also be a benchmark for CFD validation.

Geometry effect in reactive shock-elliptic bubble interactions

The shock-induced ignition and detonation wave propagation in reactive elliptic premixed bubbles are numerically studied.Close attention is paid to the bubble geometry effect on the ignition pattern and the ensuing bubble behavior.Five elliptic bubbles with different aspect ratios are examined.According to the numerical results,three typical ignition patterns are identified under the same incident shock strength and the underlying mechanisms are interpreted.The difference in ignition pattern shows that,comparing with the inert shock-bubble interaction,the geometry effect in reactive shock-bubble interaction(RSBI)has more implications.In addition to the aspect ratio,the ignition location and the distance from the ignition spot to the nearest/farthest bubble surface should also be considered as elements of the geometry effect in RSBI.